Initial implementation of channel overscroll navigation

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
+    }
+}