NavidromeApp/iOS/Views/Companion/SmartCrossfadeManager.swift

import Foundation
import AVFoundation
import Combine
import QuartzCore

// MARK: - Smart Crossfade Manager
// Dual-AVPlayer (A/B) crossfade engine.
//
// Profile fields (from Companion API):
//   silence_start = where TRAILING silence begins (crossfade trigger point)
//   silence_end   = where LEADING silence ends (seek-to point for skip)
//   loudness_lufs = integrated loudness for volume normalization
//
// Flow:
//   1. playSong() → loads item, starts playback IMMEDIATELY, then fetches profile async
//   2. Profile arrives → applies LUFS volume, installs boundary observer at silence_start - fade
//   3. Boundary fires → beginCrossfade() fades A↓ B↑ via CADisplayLink
//   4. Fade completes → swap slots, install new boundary, request next track

class SmartCrossfadeManager: ObservableObject {
    
    static let shared = SmartCrossfadeManager()
    
    // MARK: - Settings (persisted)
    @Published var isEnabled = false {
        didSet { UserDefaults.standard.set(isEnabled, forKey: "smart_crossfade_enabled") }
    }
    @Published var crossfadeDuration: TimeInterval = 5.0 {
        didSet { UserDefaults.standard.set(crossfadeDuration, forKey: "smart_crossfade_duration") }
    }
    @Published var targetLUFS: Double = -14.0 {
        didSet { UserDefaults.standard.set(targetLUFS, forKey: "smart_target_lufs") }
    }
    @Published var skipSilence: Bool = true {
        didSet { UserDefaults.standard.set(skipSilence, forKey: "smart_skip_silence") }
    }
    
    // MARK: - State
    @Published var currentProfile: SmartDJProfile?
    @Published var nextProfile: SmartDJProfile?
    @Published var isCrossfading = false
    
    // MARK: - Dual Players
    private(set) var playerA: AVPlayer = AVPlayer()
    private(set) var playerB: AVPlayer = AVPlayer()
    private var activeSlot: Slot = .a
    
    var activePlayer: AVPlayer { activeSlot == .a ? playerA : playerB }
    var standbyPlayer: AVPlayer { activeSlot == .a ? playerB : playerA }
    
    enum Slot { case a, b }
    
    // MARK: - Volume Targets (LUFS-normalized)
    private var activeMaxVolume: Float = 1.0
    private var standbyMaxVolume: Float = 1.0
    
    // MARK: - Observers
    private var boundaryObserver: Any?
    private var timeObserver: Any?
    private var statusObservation: NSKeyValueObservation?
    
    // MARK: - Crossfade Animation
    private var displayLink: CADisplayLink?
    private var fadeStartTime: CFTimeInterval = 0
    private var fadeOutStartVolume: Float = 1.0
    private var fadeInTargetVolume: Float = 1.0
    private var didHandoffVisualizer = false
    
    // MARK: - Track Info (for self-crossfade)
    private var currentSongURL: URL?
    private var currentSong: Song?
    
    // MARK: - Queue Sync
    /// The song that was loaded into standby and is now in the active player post-fade.
    /// AudioPlayer reads this in needsNextTrack to set queueIndex correctly.
    private(set) var pendingNextSong: Song?
    /// Set by AudioPlayer.notifyQueueChanged() when a queue mutation arrives mid-fade.
    /// finalizeCrossfade checks this and re-prepares standby after the swap.
    var queueChangedDuringFade: Bool = false
    
    // MARK: - Profile Cache
    private var profiles: [String: SmartDJProfile] = [:]
    private let api = CompanionAPIService()
    
    // MARK: - Callbacks
    var needsNextTrack: (() -> Void)?
    var timeUpdate: ((TimeInterval, TimeInterval) -> Void)?
    var visualizerHandoff: ((AVPlayer) -> Void)?
    
    private init() {
        isEnabled = UserDefaults.standard.bool(forKey: "smart_crossfade_enabled")
        let dur = UserDefaults.standard.double(forKey: "smart_crossfade_duration")
        crossfadeDuration = dur > 0 ? dur : 5.0
        let lufs = UserDefaults.standard.double(forKey: "smart_target_lufs")
        targetLUFS = lufs < 0 ? lufs : -14.0
        skipSilence = UserDefaults.standard.object(forKey: "smart_skip_silence") as? Bool ?? true
    }
    
    // ═══════════════════════════════════════════════════════
    // MARK: - PUBLIC API
    // ═══════════════════════════════════════════════════════
    
