// App-wide state: whether the watch is paired, the navigation path, and the latest feed.

import Foundation
import Observation
import UserNotifications
import WatchKit

enum Route: Hashable, Sendable {
    case thread(hostId: String, threadId: String)
    case newThread
}

@MainActor @Observable
final class AppModel {
    enum Mode: Equatable {
        case unpaired
        case paired(Credentials)
        /// Serves fixtures from `DemoGateway`. Nothing leaves the watch.
        case demo
    }

    /// The one instance the app delegate and notification handler share with the views.
    static let shared = AppModel(launchArguments: ProcessInfo.processInfo.arguments)

    var mode: Mode
    var path: [Route] = []
    private(set) var feed: Feed?
    private(set) var feedError: String?
    private var apnsToken: String?
    private var refreshing = false

    init(mode: Mode, feed: Feed? = nil, path: [Route] = []) {
        self.mode = mode
        self.feed = feed
        self.path = path
    }

    /// `-demo` starts in demo mode. `-screen new` or `-thread <hostId>/<threadId>` opens that
    /// screen, which is how the screenshots in watch/screenshots are taken.
    convenience init(launchArguments args: [String]) {
        let demo = args.contains("-demo")
        let mode: Mode = demo ? .demo : DeviceStore.load().map(Mode.paired) ?? .unpaired
        var path: [Route] = []
        if demo, let i = args.firstIndex(of: "-screen"), i + 1 < args.count, args[i + 1] == "new" {
            path = [.newThread]
        }
        if demo, let i = args.firstIndex(of: "-thread"), i + 1 < args.count {
            let parts = args[i + 1].split(separator: "/", maxSplits: 1).map(String.init)
            if parts.count == 2 { path = [.thread(hostId: parts[0], threadId: parts[1])] }
        }
        self.init(mode: mode, path: path)
    }

    var isPaired: Bool {
        if case .paired = mode { return true }
        return false
    }

    var api: any GatewayAPI {
        switch mode {
        case let .paired(credentials):
            GatewayClient(baseURL: credentials.gatewayURL, token: credentials.token)
        case .demo:
            DemoGateway.shared
        case .unpaired:
            GatewayClient(baseURL: URL(string: DeviceStore.defaultGatewayURL)!, token: nil)
        }
    }

    // MARK: - Pairing

    func pair(gatewayURL: URL, code: String) async throws {
        let deviceName = WKInterfaceDevice.current().name
        let response = try await GatewayClient.pair(baseURL: gatewayURL, code: code, deviceName: deviceName)
        let credentials = Credentials(gatewayURL: gatewayURL, token: response.deviceToken)
        DeviceStore.save(credentials)
        mode = .paired(credentials)
        feed = nil
        feedError = nil
        path = []
        await enableNotifications()
    }

    func startDemo() {
        mode = .demo
        feed = nil
        feedError = nil
        path = []
    }

    /// Back to the pairing screen. A real token is forgotten; the gateway URL is kept.
    func signOut() {
        if isPaired { DeviceStore.clearToken() }
        mode = .unpaired
        feed = nil
        feedError = nil
        path = []
    }

    /// The message to show for a failed call. A 401 sends the app back to pairing and returns nil.
    func message(for error: any Error) -> String? {
        if error is CancellationError { return nil }
        if let error = error as? GatewayError, error == .unauthorized {
            signOut()
            return nil
        }
        return error.localizedDescription
    }

    // MARK: - Feed

    func refreshFeed() async {
        guard mode != .unpaired, !refreshing else { return }
        refreshing = true
        defer { refreshing = false }
        do {
            feed = try await api.feed()
            feedError = nil
        } catch {
            feedError = message(for: error)
        }
    }

    func open(_ route: Route) {
        path = [route]
    }

    // MARK: - Notifications

    func enableNotifications() async {
        guard isPaired else { return }
        let center = UNUserNotificationCenter.current()
        let granted = (try? await center.requestAuthorization(options: [.alert, .sound, .badge])) ?? false
        if granted {
            WKApplication.shared().registerForRemoteNotifications()
        }
    }

    func didRegister(apnsToken data: Data) {
        apnsToken = data.map { String(format: "%02x", $0) }.joined()
        Task { await sendPushToken() }
    }

    private func sendPushToken() async {
        guard isPaired, let apnsToken else { return }
        #if DEBUG
        let environment = PushRegistration.Environment.sandbox
        #else
        let environment = PushRegistration.Environment.production
        #endif
        do {
            try await api.registerPush(PushRegistration(apnsToken: apnsToken, apnsEnvironment: environment))
        } catch {
            _ = message(for: error)
        }
    }

    func notificationArrived() {
        Task { await refreshFeed() }
    }
}

extension AppModel {
    /// A demo model with the fixture feed already loaded, for previews.
    static func preview(path: [Route] = []) -> AppModel {
        AppModel(mode: .demo, feed: DemoFixtures.previewFeed(), path: path)
    }
}