HPSFNavigationStack

HPSFNavigationStack.swift

import SwiftUI
import UIKit

struct HPSFNavigationStack<SliceID: Hashable, Content: View>: View {
    private var spec: Spec
    enum Action {
        case userNavigation([SliceID])
    }
    init(slices: [SliceID], content: @escaping (SliceID) -> Content) {
        spec = Spec(slices: slices, content: content, action: noop)
    }
    var body: some View {
        Rep(spec: spec)
    }
    func action(_ action: @escaping (Action) -> Void) -> Self {
        var copy = self
        copy.spec.action = action
        return copy
    }
}

private extension HPSFNavigationStack {
    struct Spec {
        var slices: [SliceID]
        var content: (SliceID) -> Content
        var action: (Action) -> ()
    }
    struct Rep: UIViewControllerRepresentable {
        var spec: Spec
        func makeUIViewController(context: Context) -> Impl {
            Impl(spec: spec)
        }
        func updateUIViewController(_ impl: Impl, context: Context) {
            impl.set(spec: spec)
        }
        
        final class Impl: UINavigationController, UINavigationControllerDelegate {
            init(spec: Spec) {
                self.spec = spec
                super.init(nibName: nil, bundle: nil)
                set(spec: spec)
            }
            required init?(coder aDecoder: NSCoder) {
                unsupported()
            }
            
            private var spec: Spec
            private var sliceViewControllers = [SliceIDAttachedHostingController]()
            func set(spec: Spec) {
                self.spec = spec
                let oldVCs = sliceViewControllers
                let newVCs = spec.slices.enumerated().map { (i, sliceID) in
                    if oldVCs.indices.contains(i) {
                        oldVCs[i]
                    }
                    else {
                        SliceIDAttachedHostingController(sliceID: sliceID, rootView: spec.content(sliceID))
                    }
                }
                sliceViewControllers = newVCs
                setViewControllers(newVCs, animated: true)
            }
            
            func navigationController(_ navigationController: UINavigationController, didShow viewController: UIViewController, animated: Bool) {
                let sliceIDs = viewControllers.map { $0 as! SliceIDAttachedHostingController }.map(\.sliceID)
                spec.action(.userNavigation(sliceIDs))
            }
            
            final class SliceIDAttachedHostingController: UIHostingController<Content> {
                let sliceID: SliceID
                init(sliceID: SliceID, rootView: Content) {
                    self.sliceID = sliceID
                    super.init(rootView: rootView)
                }
                required init?(coder aDecoder: NSCoder) {
                    unsupported()
                }
            }
        }
    }
}