    /// Load and play a song on the active player.
    /// Starts playback IMMEDIATELY — profile adjustments arrive async.
    func playSong(_ song: Song, url: URL) {
        log("▶ Playing: \(song.title) on \(slotName(activeSlot))")
        
        cancelCrossfade()
        removeAllObservers()
        
        currentSong = song
        currentSongURL = url
        
        // Load and play immediately — don't wait for profile
        let asset = AVURLAsset(url: url)
        let item = AVPlayerItem(asset: asset)
        activePlayer.replaceCurrentItem(with: item)
        activePlayer.volume = 1.0
        activeMaxVolume = 1.0
        activePlayer.play()
        
        // Install time observer right away for seek bar
        installTimeObserver()
        
        // Fetch profile async — apply adjustments when it arrives
        Task { @MainActor [weak self] in
            guard let self else { return }
            let profile = await self.fetchProfile(for: song)
            self.currentProfile = profile
            
            // Apply LUFS normalization
            self.activeMaxVolume = self.lufsToVolume(profile?.loudnessLUFS)
            // Only adjust volume if not already crossfading
            if !self.isCrossfading {
                self.activePlayer.volume = self.activeMaxVolume
            }
            
            // Skip leading silence (silenceEnd = where leading silence ends)
            if self.skipSilence, let silEnd = profile?.silenceEnd, silEnd > 0.3, silEnd < 10.0 {
                let current = self.activePlayer.currentTime().seconds
                // Only seek if we're still near the start
                if current < silEnd + 1.0 {
                    await self.activePlayer.seek(to: CMTime(seconds: silEnd, preferredTimescale: 1000))
                    self.log("Skipped \(String(format: "%.1f", silEnd))s leading silence")
                }
            }
            
            // Install boundary observer for crossfade trigger
            self.installCrossfadeTrigger(profile: profile)
        }
    }
    
    /// Pre-load the next song into standby (paused, vol 0, seeked past leading silence).
    /// Skipped if a crossfade is in progress — finalizeCrossfade will call needsNextTrack
    /// which calls prepareNextForCrossfade, picking up any queue changes at that point.
    func prepareNext(_ song: Song, url: URL) {
        guard !isCrossfading else {
            log("⏭ prepareNext skipped mid-fade — will pick up \(song.title) after swap")
            return
        }
        log("⏳ Preparing: \(song.title) in \(slotName(activeSlot == .a ? .b : .a))")
        pendingNextSong = song
        
        let asset = AVURLAsset(url: url)
        let item = AVPlayerItem(asset: asset)
        standbyPlayer.replaceCurrentItem(with: item)
        standbyPlayer.volume = 0.0
        standbyPlayer.pause()
        
        Task { @MainActor [weak self] in
            guard let self else { return }
            let profile = await self.fetchProfile(for: song)
            self.nextProfile = profile
            self.standbyMaxVolume = self.lufsToVolume(profile?.loudnessLUFS)
            
            // Wait for item to be ready before seeking
            if let silEnd = profile?.silenceEnd, silEnd > 0.3, silEnd < 10.0 {
                let seekTarget = CMTime(seconds: silEnd, preferredTimescale: 1000)
                let standby = self.standbyPlayer
                let observation = item.observe(\.status, options: [.new]) { observedItem, _ in
                    guard observedItem.status == .readyToPlay else { return }
                    DispatchQueue.main.async {
                        standby.seek(to: seekTarget)
                    }
                }
                self.statusObservation = observation
            }
        }
    }
    
    func pause() {
        activePlayer.pause()
        if isCrossfading { standbyPlayer.pause() }
    }
    
    func resume() {
        activePlayer.play()
        if isCrossfading { standbyPlayer.play() }
        // Reinstall the time observer if it was removed by suspendForBackground()
        // (happens when app is backgrounded while paused then brought back to foreground)
        if timeObserver == nil { installTimeObserver() }
    }
    
    func seek(to time: TimeInterval) {
        let cmTime = CMTime(seconds: time, preferredTimescale: 1000)
        
        // Remove existing boundary observer before seeking
        // to prevent it firing during the seek operation
        removeBoundaryObserver()
        
        activePlayer.seek(to: cmTime) { [weak self] finished in
            guard finished, let self else { return }
            // Reinstall boundary observer AFTER seek completes
            // Only if we haven't seeked past the trigger point
            DispatchQueue.main.async {
                if !self.isCrossfading {
                    self.installCrossfadeTrigger(profile: self.currentProfile)
                }
            }
        }
    }
    
    func stop() {
        cancelCrossfade()
        removeAllObservers()
        
        playerA.pause()
        playerA.replaceCurrentItem(with: nil)
        playerB.pause()
        playerB.replaceCurrentItem(with: nil)
        
        activeSlot = .a
        currentProfile = nil
        nextProfile = nil
        currentSong = nil
        currentSongURL = nil
        activeMaxVolume = 1.0
        standbyMaxVolume = 1.0
    }
    
