// 1. Add NavigationPath logging
NavigationStack(path: $path) {
    RootView()
        .onChange(of: path.count) { oldCount, newCount in
            print("📍 Path changed: \(oldCount) → \(newCount)")
            // If this never fires, link isn't modifying path
            // If it fires unexpectedly, something else modifies path
        }
}

// 2. Check navigationDestination is visible
// Put temporary print in destination closure
.navigationDestination(for: Recipe.self) { recipe in
    let _ = print("🔗 Destination for Recipe: \(recipe.name)")
    RecipeDetail(recipe: recipe)
}
// If this never prints, destination isn't being evaluated

// 3. Check NavigationLink is inside NavigationStack
// Visual inspection: Trace from NavigationLink up view hierarchy
// Must hit NavigationStack, not another container first

// 4. Check path state location
// @State must be in stable view (not recreated each render)
// Must be @State, @StateObject, or @Observable — not local variable

// 5. Test basic case in isolation
// Create minimal reproduction
NavigationStack {
    NavigationLink("Test", value: "test")
        .navigationDestination(for: String.self) { str in
            Text("Pushed: \(str)")
        }
}
// If this works, problem is in your specific setup

Navigation problem?
├─ Navigation tap does nothing?
│  ├─ NavigationLink inside NavigationStack?
│  │  ├─ No → Pattern 1a (Link outside Stack)
│  │  └─ Yes → Check navigationDestination
│  │
│  ├─ navigationDestination registered?
│  │  ├─ Inside lazy container? → Pattern 1b (Lazy Loading)
│  │  ├─ Type mismatch? → Pattern 1c (Type Registration)
│  │  └─ Blocked by sheet/popover? → Pattern 1d (Modal Blocking)
│  │
│  └─ Using view-based link?
│     └─ → Pattern 1e (Deprecated API)
│
├─ Unexpected pop back?
│  ├─ Immediate pop after push?
│  │  ├─ View body recreating path? → Pattern 2a (Path Recreation)
│  │  ├─ @State in wrong view? → Pattern 2a (State Location)
│  │  └─ ForEach id changing? → Pattern 2c (Identity Change)
│  │
│  ├─ Pop when shouldn't?
│  │  ├─ External code calling removeLast? → Pattern 2b (Unexpected Modification)
│  │  ├─ Task cancelled? → Pattern 2b (Async Cancellation)
│  │  └─ MainActor issue? → Pattern 2d (Threading)
│  │
│  └─ Back button behavior wrong?
│     └─ → Pattern 2e (Stack Corruption)
│
├─ Deep link not working?
│  ├─ URL not received?
│  │  ├─ onOpenURL not called? → Check URL scheme in Info.plist
│  │  └─ Universal Links issue? → Check apple-app-site-association
│  │
│  ├─ URL received, path not updated?
│  │  ├─ path.append not on MainActor? → Pattern 3a (Threading)
│  │  ├─ Timing issue (app not ready)? → Pattern 3b (Initialization)
│  │  └─ NavigationStack not created yet? → Pattern 3b (Lifecycle)
│  │
│  └─ Path updated, wrong screen shown?
│     ├─ Wrong path order? → Pattern 3c (Path Construction)
│     ├─ Wrong type appended? → Pattern 3c (Type Mismatch)
│     └─ Item not found? → Pattern 3d (Data Resolution)
│
├─ State lost?
│  ├─ Lost on tab switch?
│  │  ├─ Shared NavigationStack? → Pattern 4a (Shared State)
│  │  └─ Tab recreation? → Pattern 4a (Tab Identity)
│  │
│  ├─ Lost on background/foreground?
│  │  ├─ No SceneStorage? → Pattern 4b (No Persistence)
│  │  └─ Decode failure? → Pattern 4c (Decode Error)
│  │
│  └─ Lost on rotation/size change?
│     └─ → Pattern 4d (Layout Recreation)
│
└─ Crash?
   ├─ EXC_BAD_ACCESS in navigation code?
   │  └─ → Pattern 5a (Memory Issue)
   │
   ├─ Fatal error: type not registered?
   │  └─ → Pattern 5b (Missing Destination)
   │
   └─ Decode failure on restore?
      └─ → Pattern 5c (Restoration Crash)

