//
// ExerciseProgressView.swift
// Workouts Watch App
//
// Copyright 2025 Rouslan Zenetl. All Rights Reserved.
//

import SwiftUI
import WatchKit

/// Runs a single exercise as a horizontally-paged flow:
///
///   [Ready] → Work₁ → Rest₁ → Work₂ → … → Workₙ → Finish
///
/// A **Ready?** page leads in *only* when the exercise hasn't been started yet (a
/// resumed exercise jumps straight to its first unfinished set). The **work** phase
/// counts *up* (a stopwatch for the current set, tinted with the brand purple); the
/// user swipes left when they're done. The **rest** phase counts *down* from the
/// configurable rest time (light teal), beeps once per second in the final three
/// seconds, then auto-advances to the next work phase. Every work phase — including
/// the last — looks the same; sliding past the final set reaches a **Finish** page
/// offering **One More** (append a bonus set and keep going) and **Done** (which also
/// auto-fires after a configurable countdown, completing the exercise).
///
/// A row of phase dots tracks progress: purple for work, teal for rest, with the
/// current phase drawn as a wider dash.
struct ExerciseProgressView: View {
    @Environment(\.dismiss) private var dismiss

    /// The shared working workout document owned by the parent. We mutate the matching
    /// log in place and ask the parent to forward each change through the bridge —
    /// driving the UI from this doc (not the cache) avoids losing rapid edits to the
    /// read-after-write race.
    @Binding var doc: WorkoutDocument
    let logID: String
    let onChange: () -> Void

    /// Planned set count for this run. `One More` bumps it (and the log's `sets`).
    @State private var setCount: Int
    @State private var currentPage: Int
    @State private var showingCancelConfirm = false
    @State private var didRestorePage = false

    /// True when this run opens on the lead-in **Ready?** page (the exercise hadn't
    /// been started). A resumed exercise — or the screenshot host — skips it. Constant
    /// for the lifetime of the view, so all the page-index math below is stable.
    private let showsReady: Bool

    /// Forces the starting page (used only by the DEBUG screenshot host). When set it
    /// also suppresses the Ready page so the index is a plain work/rest cycle offset.
    private let debugInitialPage: Int?

    init(doc: Binding<WorkoutDocument>, logID: String, onChange: @escaping () -> Void, debugInitialPage: Int? = nil) {
        self._doc = doc
        self.logID = logID
        self.onChange = onChange
        self.debugInitialPage = debugInitialPage

        let log = doc.wrappedValue.logs.first { $0.id == logID }
        let sets = max(1, log?.sets ?? 1)
        _setCount = State(initialValue: sets)

        let notStarted = (log?.status ?? WorkoutStatus.notStarted.rawValue) == WorkoutStatus.notStarted.rawValue
        let ready = debugInitialPage == nil && notStarted
        self.showsReady = ready

        let base = ready ? 1 : 0
        // Resume on the first unfinished set's work page (clamped to the last set).
        let completed = min(max(0, log?.currentStateIndex ?? 0), sets - 1)
        let resume = ready ? 0 : base + completed * 2
        _currentPage = State(initialValue: debugInitialPage ?? resume)
    }

    private var log: WorkoutLogDocument? {
        doc.logs.first { $0.id == logID }
    }

    /// Offset of the work/rest cycle: `1` when a Ready page leads, else `0`.
    private var base: Int { showsReady ? 1 : 0 }

    /// Work/rest pages: Work₁, Rest₁, …, Workₙ ⇒ N sets + (N−1) rests = 2N − 1.
    private var cycleCount: Int { setCount * 2 - 1 }

    /// Ready (`base`) + cycle (`2N − 1`) + Finish (`1`).
    private var totalPages: Int { base + cycleCount + 1 }

    /// The single Finish page sits just past the last work page.
    private var finishIndex: Int { base + cycleCount }

