Initial implementation of channel overscroll navigation

submodules/ComponentFlow/BUILD

@@ -0,0 +1,14 @@
+load("@build_bazel_rules_swift//swift:swift.bzl", "swift_library")
+
+swift_library(
+    name = "ComponentFlow",
+    module_name = "ComponentFlow",
+    srcs = glob([
+        "Source/**/*.swift",
+    ]),
+    deps = [
+    ],
+    visibility = [
+        "//visibility:public",
+    ],
+)

submodules/ComponentFlow/Source/Base/ChildComponentTransitions.swift

@@ -0,0 +1,78 @@
+import Foundation
+import UIKit
+
+public extension Transition.Appear {
+    static func `default`(scale: Bool = false, alpha: Bool = false) -> Transition.Appear {
+        return Transition.Appear { component, view, transition in
+            if scale {
+                transition.animateScale(view: view, from: 0.01, to: 1.0)
+            }
+            if alpha {
+                transition.animateAlpha(view: view, from: 0.0, to: 1.0)
+            }
+        }
+    }
+
+    static func scaleIn() -> Transition.Appear {
+        return Transition.Appear { component, view, transition in
+            transition.animateScale(view: view, from: 0.01, to: 1.0)
+        }
+    }
+}
+
+public extension Transition.AppearWithGuide {
+    static func `default`(scale: Bool = false, alpha: Bool = false) -> Transition.AppearWithGuide {
+        return Transition.AppearWithGuide { component, view, guide, transition in
+            if scale {
+                transition.animateScale(view: view, from: 0.01, to: 1.0)
+            }
+            if alpha {
+                transition.animateAlpha(view: view, from: 0.0, to: 1.0)
+            }
+            transition.animatePosition(view: view, from: CGPoint(x: guide.x - view.center.x, y: guide.y - view.center.y), to: CGPoint(), additive: true)
+        }
+    }
+}
+
+public extension Transition.Disappear {
+    static let `default` = Transition.Disappear { view, transition, completion in
+        transition.setAlpha(view: view, alpha: 0.0, completion: { _ in
+            completion()
+        })
+    }
+}
+
+public extension Transition.DisappearWithGuide {
+    static func `default`(alpha: Bool = true) -> Transition.DisappearWithGuide {
+        return Transition.DisappearWithGuide { stage, view, guide, transition, completion in
+            switch stage {
+            case .begin:
+                if alpha {
+                    transition.setAlpha(view: view, alpha: 0.0, completion: { _ in
+                        completion()
+                    })
+                }
+                transition.setFrame(view: view, frame: CGRect(origin: CGPoint(x: guide.x - view.bounds.width / 2.0, y: guide.y - view.bounds.height / 2.0), size: view.bounds.size), completion: { _ in
+                    if !alpha {
+                        completion()
+                    }
+                })
+            case .update:
+                transition.setFrame(view: view, frame: CGRect(origin: CGPoint(x: guide.x - view.bounds.width / 2.0, y: guide.y - view.bounds.height / 2.0), size: view.bounds.size))
+            }
+        }
+    }
+}
+
+public extension Transition.Update {
+    static let `default` = Transition.Update { component, view, transition in
+        let frame = component.size.centered(around: component._position ?? CGPoint())
+        if view.frame != frame {
+            transition.setFrame(view: view, frame: frame)
+        }
+        let opacity = component._opacity ?? 1.0
+        if view.alpha != opacity {
+            transition.setAlpha(view: view, alpha: opacity)
+        }
+    }
+}

