import ActivityKit
import SwiftUI

@MainActor
final class LiveActivityManager: ObservableObject {
    @Published private(set) var running = false
    @Published private(set) var error: String?
    private var activity: Activity<MusicActivityAttributes>?
    private var updates: Task<Void, Never>?
    private var observer: Task<Void, Never>?
    private var last: MusicActivityAttributes.ContentState?

    init() {
        let existing = Activity<MusicActivityAttributes>.activities
            .filter { $0.activityState == .active || $0.activityState == .stale }
        if let first = existing.first {
            activity = first
            last = first.content.state
            running = true
            observe(first)
        }
        for extra in existing.dropFirst() {
            Task { await extra.end(nil, dismissalPolicy: .immediate) }
        }
    }

    static func content(_ state: MediaState, now: Date = Date()) -> MusicActivityAttributes.ContentState {
        .init(title: MusicActivityAttributes.ContentState.bounded(state.title.isEmpty ? "Без названия" : state.title),
              artist: MusicActivityAttributes.ContentState.bounded(state.artist),
              playing: state.playbackStatus == "Playing",
              position: max(0, state.position(elapsed: 0) - state.startSeconds),
              duration: max(0, state.endSeconds - state.startSeconds), updatedAt: now, connected: true)
    }

    func start(_ state: MediaState) {
        guard !running, state.hasSession, UIApplication.shared.applicationState == .active else { return }
        guard ActivityAuthorizationInfo().areActivitiesEnabled else {
            error = "Разрешите Live Activities в настройках MusicBridge на iPhone."
            return
        }
        do {
            let value = Self.content(state)
            let new = try Activity.request(attributes: MusicActivityAttributes(),
                                           content: ActivityContent(state: value, staleDate: Date().addingTimeInterval(15)),
                                           pushType: nil)
            activity = new
            last = value
            running = true
            error = nil
            observe(new)
        } catch { self.error = "Не удалось включить Live Activity: " + error.localizedDescription }
    }

    func receive(_ state: MediaState) {
        guard state.hasSession else { end(); return }
        guard let activity, running else { return }
        let value = Self.content(state)
        // Coalesce ordinary position ticks, but publish track/playback changes immediately.
        if let last, last.connected, last.title == value.title, last.artist == value.artist,
           last.playing == value.playing, last.duration == value.duration,
           abs(last.position - value.position) < 5, value.updatedAt.timeIntervalSince(last.updatedAt) < 5 { return }
        last = value
        enqueue { await activity.update(ActivityContent(state: value, staleDate: value.updatedAt.addingTimeInterval(15))) }
    }

    func unavailable() {
        guard let activity, var value = last, value.connected else { return }
        value.connected = false
        last = value
        enqueue { await activity.update(ActivityContent(state: value, staleDate: Date())) }
    }

    func end() {
        guard let activity else { return }
        self.activity = nil
        running = false
        last = nil
        observer?.cancel()
        enqueue { await activity.end(nil, dismissalPolicy: .immediate) }
    }

    private func enqueue(_ operation: @escaping @MainActor () async -> Void) {
        let previous = updates
        updates = Task { await previous?.value; await operation() }
    }

    private func observe(_ activity: Activity<MusicActivityAttributes>) {
        observer?.cancel()
        observer = Task { [weak self] in
            for await state in activity.activityStateUpdates {
                guard !Task.isCancelled, let self, self.activity?.id == activity.id else { return }
                if state == .dismissed || state == .ended {
                    self.activity = nil; self.running = false; self.last = nil
                    return
                }
            }
        }
    }
}