    /// The first unfinished set's work page (only used when resuming, so `base == 0`).
    private var resumePage: Int {
        let completed = min(max(0, log?.currentStateIndex ?? 0), setCount - 1)
        return base + completed * 2
    }

    /// Position within the work/rest cycle for the current page — `nil` on the Ready
    /// and Finish pages (which show no dots).
    private var currentCycleIndex: Int? {
        let c = currentPage - base
        return (0..<cycleCount).contains(c) ? c : nil
    }

    private var detail: String {
        guard let log else { return "" }
        if LoadType(rawValue: log.loadType) == .duration {
            return Self.durationLabel(log.durationSeconds)
        }
        return "\(log.reps) reps"
    }

    /// One-line plan summary for the Ready page, e.g. "4 sets × 8 reps".
    private var readySummary: String {
        let setsText = "\(setCount) set\(setCount == 1 ? "" : "s")"
        return detail.isEmpty ? setsText : "\(setsText) × \(detail)"
    }

    var body: some View {
        TabView(selection: $currentPage) {
            ForEach(0..<totalPages, id: \.self) { index in
                page(for: index)
                    .tag(index)
            }
        }
        .tabViewStyle(.page(indexDisplayMode: .never))
        .overlay(alignment: .bottom) {
            if let cycleIndex = currentCycleIndex {
                PhaseProgressDots(count: cycleCount, currentIndex: cycleIndex)
                    .padding(.bottom, 2)
            }
        }
        .toolbar {
            ToolbarItem(placement: .cancellationAction) {
                Button {
                    showingCancelConfirm = true
                } label: {
                    Image(systemName: "xmark")
                }
            }
        }
        .confirmationDialog("Cancel Exercise?", isPresented: $showingCancelConfirm, titleVisibility: .visible) {
            Button("Cancel Exercise", role: .destructive) { dismiss() }
            Button("Continue", role: .cancel) { }
        }
        .onChange(of: currentPage) { _, newPage in
            recordProgress(for: newPage)
        }
        .onAppear {
            // Jump to the first unfinished set. A paged TabView can settle on page 0 on
            // first layout, so re-assert once more after this run loop. (The Ready page
            // and the screenshot host both pin an explicit page, so skip the jump there.)
            guard !didRestorePage else { return }
            didRestorePage = true
            if !showsReady && debugInitialPage == nil {
                jumpToResumePage()
                Task { @MainActor in jumpToResumePage() }
            }
        }
    }

    /// Move to the resume page without animation, only if we're not already there
    /// (so a re-assert after a TabView snap-to-0 is a no-op in the common case).
    private func jumpToResumePage() {
        let target = resumePage
        guard currentPage != target else { return }
        var transaction = Transaction()
        transaction.disablesAnimations = true
        withTransaction(transaction) { currentPage = target }
    }

    @ViewBuilder
    private func page(for index: Int) -> some View {
        let isActive = index == currentPage
        if showsReady && index == 0 {
            ReadyPhaseView(summary: readySummary, onStart: start)
        } else {
            let cycleIndex = index - base
            if cycleIndex == cycleCount {
                // Finish page — confirm Done (auto-fires) or add One More.
                FinishPhaseView(
                    isActive: isActive,
                    onDone: { completeExercise(); dismiss() },
                    onOneMore: addSet
                )
            } else if cycleIndex.isMultiple(of: 2) {
                // Work phase.
                WorkPhaseView(
                    setNumber: cycleIndex / 2 + 1,
                    totalSets: setCount,
                    detail: detail,
                    isActive: isActive
                )
            } else {
                // Rest phase. Auto-advances to the next work page when the timer hits zero.
                RestPhaseView(isActive: isActive) {
                    withAnimation { advance(from: index) }
                }
            }
        }
    }

    // MARK: - Mutations

    /// Leave the Ready page for the first work phase, marking the exercise started.
    private func start() {
        beginExercise()
        withAnimation { currentPage = base }
    }