    // ═══════════════════════════════════════════════════════
    // MARK: - LUFS → Volume
    // ═══════════════════════════════════════════════════════
    
    private func lufsToVolume(_ lufs: Double?) -> Float {
        guard let lufs = lufs, lufs < 0 else { return 1.0 }
        let gainDB = targetLUFS - lufs
        let linear = pow(10.0, gainDB / 20.0)
        let clamped = Float(min(max(linear, 0.05), 1.0))
        log("LUFS \(String(format: "%.1f", lufs)) → vol \(String(format: "%.3f", clamped))")
        return clamped
    }
    
    // ═══════════════════════════════════════════════════════
    // MARK: - CROSSFADE TRIGGER
    // ═══════════════════════════════════════════════════════
    
    /// Install a boundary time observer to trigger crossfade.
    /// Uses silenceStart (trailing silence begin) as the end-of-content marker.
    /// Falls back to duration - crossfadeDuration if no profile.
    private func installCrossfadeTrigger(profile: SmartDJProfile?) {
        removeBoundaryObserver()
        
        guard let item = activePlayer.currentItem else { return }
        let duration = item.duration.seconds
        
        // If duration isn't ready yet, poll until it is
        guard duration.isFinite, duration > 0 else {
            let pollObs = activePlayer.addPeriodicTimeObserver(
                forInterval: CMTime(seconds: 0.5, preferredTimescale: 600),
                queue: .main
            ) { [weak self] _ in
                guard let self else { return }
                let dur = self.activePlayer.currentItem?.duration.seconds ?? 0
                if dur.isFinite, dur > 0 {
                    // Duration ready — remove poll, install real trigger
                    if let obs = self.boundaryObserver {
                        self.activePlayer.removeTimeObserver(obs)
                        self.boundaryObserver = nil
                    }
                    self.installCrossfadeTriggerWithDuration(dur, profile: profile)
                }
            }
            boundaryObserver = pollObs
            return
        }
        
        installCrossfadeTriggerWithDuration(duration, profile: profile)
    }
    
    private func installCrossfadeTriggerWithDuration(_ duration: TimeInterval, profile: SmartDJProfile?) {
        // silenceStart = where trailing silence begins
        let silenceStart = profile?.silenceStart ?? 0
        let contentEnd: TimeInterval
        
        // Valid if it's in the second half of the track
        if silenceStart > duration * 0.5 && silenceStart <= duration {
            contentEnd = silenceStart
        } else {
            // No valid trailing silence — use full duration
            contentEnd = duration
        }
        
        // Trigger = content end minus crossfade duration (min 1s from start)
        let triggerTime = max(1.0, contentEnd - crossfadeDuration)
        
        // Don't install if we've already seeked past the trigger
        let currentPos = activePlayer.currentTime().seconds
        if currentPos.isFinite && currentPos >= triggerTime {
            log("⏭ Skipping trigger — already past \(String(format: "%.1f", triggerTime))s")
            return
        }
        
        log("🎯 Trigger at \(String(format: "%.1f", triggerTime))s " +
            "(content \(String(format: "%.1f", contentEnd))s, " +
            "dur \(String(format: "%.1f", duration))s)")
        
        let boundary = CMTime(seconds: triggerTime, preferredTimescale: 1000)
        boundaryObserver = activePlayer.addBoundaryTimeObserver(
            forTimes: [NSValue(time: boundary)],
            queue: .main
        ) { [weak self] in
            self?.beginCrossfade()
        }
    }
    
    private func removeBoundaryObserver() {
        if let obs = boundaryObserver {
            activePlayer.removeTimeObserver(obs)
            boundaryObserver = nil
        }
    }
    
    // ═══════════════════════════════════════════════════════
    // MARK: - TIME OBSERVER
    // ═══════════════════════════════════════════════════════
    
    private func installTimeObserver() {
        removeTimeObserver()
        
        let interval = CMTime(seconds: 0.1, preferredTimescale: 600)
        timeObserver = activePlayer.addPeriodicTimeObserver(forInterval: interval, queue: .main) { [weak self] time in
            guard let self else { return }
            
            // During crossfade past midpoint, report from the INCOMING player
            // so the seek bar shows the new track's position, not -0:00
            let reportPlayer: AVPlayer
            if self.isCrossfading && self.didHandoffVisualizer {
                reportPlayer = self.standbyPlayer
            } else {
                reportPlayer = self.activePlayer
            }
            
            let current = reportPlayer.currentTime().seconds
            guard current.isFinite else { return }
            let dur = reportPlayer.currentItem?.duration.seconds ?? 0
            if dur.isFinite, dur > 0 {
                self.timeUpdate?(current, dur)
            }
        }
    }
    
    private func removeTimeObserver() {
        if let obs = timeObserver {
            activePlayer.removeTimeObserver(obs)
            timeObserver = nil
        }
    }