submodules/ComponentFlow/Source/Base/CombinedComponent.swift

@@ -0,0 +1,798 @@
+import Foundation
+import UIKit
+
+private func updateChildAnyComponent<EnvironmentType>(
+    id: _AnyChildComponent.Id,
+    component: AnyComponent<EnvironmentType>,
+    view: UIView,
+    availableSize: CGSize,
+    transition: Transition
+) -> _UpdatedChildComponent {
+    let parentContext = _AnyCombinedComponentContext.current
+
+    if !parentContext.updateContext.updatedViews.insert(id).inserted {
+        preconditionFailure("Child component can only be processed once")
+    }
+
+    let context = view.context(component: component)
+    var isEnvironmentUpdated = false
+    var isStateUpdated = false
+    var isComponentUpdated = false
+    var availableSizeUpdated = false
+
+    if context.environment.calculateIsUpdated() {
+        context.environment._isUpdated = false
+        isEnvironmentUpdated = true
+    }
+
+    if context.erasedState.isUpdated {
+        context.erasedState.isUpdated = false
+        isStateUpdated = true
+    }
+
+    if context.erasedComponent != component {
+        isComponentUpdated = true
+    }
+    context.erasedComponent = component
+
+    if context.layoutResult.availableSize != availableSize {
+        context.layoutResult.availableSize = availableSize
+        availableSizeUpdated = true
+    }
+
+    let isUpdated = isEnvironmentUpdated || isStateUpdated || isComponentUpdated || availableSizeUpdated
+
+    if !isUpdated, let size = context.layoutResult.size {
+        return _UpdatedChildComponent(
+            id: id,
+            component: component,
+            view: view,
+            context: context,
+            size: size
+        )
+    } else {
+        let size = component._update(
+            view: view,
+            availableSize: availableSize,
+            transition: transition
+        )
+        context.layoutResult.size = size
+
+        return _UpdatedChildComponent(
+            id: id,
+            component: component,
+            view: view,
+            context: context,
+            size: size
+        )
+    }
+}
+
+public class _AnyChildComponent {
+    fileprivate enum Id: Hashable {
+        case direct(Int)
+        case mapped(Int, AnyHashable)
+    }
+
+    fileprivate var directId: Int {
+        return Int(bitPattern: Unmanaged.passUnretained(self).toOpaque())
+    }
+}
+
+public final class _ConcreteChildComponent<ComponentType: Component>: _AnyChildComponent {
+    fileprivate var id: Id {
+        return .direct(self.directId)
+    }
+
+    public func update(component: ComponentType, @EnvironmentBuilder environment: () -> Environment<ComponentType.EnvironmentType>, availableSize: CGSize, transition: Transition) -> _UpdatedChildComponent {
+        let parentContext = _AnyCombinedComponentContext.current
+        if !parentContext.updateContext.configuredViews.insert(self.id).inserted {
+            preconditionFailure("Child component can only be configured once")
+        }
+
+        var transition = transition
+
+        let view: ComponentType.View
+        if let current = parentContext.childViews[self.id] {
+            // TODO: Check if the type is the same
+            view = current.view as! ComponentType.View
+        } else {
+            view = component.makeView()
+            transition = .immediate
+        }
+
+        let context = view.context(component: component)
+        EnvironmentBuilder._environment = context.erasedEnvironment
+        let _ = environment()
+        EnvironmentBuilder._environment = nil
+
+        return updateChildAnyComponent(
+            id: self.id,
+            component: AnyComponent(component),
+            view: view,
+            availableSize: availableSize,
+            transition: transition
+        )
+    }
+}
+
+public extension _ConcreteChildComponent where ComponentType.EnvironmentType == Empty {
+    func update(component: ComponentType, availableSize: CGSize, transition: Transition) -> _UpdatedChildComponent {
+        return self.update(component: component, environment: {}, availableSize: availableSize, transition: transition)
+    }
+}
+
+public final class _UpdatedChildComponentGuide {
+    fileprivate let instance: _ChildComponentGuide
+
+    fileprivate init(instance: _ChildComponentGuide) {
+        self.instance = instance
+    }
+}
+
+public final class _ChildComponentGuide {
+    fileprivate var directId: Int {
+        return Int(bitPattern: Unmanaged.passUnretained(self).toOpaque())
+    }
+
+    fileprivate var id: _AnyChildComponent.Id {
+        return .direct(self.directId)
+    }
+
+    public func update(position: CGPoint, transition: Transition) -> _UpdatedChildComponentGuide {
+        let parentContext = _AnyCombinedComponentContext.current
+
+        let previousPosition = parentContext.guides[self.id]
+
+        if parentContext.updateContext.configuredGuides.updateValue(_AnyCombinedComponentContext.UpdateContext.ConfiguredGuide(previousPosition: previousPosition ?? position, position: position), forKey: self.id) != nil {
+            preconditionFailure("Child guide can only be configured once")
+        }
+
+        for disappearingView in parentContext.disappearingChildViews {
+            if disappearingView.guideId == self.id {
+                disappearingView.transitionWithGuide?(
+                    stage: .update,
+                    view: disappearingView.view,
+                    guide: position,
+                    transition: transition,
+                    completion: disappearingView.completion
+                )
+            }
+        }
+
+        return _UpdatedChildComponentGuide(instance: self)
+    }
+}
+
+public final class _UpdatedChildComponent {
+    fileprivate let id: _AnyChildComponent.Id
+    fileprivate let component: _TypeErasedComponent
+    fileprivate let view: UIView
+    fileprivate let context: _TypeErasedComponentContext
+
+    public let size: CGSize
+
+    var _removed: Bool = false
+    var _position: CGPoint?
+    var _opacity: CGFloat?
+
+    fileprivate var transitionAppear: Transition.Appear?
+    fileprivate var transitionAppearWithGuide: (Transition.AppearWithGuide, _AnyChildComponent.Id)?
+    fileprivate var transitionDisappear: Transition.Disappear?
+    fileprivate var transitionDisappearWithGuide: (Transition.DisappearWithGuide, _AnyChildComponent.Id)?
+    fileprivate var transitionUpdate: Transition.Update?
+    fileprivate var gestures: [Gesture] = []
+
+    fileprivate init(
+        id: _AnyChildComponent.Id,
+        component: _TypeErasedComponent,
+        view: UIView,
+        context: _TypeErasedComponentContext,
+        size: CGSize
+    ) {
+        self.id = id
+        self.component = component
+        self.view = view
+        self.context = context
+        self.size = size
+    }
+
+    @discardableResult public func appear(_ transition: Transition.Appear) -> _UpdatedChildComponent {
+        self.transitionAppear = transition
+        self.transitionAppearWithGuide = nil
+        return self
+    }
+
+    @discardableResult public func appear(_ transition: Transition.AppearWithGuide, guide: _UpdatedChildComponentGuide) -> _UpdatedChildComponent {
+        self.transitionAppear = nil
+        self.transitionAppearWithGuide = (transition, guide.instance.id)
+        return self
+    }
+
+    @discardableResult public func disappear(_ transition: Transition.Disappear) -> _UpdatedChildComponent {
+        self.transitionDisappear = transition
+        self.transitionDisappearWithGuide = nil
+        return self
+    }
+
+    @discardableResult public func disappear(_ transition: Transition.DisappearWithGuide, guide: _UpdatedChildComponentGuide) -> _UpdatedChildComponent {
+        self.transitionDisappear = nil
+        self.transitionDisappearWithGuide = (transition, guide.instance.id)
+        return self
+    }
+
+    @discardableResult public func update(_ transition: Transition.Update) -> _UpdatedChildComponent {
+        self.transitionUpdate = transition
+        return self
+    }
+
+    @discardableResult public func removed(_ removed: Bool) -> _UpdatedChildComponent {
+        self._removed = removed
+        return self
+    }
+
+    @discardableResult public func position(_ position: CGPoint) -> _UpdatedChildComponent {
+        self._position = position
+        return self
+    }
+
+    @discardableResult public func opacity(_ opacity: CGFloat) -> _UpdatedChildComponent {
+        self._opacity = opacity
+        return self
+    }
+
+    @discardableResult public func gesture(_ gesture: Gesture) -> _UpdatedChildComponent {
+        self.gestures.append(gesture)
+        return self
+    }
+}
+
+public final class _EnvironmentChildComponent<EnvironmentType>: _AnyChildComponent {
+    fileprivate var id: Id {
+        return .direct(self.directId)
+    }
+
+    func update(component: AnyComponent<EnvironmentType>, @EnvironmentBuilder environment: () -> Environment<EnvironmentType>, availableSize: CGSize, transition: Transition) -> _UpdatedChildComponent {
+        let parentContext = _AnyCombinedComponentContext.current
+        if !parentContext.updateContext.configuredViews.insert(self.id).inserted {
+            preconditionFailure("Child component can only be configured once")
+        }
+
+        var transition = transition
+
+        let view: UIView
+        if let current = parentContext.childViews[self.id] {
+            // Check if the type is the same
+            view = current.view
+        } else {
+            view = component._makeView()
+            transition = .immediate
+        }
+
+        EnvironmentBuilder._environment = view.context(component: component).erasedEnvironment
+        let _ = environment()
+        EnvironmentBuilder._environment = nil
+
+        return updateChildAnyComponent(
+            id: self.id,
+            component: component,
+            view: view,
+            availableSize: availableSize,
+            transition: transition
+        )
+    }
+}
+
+public extension _EnvironmentChildComponent where EnvironmentType == Empty {
+    func update(component: AnyComponent<EnvironmentType>, availableSize: CGSize, transition: Transition) -> _UpdatedChildComponent {
+        return self.update(component: component, environment: {}, availableSize: availableSize, transition: transition)
+    }
+}
+
+public extension _EnvironmentChildComponent {
+    func update<ComponentType: Component>(_ component: ComponentType, @EnvironmentBuilder environment: () -> Environment<EnvironmentType>, availableSize: CGSize, transition: Transition) -> _UpdatedChildComponent where ComponentType.EnvironmentType == EnvironmentType {
+        return self.update(component: AnyComponent(component), environment: environment, availableSize: availableSize, transition: transition)
+    }
+
+    func update<ComponentType: Component>(_ component: ComponentType, @EnvironmentBuilder environment: () -> Environment<EnvironmentType>, availableSize: CGSize, transition: Transition) -> _UpdatedChildComponent where ComponentType.EnvironmentType == EnvironmentType, EnvironmentType == Empty {
+        return self.update(component: AnyComponent(component), environment: {}, availableSize: availableSize, transition: transition)
+    }
+}
+
+public final class _EnvironmentChildComponentFromMap<EnvironmentType>: _AnyChildComponent {
+    private let id: Id
+
+    fileprivate init(id: Id) {
+        self.id = id
+    }
+
+    public func update(component: AnyComponent<EnvironmentType>, @EnvironmentBuilder environment: () -> Environment<EnvironmentType>, availableSize: CGSize, transition: Transition) -> _UpdatedChildComponent {
+        let parentContext = _AnyCombinedComponentContext.current
+        if !parentContext.updateContext.configuredViews.insert(self.id).inserted {
+            preconditionFailure("Child component can only be configured once")
+        }
+
+        var transition = transition
+
+        let view: UIView
+        if let current = parentContext.childViews[self.id] {
+            // Check if the type is the same
+            view = current.view
+        } else {
+            view = component._makeView()
+            transition = .immediate
+        }
+
+        EnvironmentBuilder._environment = view.context(component: component).erasedEnvironment
+        let _ = environment()
+        EnvironmentBuilder._environment = nil
+
+        return updateChildAnyComponent(
+            id: self.id,
+            component: component,
+            view: view,
+            availableSize: availableSize,
+            transition: transition
+        )
+    }
+}
+
+public extension _EnvironmentChildComponentFromMap where EnvironmentType == Empty {
+    func update(component: AnyComponent<EnvironmentType>, availableSize: CGSize, transition: Transition) -> _UpdatedChildComponent {
+        return self.update(component: component, environment: {}, availableSize: availableSize, transition: transition)
+    }
+}
+
+public final class _EnvironmentChildComponentMap<EnvironmentType, Key: Hashable> {
+    private var directId: Int {
+        return Int(bitPattern: Unmanaged.passUnretained(self).toOpaque())
+    }
+
+    public subscript(_ key: Key) -> _EnvironmentChildComponentFromMap<EnvironmentType> {
+        get {
+            return _EnvironmentChildComponentFromMap<EnvironmentType>(id: .mapped(self.directId, key))
+        }
+    }
+}
+
+public final class CombinedComponentContext<ComponentType: Component> {
+    fileprivate let escapeGuard = EscapeGuard()
+
+    private let context: ComponentContext<ComponentType>
+    public let view: UIView
+
+    public let component: ComponentType
+    public let availableSize: CGSize
+    public let transition: Transition
+    private let addImpl: (_ updatedComponent: _UpdatedChildComponent) -> Void
+
+    public var environment: Environment<ComponentType.EnvironmentType> {
+        return self.context.environment
+    }
+    public var state: ComponentType.State {
+        return self.context.state
+    }
+
+    fileprivate init(
+        context: ComponentContext<ComponentType>,
+        view: UIView,
+        component: ComponentType,
+        availableSize: CGSize,
+        transition: Transition,
+        add: @escaping (_ updatedComponent: _UpdatedChildComponent) -> Void
+    ) {
+        self.context = context
+        self.view = view
+        self.component = component
+        self.availableSize = availableSize
+        self.transition = transition
+        self.addImpl = add
+    }
+
+    public func add(_ updatedComponent: _UpdatedChildComponent) {
+        self.addImpl(updatedComponent)
+    }
+}
+
+public protocol CombinedComponent: Component {
+    typealias Body = (CombinedComponentContext<Self>) -> CGSize
+
+    static var body: Body { get }
+}
+
+private class _AnyCombinedComponentContext {
+    class UpdateContext {
+        struct ConfiguredGuide {
+            var previousPosition: CGPoint
+            var position: CGPoint
+        }
+
+        var configuredViews: Set<_AnyChildComponent.Id> = Set()
+        var updatedViews: Set<_AnyChildComponent.Id> = Set()
+        var configuredGuides: [_AnyChildComponent.Id: ConfiguredGuide] = [:]
+    }
+
+    private static var _current: _AnyCombinedComponentContext?
+    static var current: _AnyCombinedComponentContext {
+        return self._current!
+    }
+
+    static func push(_ context: _AnyCombinedComponentContext) -> _AnyCombinedComponentContext? {
+        let previous = self._current
+
+        precondition(context._updateContext == nil)
+        context._updateContext = UpdateContext()
+        self._current = context
+
+        return previous
+    }
+
+    static func pop(_ context: _AnyCombinedComponentContext, stack: _AnyCombinedComponentContext?) {
+        precondition(context._updateContext != nil)
+        context._updateContext = nil
+
+        self._current = stack
+    }
+
+    class ChildView {
+        let view: UIView
+        var index: Int
+        var transition: Transition.Disappear?
+        var transitionWithGuide: (Transition.DisappearWithGuide, _AnyChildComponent.Id)?
+
+        var gestures: [UInt: UIGestureRecognizer] = [:]
+
+        init(view: UIView, index: Int) {
+            self.view = view
+            self.index = index
+        }
+
+        func updateGestures(_ gestures: [Gesture]) {
+            var validIds: [UInt] = []
+            for gesture in gestures {
+                validIds.append(gesture.id.id)
+                if let current = self.gestures[gesture.id.id] {
+                    gesture.update(gesture: current)
+                } else {
+                    let gestureInstance = gesture.create()
+                    self.gestures[gesture.id.id] = gestureInstance
+                    self.view.addGestureRecognizer(gestureInstance)
+                }
+            }
+            var removeIds: [UInt] = []
+            for id in self.gestures.keys {
+                if !validIds.contains(id) {
+                    removeIds.append(id)
+                }
+            }
+            for id in removeIds {
+                if let gestureInstance = self.gestures.removeValue(forKey: id) {
+                    self.view.removeGestureRecognizer(gestureInstance)
+                }
+            }
+        }
+    }
+
+    class DisappearingChildView {
+        let view: UIView
+        let guideId: _AnyChildComponent.Id?
+        let transition: Transition.Disappear?
+        let transitionWithGuide: Transition.DisappearWithGuide?
+        let completion: () -> Void
+
+        init(
+            view: UIView,
+            guideId: _AnyChildComponent.Id?,
+            transition: Transition.Disappear?,
+            transitionWithGuide: Transition.DisappearWithGuide?,
+            completion: @escaping () -> Void
+        ) {
+            self.view = view
+            self.guideId = guideId
+            self.transition = transition
+            self.transitionWithGuide = transitionWithGuide
+            self.completion = completion
+        }
+    }
+
+    var childViews: [_AnyChildComponent.Id: ChildView] = [:]
+    var childViewIndices: [_AnyChildComponent.Id] = []
+    var guides: [_AnyChildComponent.Id: CGPoint] = [:]
+    var disappearingChildViews: [DisappearingChildView] = []
+
+    private var _updateContext: UpdateContext?
+    var updateContext: UpdateContext {
+        return self._updateContext!
+    }
+}
+
+private final class _CombinedComponentContext<ComponentType: CombinedComponent>: _AnyCombinedComponentContext {
+    var body: ComponentType.Body?
+}
+
+private var UIView_CombinedComponentContextKey: Int?
+
+private extension UIView {
+    func getCombinedComponentContext<ComponentType: CombinedComponent>(_ type: ComponentType.Type) -> _CombinedComponentContext<ComponentType> {
+        if let context = objc_getAssociatedObject(self, &UIView_CombinedComponentContextKey) as? _CombinedComponentContext<ComponentType> {
+            return context
+        } else {
+            let context = _CombinedComponentContext<ComponentType>()
+            objc_setAssociatedObject(self, &UIView_CombinedComponentContextKey, context, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
+            return context
+        }
+    }
+}
+
+public extension Transition {
+    final class Appear {
+        private let f: (_UpdatedChildComponent, UIView, Transition) -> Void
+
+        public init(_ f: @escaping (_UpdatedChildComponent, UIView, Transition) -> Void) {
+            self.f = f
+        }
+
+        public func callAsFunction(component: _UpdatedChildComponent, view: UIView, transition: Transition) {
+            self.f(component, view, transition)
+        }
+    }
+
+    final class AppearWithGuide {
+        private let f: (_UpdatedChildComponent, UIView, CGPoint, Transition) -> Void
+
+        public init(_ f: @escaping (_UpdatedChildComponent, UIView, CGPoint, Transition) -> Void) {
+            self.f = f
+        }
+
+        public func callAsFunction(component: _UpdatedChildComponent, view: UIView, guide: CGPoint, transition: Transition) {
+            self.f(component, view, guide, transition)
+        }
+    }
+
+    final class Disappear {
+        private let f: (UIView, Transition, @escaping () -> Void) -> Void
+
+        public init(_ f: @escaping (UIView, Transition, @escaping () -> Void) -> Void) {
+            self.f = f
+        }
+
+        public func callAsFunction(view: UIView, transition: Transition, completion: @escaping () -> Void) {
+            self.f(view, transition, completion)
+        }
+    }
+
+    final class DisappearWithGuide {
+        public enum Stage {
+            case begin
+            case update
+        }
+
+        private let f: (Stage, UIView, CGPoint, Transition, @escaping () -> Void) -> Void
+
+        public init(_ f: @escaping (Stage, UIView, CGPoint, Transition, @escaping () -> Void) -> Void
+        ) {
+            self.f = f
+        }
+
+        public func callAsFunction(stage: Stage, view: UIView, guide: CGPoint, transition: Transition, completion: @escaping () -> Void) {
+            self.f(stage, view, guide, transition, completion)
+        }
+    }
+
+    final class Update {
+        private let f: (_UpdatedChildComponent, UIView, Transition) -> Void
+
+        public init(_ f: @escaping (_UpdatedChildComponent, UIView, Transition) -> Void) {
+            self.f = f
+        }
+
+        public func callAsFunction(component: _UpdatedChildComponent, view: UIView, transition: Transition) {
+            self.f(component, view, transition)
+        }
+    }
+}
+
+public extension CombinedComponent {
+    func makeView() -> UIView {
+        return UIView()
+    }
+
+    func update(view: View, availableSize: CGSize, transition: Transition) -> CGSize {
+        let context = view.getCombinedComponentContext(Self.self)
+        
+        let storedBody: Body
+        if let current = context.body {
+            storedBody = current
+        } else {
+            storedBody = Self.body
+            context.body = storedBody
+        }
+
+        let viewContext = view.context(component: self)
+
+        var nextChildIndex = 0
+        var addedChildIds = Set<_AnyChildComponent.Id>()
+
+        let contextStack = _AnyCombinedComponentContext.push(context)
+
+        let escapeStatus: EscapeGuard.Status
+        let size: CGSize
+        do {
+            let bodyContext = CombinedComponentContext<Self>(
+                context: viewContext,
+                view: view,
+                component: self,
+                availableSize: availableSize,
+                transition: transition,
+                add: { updatedChild in
+                    if !addedChildIds.insert(updatedChild.id).inserted {
+                        preconditionFailure("Child component can only be added once")
+                    }
+
+                    let index = nextChildIndex
+                    nextChildIndex += 1
+
+                    if let previousView = context.childViews[updatedChild.id] {
+                        precondition(updatedChild.view === previousView.view)
+
+                        if index != previousView.index {
+                            assert(index < previousView.index)
+                            for i in index ..< previousView.index {
+                                if let moveView = context.childViews[context.childViewIndices[i]] {
+                                    moveView.index += 1
+                                }
+                            }
+                            context.childViewIndices.remove(at: previousView.index)
+                            context.childViewIndices.insert(updatedChild.id, at: index)
+                            previousView.index = index
+                            view.insertSubview(previousView.view, at: index)
+                        }
+
+                        previousView.updateGestures(updatedChild.gestures)
+                        previousView.transition = updatedChild.transitionDisappear
+                        previousView.transitionWithGuide = updatedChild.transitionDisappearWithGuide
+
+                        (updatedChild.transitionUpdate ?? Transition.Update.default)(component: updatedChild, view: updatedChild.view, transition: transition)
+                    } else {
+                        for i in index ..< context.childViewIndices.count {
+                            if let moveView = context.childViews[context.childViewIndices[i]] {
+                                moveView.index += 1
+                            }
+                        }
+
+                        context.childViewIndices.insert(updatedChild.id, at: index)
+                        let childView = _AnyCombinedComponentContext.ChildView(view: updatedChild.view, index: index)
+                        context.childViews[updatedChild.id] = childView
+
+                        childView.updateGestures(updatedChild.gestures)
+                        childView.transition = updatedChild.transitionDisappear
+                        childView.transitionWithGuide = updatedChild.transitionDisappearWithGuide
+
+                        view.insertSubview(updatedChild.view, at: index)
+
+                        updatedChild.view.frame = updatedChild.size.centered(around: updatedChild._position ?? CGPoint())
+                        updatedChild.view.alpha = updatedChild._opacity ?? 1.0
+                        updatedChild.view.context(typeErasedComponent: updatedChild.component).erasedState._updated = { [weak viewContext] transition in
+                            guard let viewContext = viewContext else {
+                                return
+                            }
+                            viewContext.state.updated(transition: transition)
+                        }
+
+                        if let transitionAppearWithGuide = updatedChild.transitionAppearWithGuide {
+                            guard let guide = context.updateContext.configuredGuides[transitionAppearWithGuide.1] else {
+                                preconditionFailure("Guide should be configured before using")
+                            }
+                            transitionAppearWithGuide.0(
+                                component: updatedChild,
+                                view: updatedChild.view,
+                                guide: guide.previousPosition,
+                                transition: transition
+                            )
+                        } else if let transitionAppear = updatedChild.transitionAppear {
+                            transitionAppear(
+                                component: updatedChild,
+                                view: updatedChild.view,
+                                transition: transition
+                            )
+                        }
+                    }
+                }
+            )
+
+            escapeStatus = bodyContext.escapeGuard.status
+            size = storedBody(bodyContext)
+        }
+
+        assert(escapeStatus.isDeallocated, "Body context should not be stored for later use")
+
+        if nextChildIndex < context.childViewIndices.count {
+            for i in nextChildIndex ..< context.childViewIndices.count {
+                let id = context.childViewIndices[i]
+                if let childView = context.childViews.removeValue(forKey: id) {
+                    let view = childView.view
+                    let completion: () -> Void = { [weak context, weak view] in
+                        view?.removeFromSuperview()
+
+                        if let context = context {
+                            for i in 0 ..< context.disappearingChildViews.count {
+                                if context.disappearingChildViews[i].view === view {
+                                    context.disappearingChildViews.remove(at: i)
+                                    break
+                                }
+                            }
+                        }
+                    }
+                    if let transitionWithGuide = childView.transitionWithGuide {
+                        guard let guide = context.updateContext.configuredGuides[transitionWithGuide.1] else {
+                            preconditionFailure("Guide should be configured before using")
+                        }
+                        context.disappearingChildViews.append(_AnyCombinedComponentContext.DisappearingChildView(
+                            view: view,
+                            guideId: transitionWithGuide.1,
+                            transition: nil,
+                            transitionWithGuide: transitionWithGuide.0,
+                            completion: completion
+                        ))
+                        view.isUserInteractionEnabled = false
+                        transitionWithGuide.0(
+                            stage: .begin,
+                            view: view,
+                            guide: guide.position,
+                            transition: transition,
+                            completion: completion
+                        )
+                    } else if let simpleTransition = childView.transition {
+                        context.disappearingChildViews.append(_AnyCombinedComponentContext.DisappearingChildView(
+                            view: view,
+                            guideId: nil,
+                            transition: simpleTransition,
+                            transitionWithGuide: nil,
+                            completion: completion
+                        ))
+                        view.isUserInteractionEnabled = false
+                        simpleTransition(
+                            view: view,
+                            transition: transition,
+                            completion: completion
+                        )
+                    } else {
+                        childView.view.removeFromSuperview()
+                    }
+                }
+            }
+            context.childViewIndices.removeSubrange(nextChildIndex...)
+        }
+
+        if addedChildIds != context.updateContext.updatedViews {
+            preconditionFailure("Updated and added child lists do not match")
+        }
+
+        context.guides.removeAll()
+        for (id, guide) in context.updateContext.configuredGuides {
+            context.guides[id] = guide.position
+        }
+
+        _AnyCombinedComponentContext.pop(context, stack: contextStack)
+
+        return size
+    }
+}
+
+public extension CombinedComponent {
+    static func Child<Environment>(environment: Environment.Type) -> _EnvironmentChildComponent<Environment> {
+        return _EnvironmentChildComponent<Environment>()
+    }
+
+    static func ChildMap<Environment, Key: Hashable>(environment: Environment.Type, keyedBy keyType: Key.Type) -> _EnvironmentChildComponentMap<Environment, Key> {
+        return _EnvironmentChildComponentMap<Environment, Key>()
+    }
+
+    static func Child<ComponentType: Component>(_ type: ComponentType.Type) -> _ConcreteChildComponent<ComponentType> {
+        return _ConcreteChildComponent<ComponentType>()
+    }
+
+    static func Guide() -> _ChildComponentGuide {
+        return _ChildComponentGuide()
+    }
+}