    /// Programmatically move one page right (used by the rest auto-advance), guarding
    /// against overrun if the user swiped away in the meantime.
    private func advance(from index: Int) {
        guard currentPage == index, index + 1 < totalPages else { return }
        currentPage = index + 1
    }

    /// Flip a not-yet-started exercise to in-progress the moment the user taps Start.
    private func beginExercise() {
        guard let i = doc.logs.firstIndex(where: { $0.id == logID }) else { return }
        guard doc.logs[i].status == WorkoutStatus.notStarted.rawValue else { return }
        doc.logs[i].status = WorkoutStatus.inProgress.rawValue
        recomputeWorkoutStatus()
        doc.updatedAt = Date()
        onChange()
    }

    /// Append a bonus set from the Finish page: mark every prior set done, grow the
    /// plan, and slide forward into the bonus set's work phase.
    ///
    /// Growing `setCount` and advancing `currentPage` in one animated transaction makes
    /// the new work phase slide in from the right. (We land on work, not a rest, because
    /// the Finish page's own auto-finish countdown already served as the between-set
    /// breather — and the rest page would otherwise sit at the very index the Finish
    /// page occupied, which a paged TabView can't animate to.)
    private func addSet() {
        let newCount = setCount + 1

        if let i = doc.logs.firstIndex(where: { $0.id == logID }) {
            doc.logs[i].sets = newCount
            doc.logs[i].currentStateIndex = newCount - 1   // every prior set is now complete
            doc.logs[i].status = WorkoutStatus.inProgress.rawValue
            doc.logs[i].completed = false
            recomputeWorkoutStatus()
            doc.updatedAt = Date()
            onChange()
        }

        withAnimation {
            setCount = newCount
            currentPage += 1
        }
    }

    /// Map a page to completed-set count and record forward progress.
    ///
    /// Paging tops out at `setCount − 1` completed sets — the final set is marked done
    /// only by an explicit **Done** (`completeExercise`). Progress is **monotonic**:
    /// completing a work phase advances the count (and forwards it to the phone), but
    /// swiping back — or a transient TabView snap to page 0 — never un-counts a set.
    private func recordProgress(for pageIndex: Int) {
        if showsReady && pageIndex == 0 { return }   // Ready page records nothing
        let cycleIndex = pageIndex - base
        let reached = min(max(0, (cycleIndex + 1) / 2), setCount - 1)

        guard let i = doc.logs.firstIndex(where: { $0.id == logID }) else { return }
        guard reached > doc.logs[i].currentStateIndex else { return }

        doc.logs[i].currentStateIndex = reached
        doc.logs[i].status = WorkoutStatus.inProgress.rawValue
        doc.logs[i].completed = false

        recomputeWorkoutStatus()
        doc.updatedAt = Date()
        onChange()
    }

    private func completeExercise() {
        guard let i = doc.logs.firstIndex(where: { $0.id == logID }) else { return }
        doc.logs[i].currentStateIndex = setCount
        doc.logs[i].status = WorkoutStatus.completed.rawValue
        doc.logs[i].completed = true

        recomputeWorkoutStatus()
        doc.updatedAt = Date()
        onChange()
    }

    private func recomputeWorkoutStatus() {
        let statuses = doc.logs.map { WorkoutStatus(rawValue: $0.status) ?? .notStarted }
        let allCompleted = !statuses.isEmpty && statuses.allSatisfy { $0 == .completed }
        let anyInProgress = statuses.contains { $0 == .inProgress }
        let allNotStarted = statuses.allSatisfy { $0 == .notStarted }

        if allCompleted {
            doc.status = WorkoutStatus.completed.rawValue
            doc.end = Date()
        } else if anyInProgress || !allNotStarted {
            doc.status = WorkoutStatus.inProgress.rawValue
            doc.end = nil
        } else {
            doc.status = WorkoutStatus.notStarted.rawValue
            doc.end = nil
        }
    }

