// ── Timer Engine ───────────────────────────────────────────────
// Core timer types, state machine, and lifecycle management
// Ported from web/src/lib/timer-engine.ts

import Foundation

// MARK: - Timer Types

enum CMTimerType: String, Codable, CaseIterable, Identifiable {
    case alarm
    case countdown
    case pomodoro
    case event

    var id: String { rawValue }

    var label: String {
        switch self {
        case .alarm: return "Alarm"
        case .countdown: return "Countdown"
        case .pomodoro: return "Pomodoro"
        case .event: return "Event"
        }
    }
}

// MARK: - Timer State

enum CMTimerState: String, Codable {
    case idle
    case active
    case warning
    case firing
    case snoozed
    case dismissed
    case completed
    case paused
}

// MARK: - Pomodoro Config

struct PomodoroConfig: Codable, Equatable {
    var workMinutes: Int
    var breakMinutes: Int
    var longBreakMinutes: Int
    var rounds: Int

    static let `default` = PomodoroConfig(
        workMinutes: 25,
        breakMinutes: 5,
        longBreakMinutes: 15,
        rounds: 4
    )
}

// MARK: - Pomodoro State

struct PomodoroState: Codable {
    var currentRound: Int
    var isBreak: Bool
    var isLongBreak: Bool
    var completedRounds: Int
}

// MARK: - Timer Model

struct CMTimer: Codable, Identifiable, Equatable {
    let id: String
    let type: CMTimerType
    var label: String
    var description: String?
    var urgency: UrgencyLevel
    var state: CMTimerState

    // Time fields
    var targetTime: Date        // when the timer fires
    var duration: TimeInterval? // seconds — for countdowns/pomodoro
    let createdAt: Date
    var startedAt: Date?
    var pausedAt: Date?
    var firedAt: Date?
    var dismissedAt: Date?
    var completedAt: Date?

    // Elapsed tracking for pause/resume
    var elapsedBeforePause: TimeInterval // seconds accumulated before last pause

    // Cascade
    var cascade: CascadeConfig
    var warnings: [CascadeWarning]

    // Pomodoro-specific
    var pomodoroConfig: PomodoroConfig?
    var pomodoroState: PomodoroState?

    // Snooze
    var snoozeCount: Int
    var snoozedUntil: Date?

    // Metadata
    var category: String?
    var tags: [String]?
    var linkedTimerId: String?

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

// MARK: - Factory Functions

struct CreateAlarmParams {
    let label: String
    let targetTime: Date
    var urgency: UrgencyLevel = .standard
    var cascade: CascadeConfig? = nil
    var category: String? = nil
    var description: String? = nil
}

func createAlarm(_ params: CreateAlarmParams) -> CMTimer {
    let cascade = params.cascade ?? CascadeConfig(preset: .standard, intervals: [])
    let intervals = getCascadeIntervals(cascade)
    let now = Date()

    return CMTimer(
        id: UUID().uuidString,
        type: .alarm,
        label: params.label,
        description: params.description,
        urgency: params.urgency,
        state: .active,
        targetTime: params.targetTime,
        duration: params.targetTime.timeIntervalSince(now),
        createdAt: now,
        startedAt: now,
        pausedAt: nil,
        firedAt: nil,
        dismissedAt: nil,
        completedAt: nil,
        elapsedBeforePause: 0,
        cascade: cascade,
        warnings: calculateCascadeWarnings(targetTime: params.targetTime, intervals: intervals, now: now),
        pomodoroConfig: nil,
        pomodoroState: nil,
        snoozeCount: 0,
        snoozedUntil: nil,
        category: params.category,
        tags: nil,
        linkedTimerId: nil
    )
}

struct CreateCountdownParams {
    let label: String
    let durationSeconds: TimeInterval
    var urgency: UrgencyLevel = .standard
    var cascade: CascadeConfig? = nil
    var category: String? = nil
    var description: String? = nil
}

