// ── Routine Engine ────────────────────────────────────────────
// Ordered sequences of timed steps with transitions, state machine, and templates
// Ported from web/src/lib/routines.ts

import Foundation

// MARK: - Types

enum TransitionType: String, Codable, CaseIterable, Identifiable {
    case immediate
    case oneMinBreak = "1m_break"
    case fiveMinBreak = "5m_break"
    case custom

    var id: String { rawValue }

    var label: String {
        switch self {
        case .immediate: return "Immediate"
        case .oneMinBreak: return "1 min break"
        case .fiveMinBreak: return "5 min break"
        case .custom: return "Custom break"
        }
    }

    var minutes: Int {
        switch self {
        case .immediate: return 0
        case .oneMinBreak: return 1
        case .fiveMinBreak: return 5
        case .custom: return 0
        }
    }
}

enum RoutineStatus: String, Codable {
    case template
    case ready
    case active
    case paused
    case completed
    case cancelled
}

enum StepStatus: String, Codable {
    case pending
    case active
    case skipped
    case completed
}

// MARK: - Routine Step

struct CMRoutineStep: Codable, Identifiable, Equatable {
    let id: String
    var label: String
    var durationMinutes: Int
    var transition: TransitionType
    var customTransitionMinutes: Int?
    var notes: String?
    var status: StepStatus
    var startedAt: Date?
    var completedAt: Date?

    init(
        id: String = UUID().uuidString,
        label: String,
        durationMinutes: Int,
        transition: TransitionType = .immediate,
        customTransitionMinutes: Int? = nil,
        notes: String? = nil,
        status: StepStatus = .pending,
        startedAt: Date? = nil,
        completedAt: Date? = nil
    ) {
        self.id = id
        self.label = label
        self.durationMinutes = durationMinutes
        self.transition = transition
        self.customTransitionMinutes = customTransitionMinutes
        self.notes = notes
        self.status = status
        self.startedAt = startedAt
        self.completedAt = completedAt
    }

    var transitionMinutes: Int {
        switch transition {
        case .custom: return customTransitionMinutes ?? 0
        default: return transition.minutes
        }
    }
}

// MARK: - Routine

struct CMRoutine: Codable, Identifiable, Equatable {
    let id: String
    var name: String
    var routineDescription: String?
    var steps: [CMRoutineStep]
    var totalDurationMinutes: Int
    var status: RoutineStatus
    var currentStepIndex: Int
    let createdAt: Date
    var startedAt: Date?
    var pausedAt: Date?
    var completedAt: Date?
    var elapsedBeforePause: TimeInterval
    var isTemplate: Bool

    init(
        id: String = UUID().uuidString,
        name: String,
        routineDescription: String? = nil,
        steps: [CMRoutineStep],
        isTemplate: Bool = false
    ) {
        self.id = id
        self.name = name
        self.routineDescription = routineDescription
        self.steps = steps
        self.totalDurationMinutes = CMRoutine.calculateTotalDuration(steps: steps)
        self.status = isTemplate ? .template : .ready
        self.currentStepIndex = 0
        self.createdAt = Date()
        self.startedAt = nil
        self.pausedAt = nil
        self.completedAt = nil
        self.elapsedBeforePause = 0
        self.isTemplate = isTemplate
    }

    static func calculateTotalDuration(steps: [CMRoutineStep]) -> Int {
        steps.enumerated().reduce(0) { total, pair in
            let (idx, step) = pair
            let transition = idx < steps.count - 1 ? step.transitionMinutes : 0
            return total + step.durationMinutes + transition
        }
    }
}

// MARK: - State Machine

extension CMRoutine {
    mutating func start() {
        guard status == .ready || status == .template else { return }
        guard !steps.isEmpty else { return }

        let now = Date()
        for i in steps.indices {
            steps[i].status = i == 0 ? .active : .pending
            steps[i].startedAt = i == 0 ? now : nil
            steps[i].completedAt = nil
        }

        status = .active
        currentStepIndex = 0
        startedAt = now
        pausedAt = nil
        completedAt = nil
        elapsedBeforePause = 0
    }

    mutating func pause() {
        guard status == .active else { return }
        let now = Date()
        if let currentStep = currentStep, let stepStart = currentStep.startedAt {
            elapsedBeforePause += now.timeIntervalSince(stepStart)
        }
        status = .paused
        pausedAt = now
    }

    mutating func resume() {
        guard status == .paused else { return }
        let now = Date()
        steps[currentStepIndex].startedAt = now
        status = .active
        pausedAt = nil
    }

    mutating func completeCurrentStep() {
        guard status == .active else { return }
        guard currentStepIndex < steps.count else { return }

        let now = Date()
        steps[currentStepIndex].status = .completed
        steps[currentStepIndex].completedAt = now

        let nextIndex = currentStepIndex + 1
        if nextIndex >= steps.count {
            status = .completed
            completedAt = now
            currentStepIndex = nextIndex
            elapsedBeforePause = 0
        } else {
            steps[nextIndex].status = .active
            steps[nextIndex].startedAt = now
            currentStepIndex = nextIndex
            elapsedBeforePause = 0
        }
    }

    mutating func skipCurrentStep() {
        guard status == .active else { return }
        guard currentStepIndex < steps.count else { return }

        let now = Date()
        steps[currentStepIndex].status = .skipped
        steps[currentStepIndex].completedAt = now

        let nextIndex = currentStepIndex + 1
        if nextIndex >= steps.count {
            status = .completed
            completedAt = now
            currentStepIndex = nextIndex
            elapsedBeforePause = 0
        } else {
            steps[nextIndex].status = .active
            steps[nextIndex].startedAt = now
            currentStepIndex = nextIndex
            elapsedBeforePause = 0
        }
    }

    mutating func cancel() {
        guard status != .completed && status != .cancelled else { return }
        status = .cancelled
        completedAt = Date()
    }
}