submodules/ComponentFlow/Source/Base/Component.swift

@@ -0,0 +1,203 @@
+import Foundation
+import UIKit
+import ObjectiveC
+
+public class ComponentLayoutResult {
+    var availableSize: CGSize?
+    var size: CGSize?
+}
+
+public protocol _TypeErasedComponentContext: AnyObject {
+    var erasedEnvironment: _Environment { get }
+    var erasedState: ComponentState { get }
+
+    var layoutResult: ComponentLayoutResult { get }
+}
+
+class AnyComponentContext<EnvironmentType>: _TypeErasedComponentContext {
+    var erasedComponent: AnyComponent<EnvironmentType> {
+        get {
+            preconditionFailure()
+        } set(value) {
+            preconditionFailure()
+        }
+    }
+    var erasedState: ComponentState {
+        preconditionFailure()
+    }
+    var erasedEnvironment: _Environment {
+        return self.environment
+    }
+
+    let layoutResult: ComponentLayoutResult
+    var environment: Environment<EnvironmentType>
+
+    init(environment: Environment<EnvironmentType>) {
+        self.layoutResult = ComponentLayoutResult()
+        self.environment = environment
+    }
+}
+
+class ComponentContext<ComponentType: Component>: AnyComponentContext<ComponentType.EnvironmentType> {
+    override var erasedComponent: AnyComponent<ComponentType.EnvironmentType> {
+        get {
+            return AnyComponent(self.component)
+        } set(value) {
+            self.component = value.wrapped as! ComponentType
+        }
+    }
+
+    var component: ComponentType
+    let state: ComponentType.State
+
+    override var erasedState: ComponentState {
+        return self.state
+    }
+
+    init(component: ComponentType, environment: Environment<ComponentType.EnvironmentType>, state: ComponentType.State) {
+        self.component = component
+        self.state = state
+        
+        super.init(environment: environment)
+    }
+}
+
+private var UIView_TypeErasedComponentContextKey: Int?
+
+extension UIView {
+    func context<EnvironmentType>(component: AnyComponent<EnvironmentType>) -> AnyComponentContext<EnvironmentType> {
+        return self.context(typeErasedComponent: component) as! AnyComponentContext<EnvironmentType>
+    }
+
+    func context<ComponentType: Component>(component: ComponentType) -> ComponentContext<ComponentType> {
+        return self.context(typeErasedComponent: component) as! ComponentContext<ComponentType>
+    }
+
+    func context(typeErasedComponent component: _TypeErasedComponent) -> _TypeErasedComponentContext{
+        if let context = objc_getAssociatedObject(self, &UIView_TypeErasedComponentContextKey) as? _TypeErasedComponentContext {
+            return context
+        } else {
+            let context = component._makeContext()
+            objc_setAssociatedObject(self, &UIView_TypeErasedComponentContextKey, context, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
+            return context
+        }
+    }
+}
+
+public class ComponentState {
+    var _updated: ((Transition) -> Void)?
+    var isUpdated: Bool = false
+    
+    public final func updated(transition: Transition = .immediate) {
+        self.isUpdated = true
+        self._updated?(transition)
+    }
+}
+
+public final class EmptyComponentState: ComponentState {
+}
+
+public protocol _TypeErasedComponent {
+    func _makeView() -> UIView
+    func _makeContext() -> _TypeErasedComponentContext
+    func _update(view: UIView, availableSize: CGSize, transition: Transition) -> CGSize
+    func _isEqual(to other: _TypeErasedComponent) -> Bool
+}
+
+public protocol Component: _TypeErasedComponent, Equatable {
+    associatedtype EnvironmentType = Empty
+    associatedtype View: UIView = UIView
+    associatedtype State: ComponentState = EmptyComponentState
+    
+    func makeView() -> View
+    func makeState() -> State
+    func update(view: View, availableSize: CGSize, transition: Transition) -> CGSize
+}
+
+public extension Component {
+    func _makeView() -> UIView {
+        return self.makeView()
+    }
+
+    func _makeContext() -> _TypeErasedComponentContext {
+        return ComponentContext<Self>(component: self, environment: Environment<EnvironmentType>(), state: self.makeState())
+    }
+
+    func _update(view: UIView, availableSize: CGSize, transition: Transition) -> CGSize {
+        return self.update(view: view as! Self.View, availableSize: availableSize, transition: transition)
+    }
+
+    func _isEqual(to other: _TypeErasedComponent) -> Bool {
+        if let other = other as? Self {
+            return self == other
+        } else {
+            return false
+        }
+    }
+}
+
+public extension Component where Self.View == UIView {
+    func makeView() -> UIView {
+        return UIView()
+    }
+}
+
+public extension Component where Self.State == EmptyComponentState {
+    func makeState() -> State {
+        return EmptyComponentState()
+    }
+}
+
+public class ComponentGesture {
+    public static func tap(action: @escaping() -> Void) -> ComponentGesture {
+        preconditionFailure()
+    }
+}
+
+public class AnyComponent<EnvironmentType>: _TypeErasedComponent, Equatable {
+    fileprivate let wrapped: _TypeErasedComponent
+
+    public init<ComponentType: Component>(_ component: ComponentType) where ComponentType.EnvironmentType == EnvironmentType {
+        self.wrapped = component
+    }
+
+    public static func ==(lhs: AnyComponent<EnvironmentType>, rhs: AnyComponent<EnvironmentType>) -> Bool {
+        return lhs.wrapped._isEqual(to: rhs.wrapped)
+    }
+
+    public func _makeView() -> UIView {
+        return self.wrapped._makeView()
+    }
+
+    public func _makeContext() -> _TypeErasedComponentContext {
+        return self.wrapped._makeContext()
+    }
+
+    public func _update(view: UIView, availableSize: CGSize, transition: Transition) -> CGSize {
+        return self.wrapped._update(view: view, availableSize: availableSize, transition: transition)
+    }
+
+    public func _isEqual(to other: _TypeErasedComponent) -> Bool {
+        return self.wrapped._isEqual(to: other)
+    }
+}
+
+public final class AnyComponentWithIdentity<Environment>: Equatable {
+    public let id: AnyHashable
+    public let component: AnyComponent<Environment>
+
+    public init<IdType: Hashable>(id: IdType, component: AnyComponent<Environment>) {
+        self.id = AnyHashable(id)
+        self.component = component
+    }
+
+    public static func == (lhs: AnyComponentWithIdentity<Environment>, rhs: AnyComponentWithIdentity<Environment>) -> Bool {
+        if lhs.id != rhs.id {
+            return false
+        }
+        if lhs.component != rhs.component {
+            return false
+        }
+        return true
+    }
+}