// Check view hierarchy — NavigationLink must be INSIDE NavigationStack

// ❌ WRONG — Link outside stack
struct ContentView: View {
    var body: some View {
        VStack {
            NavigationLink("Go", value: "test")  // Outside stack!
            NavigationStack {
                Text("Root")
            }
        }
    }
}

// Check: Add background color to NavigationStack
NavigationStack {
    Color.red  // If link is on red, it's inside
}

// ✅ CORRECT — Link inside stack
struct ContentView: View {
    var body: some View {
        NavigationStack {
            VStack {
                NavigationLink("Go", value: "test")  // Inside stack
                Text("Root")
            }
            .navigationDestination(for: String.self) { str in
                Text("Pushed: \(str)")
            }
        }
    }
}

// ❌ WRONG — Destination inside lazy container (may not be loaded)
ScrollView {
    LazyVStack {
        ForEach(items) { item in
            NavigationLink(item.name, value: item)
                .navigationDestination(for: Item.self) { item in
                    ItemDetail(item: item)  // May not be evaluated!
                }
        }
    }
}

// ✅ CORRECT — Destination outside lazy container
ScrollView {
    LazyVStack {
        ForEach(items) { item in
            NavigationLink(item.name, value: item)
        }
    }
}
.navigationDestination(for: Item.self) { item in
    ItemDetail(item: item)  // Always available
}

// Check: Value type must EXACTLY match destination type

// Link uses Recipe
NavigationLink(recipe.name, value: recipe)  // value is Recipe

// Destination registered for... Recipe.ID?
.navigationDestination(for: Recipe.ID.self) { id in  // ❌ Wrong type!
    RecipeDetail(id: id)
}

// Match types exactly
NavigationLink(recipe.name, value: recipe)  // Recipe

.navigationDestination(for: Recipe.self) { recipe in  // ✅ Recipe
    RecipeDetail(recipe: recipe)
}

// OR change link to use ID
NavigationLink(recipe.name, value: recipe.id)  // Recipe.ID

.navigationDestination(for: Recipe.ID.self) { id in  // ✅ Recipe.ID
    RecipeDetail(id: id)
}

// ❌ WRONG — Path created in view body (reset every render)
struct ContentView: View {
    var body: some View {
        let path = NavigationPath()  // Recreated every time!
        NavigationStack(path: .constant(path)) {
            // ...
        }
    }
}

// ❌ WRONG — @State in child view that gets recreated
struct ParentView: View {
    @State var showChild = true
    var body: some View {
        if showChild {
            ChildView()  // Recreated when showChild toggles
        }
    }
}

struct ChildView: View {
    @State var path = NavigationPath()  // Lost when ChildView recreated
    // ...
}

// ✅ CORRECT — @State at stable level
struct ContentView: View {
    @State private var path = NavigationPath()  // Persists across renders

    var body: some View {
        NavigationStack(path: $path) {
            RootView()
        }
    }
}

// ✅ CORRECT — @StateObject for ObservableObject
struct ContentView: View {
    @StateObject private var navModel = NavigationModel()

    var body: some View {
        NavigationStack(path: $navModel.path) {
            RootView()
        }
    }
}

// ❌ WRONG — Modifying path from background task
func loadAndNavigate() async {
    let recipe = await fetchRecipe()
    path.append(recipe)  // ⚠️ Not on MainActor!
}

// Check: Search for path.append, path.removeLast outside @MainActor context

// ✅ CORRECT — Ensure MainActor
@MainActor
func loadAndNavigate() async {
    let recipe = await fetchRecipe()
    path.append(recipe)  // ✅ MainActor isolated
}

// OR explicitly dispatch
func loadAndNavigate() async {
    let recipe = await fetchRecipe()
    await MainActor.run {
        path.append(recipe)
    }
}

// ✅ BEST — Use @Observable with @MainActor
@Observable
@MainActor
class Router {
    var path = NavigationPath()

    func navigate(to value: any Hashable) {
        path.append(value)
    }
}

// ❌ WRONG — May be called before NavigationStack exists
.onOpenURL { url in
    handleDeepLink(url)  // NavigationStack may not be rendered yet
}

func handleDeepLink(_ url: URL) {
    path.append(parsedValue)  // Modifies path that doesn't exist yet
}

// ✅ CORRECT — Defer deep link handling
@State private var pendingDeepLink: URL?
@State private var isReady = false

var body: some View {
    NavigationStack(path: $path) {
        RootView()
            .onAppear {
                isReady = true
                if let url = pendingDeepLink {
                    handleDeepLink(url)
                    pendingDeepLink = nil
                }
            }
    }
    .onOpenURL { url in
        if isReady {
            handleDeepLink(url)
        } else {
            pendingDeepLink = url  // Queue for later
        }
    }
}