    // MARK: - Formatting

    static func durationLabel(_ seconds: Int) -> String {
        let mins = seconds / 60
        let secs = seconds % 60
        if mins > 0 && secs > 0 { return "\(mins)m \(secs)s" }
        if mins > 0 { return "\(mins) min" }
        return "\(secs) sec"
    }
}

// MARK: - Phase Progress Dots

/// Compact progress row for the work/rest cycle: purple dots for work, teal for rest,
/// with the active phase drawn as a wider dash. Dots are deliberately a touch thick so
/// the count of remaining sets reads at a glance.
private struct PhaseProgressDots: View {
    let count: Int
    let currentIndex: Int

    var body: some View {
        HStack(spacing: 4) {
            ForEach(0..<count, id: \.self) { i in
                let isWork = i.isMultiple(of: 2)
                let isCurrent = i == currentIndex
                Capsule()
                    .fill(isWork ? Color.workTint : Color.restTint)
                    .frame(width: isCurrent ? 12 : 6, height: 6)
                    .opacity(isCurrent ? 1 : 0.45)
            }
        }
    }
}

// MARK: - Ready Phase

private struct ReadyPhaseView: View {
    let summary: String
    let onStart: () -> Void

    var body: some View {
        VStack(spacing: 10) {
            Text("Ready?")
                .font(.system(size: 30, weight: .bold, design: .rounded))

            if !summary.isEmpty {
                Text(summary)
                    .font(.subheadline)
                    .foregroundStyle(.secondary)
            }

            Button(action: onStart) {
                Label("Start", systemImage: "play.fill")
                    .frame(maxWidth: .infinity)
            }
            .buttonStyle(.borderedProminent)
            .tint(.workTint)
            .padding(.top, 4)
        }
        .padding(.horizontal)
        .frame(maxWidth: .infinity, maxHeight: .infinity)
    }
}

// MARK: - Work Phase

private struct WorkPhaseView: View {
    let setNumber: Int
    let totalSets: Int
    let detail: String
    let isActive: Bool

    /// Wall-clock anchor for the count-up stopwatch. Driving the display from a fixed
    /// start date (rendered by SwiftUI's timer text) instead of incrementing a counter
    /// on a run-loop `Timer` keeps it advancing in the Always-On / wrist-down state,
    /// where that timer is throttled and stops firing.
    @State private var startDate = Date()

    var body: some View {
        VStack(spacing: 6) {
            Text("\(setNumber) of \(totalSets)")
                .font(.headline)
                .foregroundStyle(.secondary)

            Text(startDate, style: .timer)
                .font(.system(size: 48, weight: .bold, design: .rounded))
                .monospacedDigit()
                .foregroundStyle(Color.workTint)

            if !detail.isEmpty {
                Text(detail)
                    .font(.subheadline)
                    .foregroundStyle(.secondary)
            }
        }
        .frame(maxWidth: .infinity, maxHeight: .infinity)
        .onAppear { if isActive { restart() } }
        .onChange(of: isActive) { _, active in if active { restart() } }
    }

    private func restart() {
        startDate = Date()
        WKInterfaceDevice.current().play(.start)
    }
}

// MARK: - Rest Phase

private struct RestPhaseView: View {
    let isActive: Bool
    /// Invoked once the countdown reaches zero (auto-advance to the next work phase).
    let onFinished: () -> Void

    @AppStorage("restSeconds") private var restSeconds: Int = 45

    /// Wall-clock window for the countdown. SwiftUI renders the remaining time from this
    /// range (so the display keeps counting down in the Always-On / wrist-down state),
    /// and the haptics + auto-advance below are derived from `endDate` rather than a
    /// decremented counter — so they stay correct even after the run-loop `Timer` was
    /// throttled while the wrist was down.
    @State private var startDate = Date()
    @State private var endDate = Date()
    /// Lowest remaining-second we've already pinged, so a burst of catch-up ticks after a
    /// stall doesn't double-beep.
    @State private var lastPingSecond = Int.max
    /// Guards the auto-advance so it fires exactly once even if ticks pile up.
    @State private var didFinish = false
    private let ticker = Timer.publish(every: 1.0, on: .main, in: .common).autoconnect()

    var body: some View {
        VStack(spacing: 6) {
            Text("Rest")
                .font(.headline)
                .foregroundStyle(.secondary)