submodules/ComponentFlow/Source/Base/Environment.swift

@@ -0,0 +1,219 @@
+import Foundation
+import UIKit
+
+public final class Empty: Equatable {
+    static let shared: Empty = Empty()
+
+    public static func ==(lhs: Empty, rhs: Empty) -> Bool {
+        return true
+    }
+}
+
+public class _Environment {
+    fileprivate var data: [Int: _EnvironmentValue] = [:]
+    var _isUpdated: Bool = false
+
+    func calculateIsUpdated() -> Bool {
+        if self._isUpdated {
+            return true
+        }
+        for (_, item) in self.data {
+            if let parentEnvironment = item.parentEnvironment, parentEnvironment.calculateIsUpdated() {
+                return true
+            }
+        }
+        return false
+    }
+
+    fileprivate func set<T: Equatable>(index: Int, value: EnvironmentValue<T>) {
+        if let current = self.data[index] {
+            self.data[index] = value
+            if current as! EnvironmentValue<T> != value {
+                self._isUpdated = true
+            }
+        } else {
+            self.data[index] = value
+            self._isUpdated = true
+        }
+    }
+}
+
+private enum EnvironmentValueStorage<T> {
+    case direct(T)
+    case reference(_Environment, Int)
+}
+
+public class _EnvironmentValue {
+    fileprivate let parentEnvironment: _Environment?
+
+    fileprivate init(parentEnvironment: _Environment?) {
+        self.parentEnvironment = parentEnvironment
+    }
+}
+
+@dynamicMemberLookup
+public final class EnvironmentValue<T: Equatable>: _EnvironmentValue, Equatable {
+    private var storage: EnvironmentValueStorage<T>
+
+    fileprivate var value: T {
+        switch self.storage {
+        case let .direct(value):
+            return value
+        case let .reference(environment, index):
+            return (environment.data[index] as! EnvironmentValue<T>).value
+        }
+    }
+
+    fileprivate init(_ value: T) {
+        self.storage = .direct(value)
+
+        super.init(parentEnvironment: nil)
+    }
+
+    fileprivate init(environment: _Environment, index: Int) {
+        self.storage = .reference(environment, index)
+
+        super.init(parentEnvironment: environment)
+    }
+
+    public static func ==(lhs: EnvironmentValue<T>, rhs: EnvironmentValue<T>) -> Bool {
+        if lhs === rhs {
+            return true
+        }
+        // TODO: follow the reference chain for faster equality checking
+        return lhs.value == rhs.value
+    }
+
+    public subscript<V>(dynamicMember keyPath: KeyPath<T, V>) -> V {
+        return self.value[keyPath: keyPath]
+    }
+}
+
+public class Environment<T>: _Environment {
+    private let file: StaticString
+    private let line: Int
+
+    public init(_ file: StaticString = #file, _ line: Int = #line) {
+        self.file = file
+        self.line = line
+    }
+}
+
+public extension Environment where T == Empty {
+    static let value: Environment<Empty> = {
+        let result = Environment<Empty>()
+        result.set(index: 0, value: EnvironmentValue(Empty()))
+        return result
+    }()
+}
+
+public extension Environment {
+    subscript(_ t1: T.Type) -> EnvironmentValue<T> where T: Equatable {
+        return EnvironmentValue(environment: self, index: 0)
+    }
+
+    subscript<T1, T2>(_ t1: T1.Type) -> EnvironmentValue<T1> where T == (T1, T2), T1: Equatable, T2: Equatable {
+        return EnvironmentValue(environment: self, index: 0)
+    }
+
+    subscript<T1, T2>(_ t2: T2.Type) -> EnvironmentValue<T2> where T == (T1, T2), T1: Equatable, T2: Equatable {
+        return EnvironmentValue(environment: self, index: 1)
+    }
+
+    subscript<T1, T2, T3>(_ t1: T1.Type) -> EnvironmentValue<T1> where T == (T1, T2, T3), T1: Equatable, T2: Equatable, T3: Equatable {
+        return EnvironmentValue(environment: self, index: 0)
+    }
+
+    subscript<T1, T2, T3>(_ t2: T2.Type) -> EnvironmentValue<T2> where T == (T1, T2, T3), T1: Equatable, T2: Equatable, T3: Equatable {
+        return EnvironmentValue(environment: self, index: 1)
+    }
+
+    subscript<T1, T2, T3>(_ t3: T3.Type) -> EnvironmentValue<T3> where T == (T1, T2, T3), T1: Equatable, T2: Equatable, T3: Equatable {
+        return EnvironmentValue(environment: self, index: 2)
+    }
+
+    subscript<T1, T2, T3, T4>(_ t1: T1.Type) -> EnvironmentValue<T1> where T == (T1, T2, T3, T4), T1: Equatable, T2: Equatable, T3: Equatable, T4: Equatable {
+        return EnvironmentValue(environment: self, index: 0)
+    }
+
+    subscript<T1, T2, T3, T4>(_ t2: T2.Type) -> EnvironmentValue<T2> where T == (T1, T2, T3, T4), T1: Equatable, T2: Equatable, T3: Equatable, T4: Equatable {
+        return EnvironmentValue(environment: self, index: 1)
+    }
+
+    subscript<T1, T2, T3, T4>(_ t3: T3.Type) -> EnvironmentValue<T3> where T == (T1, T2, T3, T4), T1: Equatable, T2: Equatable, T3: Equatable, T4: Equatable {
+        return EnvironmentValue(environment: self, index: 2)
+    }
+
+    subscript<T1, T2, T3, T4>(_ t4: T4.Type) -> EnvironmentValue<T4> where T == (T1, T2, T3, T4), T1: Equatable, T2: Equatable, T3: Equatable, T4: Equatable {
+        return EnvironmentValue(environment: self, index: 3)
+    }
+}
+
+@resultBuilder
+public struct EnvironmentBuilder {
+    static var _environment: _Environment?
+    private static func current<T>(_ type: T.Type) -> Environment<T> {
+        return self._environment as! Environment<T>
+    }
+
+    public struct Partial<T: Equatable> {
+        fileprivate var value: EnvironmentValue<T>
+    }
+
+    public static func buildBlock() -> Environment<Empty> {
+        let result = self.current(Empty.self)
+        result.set(index: 0, value: EnvironmentValue(Empty.shared))
+        return result
+    }
+
+    public static func buildExpression<T: Equatable>(_ expression: T) -> Partial<T> {
+        return Partial<T>(value: EnvironmentValue(expression))
+    }
+
+    public static func buildExpression<T: Equatable>(_ expression: EnvironmentValue<T>) -> Partial<T> {
+        return Partial<T>(value: expression)
+    }
+
+    public static func buildBlock<T1: Equatable>(_ t1: Partial<T1>) -> Environment<T1> {
+        let result = self.current(T1.self)
+        result.set(index: 0, value: t1.value)
+        return result
+    }
+
+    public static func buildBlock<T1: Equatable, T2: Equatable>(_ t1: Partial<T1>, _ t2: Partial<T2>) -> Environment<(T1, T2)> {
+        let result = self.current((T1, T2).self)
+        result.set(index: 0, value: t1.value)
+        result.set(index: 1, value: t2.value)
+        return result
+    }
+
+    public static func buildBlock<T1: Equatable, T2: Equatable, T3: Equatable>(_ t1: Partial<T1>, _ t2: Partial<T2>, _ t3: Partial<T3>) -> Environment<(T1, T2, T3)> {
+        let result = self.current((T1, T2, T3).self)
+        result.set(index: 0, value: t1.value)
+        result.set(index: 1, value: t2.value)
+        result.set(index: 2, value: t3.value)
+        return result
+    }
+
+    public static func buildBlock<T1: Equatable, T2: Equatable, T3: Equatable, T4: Equatable>(_ t1: Partial<T1>, _ t2: Partial<T2>, _ t3: Partial<T3>, _ t4: Partial<T4>) -> Environment<(T1, T2, T3, T4)> {
+        let result = self.current((T1, T2, T3, T4).self)
+        result.set(index: 0, value: t1.value)
+        result.set(index: 1, value: t2.value)
+        result.set(index: 2, value: t3.value)
+        result.set(index: 3, value: t4.value)
+        return result
+    }
+}
+
+@propertyWrapper
+public struct ZeroEquatable<T>: Equatable {
+    public var wrappedValue: T
+
+    public init(_ wrappedValue: T) {
+        self.wrappedValue = wrappedValue
+    }
+
+    public static func ==(lhs: ZeroEquatable<T>, rhs: ZeroEquatable<T>) -> Bool {
+        return true
+    }
+}

submodules/ComponentFlow/Source/Base/Transition.swift

@@ -0,0 +1,270 @@
+import Foundation
+import UIKit
+
+private extension UIView {
+    static var animationDurationFactor: Double {
+        return 1.0
+    }
+}
+
+@objc private class CALayerAnimationDelegate: NSObject, CAAnimationDelegate {
+    private let keyPath: String?
+    var completion: ((Bool) -> Void)?
+
+    init(animation: CAAnimation, completion: ((Bool) -> Void)?) {
+        if let animation = animation as? CABasicAnimation {
+            self.keyPath = animation.keyPath
+        } else {
+            self.keyPath = nil
+        }
+        self.completion = completion
+
+        super.init()
+    }
+
+    @objc func animationDidStop(_ anim: CAAnimation, finished flag: Bool) {
+        if let anim = anim as? CABasicAnimation {
+            if anim.keyPath != self.keyPath {
+                return
+            }
+        }
+        if let completion = self.completion {
+            completion(flag)
+        }
+    }
+}
+
+private func makeSpringAnimation(keyPath: String) -> CASpringAnimation {
+    let springAnimation = CASpringAnimation(keyPath: keyPath)
+    springAnimation.mass = 3.0;
+    springAnimation.stiffness = 1000.0
+    springAnimation.damping = 500.0
+    springAnimation.duration = 0.5
+    springAnimation.timingFunction = CAMediaTimingFunction(name: .linear)
+    return springAnimation
+}
+
+private extension CALayer {
+    func makeAnimation(from: AnyObject, to: AnyObject, keyPath: String, duration: Double, delay: Double, curve: Transition.Animation.Curve, removeOnCompletion: Bool, additive: Bool, completion: ((Bool) -> Void)? = nil) -> CAAnimation {
+        switch curve {
+        case .spring:
+            let animation = makeSpringAnimation(keyPath: keyPath)
+            animation.fromValue = from
+            animation.toValue = to
+            animation.isRemovedOnCompletion = removeOnCompletion
+            animation.fillMode = .forwards
+            if let completion = completion {
+                animation.delegate = CALayerAnimationDelegate(animation: animation, completion: completion)
+            }
+
+            let k = Float(UIView.animationDurationFactor)
+            var speed: Float = 1.0
+            if k != 0 && k != 1 {
+                speed = Float(1.0) / k
+            }
+
+            animation.speed = speed * Float(animation.duration / duration)
+            animation.isAdditive = additive
+
+            if !delay.isZero {
+                animation.beginTime = self.convertTime(CACurrentMediaTime(), from: nil) + delay * UIView.animationDurationFactor
+                animation.fillMode = .both
+            }
+
+            return animation
+        default:
+            let k = Float(UIView.animationDurationFactor)
+            var speed: Float = 1.0
+            if k != 0 && k != 1 {
+                speed = Float(1.0) / k
+            }
+
+            let animation = CABasicAnimation(keyPath: keyPath)
+            animation.fromValue = from
+            animation.toValue = to
+            animation.duration = duration
+            animation.timingFunction = curve.asTimingFunction()
+            animation.isRemovedOnCompletion = removeOnCompletion
+            animation.fillMode = .forwards
+            animation.speed = speed
+            animation.isAdditive = additive
+            if let completion = completion {
+                animation.delegate = CALayerAnimationDelegate(animation: animation, completion: completion)
+            }
+
+            if !delay.isZero {
+                animation.beginTime = self.convertTime(CACurrentMediaTime(), from: nil) + delay * UIView.animationDurationFactor
+                animation.fillMode = .both
+            }
+
+            return animation
+        }
+    }
+
+    func animate(from: AnyObject, to: AnyObject, keyPath: String, duration: Double, delay: Double, curve: Transition.Animation.Curve, removeOnCompletion: Bool, additive: Bool, completion: ((Bool) -> Void)? = nil) {
+        let animation = self.makeAnimation(from: from, to: to, keyPath: keyPath, duration: duration, delay: delay, curve: curve, removeOnCompletion: removeOnCompletion, additive: additive, completion: completion)
+        self.add(animation, forKey: additive ? nil : keyPath)
+    }
+}
+
+private extension Transition.Animation.Curve {
+    func asTimingFunction() -> CAMediaTimingFunction {
+        switch self {
+        case .easeInOut:
+            return CAMediaTimingFunction(name: .easeInEaseOut)
+        case .spring:
+            preconditionFailure()
+        }
+    }
+}
+
+public struct Transition {
+    public enum Animation {
+        public enum Curve {
+            case easeInOut
+            case spring
+        }
+
+        case none
+        case curve(duration: Double, curve: Curve)
+    }
+    
+    public var animation: Animation
+    private var _userData: [Any] = []
+
+    public func userData<T>(_ type: T.Type) -> T? {
+        for item in self._userData {
+            if let item = item as? T {
+                return item
+            }
+        }
+        return nil
+    }
+
+    public func withUserData(_ userData: Any) -> Transition {
+        var result = self
+        result._userData.append(userData)
+        return result
+    }
+    
+    public static var immediate: Transition = Transition(animation: .none)
+    
+    public static func easeInOut(duration: Double) -> Transition {
+        return Transition(animation: .curve(duration: duration, curve: .easeInOut))
+    }
+
+    public init(animation: Animation) {
+        self.animation = animation
+    }
+    
+    public func setFrame(view: UIView, frame: CGRect, completion: ((Bool) -> Void)? = nil) {
+        if view.frame == frame {
+            completion?(true)
+            return
+        }
+        switch self.animation {
+        case .none:
+            view.frame = frame
+            completion?(true)
+        case .curve:
+            let previousPosition = view.center
+            let previousBounds = view.bounds
+            view.frame = frame
+
+            self.animatePosition(view: view, from: previousPosition, to: view.center, completion: completion)
+            self.animateBounds(view: view, from: previousBounds, to: view.bounds)
+        }
+    }
+    
+    public func setAlpha(view: UIView, alpha: CGFloat, completion: ((Bool) -> Void)? = nil) {
+        if view.alpha == alpha {
+            completion?(true)
+            return
+        }
+        switch self.animation {
+        case .none:
+            view.alpha = alpha
+            completion?(true)
+        case .curve:
+            let previousAlpha = view.alpha
+            view.alpha = alpha
+            self.animateAlpha(view: view, from: previousAlpha, to: alpha, completion: completion)
+        }
+    }
+
+    public func animateScale(view: UIView, from fromValue: CGFloat, to toValue: CGFloat, additive: Bool = false, completion: ((Bool) -> Void)? = nil) {
+        switch self.animation {
+        case .none:
+            completion?(true)
+        case let .curve(duration, curve):
+            view.layer.animate(
+                from: fromValue as NSNumber,
+                to: toValue as NSNumber,
+                keyPath: "transform.scale",
+                duration: duration,
+                delay: 0.0,
+                curve: curve,
+                removeOnCompletion: true,
+                additive: additive,
+                completion: completion
+            )
+        }
+    }
+
+    public func animateAlpha(view: UIView, from fromValue: CGFloat, to toValue: CGFloat, additive: Bool = false, completion: ((Bool) -> Void)? = nil) {
+        switch self.animation {
+        case .none:
+            completion?(true)
+        case let .curve(duration, curve):
+            view.layer.animate(
+                from: fromValue as NSNumber,
+                to: toValue as NSNumber,
+                keyPath: "opacity",
+                duration: duration,
+                delay: 0.0,
+                curve: curve,
+                removeOnCompletion: true,
+                additive: additive,
+                completion: completion
+            )
+        }
+    }
+
+    public func animatePosition(view: UIView, from fromValue: CGPoint, to toValue: CGPoint, additive: Bool = false, completion: ((Bool) -> Void)? = nil) {
+        switch self.animation {
+        case .none:
+            completion?(true)
+        case let .curve(duration, curve):
+            view.layer.animate(
+                from: NSValue(cgPoint: fromValue),
+                to: NSValue(cgPoint: toValue),
+                keyPath: "position",
+                duration: duration,
+                delay: 0.0,
+                curve: curve,
+                removeOnCompletion: true,
+                additive: additive,
+                completion: completion
+            )
+        }
+    }
+
+    public func animateBounds(view: UIView, from fromValue: CGRect, to toValue: CGRect, additive: Bool = false, completion: ((Bool) -> Void)? = nil) {
+        switch self.animation {
+        case .none:
+            break
+        case let .curve(duration, curve):
+            view.layer.animate(
+                from: NSValue(cgRect: fromValue),
+                to: NSValue(cgRect: toValue),
+                keyPath: "bounds",
+                duration: duration,
+                delay: 0.0,
+                curve: curve,
+                removeOnCompletion: true,
+                additive: additive,
+                completion: completion
+            )
+        }
+    }
+}