func createCountdown(_ params: CreateCountdownParams) -> CMTimer {
    let now = Date()
    let targetTime = now.addingTimeInterval(params.durationSeconds)
    let cascade = params.cascade ?? CascadeConfig(preset: .standard, intervals: [])
    let intervals = getCascadeIntervals(cascade)

    return CMTimer(
        id: UUID().uuidString,
        type: .countdown,
        label: params.label,
        description: params.description,
        urgency: params.urgency,
        state: .active,
        targetTime: targetTime,
        duration: params.durationSeconds,
        createdAt: now,
        startedAt: now,
        pausedAt: nil,
        firedAt: nil,
        dismissedAt: nil,
        completedAt: nil,
        elapsedBeforePause: 0,
        cascade: cascade,
        warnings: calculateCascadeWarnings(targetTime: targetTime, intervals: intervals, now: now),
        pomodoroConfig: nil,
        pomodoroState: nil,
        snoozeCount: 0,
        snoozedUntil: nil,
        category: params.category,
        tags: nil,
        linkedTimerId: nil
    )
}

struct CreatePomodoroParams {
    var label: String = "Focus Session"
    var config: PomodoroConfig = .default
    var urgency: UrgencyLevel = .standard
}

func createPomodoro(_ params: CreatePomodoroParams = CreatePomodoroParams()) -> CMTimer {
    let now = Date()
    let durationSeconds = TimeInterval(params.config.workMinutes * 60)
    let targetTime = now.addingTimeInterval(durationSeconds)

    return CMTimer(
        id: UUID().uuidString,
        type: .pomodoro,
        label: params.label,
        description: nil,
        urgency: params.urgency,
        state: .active,
        targetTime: targetTime,
        duration: durationSeconds,
        createdAt: now,
        startedAt: now,
        pausedAt: nil,
        firedAt: nil,
        dismissedAt: nil,
        completedAt: nil,
        elapsedBeforePause: 0,
        cascade: CascadeConfig(preset: .minimal, intervals: []),
        warnings: calculateCascadeWarnings(targetTime: targetTime, intervals: [1], now: now),
        pomodoroConfig: params.config,
        pomodoroState: PomodoroState(
            currentRound: 1,
            isBreak: false,
            isLongBreak: false,
            completedRounds: 0
        ),
        snoozeCount: 0,
        snoozedUntil: nil,
        category: nil,
        tags: nil,
        linkedTimerId: nil
    )
}

// MARK: - State Transitions

func pauseTimer(_ timer: CMTimer) -> CMTimer {
    guard timer.state == .active || timer.state == .warning else { return timer }
    var t = timer
    let now = Date()
    let elapsed = t.elapsedBeforePause + now.timeIntervalSince(t.startedAt ?? now)
    t.state = .paused
    t.pausedAt = now
    t.elapsedBeforePause = elapsed
    return t
}

func resumeTimer(_ timer: CMTimer) -> CMTimer {
    guard timer.state == .paused else { return timer }
    var t = timer
    let now = Date()
    let remainingSeconds = (t.duration ?? 0) - t.elapsedBeforePause
    let newTargetTime = now.addingTimeInterval(remainingSeconds)

    let intervals = getCascadeIntervals(t.cascade)
    t.state = .active
    t.startedAt = now
    t.pausedAt = nil
    t.targetTime = newTargetTime
    t.warnings = calculateCascadeWarnings(targetTime: newTargetTime, intervals: intervals, now: now)
    return t
}

func fireTimer(_ timer: CMTimer) -> CMTimer {
    guard timer.state != .dismissed && timer.state != .completed else { return timer }
    var t = timer
    t.state = .firing
    t.firedAt = Date()
    return t
}

func snoozeTimer(_ timer: CMTimer, snoozeMinutes: Int) -> CMTimer {
    guard timer.state == .firing else { return timer }
    var t = timer
    let now = Date()
    let snoozeUntil = now.addingTimeInterval(TimeInterval(snoozeMinutes * 60))
    let intervals = getCascadeIntervals(t.cascade).filter { $0 <= snoozeMinutes }