            Text(timerInterval: startDate...endDate, countsDown: true)
                .font(.system(size: 54, weight: .bold, design: .rounded))
                .monospacedDigit()
                .foregroundStyle(Color.restTint)
        }
        .frame(maxWidth: .infinity, maxHeight: .infinity)
        .onAppear { if isActive { start() } }
        .onChange(of: isActive) { _, active in if active { start() } }
        .onReceive(ticker) { _ in tick() }
    }

    private func start() {
        startDate = Date()
        endDate = startDate.addingTimeInterval(Double(max(1, restSeconds)))
        lastPingSecond = Int.max
        didFinish = false
        WKInterfaceDevice.current().play(.start)
    }

    private func tick() {
        guard isActive, !didFinish else { return }
        // Round up so the final whole second still pings before we reach zero.
        let remaining = Int(ceil(endDate.timeIntervalSinceNow))

        if remaining <= 0 {
            // Time's up — final cue and slide to the next work phase. If the wrist was
            // down the timer may have stalled; this then fires on the first tick once the
            // app gets runtime again (e.g. the wrist comes up), never losing the rest.
            didFinish = true
            WKInterfaceDevice.current().play(.stop)
            onFinished()
        } else if remaining <= 3 && remaining < lastPingSecond {
            // Once-per-second countdown ping for the final three seconds.
            lastPingSecond = remaining
            WKInterfaceDevice.current().play(.notification)
        }
    }
}

// MARK: - Finish Phase

/// Terminal page after the last set. **Done** completes the exercise and dismisses —
/// and fires automatically after a configurable countdown so the user doesn't have to
/// tap with sweaty hands. **One More** appends a bonus set instead.
private struct FinishPhaseView: View {
    let isActive: Bool
    let onDone: () -> Void
    let onOneMore: () -> Void

    @AppStorage("doneCountdownSeconds") private var doneCountdownSeconds: Int = 5

    /// Wall-clock deadline for the auto-Done (same Always-On rationale as the rest
    /// timer). `remaining` is what the Done button shows.
    @State private var endDate = Date()
    @State private var remaining = 0
    /// Fires the auto-Done exactly once, and latches off while the page isn't active.
    @State private var didFire = false
    private let ticker = Timer.publish(every: 0.25, on: .main, in: .common).autoconnect()

    var body: some View {
        VStack(spacing: 8) {
            Text("Finished!")
                .font(.headline)
                .foregroundStyle(.secondary)

            Button(action: fire) {
                Label(remaining > 0 ? "Done · \(remaining)" : "Done", systemImage: "checkmark")
                    .frame(maxWidth: .infinity)
            }
            .buttonStyle(.borderedProminent)
            .tint(Color.workTint)

            Button(action: onOneMore) {
                Label("One More", systemImage: "plus")
                    .frame(maxWidth: .infinity)
            }
            .buttonStyle(.bordered)
        }
        .padding(.horizontal)
        .frame(maxWidth: .infinity, maxHeight: .infinity)
        .onAppear { if isActive { start() } }
        .onChange(of: isActive) { _, active in active ? start() : (didFire = true) }
        .onReceive(ticker) { _ in tick() }
    }

    private func start() {
        let total = max(1, doneCountdownSeconds)
        endDate = Date().addingTimeInterval(Double(total))
        remaining = total
        didFire = false
    }

    private func tick() {
        guard isActive, !didFire else { return }
        let r = Int(ceil(endDate.timeIntervalSinceNow))
        remaining = max(0, r)
        if r <= 0 { fire() }
    }

    private func fire() {
        guard !didFire else { return }
        didFire = true
        WKInterfaceDevice.current().play(.success)
        onDone()
    }
}