submodules/ComponentFlow/Source/Components/Button.swift

@@ -0,0 +1,68 @@
+import Foundation
+import UIKit
+
+final class Button: CombinedComponent, Equatable {
+    let content: AnyComponent<Empty>
+    let insets: UIEdgeInsets
+    let action: () -> Void
+
+    init(
+        content: AnyComponent<Empty>,
+        insets: UIEdgeInsets,
+        action: @escaping () -> Void
+    ) {
+        self.content = content
+        self.insets = insets
+        self.action = action
+    }
+
+    static func ==(lhs: Button, rhs: Button) -> Bool {
+        if lhs.content != rhs.content {
+            return false
+        }
+        if lhs.insets != rhs.insets {
+            return false
+        }
+        return true
+    }
+
+    final class State: ComponentState {
+        var isHighlighted = false
+
+        override init() {
+            super.init()
+        }
+    }
+
+    func makeState() -> State {
+        return State()
+    }
+
+    static var body: Body {
+        let content = Child(environment: Empty.self)
+
+        return { context in
+            let content = content.update(
+                component: context.component.content,
+                availableSize: CGSize(width: context.availableSize.width, height: 44.0), transition: context.transition
+            )
+
+            let size = CGSize(width: content.size.width + context.component.insets.left + context.component.insets.right, height: content.size.height + context.component.insets.top + context.component.insets.bottom)
+
+            let component = context.component
+
+            context.add(content
+                .position(CGPoint(x: size.width / 2.0, y: size.height / 2.0))
+                .opacity(context.state.isHighlighted ? 0.2 : 1.0)
+                .update(Transition.Update { component, view, transition in
+                    view.frame = component.size.centered(around: component._position ?? CGPoint())
+                })
+                .gesture(.tap {
+                    component.action()
+                })
+            )
+            
+            return size
+        }
+    }
+}

submodules/ComponentFlow/Source/Components/List.swift

@@ -0,0 +1,48 @@
+import Foundation
+import UIKit
+
+public final class List<ChildEnvironment: Equatable>: CombinedComponent {
+    public typealias EnvironmentType = ChildEnvironment
+
+    private let items: [AnyComponentWithIdentity<ChildEnvironment>]
+    private let appear: Transition.Appear
+
+    public init(_ items: [AnyComponentWithIdentity<ChildEnvironment>], appear: Transition.Appear = .default()) {
+        self.items = items
+        self.appear = appear
+    }
+
+    public static func ==(lhs: List<ChildEnvironment>, rhs: List<ChildEnvironment>) -> Bool {
+        if lhs.items != rhs.items {
+            return false
+        }
+        return true
+    }
+
+    public static var body: Body {
+        let children = ChildMap(environment: ChildEnvironment.self, keyedBy: AnyHashable.self)
+
+        return { context in
+            let updatedChildren = context.component.items.map { item in
+                return children[item.id].update(
+                    component: item.component, environment: {
+                        context.environment[ChildEnvironment.self]
+                    },
+                    availableSize: context.availableSize,
+                    transition: context.transition
+                )
+            }
+
+            var nextOrigin: CGFloat = 0.0
+            for child in updatedChildren {
+                context.add(child
+                    .position(CGPoint(x: child.size.width / 2.0, y: nextOrigin + child.size.height / 2.0))
+                    .appear(context.component.appear)
+                )
+                nextOrigin += child.size.height
+            }
+
+            return context.availableSize
+        }
+    }
+}

submodules/ComponentFlow/Source/Components/Rectangle.swift

@@ -0,0 +1,41 @@
+import Foundation
+import UIKit
+
+public final class Rectangle: Component {
+    private let color: UIColor
+    private let width: CGFloat?
+    private let height: CGFloat?
+    
+    public init(color: UIColor, width: CGFloat? = nil, height: CGFloat? = nil) {
+        self.color = color
+        self.width = width
+        self.height = height
+    }
+
+    public static func ==(lhs: Rectangle, rhs: Rectangle) -> Bool {
+        if !lhs.color.isEqual(rhs.color) {
+            return false
+        }
+        if lhs.width != rhs.width {
+            return false
+        }
+        if lhs.height != rhs.height {
+            return false
+        }
+        return true
+    }
+    
+    public func update(view: UIView, availableSize: CGSize, transition: Transition) -> CGSize {
+        var size = availableSize
+        if let width = self.width {
+            size.width = min(size.width, width)
+        }
+        if let height = self.height {
+            size.height = min(size.height, height)
+        }
+
+        view.backgroundColor = self.color
+
+        return size
+    }
+}

submodules/ComponentFlow/Source/Components/Text.swift

@@ -0,0 +1,101 @@
+import Foundation
+import UIKit
+
+public final class Text: Component {
+    private final class MeasureState: Equatable {
+        let attributedText: NSAttributedString
+        let availableSize: CGSize
+        let size: CGSize
+        
+        init(attributedText: NSAttributedString, availableSize: CGSize, size: CGSize) {
+            self.attributedText = attributedText
+            self.availableSize = availableSize
+            self.size = size
+        }
+
+        static func ==(lhs: MeasureState, rhs: MeasureState) -> Bool {
+            if !lhs.attributedText.isEqual(rhs.attributedText) {
+                return false
+            }
+            if lhs.availableSize != rhs.availableSize {
+                return false
+            }
+            if lhs.size != rhs.size {
+                return false
+            }
+            return true
+        }
+    }
+    
+    public final class View: UIView {
+        private var measureState: MeasureState?
+
+        func update(component: Text, availableSize: CGSize) -> CGSize {
+            let attributedText = NSAttributedString(string: component.text, attributes: [
+                NSAttributedString.Key.font: component.font,
+                NSAttributedString.Key.foregroundColor: component.color
+            ])
+            
+            if let measureState = self.measureState {
+                if measureState.attributedText.isEqual(to: attributedText) && measureState.availableSize == availableSize {
+                    return measureState.size
+                }
+            }
+            
+            var boundingRect = attributedText.boundingRect(with: availableSize, options: .usesLineFragmentOrigin, context: nil)
+            boundingRect.size.width = ceil(boundingRect.size.width)
+            boundingRect.size.height = ceil(boundingRect.size.height)
+
+            let measureState = MeasureState(attributedText: attributedText, availableSize: availableSize, size: boundingRect.size)
+            if #available(iOS 10.0, *) {
+                let renderer = UIGraphicsImageRenderer(bounds: CGRect(origin: CGPoint(), size: measureState.size))
+                let image = renderer.image { context in
+                    UIGraphicsPushContext(context.cgContext)
+                    measureState.attributedText.draw(at: CGPoint())
+                    UIGraphicsPopContext()
+                }
+                self.layer.contents = image.cgImage
+            } else {
+                UIGraphicsBeginImageContextWithOptions(measureState.size, false, 0.0)
+                measureState.attributedText.draw(at: CGPoint())
+                self.layer.contents = UIGraphicsGetImageFromCurrentImageContext()?.cgImage
+                UIGraphicsEndImageContext()
+            }
+
+            self.measureState = measureState
+            
+            return boundingRect.size
+        }
+    }
+    
+    public let text: String
+    public let font: UIFont
+    public let color: UIColor
+    
+    public init(text: String, font: UIFont, color: UIColor) {
+        self.text = text
+        self.font = font
+        self.color = color
+    }
+
+    public static func ==(lhs: Text, rhs: Text) -> Bool {
+        if lhs.text != rhs.text {
+            return false
+        }
+        if !lhs.font.isEqual(rhs.font) {
+            return false
+        }
+        if !lhs.color.isEqual(rhs.color) {
+            return false
+        }
+        return true
+    }
+    
+    public func makeView() -> View {
+        return View()
+    }
+    
+    public func update(view: View, availableSize: CGSize, transition: Transition) -> CGSize {
+        return view.update(component: self, availableSize: availableSize)
+    }
+}

submodules/ComponentFlow/Source/Gestures/Gesture.swift

@@ -0,0 +1,29 @@
+import Foundation
+import UIKit
+
+public class Gesture {
+    class Id {
+        private var _id: UInt = 0
+        public var id: UInt {
+            return self._id
+        }
+
+        init() {
+            self._id = UInt(bitPattern: Unmanaged.passUnretained(self).toOpaque())
+        }
+    }
+
+    let id: Id
+
+    init(id: Id) {
+        self.id = id
+    }
+
+    func create() -> UIGestureRecognizer {
+        preconditionFailure()
+    }
+
+    func update(gesture: UIGestureRecognizer) {
+        preconditionFailure()
+    }
+}

submodules/ComponentFlow/Source/Gestures/PanGesture.swift

@@ -0,0 +1,59 @@
+import Foundation
+import UIKit
+
+public extension Gesture {
+    enum PanGestureState {
+        case began
+        case updated(offset: CGPoint)
+        case ended
+    }
+
+    private final class PanGesture: Gesture {
+        private class Impl: UIPanGestureRecognizer {
+            var action: (PanGestureState) -> Void
+
+            init(action: @escaping (PanGestureState) -> Void) {
+                self.action = action
+
+                super.init(target: nil, action: nil)
+                self.addTarget(self, action: #selector(self.onAction))
+            }
+
+            @objc private func onAction() {
+                switch self.state {
+                case .began:
+                    self.action(.began)
+                case .ended, .cancelled:
+                    self.action(.ended)
+                case .changed:
+                    let offset = self.translation(in: self.view)
+                    self.action(.updated(offset: offset))
+                default:
+                    break
+                }
+            }
+        }
+
+        static let id = Id()
+
+        private let action: (PanGestureState) -> Void
+
+        init(action: @escaping (PanGestureState) -> Void) {
+            self.action = action
+
+            super.init(id: Self.id)
+        }
+
+        override func create() -> UIGestureRecognizer {
+            return Impl(action: self.action)
+        }
+
+        override func update(gesture: UIGestureRecognizer) {
+            (gesture as! Impl).action = action
+        }
+    }
+
+    static func pan(_ action: @escaping (PanGestureState) -> Void) -> Gesture {
+        return PanGesture(action: action)
+    }
+}

submodules/ComponentFlow/Source/Gestures/TapGesture.swift

@@ -0,0 +1,43 @@
+import Foundation
+import UIKit
+
+public extension Gesture {
+    private final class TapGesture: Gesture {
+        private class Impl: UITapGestureRecognizer {
+            var action: () -> Void
+
+            init(action: @escaping () -> Void) {
+                self.action = action
+
+                super.init(target: nil, action: nil)
+                self.addTarget(self, action: #selector(self.onAction))
+            }
+
+            @objc private func onAction() {
+                self.action()
+            }
+        }
+
+        static let id = Id()
+
+        private let action: () -> Void
+
+        init(action: @escaping () -> Void) {
+            self.action = action
+
+            super.init(id: Self.id)
+        }
+
+        override func create() -> UIGestureRecognizer {
+            return Impl(action: self.action)
+        }
+
+        override func update(gesture: UIGestureRecognizer) {
+            (gesture as! Impl).action = action
+        }
+    }
+
+    static func tap(_ action: @escaping () -> Void) -> Gesture {
+        return TapGesture(action: action)
+    }
+}