    t.state = .snoozed
    t.targetTime = snoozeUntil
    t.snoozedUntil = snoozeUntil
    t.snoozeCount += 1
    t.warnings = calculateCascadeWarnings(targetTime: snoozeUntil, intervals: intervals, now: now)
    return t
}

func dismissTimer(_ timer: CMTimer) -> CMTimer {
    var t = timer
    t.state = .dismissed
    t.dismissedAt = Date()
    return t
}

func completeTimer(_ timer: CMTimer) -> CMTimer {
    var t = timer
    t.state = .completed
    t.completedAt = Date()
    return t
}

// MARK: - Pomodoro Transitions

func advancePomodoro(_ timer: CMTimer) -> CMTimer? {
    guard timer.type == .pomodoro,
          let config = timer.pomodoroConfig,
          let state = timer.pomodoroState else { return nil }

    var t = timer
    let now = Date()

    if state.isBreak || state.isLongBreak {
        // Long break finished → all done
        if state.isLongBreak {
            return completeTimer(t)
        }
        // Short break finished → start next work round
        let nextRound = state.currentRound + 1
        if nextRound > config.rounds {
            return completeTimer(t)
        }
        let durationSeconds = TimeInterval(config.workMinutes * 60)
        t.state = .active
        t.targetTime = now.addingTimeInterval(durationSeconds)
        t.duration = durationSeconds
        t.startedAt = now
        t.firedAt = nil
        t.elapsedBeforePause = 0
        t.warnings = calculateCascadeWarnings(targetTime: t.targetTime, intervals: [1], now: now)
        t.pomodoroState = PomodoroState(
            currentRound: nextRound,
            isBreak: false,
            isLongBreak: false,
            completedRounds: state.completedRounds
        )
        return t
    } else {
        // Work finished → start break
        let completedRounds = state.completedRounds + 1
        let isLongBreak = completedRounds >= config.rounds

        if isLongBreak {
            // All rounds done, long break
            let durationSeconds = TimeInterval(config.longBreakMinutes * 60)
            t.state = .active
            t.targetTime = now.addingTimeInterval(durationSeconds)
            t.duration = durationSeconds
            t.startedAt = now
            t.firedAt = nil
            t.elapsedBeforePause = 0
            t.warnings = []
            t.pomodoroState = PomodoroState(
                currentRound: state.currentRound,
                isBreak: false,
                isLongBreak: true,
                completedRounds: completedRounds
            )
            return t
        }

        let durationSeconds = TimeInterval(config.breakMinutes * 60)
        t.state = .active
        t.targetTime = now.addingTimeInterval(durationSeconds)
        t.duration = durationSeconds
        t.startedAt = now
        t.firedAt = nil
        t.elapsedBeforePause = 0
        t.warnings = []
        t.pomodoroState = PomodoroState(
            currentRound: state.currentRound,
            isBreak: true,
            isLongBreak: false,
            completedRounds: completedRounds
        )
        return t
    }
}

// MARK: - Utility

func getRemainingSeconds(_ timer: CMTimer, now: Date = Date()) -> TimeInterval {
    if timer.state == .paused {
        return (timer.duration ?? 0) - timer.elapsedBeforePause
    }
    return max(0, timer.targetTime.timeIntervalSince(now))
}

func isTimerActive(_ timer: CMTimer) -> Bool {
    [.active, .warning, .snoozed].contains(timer.state)
}

func shouldTimerFire(_ timer: CMTimer, now: Date = Date()) -> Bool {
    if timer.state == .snoozed, let snoozedUntil = timer.snoozedUntil, now >= snoozedUntil {
        return true
    }
    if (timer.state == .active || timer.state == .warning) && now >= timer.targetTime {
        return true
    }
    return false
}