import Foundation
import HostRegistry
import Observation
import SwiftUI

/// T-iOS-15 · Navigation + lifecycle owner: Pairing → SessionList → Terminal
/// with the production dependency graph (plan §7 T-iOS-15 step 1).
///
/// - Cold start: read the host store once — no paired host → Pairing, else
///   SessionList (`ColdStartPolicy.initialRoute`).
/// - `SessionListScreen.onOpen` → build ONE `TerminalSessionController`
///   (single foreground session, plan §1) and push the terminal.
/// - Back → `closeTerminal()` → `engine.close()` (detach; PTY keeps running).
/// - scenePhase is forwarded to the open controller (`.background` →
///   suspend/close, `.active` → resume/rebuild). The privacy shade is view
///   layer (RootView + PrivacyShadePolicy), not coordinator state.
@MainActor
@Observable
final class AppCoordinator {
    private(set) var route: ColdStartPolicy.RootRoute = .loading
    private(set) var terminalController: TerminalSessionController?
    /// First-run pairing VM (root route). Recreated per entry to keep pairing
    /// state machines single-shot.
    private(set) var rootPairingViewModel: PairingViewModel?
    /// Add-host pairing VM (sheet from the list header).
    private(set) var addHostPairingViewModel: PairingViewModel?
    var isAddHostPresented = false

    let sessionList: SessionListViewModel
    @ObservationIgnored let environment: AppEnvironment

    init(environment: AppEnvironment) {
        self.environment = environment
        sessionList = SessionListViewModel(
            hostStore: environment.hostStore,
            http: environment.http,
            clock: ContinuousClock()
        )
    }

    // MARK: - Cold start

    /// Decide the boot route from the host store. A store READ failure routes
    /// to the session list, whose own `reloadHosts` surfaces the explicit
    /// error copy (never a silent empty pairing screen hiding a broken store).
    func bootstrap() async {
        guard route == .loading else { return }
        do {
            let hosts = try await environment.hostStore.loadAll()
            route = ColdStartPolicy.initialRoute(pairedHostCount: hosts.count)
        } catch {
            route = .sessions
        }
        if route == .pairing {
            rootPairingViewModel = makePairingViewModel()
        }
    }

    /// First-run pairing done → move to the list (the paired host is already
    /// in the store — PairingViewModel upserts before signalling).
    func completeFirstPairing(_ host: HostRegistry.Host) {
        rootPairingViewModel = nil
        route = .sessions
        Task { await sessionList.reloadHosts() }
    }

    // MARK: - Add-host sheet (list header hook)

    func presentAddHost() {
        addHostPairingViewModel = makePairingViewModel()
        isAddHostPresented = true
    }

    func completeAddHost(_ host: HostRegistry.Host) {
        isAddHostPresented = false
        addHostDismissed()
    }

    /// Sheet gone (paired OR cancelled): drop the VM and refresh hosts — the
    /// list VM keeps the active host if it still exists.
    func addHostDismissed() {
        addHostPairingViewModel = nil
        Task { await sessionList.reloadHosts() }
    }

    // MARK: - Terminal open/close

    /// `SessionListScreen.onOpen` (one navigation signal per tap) and the
    /// "继续上次" banner both land here. `sessionId == nil` = new session.
    func open(_ request: SessionListViewModel.OpenRequest) {
        guard terminalController == nil else { return } // one foreground session
        let controller = TerminalSessionController(
            host: request.host,
            sessionId: request.sessionId,
            environment: environment,
            onPendingChanged: { [weak self] sessionId, pending in
                self?.sessionList.setPendingApproval(sessionId: sessionId, pending: pending)
            }
        )
        terminalController = controller
        controller.start()
    }

    /// Back navigation popped the terminal: explicit detach.
    func closeTerminal() {
        terminalController?.teardown()
        terminalController = nil
    }

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

    var continueLastSessionId: UUID? {
        ColdStartPolicy.continueLastSessionId(
            activeHost: sessionList.activeHost,
            store: environment.lastSessionStore
        )
    }

    func openContinueLast() {
        guard let host = sessionList.activeHost, let sessionId = continueLastSessionId else {
            return
        }
        open(SessionListViewModel.OpenRequest(id: UUID(), host: host, sessionId: sessionId))
    }

    // MARK: - scenePhase (plan §7 T-iOS-15 step 3)

    func handleScenePhase(_ phase: ScenePhase) {
        switch phase {
        case .background:
            terminalController?.suspend()
        case .active:
            terminalController?.resumeIfNeeded()
        case .inactive:
            break // transient; shade covers it at the view layer
        @unknown default:
            break
        }
    }

    // MARK: - Helpers

    private func makePairingViewModel() -> PairingViewModel {
        PairingViewModel(store: environment.hostStore, probe: environment.probe)
    }
}