// ── Shared Timer Data (App Groups) ────────────────────────────
// Bridges timer data between iOS app, watchOS, and WidgetKit
// Uses App Group UserDefaults suite for cross-process persistence

import Foundation

// MARK: - App Group Constants

enum AppGroupConstants {
    static let suiteName = "group.com.chronomind.shared"
    static let timersKey = "chronomind-timers"
    static let activeTimerKey = "chronomind-active-timer"
    static let lastUpdateKey = "chronomind-last-update"
}

// MARK: - Shared Timer Snapshot (lightweight for widgets/watch)

struct TimerSnapshot: Codable, Identifiable, Equatable {
    let id: String
    let label: String
    let type: CMTimerType
    let urgency: UrgencyLevel
    let state: CMTimerState
    let targetTime: Date
    let duration: TimeInterval?
    let startedAt: Date?
    let elapsedBeforePause: TimeInterval
    let snoozeCount: Int
    let category: String?

    // Pomodoro
    let pomodoroCurrentRound: Int?
    let pomodoroTotalRounds: Int?
    let pomodoroIsBreak: Bool?

    // Cascade
    let nextWarningTime: Date?
    let totalWarnings: Int
    let firedWarnings: Int

    static func == (lhs: TimerSnapshot, rhs: TimerSnapshot) -> Bool {
        lhs.id == rhs.id
    }
}

// MARK: - Snapshot Conversion

extension CMTimer {
    /// Convert full timer to lightweight snapshot for widgets/watch
    func toSnapshot() -> TimerSnapshot {
        let nextWarning = warnings.first(where: { !$0.fired })?.scheduledTime
        let firedCount = warnings.filter { $0.fired }.count

        return TimerSnapshot(
            id: id,
            label: label,
            type: type,
            urgency: urgency,
            state: state,
            targetTime: targetTime,
            duration: duration,
            startedAt: startedAt,
            elapsedBeforePause: elapsedBeforePause,
            snoozeCount: snoozeCount,
            category: category,
            pomodoroCurrentRound: pomodoroState?.currentRound,
            pomodoroTotalRounds: pomodoroConfig?.rounds,
            pomodoroIsBreak: pomodoroState?.isBreak,
            nextWarningTime: nextWarning,
            totalWarnings: warnings.count,
            firedWarnings: firedCount
        )
    }
}

// MARK: - Shared Data Manager

final class SharedTimerDataManager {
    static let shared = SharedTimerDataManager()

    private let defaults: UserDefaults?
    private let encoder = JSONEncoder()
    private let decoder = JSONDecoder()

    private init() {
        defaults = UserDefaults(suiteName: AppGroupConstants.suiteName)
    }

    // MARK: - Write (from iOS app)

    /// Write full timer list as snapshots to App Group
    func writeTimers(_ timers: [CMTimer]) {
        let snapshots = timers.map { $0.toSnapshot() }
        writeSnapshots(snapshots)
    }

    /// Write snapshots directly
    func writeSnapshots(_ snapshots: [TimerSnapshot]) {
        guard let data = try? encoder.encode(snapshots) else { return }
        defaults?.set(data, forKey: AppGroupConstants.timersKey)
        defaults?.set(Date(), forKey: AppGroupConstants.lastUpdateKey)
    }

    /// Write the currently active/next-firing timer for quick widget access
    func writeActiveTimer(_ timer: CMTimer?) {
        if let timer = timer {
            let snapshot = timer.toSnapshot()
            guard let data = try? encoder.encode(snapshot) else { return }
            defaults?.set(data, forKey: AppGroupConstants.activeTimerKey)
        } else {
            defaults?.removeObject(forKey: AppGroupConstants.activeTimerKey)
        }
    }

    // MARK: - Read (from widgets/watch)

    /// Read all timer snapshots from App Group
    func readSnapshots() -> [TimerSnapshot] {
        guard let data = defaults?.data(forKey: AppGroupConstants.timersKey),
              let snapshots = try? decoder.decode([TimerSnapshot].self, from: data) else {
            return []
        }
        return snapshots
    }

    /// Read the active/next timer snapshot
    func readActiveTimer() -> TimerSnapshot? {
        guard let data = defaults?.data(forKey: AppGroupConstants.activeTimerKey),
              let snapshot = try? decoder.decode(TimerSnapshot.self, from: data) else {
            return nil
        }
        return snapshot
    }

    /// Last time data was updated by the iOS app
    func lastUpdateTime() -> Date? {
        defaults?.object(forKey: AppGroupConstants.lastUpdateKey) as? Date
    }

    // MARK: - Active Timers (filtered)

    /// Get only active timer snapshots sorted by target time
    func readActiveSnapshots() -> [TimerSnapshot] {
        readSnapshots()
            .filter { [.active, .warning, .snoozed, .firing].contains($0.state) }
            .sorted { $0.targetTime < $1.targetTime }
    }

    /// Get the next firing timer (active or warning, earliest target)
    func readNextFiringTimer() -> TimerSnapshot? {
        readSnapshots()
            .filter { [.active, .warning].contains($0.state) }
            .sorted { $0.targetTime < $1.targetTime }
            .first
    }
}

// MARK: - TimerSnapshot Helpers

extension TimerSnapshot {
    /// Remaining seconds from now
    func remainingSeconds(now: Date = Date()) -> TimeInterval {
        if state == .paused {
            return (duration ?? 0) - elapsedBeforePause
        }
        return max(0, targetTime.timeIntervalSince(now))
    }

    /// Whether this timer has fired (past target time)
    func hasFired(now: Date = Date()) -> Bool {
        now >= targetTime
    }

    /// Urgency color hex string
    var urgencyColorHex: String {
        getUrgencyConfig(urgency).colorHex
    }

    /// Compact remaining time string
    func remainingCompact(now: Date = Date()) -> String {
        formatDurationCompact(remainingSeconds(now: now))
    }
}