import HostRegistry
import SwiftUI

/// T-iOS-15 · Root of the app: route switch (Pairing / SessionList), terminal
/// push, add-host sheet, scenePhase forwarding and the privacy shade.
///
/// The shade is the TOPMOST layer of this ZStack and appears whenever
/// `scenePhase != .active` (exact rule — PrivacyShadePolicy + tests); it
/// covers the whole navigation tree, terminal included. Sheets live above any
/// overlay, but no sheet renders terminal bytes (pairing / plan gate only).
struct RootView: View {
    @Bindable var coordinator: AppCoordinator
    @Environment(\.scenePhase) private var scenePhase

    var body: some View {
        ZStack {
            NavigationStack {
                rootContent
                    .navigationDestination(isPresented: terminalBinding) {
                        terminalDestination
                    }
            }
            if PrivacyShadePolicy.isShadeVisible(for: scenePhase) {
                PrivacyShadeView()
            }
        }
        .task { await coordinator.bootstrap() }
        .onChange(of: scenePhase) { _, phase in
            coordinator.handleScenePhase(phase)
        }
        .sheet(
            isPresented: $coordinator.isAddHostPresented,
            onDismiss: { coordinator.addHostDismissed() }
        ) {
            addHostSheet
        }
    }

    // MARK: - Route switch

    @ViewBuilder private var rootContent: some View {
        switch coordinator.route {
        case .loading:
            ProgressView()
        case .pairing:
            firstRunPairing
        case .sessions:
            sessionList
        }
    }

    @ViewBuilder private var firstRunPairing: some View {
        if let viewModel = coordinator.rootPairingViewModel {
            PairingScreen(viewModel: viewModel) { host in
                coordinator.completeFirstPairing(host)
            }
        } else {
            ProgressView()
        }
    }

    private var sessionList: some View {
        SessionListScreen(
            viewModel: coordinator.sessionList,
            onOpen: { coordinator.open($0) },
            onAddHost: { coordinator.presentAddHost() }
        )
        .safeAreaInset(edge: .bottom) { continueLastBanner }
    }

    // MARK: - "继续上次" highlight (cold start step 5)

    @ViewBuilder private var continueLastBanner: some View {
        if coordinator.continueLastSessionId != nil {
            Button {
                coordinator.openContinueLast()
            } label: {
                Label(RootCopy.continueLast, systemImage: "arrow.uturn.forward.circle.fill")
                    .frame(maxWidth: .infinity)
            }
            .buttonStyle(.borderedProminent)
            .padding(.horizontal, RootMetrics.bannerHorizontalPadding)
            .padding(.vertical, RootMetrics.bannerVerticalPadding)
            .background(.thinMaterial)
        }
    }

    // MARK: - Terminal push

    private var terminalBinding: Binding<Bool> {
        Binding(
            get: { coordinator.terminalController != nil },
            set: { presented in
                guard !presented else { return }
                coordinator.closeTerminal() // back → engine.close() (detach)
            }
        )
    }

    @ViewBuilder private var terminalDestination: some View {
        if let controller = coordinator.terminalController {
            TerminalContainerView(controller: controller)
        }
    }

    // MARK: - Add-host sheet (multi-host entry, list header)

    @ViewBuilder private var addHostSheet: some View {
        if let viewModel = coordinator.addHostPairingViewModel {
            NavigationStack {
                PairingScreen(viewModel: viewModel) { host in
                    coordinator.completeAddHost(host)
                }
            }
        }
    }
}

private enum RootMetrics {
    static let bannerHorizontalPadding: CGFloat = 16
    static let bannerVerticalPadding: CGFloat = 8
}

private enum RootCopy {
    static let continueLast = "继续上次会话"
}