UINavigationController.popPublisher implementation

UINavigationController+PopPublisher.swift

import Combine
import CocoaAliases // https://github.com/capturecontext/cocoa-aliases
import FoundationExtensions // https://github.com/capturecontext/swift-foundation-extensions

// MARK: - Swizzling
// Swizzle methods that may pop some viewControllers
// with tracking versions which forward popped controllers
// to UINavigationController.popSubject

// Swift swizzling causes infinite recursion for objc methods
//
// Forum:
// https://forums.swift.org/t/dynamicreplacement-causes-infinite-recursion/52768
//
// Swift issues:
// https://github.com/apple/swift/issues/62214
// https://github.com/apple/swift/issues/53916
//
// Have to use objc swizzling
//
//extension UINavigationController {
//	@_dynamicReplacement(for: popViewController(animated:))
//	public func _trackedPopViewController(
//		animated: Bool
//	) -> CocoaViewController? {
//		let controller = popViewController(animated: animated)
//		controller.map { handlePop(of: [$0]) }
//		return controller
//	}
//
//	@_dynamicReplacement(for: popToRootViewController(animated:))
//	public func _trackedPopToRootViewController(
//		animated: Bool
//	) -> [CocoaViewController]? {
//		let controllers = popToRootViewController(animated: animated)
//		controllers.map(handlePop)
//		return controllers
//	}
//
//	@_dynamicReplacement(for: popToViewController(_:animated:))
//	public func _trackedPopToViewController(
//		_ controller: CocoaViewController,
//		animated: Bool
//	) -> [CocoaViewController]? {
//		let controllers = popToViewController(controller, animated: animated)
//		controllers.map(handlePop)
//		return controllers
//	}
//
//	@_dynamicReplacement(for: setViewControllers(_:animated:))
//	public func _trackedSetViewControllers(
//		_ controllers: [CocoaViewController],
//		animated: Bool
//	) {
//		let poppedControllers = viewControllers.filter { oldController in
//			!controllers.contains { $0 === oldController }
//		}
//
//		setViewControllers(controllers, animated: animated)
//		handlePop(of: poppedControllers)
//	}
//}

extension UINavigationController {
	// Runs once in app lifetime
	// Repeated calls do nothing
	public static let enablePopPublisher: () -> Void = {
		UINavigationController._swizzle(
			#selector(popViewController(animated:)),
			with: #selector(__swizzledPopViewController)
		)

		UINavigationController._swizzle(
			#selector(popToViewController(_:animated:)),
			with: #selector(__swizzledPopToViewController)
		)

		UINavigationController._swizzle(
			#selector(popToRootViewController(animated:)),
			with: #selector(__swizzledPopToRootViewController)
		)

		UINavigationController._swizzle(
			#selector(setViewControllers(_:animated:)),
			with: #selector(__swizzledSetViewControllers)
		)

		return {}
	}()

	// Swizzle automatically when the first
	// navigationController loads it's view
	open override func loadView() {
		UINavigationController.enablePopPublisher()
		super.viewDidLoad()
	}

	@objc dynamic func __swizzledPopViewController(
		animated: Bool
	) -> CocoaViewController? {
		let controller = __swizzledPopViewController(animated: animated)
		controller.map { handlePop(of: [$0]) }
		return controller
	}

	@objc dynamic func __swizzledPopToRootViewController(
		animated: Bool
	) -> [CocoaViewController]? {
		let controllers = __swizzledPopToRootViewController(animated: animated)
		controllers.map(handlePop)
		return controllers
	}

	@objc dynamic func __swizzledPopToViewController(
		_ controller: CocoaViewController,
		animated: Bool
	) -> [CocoaViewController]? {
		let controllers = __swizzledPopToViewController(controller, animated: animated)
		controllers.map(handlePop)
		return controllers
	}

	@objc dynamic func __swizzledSetViewControllers(
		_ controllers: [CocoaViewController],
		animated: Bool
	) {
		let poppedControllers = viewControllers.filter { oldController in
			!controllers.contains { $0 === oldController }
		}

		__swizzledSetViewControllers(controllers, animated: animated)
		handlePop(of: poppedControllers)
	}
}

// MARK: Objc swizzling helper

#warning("Move to FoundationExtensions")
fileprivate protocol NSObjectSwizzling: NSObjectProtocol {}
extension NSObjectSwizzling {
	static func _swizzle(
		_ originalSelector: Selector,
		with swizzledSelector: Selector
	) {
		let originalMethod = class_getInstanceMethod(
			Self.self,
			originalSelector
		)

		let swizzledMethod = class_getInstanceMethod(
			Self.self,
			swizzledSelector
		)

		guard
			let originalMethod,
			let swizzledMethod
		else { return }

		method_exchangeImplementations(originalMethod, swizzledMethod)
	}
}

extension NSObject: NSObjectSwizzling {}

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