submodules/ComponentFlow/Source/Host/ComponentHostView.swift

@@ -0,0 +1,69 @@
+import Foundation
+import UIKit
+
+public final class ComponentHostView<EnvironmentType>: UIView {
+    private var componentView: UIView?
+    private(set) var isUpdating: Bool = false
+    
+    public init() {
+        super.init(frame: CGRect())
+    }
+    
+    required public init?(coder: NSCoder) {
+        fatalError("init(coder:) has not been implemented")
+    }
+    
+    public func update(transition: Transition, component: AnyComponent<EnvironmentType>, @EnvironmentBuilder environment: () -> Environment<EnvironmentType>, containerSize: CGSize) -> CGSize {
+        self._update(transition: transition, component: component, maybeEnvironment: environment, updateEnvironment: true, containerSize: containerSize)
+    }
+
+    private func _update(transition: Transition, component: AnyComponent<EnvironmentType>, maybeEnvironment: () -> Environment<EnvironmentType>, updateEnvironment: Bool, containerSize: CGSize) -> CGSize {
+        precondition(!self.isUpdating)
+        self.isUpdating = true
+
+        precondition(containerSize.width.isFinite)
+        precondition(containerSize.width < .greatestFiniteMagnitude)
+        precondition(containerSize.height.isFinite)
+        precondition(containerSize.height < .greatestFiniteMagnitude)
+        
+        let componentView: UIView
+        if let current = self.componentView {
+            componentView = current
+        } else {
+            componentView = component._makeView()
+            self.componentView = componentView
+            self.addSubview(componentView)
+        }
+
+        let context = componentView.context(component: component)
+
+        let componentState: ComponentState = context.erasedState
+
+        if updateEnvironment {
+            EnvironmentBuilder._environment = context.erasedEnvironment
+            let _ = maybeEnvironment()
+            EnvironmentBuilder._environment = nil
+        }
+
+        componentState._updated = { [weak self] transition in
+            guard let strongSelf = self else {
+                return
+            }
+            let _ = strongSelf._update(transition: transition, component: component, maybeEnvironment: {
+                preconditionFailure()
+            } as () -> Environment<EnvironmentType>, updateEnvironment: false, containerSize: containerSize)
+        }
+
+        let updatedSize = component._update(view: componentView, availableSize: containerSize, transition: transition)
+        transition.setFrame(view: componentView, frame: CGRect(origin: CGPoint(), size: updatedSize))
+
+        self.isUpdating = false
+
+        return updatedSize
+    }
+    
+    override public func hitTest(_ point: CGPoint, with event: UIEvent?) -> UIView? {
+        let result = super.hitTest(point, with: event)
+        return result
+    }
+}

submodules/ComponentFlow/Source/Host/NavigationLayoutEnvironment.swift

@@ -0,0 +1,8 @@
+import Foundation
+import UIKit
+
+public struct NavigationLayout: Equatable {
+    public var statusBarHeight: CGFloat
+    public var inputHeight: CGFloat
+    public var bottomNavigationHeight: CGFloat
+}

submodules/ComponentFlow/Source/Host/RootHostView.swift

@@ -0,0 +1,134 @@
+import Foundation
+import UIKit
+
+public final class RootHostView<EnvironmentType: Equatable>: UIViewController {
+    private let content: AnyComponent<(NavigationLayout, EnvironmentType)>
+
+    private var keyboardWillChangeFrameObserver: NSObjectProtocol?
+    private var inputHeight: CGFloat = 0.0
+
+    private let environment: Environment<EnvironmentType>
+    private var componentView: ComponentHostView<(NavigationLayout, EnvironmentType)>
+
+    private var scheduledTransition: Transition?
+
+    public init(
+        content: AnyComponent<(NavigationLayout, EnvironmentType)>,
+        @EnvironmentBuilder environment: () -> Environment<EnvironmentType>
+    ) {
+        self.content = content
+
+        self.environment = Environment<EnvironmentType>()
+        self.componentView = ComponentHostView<(NavigationLayout, EnvironmentType)>()
+
+        EnvironmentBuilder._environment = self.environment
+        let _ = environment()
+        EnvironmentBuilder._environment = nil
+
+        super.init(nibName: nil, bundle: nil)
+
+        NotificationCenter.default.addObserver(forName: UIApplication.keyboardWillChangeFrameNotification, object: nil, queue: nil, using: { [weak self] notification in
+            guard let strongSelf = self else {
+                return
+            }
+            guard let keyboardFrame = notification.userInfo?[UIApplication.keyboardFrameEndUserInfoKey] as? CGRect else {
+                return
+            }
+
+            var duration: Double = (notification.userInfo?[UIResponder.keyboardAnimationDurationUserInfoKey] as? NSNumber)?.doubleValue ?? 0.0
+            if duration > Double.ulpOfOne {
+                duration = 0.5
+            }
+            let curve: UInt = (notification.userInfo?[UIResponder.keyboardAnimationCurveUserInfoKey] as? NSNumber)?.uintValue ?? 7
+
+            let transition: Transition
+            if curve == 7 {
+                transition = Transition(animation: .curve(duration: duration, curve: .spring))
+            } else {
+                transition = Transition(animation: .curve(duration: duration, curve: .easeInOut))
+            }
+
+            strongSelf.updateKeyboardLayout(keyboardFrame: keyboardFrame, transition: transition)
+        })
+    }
+
+    required public init?(coder: NSCoder) {
+        fatalError("init(coder:) has not been implemented")
+    }
+
+    deinit {
+        self.keyboardWillChangeFrameObserver.flatMap(NotificationCenter.default.removeObserver)
+    }
+
+    private func updateKeyboardLayout(keyboardFrame: CGRect, transition: Transition) {
+        self.inputHeight = max(0.0, self.view.bounds.height - keyboardFrame.minY)
+        if self.componentView.isUpdating || true {
+            if let _ = self.scheduledTransition {
+                if case .curve = transition.animation {
+                    self.scheduledTransition = transition
+                }
+            } else {
+                self.scheduledTransition = transition
+            }
+            self.view.setNeedsLayout()
+        } else {
+            self.updateComponent(size: self.view.bounds.size, transition: transition)
+        }
+    }
+
+    private func updateComponent(size: CGSize, transition: Transition) {
+        self.environment._isUpdated = false
+
+        transition.setFrame(view: self.componentView, frame: CGRect(origin: CGPoint(), size: size))
+        self.componentView.update(
+            transition: transition,
+            component: self.content,
+            environment: {
+                NavigationLayout(
+                    statusBarHeight: size.width > size.height ? 0.0 : 40.0,
+                    inputHeight: self.inputHeight,
+                    bottomNavigationHeight: 22.0
+                )
+                self.environment[EnvironmentType.self]
+            },
+            containerSize: size
+        )
+    }
+
+    public func updateEnvironment(@EnvironmentBuilder environment: () -> Environment<EnvironmentType>) {
+        EnvironmentBuilder._environment = self.environment
+        let _ = environment()
+        EnvironmentBuilder._environment = nil
+
+        if self.environment.calculateIsUpdated() {
+            if !self.view.bounds.size.width.isZero {
+                self.updateComponent(size: self.view.bounds.size, transition: .immediate)
+            }
+        }
+    }
+
+    override public func viewDidLoad() {
+        super.viewDidLoad()
+
+        self.view.addSubview(self.componentView)
+
+        if !self.view.bounds.size.width.isZero {
+            self.updateComponent(size: self.view.bounds.size, transition: .immediate)
+        }
+    }
+
+    override public func viewDidLayoutSubviews() {
+        super.viewDidLayoutSubviews()
+
+        if let scheduledTransition = self.scheduledTransition {
+            self.scheduledTransition = nil
+            self.updateComponent(size: self.view.bounds.size, transition: scheduledTransition)
+        }
+    }
+
+    override public func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator) {
+        super.viewWillTransition(to: size, with: coordinator)
+
+        self.updateComponent(size: size, transition: coordinator.isAnimated ? .easeInOut(duration: 0.3) : .immediate)
+    }
+}

submodules/ComponentFlow/Source/Utils/Color.swift

@@ -0,0 +1,8 @@
+import Foundation
+import UIKit
+
+extension UIColor {
+    convenience init(rgb: UInt32) {
+        self.init(red: CGFloat((rgb >> 16) & 0xff) / 255.0, green: CGFloat((rgb >> 8) & 0xff) / 255.0, blue: CGFloat(rgb & 0xff) / 255.0, alpha: 1.0)
+    }
+}

submodules/ComponentFlow/Source/Utils/Condition.swift

@@ -0,0 +1,9 @@
+import Foundation
+
+public func Condition<R>(_ f: @autoclosure () -> Bool, _ pass: () -> R) -> R? {
+    if f() {
+        return pass()
+    } else {
+        return nil
+    }
+}

submodules/ComponentFlow/Source/Utils/EscapeGuard.swift

@@ -0,0 +1,13 @@
+import Foundation
+
+final class EscapeGuard {
+    final class Status {
+        fileprivate(set) var isDeallocated: Bool = false
+    }
+
+    let status = Status()
+
+    deinit {
+        self.status.isDeallocated = true
+    }
+}

submodules/ComponentFlow/Source/Utils/Insets.swift

@@ -0,0 +1,8 @@
+import Foundation
+import UIKit
+
+public extension UIEdgeInsets {
+    init(_ value: CGFloat) {
+        self.init(top: value, left: value, bottom: value, right: value)
+    }
+}

submodules/ComponentFlow/Source/Utils/Rect.swift

@@ -0,0 +1,8 @@
+import Foundation
+import UIKit
+
+public extension CGRect {
+    var center: CGPoint {
+        return CGPoint(x: self.midX, y: self.midY)
+    }
+}

submodules/ComponentFlow/Source/Utils/Size.swift

@@ -0,0 +1,28 @@
+import Foundation
+import UIKit
+
+public extension CGSize {
+    func centered(in rect: CGRect) -> CGRect {
+        return CGRect(origin: CGPoint(x: rect.minX + floor((rect.width - self.width) / 2.0), y: rect.minY + floor((rect.height - self.height) / 2.0)), size: self)
+    }
+
+    func centered(around position: CGPoint) -> CGRect {
+        return CGRect(origin: CGPoint(x: position.x - self.width / 2.0, y: position.y - self.height / 2.0), size: self)
+    }
+
+    func leftCentered(in rect: CGRect) -> CGRect {
+        return CGRect(origin: CGPoint(x: rect.minX, y: rect.minY + floor((rect.height - self.height) / 2.0)), size: self)
+    }
+
+    func rightCentered(in rect: CGRect) -> CGRect {
+        return CGRect(origin: CGPoint(x: rect.maxX - self.width, y: rect.minY + floor((rect.height - self.height) / 2.0)), size: self)
+    }
+
+    func topCentered(in rect: CGRect) -> CGRect {
+        return CGRect(origin: CGPoint(x: rect.minX + floor((rect.width - self.width) / 2.0), y: 0.0), size: self)
+    }
+
+    func bottomCentered(in rect: CGRect) -> CGRect {
+        return CGRect(origin: CGPoint(x: rect.minX + floor((rect.width - self.width) / 2.0), y: rect.maxY - self.height), size: self)
+    }
+}

submodules/TelegramCore/Sources/TelegramEngine/Peers/TelegramEnginePeers.swift

@@ -478,5 +478,35 @@ public extension TelegramEngine {
         public func updatePeerDescription(peerId: PeerId, description: String?) -> Signal<Void, UpdatePeerDescriptionError> {
             return _internal_updatePeerDescription(account: self.account, peerId: peerId, description: description)
         }
+
+        public func getNextUnreadChannel(peerId: PeerId) -> Signal<EnginePeer?, NoError> {
+            return self.account.postbox.transaction { transaction -> EnginePeer? in
+                var peers: [RenderedPeer] = []
+                peers.append(contentsOf: transaction.getTopChatListEntries(groupId: .root, count: 100))
+                peers.append(contentsOf: transaction.getTopChatListEntries(groupId: Namespaces.PeerGroup.archive, count: 100))
+
+                var results: [(EnginePeer, Int32)] = []
+
+                for peer in peers {
+                    guard let channel = peer.chatMainPeer as? TelegramChannel, case .broadcast = channel.info else {
+                        continue
+                    }
+                    if channel.id == peerId {
+                        continue
+                    }
+                    guard let readState = transaction.getCombinedPeerReadState(channel.id), readState.count != 0 else {
+                        continue
+                    }
+                    guard let topMessageIndex = transaction.getTopPeerMessageIndex(peerId: channel.id) else {
+                        continue
+                    }
+                    results.append((EnginePeer(channel), topMessageIndex.timestamp))
+                }
+
+                results.sort(by: { $0.1 > $1.1 })
+
+                return results.first?.0
+            }
+        }
     }
 }

submodules/TelegramUI/BUILD

@@ -238,6 +238,7 @@ swift_library(
         "//submodules/ImportStickerPackUI:ImportStickerPackUI",
         "//submodules/GradientBackground:GradientBackground",
         "//submodules/WallpaperBackgroundNode:WallpaperBackgroundNode",
+        "//submodules/ComponentFlow:ComponentFlow",
     ] + select({
         "@build_bazel_rules_apple//apple:ios_armv7": [],
         "@build_bazel_rules_apple//apple:ios_arm64": appcenter_targets,

submodules/TelegramUI/Sources/ChatController.swift

@@ -454,6 +454,8 @@ public final class ChatControllerImpl: TelegramBaseController, ChatController, G
     }
     
     private var importStateDisposable: Disposable?
+
+    private var nextChannelToReadDisposable: Disposable?
     
