Initial implementation of channel overscroll navigation

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
+    }
+}