// ❌ WRONG — Wrong order (child before parent)
// URL: myapp://category/desserts/recipe/apple-pie
func handleDeepLink(_ url: URL) {
    path.append(recipe)    // Recipe pushed first
    path.append(category)  // Category pushed second — WRONG ORDER
}
// User sees Category screen, not Recipe screen

// ✅ CORRECT — Parent before child
func handleDeepLink(_ url: URL) {
    path.removeLast(path.count)  // Clear existing

    // Build hierarchy: parent → child
    path.append(category)  // First: Category
    path.append(recipe)    // Second: Recipe (shows this screen)
}

// For complex paths, build array first
var newPath: [any Hashable] = []
// Parse URL segments...
newPath.append(category)
newPath.append(subcategory)
newPath.append(item)

// Then apply
path = NavigationPath(newPath)

// ❌ WRONG — Single NavigationStack wrapping TabView
NavigationStack(path: $path) {
    TabView {
        Tab("Home") { HomeView() }
        Tab("Settings") { SettingsView() }
    }
}
// All tabs share same navigation — state mixed/lost

// ❌ WRONG — Same @State used across tabs
@State var path = NavigationPath()  // Shared
TabView {
    Tab("Home") {
        NavigationStack(path: $path) { ... }  // Uses shared path
    }
    Tab("Settings") {
        NavigationStack(path: $path) { ... }  // Same path!
    }
}

// ✅ CORRECT — Each tab has own NavigationStack
TabView {
    Tab("Home", systemImage: "house") {
        NavigationStack {  // Own stack
            HomeView()
                .navigationDestination(for: HomeItem.self) { ... }
        }
    }
    Tab("Settings", systemImage: "gear") {
        NavigationStack {  // Own stack
            SettingsView()
                .navigationDestination(for: SettingItem.self) { ... }
        }
    }
}

// For per-tab path tracking:
struct HomeTab: View {
    @State private var path = NavigationPath()  // Tab-specific

    var body: some View {
        NavigationStack(path: $path) {
            HomeView()
        }
    }
}

// ❌ WRONG — No persistence mechanism
@State private var path = NavigationPath()
// Path lost when app terminates

// ✅ CORRECT — Use SceneStorage + Codable
struct ContentView: View {
    @StateObject private var navModel = NavigationModel()
    @SceneStorage("navigation") private var savedData: Data?

    var body: some View {
        NavigationStack(path: $navModel.path) {
            RootView()
        }
        .task {
            // Restore on appear
            if let data = savedData {
                navModel.restore(from: data)
            }
            // Save on changes
            for await _ in navModel.objectWillChange.values {
                savedData = navModel.encoded()
            }
        }
    }
}

@MainActor
class NavigationModel: ObservableObject {
    @Published var path = NavigationPath()

    func encoded() -> Data? {
        guard let codable = path.codable else { return nil }
        return try? JSONEncoder().encode(codable)
    }

    func restore(from data: Data) {
        guard let codable = try? JSONDecoder().decode(
            NavigationPath.CodableRepresentation.self,
            from: data
        ) else { return }
        path = NavigationPath(codable)
    }
}

// Every type pushed on path needs a destination

// You push Recipe
path.append(recipe)  // Recipe type

// But only registered Category
.navigationDestination(for: Category.self) { ... }
// No destination for Recipe!

// Register ALL types you might push
NavigationStack(path: $path) {
    RootView()
        .navigationDestination(for: Category.self) { category in
            CategoryView(category: category)
        }
        .navigationDestination(for: Recipe.self) { recipe in
            RecipeDetail(recipe: recipe)
        }
        .navigationDestination(for: Chef.self) { chef in
            ChefProfile(chef: chef)
        }
}

// Or use enum route type for single registration
enum AppRoute: Hashable {
    case category(Category)
    case recipe(Recipe)
    case chef(Chef)
}

.navigationDestination(for: AppRoute.self) { route in
    switch route {
    case .category(let cat): CategoryView(category: cat)
    case .recipe(let recipe): RecipeDetail(recipe: recipe)
    case .chef(let chef): ChefProfile(chef: chef)
    }
}