     public init(context: AccountContext, chatLocation: ChatLocation, chatLocationContextHolder: Atomic<ChatLocationContextHolder?> = Atomic<ChatLocationContextHolder?>(value: nil), subject: ChatControllerSubject? = nil, botStart: ChatControllerInitialBotStart? = nil, mode: ChatControllerPresentationMode = .standard(previewing: false), peekData: ChatPeekTimeout? = nil, peerNearbyData: ChatPeerNearbyData? = nil) {
         let _ = ChatControllerCount.modify { value in
@@ -3295,6 +3297,23 @@ public final class ChatControllerImpl: TelegramBaseController, ChatController, G
                             }.updatedIsNotAccessible(isNotAccessible).updatedContactStatus(contactStatus).updatedHasBots(hasBots).updatedHasBotCommands(hasBotCommands).updatedIsArchived(isArchived).updatedPeerIsMuted(peerIsMuted).updatedPeerDiscussionId(peerDiscussionId).updatedPeerGeoLocation(peerGeoLocation).updatedExplicitelyCanPinMessages(explicitelyCanPinMessages).updatedHasScheduledMessages(hasScheduledMessages)
                                 .updatedAutoremoveTimeout(autoremoveTimeout)
                         })
+
+                        if let channel = renderedPeer?.chatMainPeer as? TelegramChannel, case .broadcast = channel.info {
+                            if strongSelf.nextChannelToReadDisposable == nil {
+                                strongSelf.nextChannelToReadDisposable = (strongSelf.context.engine.peers.getNextUnreadChannel(peerId: channel.id)
+                                |> deliverOnMainQueue
+                                |> then(.complete() |> delay(1.0, queue: .mainQueue()))
+                                |> restart).start(next: { nextPeer in
+                                    guard let strongSelf = self else {
+                                        return
+                                    }
+
+                                    strongSelf.chatDisplayNode.historyNode.offerNextChannelToRead = true
+                                    strongSelf.chatDisplayNode.historyNode.nextChannelToRead = nextPeer
+                                })
+                            }
+                        }
+
                         if !strongSelf.didSetChatLocationInfoReady {
                             strongSelf.didSetChatLocationInfoReady = true
                             strongSelf._chatLocationInfoReady.set(.single(true))
@@ -3867,6 +3886,7 @@ public final class ChatControllerImpl: TelegramBaseController, ChatController, G
         self.selectAddMemberDisposable.dispose()
         self.addMemberDisposable.dispose()
         self.importStateDisposable?.dispose()
+        self.nextChannelToReadDisposable?.dispose()
     }
     
     public func updatePresentationMode(_ mode: ChatControllerPresentationMode) {
@@ -7011,9 +7031,28 @@ public final class ChatControllerImpl: TelegramBaseController, ChatController, G
                 }
             }
         })
+
+        self.chatDisplayNode.historyNode.openNextChannelToRead = { [weak self] peer in
+            guard let strongSelf = self else {
+                return
+            }
+            if let navigationController = strongSelf.effectiveNavigationController, let snapshotView = strongSelf.chatDisplayNode.view.snapshotView(afterScreenUpdates: false) {
+                snapshotView.frame = strongSelf.view.bounds
+                strongSelf.view.addSubview(snapshotView)
+                strongSelf.context.sharedContext.navigateToChatController(NavigateToChatControllerParams(navigationController: navigationController, context: strongSelf.context, chatLocation: .peer(peer.id), animated: false, completion: { nextController in
+                    (nextController as! ChatControllerImpl).animateFromPreviousController(snapshotView: snapshotView)
+                }))
+            }
+        }
         
         self.displayNodeDidLoad()
     }
+
+    private var storedAnimateFromSnapshotView: UIView?
+
+    private func animateFromPreviousController(snapshotView: UIView) {
+        self.storedAnimateFromSnapshotView = snapshotView
+    }
     
     override public func viewWillAppear(_ animated: Bool) {
         #if DEBUG
@@ -7415,6 +7454,17 @@ public final class ChatControllerImpl: TelegramBaseController, ChatController, G
                 return state.updatedInputMode({ _ in .text })
             })
         }
+
+        if let snapshotView = self.storedAnimateFromSnapshotView {
+            self.storedAnimateFromSnapshotView = nil
+
+            snapshotView.frame = self.view.bounds.offsetBy(dx: 0.0, dy: -self.view.bounds.height)
+            self.view.insertSubview(snapshotView, at: 0)
+
+            self.view.layer.animateBoundsOriginYAdditive(from: -self.view.bounds.height, to: 0.0, duration: 0.5, timingFunction: kCAMediaTimingFunctionSpring, removeOnCompletion: true, completion: { [weak snapshotView] _ in
+                snapshotView?.removeFromSuperview()
+            })
+        }
     }
     
     override public func viewWillDisappear(_ animated: Bool) {

submodules/TelegramUI/Sources/ChatHistoryListNode.swift

@@ -17,6 +17,7 @@ import ListMessageItem
 import AccountContext
 import ChatInterfaceState
 import ChatListUI
+import ComponentFlow
 
 extension ChatReplyThreadMessage {
     var effectiveTopId: MessageId {
@@ -546,6 +547,13 @@ public final class ChatHistoryListNode: ListView, ChatHistoryNode {
     let topVisibleMessageRange = ValuePromise<ChatTopVisibleMessageRange?>(nil, ignoreRepeated: true)
     
     var isSelectionGestureEnabled = true
+
+    private var overscrollView: ComponentHostView<Empty>?
+    var nextChannelToRead: EnginePeer?
+    var offerNextChannelToRead: Bool = false
+    private var currentOverscrollExpandProgress: CGFloat = 0.0
+    private var feedback: HapticFeedback?
+    var openNextChannelToRead: ((EnginePeer) -> Void)?
     
     private let clientId: Atomic<Int32>
     
@@ -1115,11 +1123,14 @@ public final class ChatHistoryListNode: ListView, ChatHistoryNode {
                 
                 if strongSelf.tagMask == nil {
                     var atBottom = false
+                    var offsetFromBottom: CGFloat?
                     switch offset {
                         case let .known(offsetValue):
                             if offsetValue.isLessThanOrEqualTo(0.0) {
                                 atBottom = true
+                                offsetFromBottom = offsetValue
                             }
+                            //print("offsetValue: \(offsetValue)")
                         default:
                             break
                     }
@@ -1130,6 +1141,8 @@ public final class ChatHistoryListNode: ListView, ChatHistoryNode {
                         
                         strongSelf.isScrollAtBottomPositionUpdated?()
                     }
+
+                    strongSelf.maybeUpdateOverscrollAction(offset: offsetFromBottom)
                 }
             }
         }
@@ -1150,10 +1163,22 @@ public final class ChatHistoryListNode: ListView, ChatHistoryNode {
             self?.isInteractivelyScrollingPromise.set(true)
             self?.beganDragging?()
         }
+
+        self.endedInteractiveDragging = { [weak self] in
+            guard let strongSelf = self else {
+                return
+            }
+            if let channel = strongSelf.nextChannelToRead, strongSelf.currentOverscrollExpandProgress >= 0.99 {
+                strongSelf.openNextChannelToRead?(channel)
+            }
+        }
         
         self.didEndScrolling = { [weak self] in
-            self?.isInteractivelyScrollingValue = false
-            self?.isInteractivelyScrollingPromise.set(false)
+            guard let strongSelf = self else {
+                return
+            }
+            strongSelf.isInteractivelyScrollingValue = false
+            strongSelf.isInteractivelyScrollingPromise.set(false)
         }
         
         let selectionRecognizer = ChatHistoryListSelectionRecognizer(target: self, action: #selector(self.selectionPanGesture(_:)))
@@ -1177,6 +1202,64 @@ public final class ChatHistoryListNode: ListView, ChatHistoryNode {
     public func setLoadStateUpdated(_ f: @escaping (ChatHistoryNodeLoadState, Bool) -> Void) {
         self.loadStateUpdated = f
     }
+
+    private func maybeUpdateOverscrollAction(offset: CGFloat?) {
+        if let offset = offset, offset < 0.0, self.offerNextChannelToRead {
+            let overscrollView: ComponentHostView<Empty>
+            if let current = self.overscrollView {
+                overscrollView = current
+            } else {
+                overscrollView = ComponentHostView<Empty>()
+                overscrollView.layer.sublayerTransform = CATransform3DMakeRotation(CGFloat.pi, 0.0, 0.0, 1.0)
+                self.overscrollView = overscrollView
+                self.view.addSubview(overscrollView)
+            }
+
+            let expandProgress: CGFloat = min(1.0, max(-offset, 0.0) / 110.0)
+
+            let text: String
+            if self.nextChannelToRead != nil {
+                if expandProgress >= 0.99 {
+                    //TODO:localize
+                    text = "Release to go to the next unread channel"
+                } else {
+                    text = "Swipe up to go to the next unread channel"
+                }
+
+                let previousType = self.currentOverscrollExpandProgress >= 0.99
+                let currentType = expandProgress >= 0.99
+
+                if previousType != currentType {
+                    if self.feedback == nil {
+                        self.feedback = HapticFeedback()
+                    }
+                    self.feedback?.tap()
+                }
+
+                self.currentOverscrollExpandProgress = expandProgress
+            } else {
+                text = "You have no unread channels"
+            }
+
+            let overscrollSize = overscrollView.update(
+                transition: .immediate,
+                component: AnyComponent(ChatOverscrollControl(
+                    text: text,
+                    backgroundColor: selectDateFillStaticColor(theme: self.currentPresentationData.theme.theme, wallpaper: self.currentPresentationData.theme.wallpaper),
+                    foregroundColor: bubbleVariableColor(variableColor: self.currentPresentationData.theme.theme.chat.serviceMessage.dateTextColor, wallpaper: self.currentPresentationData.theme.wallpaper),
+                    peer: self.nextChannelToRead,
+                    context: self.context,
+                    expandProgress: expandProgress
+                )),
+                environment: {},
+                containerSize: CGSize(width: self.bounds.width, height: 200.0)
+            )
+            overscrollView.frame = CGRect(origin: CGPoint(x: floor((self.bounds.width - overscrollSize.width) / 2.0), y: -offset + self.insets.top - overscrollSize.height - 10.0), size: overscrollSize)
+        } else if let overscrollView = self.overscrollView {
+            self.overscrollView = nil
+            overscrollView.removeFromSuperview()
+        }
+    }
     
     func refreshPollActionsForVisibleMessages() {
         let _ = self.clientId.swap(nextClientId)

