import Foundation
import Observation
import SwiftData
#if os(iOS)
import ActivityKit
#endif

@MainActor
@Observable
final class TaskViewModel {
    private(set) var tasks: [TaskItem] = []
    private(set) var activeTimerStartDates: [UUID: Date] = [:]
    private(set) var elapsedSeconds: [UUID: Int] = [:]

    private var context: ModelContext?
    private var timerTasks: [UUID: Task<Void, Never>] = [:]
#if os(iOS)
    private var liveActivities: [UUID: Activity<TimerActivityAttributes>] = [:]
#endif

    func setup(context: ModelContext) {
        self.context = context
        fetchTasks()
    }

    func fetchTasks() {
        guard let context else { return }
        let descriptor = FetchDescriptor<TaskItem>(sortBy: [SortDescriptor(\.name)])
        tasks = (try? context.fetch(descriptor)) ?? []
    }

    func addTask(name: String, icon: String, type: TaskType, category: Category? = nil) {
        guard let context else { return }
        let item = TaskItem(name: name, icon: icon, type: type, category: category)
        context.insert(item)
        try? context.save()
        fetchTasks()
    }

    func deleteTask(_ task: TaskItem) {
        stopTimer(for: task)
        guard let context else { return }
        context.delete(task)
        try? context.save()
        fetchTasks()
    }

    func addCount(to task: TaskItem) {
        guard let context else { return }
        let log = TaskLog(date: .now, duration: 0, count: 1)
        log.task = task
        context.insert(log)
        try? context.save()
    }

    func toggleTimer(for task: TaskItem) {
        if activeTimerStartDates[task.id] != nil {
            stopTimer(for: task)
        } else {
            startTimer(for: task)
        }
    }

    func isTimerRunning(for taskID: UUID) -> Bool {
        activeTimerStartDates[taskID] != nil
    }

    func formattedElapsed(for taskID: UUID) -> String {
        let s = elapsedSeconds[taskID] ?? 0
        let h = s / 3600
        let m = (s % 3600) / 60
        let sec = s % 60
        return h > 0
            ? String(format: "%d:%02d:%02d", h, m, sec)
            : String(format: "%02d:%02d", m, sec)
    }

    func todayCount(for task: TaskItem) -> Int {
        task.logs
            .filter { Calendar.current.isDateInToday($0.date) }
            .reduce(0) { $0 + $1.count }
    }

    // MARK: - Timer

    private func startTimer(for task: TaskItem) {
        let startDate = Date.now
        activeTimerStartDates[task.id] = startDate
        elapsedSeconds[task.id] = 0
        startLiveActivity(for: task, startDate: startDate)

        let taskID = task.id
        timerTasks[taskID] = Task { [weak self] in
            while !Task.isCancelled {
                try? await Task.sleep(for: .seconds(1))
                guard !Task.isCancelled, let self else { break }
                let elapsed = Int(Date.now.timeIntervalSince(startDate))
                self.elapsedSeconds[taskID] = elapsed
                await self.updateLiveActivity(taskID: taskID, elapsed: elapsed, startDate: startDate)
            }
        }
    }

    private func stopTimer(for task: TaskItem) {
        guard let startDate = activeTimerStartDates[task.id] else { return }

        timerTasks[task.id]?.cancel()
        timerTasks.removeValue(forKey: task.id)

        let duration = Date.now.timeIntervalSince(startDate)
        activeTimerStartDates.removeValue(forKey: task.id)
        elapsedSeconds.removeValue(forKey: task.id)

        endLiveActivity(for: task)

        guard let context else { return }
        let log = TaskLog(date: .now, duration: duration, count: 0)
        log.task = task
        context.insert(log)
        try? context.save()
    }

    // MARK: - ActivityKit

    private func startLiveActivity(for task: TaskItem, startDate: Date) {
#if os(iOS)
        guard ActivityAuthorizationInfo().areActivitiesEnabled else { return }
        let attrs = TimerActivityAttributes(taskName: task.name, taskIcon: task.icon)
        let state = TimerActivityAttributes.ContentState(startDate: startDate, elapsedSeconds: 0)
        let content = ActivityContent(state: state, staleDate: nil)
        do {
            let activity = try Activity.request(attributes: attrs, content: content)
            liveActivities[task.id] = activity
        } catch {
            // Live Activity unavailable (simulator, denied, or OS < 16.2)
        }
#endif
    }

    private func updateLiveActivity(taskID: UUID, elapsed: Int, startDate: Date) async {
#if os(iOS)
        guard let activity = liveActivities[taskID] else { return }
        let state = TimerActivityAttributes.ContentState(startDate: startDate, elapsedSeconds: elapsed)
        await activity.update(ActivityContent(state: state, staleDate: nil))
#endif
    }

    private func endLiveActivity(for task: TaskItem) {
#if os(iOS)
        guard let activity = liveActivities[task.id] else { return }
        liveActivities.removeValue(forKey: task.id)
        Task {
            await activity.end(nil, dismissalPolicy: .immediate)
        }
#endif
    }
}