// MARK: - Utility

extension CMRoutine {
    var currentStep: CMRoutineStep? {
        guard currentStepIndex < steps.count else { return nil }
        return steps[currentStepIndex]
    }

    var nextStep: CMRoutineStep? {
        let nextIdx = currentStepIndex + 1
        guard nextIdx < steps.count else { return nil }
        return steps[nextIdx]
    }

    var completedStepCount: Int {
        steps.filter { $0.status == .completed }.count
    }

    var skippedStepCount: Int {
        steps.filter { $0.status == .skipped }.count
    }

    var progress: Double {
        guard !steps.isEmpty else { return 0 }
        let done = steps.filter { $0.status == .completed || $0.status == .skipped }.count
        return Double(done) / Double(steps.count)
    }

    func remainingStepSeconds(now: Date = Date()) -> TimeInterval {
        if status == .paused {
            guard let currentStep = currentStep else { return 0 }
            return TimeInterval(currentStep.durationMinutes * 60) - elapsedBeforePause
        }
        guard status == .active else { return 0 }
        guard let currentStep = currentStep, let stepStart = currentStep.startedAt else { return 0 }
        let elapsed = elapsedBeforePause + now.timeIntervalSince(stepStart)
        return max(0, TimeInterval(currentStep.durationMinutes * 60) - elapsed)
    }

    func shouldStepComplete(now: Date = Date()) -> Bool {
        status == .active && remainingStepSeconds(now: now) <= 0
    }

    func instantiate() -> CMRoutine {
        guard isTemplate || status == .template else { return self }
        let newSteps = steps.map { step in
            CMRoutineStep(
                label: step.label,
                durationMinutes: step.durationMinutes,
                transition: step.transition,
                customTransitionMinutes: step.customTransitionMinutes,
                notes: step.notes
            )
        }
        return CMRoutine(name: name, routineDescription: routineDescription, steps: newSteps)
    }
}

// MARK: - Built-in Templates

struct RoutineTemplates {
    static let morning = CMRoutine(
        name: "Morning Routine",
        routineDescription: "Start your day with intention",
        steps: [
            CMRoutineStep(label: "Wake Up + Hydrate", durationMinutes: 5, notes: "Drink a glass of water"),
            CMRoutineStep(label: "Meditation", durationMinutes: 15, transition: .oneMinBreak, notes: "Mindfulness or breathing exercise"),
            CMRoutineStep(label: "Exercise", durationMinutes: 30, transition: .oneMinBreak, notes: "Workout, yoga, or a walk"),
            CMRoutineStep(label: "Shower + Get Ready", durationMinutes: 20),
            CMRoutineStep(label: "Breakfast", durationMinutes: 15),
        ],
        isTemplate: true
    )

    static let workout = CMRoutine(
        name: "Workout",
        routineDescription: "Structured workout with warm-up and cool-down",
        steps: [
            CMRoutineStep(label: "Warm Up", durationMinutes: 5, notes: "Light stretching and mobility"),
            CMRoutineStep(label: "Main Workout", durationMinutes: 30, transition: .oneMinBreak, notes: "Strength or cardio"),
            CMRoutineStep(label: "Cool Down", durationMinutes: 5, notes: "Stretching and foam rolling"),
            CMRoutineStep(label: "Hydrate + Recovery", durationMinutes: 5),
        ],
        isTemplate: true
    )

    static let cookingPrep = CMRoutine(
        name: "Cooking Prep",
        routineDescription: "Organized meal preparation",
        steps: [
            CMRoutineStep(label: "Gather Ingredients", durationMinutes: 5, notes: "Get everything out"),
            CMRoutineStep(label: "Prep & Chop", durationMinutes: 15, notes: "Wash, peel, and chop"),
            CMRoutineStep(label: "Cook", durationMinutes: 25, transition: .fiveMinBreak, notes: "Follow the recipe"),
            CMRoutineStep(label: "Plate & Serve", durationMinutes: 5),
        ],
        isTemplate: true
    )

    static let eveningWindDown = CMRoutine(
        name: "Evening Wind-Down",
        routineDescription: "Prepare your mind and body for rest",
        steps: [
            CMRoutineStep(label: "Screen-Free Time", durationMinutes: 15, notes: "Put devices away"),
            CMRoutineStep(label: "Light Stretching", durationMinutes: 10, transition: .oneMinBreak, notes: "Gentle yoga or stretching"),
            CMRoutineStep(label: "Journal / Reflect", durationMinutes: 10, notes: "Write about your day"),
            CMRoutineStep(label: "Read", durationMinutes: 20, notes: "Read a book or magazine"),
        ],
        isTemplate: true
    )

    static let all: [CMRoutine] = [morning, workout, cookingPrep, eveningWindDown]
}