submodules/TelegramUI/Sources/ChatOverscrollControl.swift

@@ -0,0 +1,518 @@
+import UIKit
+import ComponentFlow
+import Display
+import TelegramCore
+import Postbox
+import AccountContext
+import AvatarNode
+
+final class BlurredRoundedRectangle: Component {
+    let color: UIColor
+
+    init(color: UIColor) {
+        self.color = color
+    }
+
+    static func ==(lhs: BlurredRoundedRectangle, rhs: BlurredRoundedRectangle) -> Bool {
+        if !lhs.color.isEqual(rhs.color) {
+            return false
+        }
+        return true
+    }
+
+    final class View: UIView {
+        private let background: NavigationBackgroundNode
+
+        init() {
+            self.background = NavigationBackgroundNode(color: .clear)
+
+            super.init(frame: CGRect())
+
+            self.addSubview(self.background.view)
+        }
+
+        required init?(coder aDecoder: NSCoder) {
+            preconditionFailure()
+        }
+
+        func update(component: BlurredRoundedRectangle, availableSize: CGSize, transition: Transition) -> CGSize {
+            transition.setFrame(view: self.background.view, frame: CGRect(origin: CGPoint(), size: availableSize))
+            self.background.updateColor(color: component.color, transition: .immediate)
+            self.background.update(size: availableSize, cornerRadius: min(availableSize.width, availableSize.height) / 2.0, transition: .immediate)
+
+            return availableSize
+        }
+    }
+
+    func makeView() -> View {
+        return View()
+    }
+
+    func update(view: View, availableSize: CGSize, transition: Transition) -> CGSize {
+        return view.update(component: self, availableSize: availableSize, transition: transition)
+    }
+}
+
+final class RadialProgressComponent: Component {
+    let color: UIColor
+    let lineWidth: CGFloat
+    let value: CGFloat
+
+    init(
+        color: UIColor,
+        lineWidth: CGFloat,
+        value: CGFloat
+    ) {
+        self.color = color
+        self.lineWidth = lineWidth
+        self.value = value
+    }
+
+    static func ==(lhs: RadialProgressComponent, rhs: RadialProgressComponent) -> Bool {
+        if !lhs.color.isEqual(rhs.color) {
+            return false
+        }
+        if lhs.lineWidth != rhs.lineWidth {
+            return false
+        }
+        if lhs.value != rhs.value {
+            return false
+        }
+        return true
+    }
+
+    final class View: UIView {
+        init() {
+            super.init(frame: CGRect())
+        }
+
+        required init?(coder aDecoder: NSCoder) {
+            preconditionFailure()
+        }
+
+        func update(component: RadialProgressComponent, availableSize: CGSize, transition: Transition) -> CGSize {
+            func draw(context: CGContext) {
+                let diameter = availableSize.width
+
+                context.saveGState()
+
+                context.setBlendMode(.normal)
+                context.setFillColor(component.color.cgColor)
+                context.setStrokeColor(component.color.cgColor)
+
+                var progress: CGFloat
+                var startAngle: CGFloat
+                var endAngle: CGFloat
+
+                let value = component.value
+
+                progress = value
+                startAngle = -CGFloat.pi / 2.0
+                endAngle = CGFloat(progress) * 2.0 * CGFloat.pi + startAngle
+
+                if progress > 1.0 {
+                    progress = 2.0 - progress
+                    let tmp = startAngle
+                    startAngle = endAngle
+                    endAngle = tmp
+                }
+                progress = min(1.0, progress)
+
+                let lineWidth: CGFloat = component.lineWidth
+
+                let pathDiameter: CGFloat
+
+                pathDiameter = diameter - lineWidth
+
+                var angle: Double = 0.0
+                angle *= 4.0
+
+                context.translateBy(x: diameter / 2.0, y: diameter / 2.0)
+                context.rotate(by: CGFloat(angle.truncatingRemainder(dividingBy: Double.pi * 2.0)))
+                context.translateBy(x: -diameter / 2.0, y: -diameter / 2.0)
+
+                let path = UIBezierPath(arcCenter: CGPoint(x: diameter / 2.0, y: diameter / 2.0), radius: pathDiameter / 2.0, startAngle: startAngle, endAngle: endAngle, clockwise: true)
+                path.lineWidth = lineWidth
+                path.lineCapStyle = .round
+                path.stroke()
+
+                context.restoreGState()
+            }
+
+            if #available(iOS 10.0, *) {
+                let renderer = UIGraphicsImageRenderer(bounds: CGRect(origin: CGPoint(), size: availableSize))
+                let image = renderer.image { context in
+                    UIGraphicsPushContext(context.cgContext)
+                    draw(context: context.cgContext)
+                    UIGraphicsPopContext()
+                }
+                self.layer.contents = image.cgImage
+            } else {
+                UIGraphicsBeginImageContextWithOptions(availableSize, false, 0.0)
+                draw(context: UIGraphicsGetCurrentContext()!)
+                self.layer.contents = UIGraphicsGetImageFromCurrentImageContext()?.cgImage
+                UIGraphicsEndImageContext()
+            }
+
+            return availableSize
+        }
+    }
+
+    func makeView() -> View {
+        return View()
+    }
+
+    func update(view: View, availableSize: CGSize, transition: Transition) -> CGSize {
+        return view.update(component: self, availableSize: availableSize, transition: transition)
+    }
+}
+
+final class CheckComponent: Component {
+    let color: UIColor
+    let lineWidth: CGFloat
+    let value: CGFloat
+
+    init(
+        color: UIColor,
+        lineWidth: CGFloat,
+        value: CGFloat
+    ) {
+        self.color = color
+        self.lineWidth = lineWidth
+        self.value = value
+    }
+
+    static func ==(lhs: CheckComponent, rhs: CheckComponent) -> Bool {
+        if !lhs.color.isEqual(rhs.color) {
+            return false
+        }
+        if lhs.lineWidth != rhs.lineWidth {
+            return false
+        }
+        if lhs.value != rhs.value {
+            return false
+        }
+        return true
+    }
+
+    final class View: UIView {
+        init() {
+            super.init(frame: CGRect())
+        }
+
+        required init?(coder aDecoder: NSCoder) {
+            preconditionFailure()
+        }
+
+        func update(component: CheckComponent, availableSize: CGSize, transition: Transition) -> CGSize {
+            func draw(context: CGContext) {
+                let size = availableSize
+
+                let diameter = size.width
+
+                let factor = diameter / 50.0
+
+                context.saveGState()
+
+                context.setBlendMode(.normal)
+                context.setFillColor(component.color.cgColor)
+                context.setStrokeColor(component.color.cgColor)
+
+                let center = CGPoint(x: diameter / 2.0, y: diameter / 2.0)
+
+                let lineWidth = component.lineWidth
+
+                context.setLineWidth(max(1.7, lineWidth * factor))
+                context.setLineCap(.round)
+                context.setLineJoin(.round)
+                context.setMiterLimit(10.0)
+
+                let progress = component.value
+                let firstSegment: CGFloat = max(0.0, min(1.0, progress * 3.0))
+
+                var s = CGPoint(x: center.x - 10.0 * factor, y: center.y + 1.0 * factor)
+                var p1 = CGPoint(x: 7.0 * factor, y: 7.0 * factor)
+                var p2 = CGPoint(x: 13.0 * factor, y: -15.0 * factor)
+
+                if diameter < 36.0 {
+                    s = CGPoint(x: center.x - 7.0 * factor, y: center.y + 1.0 * factor)
+                    p1 = CGPoint(x: 4.5 * factor, y: 4.5 * factor)
+                    p2 = CGPoint(x: 10.0 * factor, y: -11.0 * factor)
+                }
+
+                if !firstSegment.isZero {
+                    if firstSegment < 1.0 {
+                        context.move(to: CGPoint(x: s.x + p1.x * firstSegment, y: s.y + p1.y * firstSegment))
+                        context.addLine(to: s)
+                    } else {
+                        let secondSegment = (progress - 0.33) * 1.5
+                        context.move(to: CGPoint(x: s.x + p1.x + p2.x * secondSegment, y: s.y + p1.y + p2.y * secondSegment))
+                        context.addLine(to: CGPoint(x: s.x + p1.x, y: s.y + p1.y))
+                        context.addLine(to: s)
+                    }
+                }
+                context.strokePath()
+
+                context.restoreGState()
+            }
+
+            if #available(iOS 10.0, *) {
+                let renderer = UIGraphicsImageRenderer(bounds: CGRect(origin: CGPoint(), size: availableSize))
+                let image = renderer.image { context in
+                    UIGraphicsPushContext(context.cgContext)
+                    draw(context: context.cgContext)
+                    UIGraphicsPopContext()
+                }
+                self.layer.contents = image.cgImage
+            } else {
+                UIGraphicsBeginImageContextWithOptions(availableSize, false, 0.0)
+                draw(context: UIGraphicsGetCurrentContext()!)
+                self.layer.contents = UIGraphicsGetImageFromCurrentImageContext()?.cgImage
+                UIGraphicsEndImageContext()
+            }
+
+            return availableSize
+        }
+    }
+
+    func makeView() -> View {
+        return View()
+    }
+
+    func update(view: View, availableSize: CGSize, transition: Transition) -> CGSize {
+        return view.update(component: self, availableSize: availableSize, transition: transition)
+    }
+}
+
+final class AvatarComponent: Component {
+    let context: AccountContext
+    let peer: EnginePeer
+
+    init(context: AccountContext, peer: EnginePeer) {
+        self.context = context
+        self.peer = peer
+    }
+
+    static func ==(lhs: AvatarComponent, rhs: AvatarComponent) -> Bool {
+        if lhs.context !== rhs.context {
+            return false
+        }
+        if lhs.peer != rhs.peer {
+            return false
+        }
+        return true
+    }
+
+    final class View: UIView {
+        private let avatarNode: AvatarNode
+
+        init() {
+            self.avatarNode = AvatarNode(font: avatarPlaceholderFont(size: 26.0))
+
+            super.init(frame: CGRect())
+
+            self.addSubview(self.avatarNode.view)
+        }
+
+        required init?(coder aDecoder: NSCoder) {
+            preconditionFailure()
+        }
+
+        func update(component: AvatarComponent, availableSize: CGSize, transition: Transition) -> CGSize {
+            self.avatarNode.frame = CGRect(origin: CGPoint(), size: availableSize)
+            self.avatarNode.setPeer(context: component.context, theme: component.context.sharedContext.currentPresentationData.with({ $0 }).theme, peer: component.peer._asPeer(), synchronousLoad: true)
+
+            return availableSize
+        }
+    }
+
+    func makeView() -> View {
+        return View()
+    }
+
+    func update(view: View, availableSize: CGSize, transition: Transition) -> CGSize {
+        return view.update(component: self, availableSize: availableSize, transition: transition)
+    }
+}
+
+final class ChatOverscrollControl: CombinedComponent {
+    let text: String
+    let backgroundColor: UIColor
+    let foregroundColor: UIColor
+    let peer: EnginePeer?
+    let context: AccountContext
+    let expandProgress: CGFloat
+
+    init(
+        text: String,
+        backgroundColor: UIColor,
+        foregroundColor: UIColor,
+        peer: EnginePeer?,
+        context: AccountContext,
+        expandProgress: CGFloat
+    ) {
+        self.text = text
+        self.backgroundColor = backgroundColor
+        self.foregroundColor = foregroundColor
+        self.peer = peer
+        self.context = context
+        self.expandProgress = expandProgress
+    }
+
+    static func ==(lhs: ChatOverscrollControl, rhs: ChatOverscrollControl) -> Bool {
+        if lhs.text != rhs.text {
+            return false
+        }
+        if !lhs.backgroundColor.isEqual(rhs.backgroundColor) {
+            return false
+        }
+        if !lhs.foregroundColor.isEqual(rhs.foregroundColor) {
+            return false
+        }
+        if lhs.peer != rhs.peer {
+            return false
+        }
+        if lhs.context !== rhs.context {
+            return false
+        }
+        if lhs.expandProgress != rhs.expandProgress {
+            return false
+        }
+        return true
+    }
+
+    static var body: Body {
+        let avatarBackground = Child(BlurredRoundedRectangle.self)
+        let avatarExpandProgress = Child(RadialProgressComponent.self)
+        let avatarCheck = Child(CheckComponent.self)
+        let avatar = Child(AvatarComponent.self)
+        let textBackground = Child(BlurredRoundedRectangle.self)
+        let text = Child(Text.self)
+
+        return { context in
+            let text = text.update(
+                component: Text(
+                    text: context.component.text,
+                    font: Font.regular(12.0),
+                    color: context.component.foregroundColor
+                ),
+                availableSize: CGSize(width: context.availableSize.width, height: 100.0),
+                transition: context.transition
+            )
+
+            let textHorizontalPadding: CGFloat = 6.0
+            let textVerticalPadding: CGFloat = 2.0
+            let avatarSize: CGFloat = 48.0
+            let avatarPadding: CGFloat = 8.0
+            let avatarTextSpacing: CGFloat = 8.0
+            let avatarProgressPadding: CGFloat = 2.5
+
+            let avatarBackgroundSize: CGFloat = context.component.peer != nil ? (avatarSize + avatarPadding * 2.0) : avatarSize
+
+            let avatarBackground = avatarBackground.update(
+                component: BlurredRoundedRectangle(
+                    color: context.component.backgroundColor
+                ),
+                availableSize: CGSize(width: avatarBackgroundSize, height: avatarBackgroundSize),
+                transition: context.transition
+            )
+
+            let avatarCheck = Condition(context.component.peer == nil, { () -> _UpdatedChildComponent in
+                let avatarCheckSize = avatarBackgroundSize + 2.0
+
+                return avatarCheck.update(
+                    component: CheckComponent(
+                        color: context.component.foregroundColor,
+                        lineWidth: 2.5,
+                        value: 1.0
+                    ),
+                    availableSize: CGSize(width: avatarCheckSize, height: avatarCheckSize),
+                    transition: context.transition
+                )
+            })
+
+            let avatarExpandProgress = avatarExpandProgress.update(
+                component: RadialProgressComponent(
+                    color: context.component.foregroundColor,
+                    lineWidth: 2.5,
+                    value: context.component.peer == nil ? 0.0 : context.component.expandProgress
+                ),
+                availableSize: CGSize(width: avatarBackground.size.width - avatarProgressPadding * 2.0, height: avatarBackground.size.height - avatarProgressPadding * 2.0),
+                transition: context.transition
+            )
+
+            let textBackground = textBackground.update(
+                component: BlurredRoundedRectangle(
+                    color: context.component.backgroundColor
+                ),
+                availableSize: CGSize(width: text.size.width + textHorizontalPadding * 2.0, height: text.size.height + textVerticalPadding * 2.0),
+                transition: context.transition
+            )
+
+            let size = CGSize(width: context.availableSize.width, height: avatarBackground.size.height + avatarTextSpacing + textBackground.size.height)
+
+            let avatarBackgroundFrame = avatarBackground.size.topCentered(in: CGRect(origin: CGPoint(), size: size))
+
+            let avatar = context.component.peer.flatMap { peer in
+                avatar.update(
+                    component: AvatarComponent(
+                        context: context.component.context,
+                        peer: peer
+                    ),
+                    availableSize: CGSize(width: avatarSize, height: avatarSize),
+                    transition: context.transition
+                )
+            }
+
+            context.add(avatarBackground
+                .position(CGPoint(
+                    x: avatarBackgroundFrame.midX,
+                    y: avatarBackgroundFrame.midY
+                ))
+            )
+
+            if let avatarCheck = avatarCheck {
+                context.add(avatarCheck
+                    .position(CGPoint(
+                        x: avatarBackgroundFrame.midX,
+                        y: avatarBackgroundFrame.midY
+                    ))
+                )
+            }
+
+            context.add(avatarExpandProgress
+                .position(CGPoint(
+                    x: avatarBackgroundFrame.midX,
+                    y: avatarBackgroundFrame.midY
+                ))
+            )
+
+            if let avatar = avatar {
+                context.add(avatar
+                    .position(CGPoint(
+                        x: avatarBackgroundFrame.midX,
+                        y: avatarBackgroundFrame.midY
+                    ))
+                )
+            }
+
+            let textBackgroundFrame = textBackground.size.bottomCentered(in: CGRect(origin: CGPoint(), size: size))
+            context.add(textBackground
+                .position(CGPoint(
+                    x: textBackgroundFrame.midX,
+                    y: textBackgroundFrame.midY
+                ))
+            )
+
+            let textFrame = text.size.centered(in: textBackgroundFrame)
+            context.add(text
+                .position(CGPoint(
+                    x: textFrame.midX,
+                    y: textFrame.midY
+                ))
+            )
+
+            return size
+        }
+    }
+}