// ❌ WRONG — Force unwrap decode
func restore(from data: Data) {
    let codable = try! JSONDecoder().decode(  // 💥 Crashes!
        NavigationPath.CodableRepresentation.self,
        from: data
    )
    path = NavigationPath(codable)
}

// Crash reasons:
// - Saved path contains type that no longer exists
// - Codable encoding changed between versions
// - Saved item was deleted

// ✅ CORRECT — Graceful decode with fallback
func restore(from data: Data) {
    do {
        let codable = try JSONDecoder().decode(
            NavigationPath.CodableRepresentation.self,
            from: data
        )
        path = NavigationPath(codable)
    } catch {
        print("Navigation restore failed: \(error)")
        path = NavigationPath()  // Start fresh
        // Optionally clear bad saved data
    }
}

// ✅ BETTER — Store IDs, resolve to objects
class NavigationModel: ObservableObject, Codable {
    var selectedIds: [String] = []  // Store IDs

    func resolvedPath(dataModel: DataModel) -> NavigationPath {
        var path = NavigationPath()
        for id in selectedIds {
            if let item = dataModel.item(withId: id) {
                path.append(item)
            }
            // Missing items silently skipped
        }
        return path
    }
}

// Release build with diagnostic logging
#if DEBUG || DIAGNOSTIC
NavigationStack(path: $path) {
    // ...
}
.onChange(of: path.count) { old, new in
    Analytics.log("nav_path_change", ["old": old, "new": new])
}
#endif

// Check analytics for:
// - path.count going to 0 unexpectedly → Path recreation
// - path.count increasing but no push → Missing destination
// - No path changes at all → Link not firing

// iOS 18 changes that affect navigation:
// 1. Stricter MainActor enforcement
// 2. Changes to view identity in TabView
// 3. New navigation lifecycle timing

// Most common iOS 18 issue:
// Code that worked by accident now fails

// Check: Any path modifications in async contexts without @MainActor?
Task {
    let result = await fetch()
    path.append(result)  // ⚠️ iOS 18 stricter about this
}

// Root cause found: NavigationPath modified from async context
// iOS 17 was lenient, iOS 18 enforces MainActor properly

// ❌ Old code (worked on iOS 17, breaks on iOS 18)
func loadAndNavigate() async {
    let recipe = await fetchRecipe()
    path.append(recipe)  // Race condition
}

// ✅ Fix: Explicit MainActor isolation
@MainActor
func loadAndNavigate() async {
    let recipe = await fetchRecipe()
    path.append(recipe)  // ✅ Safe
}

// OR: Annotate entire class
@Observable
@MainActor
class Router {
    var path = NavigationPath()

    func navigate(to value: any Hashable) {
        path.append(value)
    }
}

// 1. Test on iOS 17 device — still works
// 2. Test on iOS 18 device — now works
// 3. Test all navigation paths
// 4. Submit expedited review

// Expedited review justification:
// "Critical bug fix for iOS 18 compatibility affecting 20% of users"

Root cause identified: Navigation code wasn't properly isolated
to the main thread. iOS 18 enforces this more strictly than iOS 17.

Fix: Add @MainActor annotation to navigation code.
Already tested on iOS 17 (no regression) and iOS 18 (fixes issue).

Timeline:
- Fix ready: Now
- QA validation: 1 hour
- App Store submission: Today
- Available to users: 24-48 hours (expedited review)

Workaround for affected users: Force quit and relaunch app
often clears the issue temporarily.

iOS 18 Navigation Fix

Root cause: NavigationPath modifications in async contexts
without @MainActor isolation. iOS 17 was permissive, iOS 18 enforces.

Fix applied:
- Added @MainActor to Router class
- Updated all path.append/removeLast calls to be MainActor-isolated
- Added Swift 6 concurrency checking to catch future issues

Files changed: Router.swift, ContentView.swift, DeepLinkHandler.swift

Testing needed:
- All navigation flows
- Deep links from cold start
- Tab switching with navigation state
- Background/foreground with navigation state

// Move destination OUTSIDE lazy container
List {
    ForEach(items) { item in
        NavigationLink(item.name, value: item)
    }
}
.navigationDestination(for: Item.self) { item in
    ItemDetail(item: item)
}

// Use @State, not computed
@State private var path = NavigationPath()  // ✅ Persists

// NOT
var path: NavigationPath { NavigationPath() }  // ❌ Reset every time