    /// Called when app enters background — removes the 10Hz time observer that
    /// drives @Published currentTime/duration updates and burns main-thread CPU.
    func suspendForBackground() {
        removeTimeObserver()
        displayLink?.invalidate()
        displayLink = nil
    }

    /// Called when app returns to foreground — reinstalls the time observer.
    func resumeFromBackground() {
        guard timeObserver == nil else { return }
        installTimeObserver()
    }
    
    private func removeAllObservers() {
        removeBoundaryObserver()
        removeTimeObserver()
        statusObservation?.invalidate()
        statusObservation = nil
    }
    
    // ═══════════════════════════════════════════════════════
    // MARK: - CROSSFADE EXECUTION
    // ═══════════════════════════════════════════════════════
    
    private func beginCrossfade() {
        guard !isCrossfading else { return }
        
        // If standby has nothing, load self-crossfade
        if standbyPlayer.currentItem == nil {
            guard let url = currentSongURL else {
                log("⚠️ No standby and no current URL")
                return
            }
            log("🔁 No next track — self-crossfade")
            let asset = AVURLAsset(url: url)
            let item = AVPlayerItem(asset: asset)
            standbyPlayer.replaceCurrentItem(with: item)
            standbyMaxVolume = activeMaxVolume
            nextProfile = currentProfile
            pendingNextSong = currentSong   // self-crossfade: "next" == current
            
            // Seek past leading silence
            if skipSilence, let silEnd = currentProfile?.silenceEnd, silEnd > 0.3, silEnd < 10.0 {
                standbyPlayer.seek(to: CMTime(seconds: silEnd, preferredTimescale: 1000))
            }
        }
        
        log("🔀 BEGIN (\(String(format: "%.1f", crossfadeDuration))s)")
        isCrossfading = true
        didHandoffVisualizer = false
        
        fadeOutStartVolume = activePlayer.volume
        fadeInTargetVolume = standbyMaxVolume
        
        standbyPlayer.volume = 0.0
        standbyPlayer.play()
        
        fadeStartTime = CACurrentMediaTime()
        displayLink = CADisplayLink(target: self, selector: #selector(crossfadeTick))
        displayLink?.add(to: .main, forMode: .common)
    }
    
    @objc private func crossfadeTick() {
        let elapsed = CACurrentMediaTime() - fadeStartTime
        let progress = Float(min(elapsed / crossfadeDuration, 1.0))
        
        // Equal-power crossfade
        let fadeOut = cosf(progress * .pi / 2.0)
        let fadeIn  = sinf(progress * .pi / 2.0)
        
        activePlayer.volume = fadeOutStartVolume * fadeOut
        standbyPlayer.volume = fadeInTargetVolume * fadeIn
        
        if progress >= 0.5 && !didHandoffVisualizer {
            didHandoffVisualizer = true
            visualizerHandoff?(standbyPlayer)
        }
        
        if progress >= 1.0 {
            finalizeCrossfade()
        }
    }
    
    private func finalizeCrossfade() {
        displayLink?.invalidate()
        displayLink = nil
        
        let outgoing = activePlayer
        outgoing.pause()
        outgoing.replaceCurrentItem(with: nil)
        
        removeAllObservers()
        
        activeSlot = (activeSlot == .a) ? .b : .a
        
        currentProfile = nextProfile
        nextProfile = nil
        activeMaxVolume = standbyMaxVolume
        standbyMaxVolume = 1.0
        
        activePlayer.volume = activeMaxVolume
        isCrossfading = false
        
        log("🔀 DONE → \(slotName(activeSlot))")
        
        installTimeObserver()
        installCrossfadeTrigger(profile: currentProfile)
        
        // needsNextTrack reads pendingNextSong to sync queueIndex, then clears it via
        // prepareNextForCrossfade which sets the new pendingNextSong for the NEXT fade.
        needsNextTrack?()
        pendingNextSong = nil
        
        // If queue changed while we were fading, needsNextTrack → prepareNextForCrossfade
        // already ran and picked up the current queue state. Just clear the flag.
        queueChangedDuringFade = false
    }
    
    private func cancelCrossfade() {
        displayLink?.invalidate()
        displayLink = nil
        isCrossfading = false
        didHandoffVisualizer = false
    }
    
    // ═══════════════════════════════════════════════════════
    // MARK: - PROFILE FETCHING
    // ═══════════════════════════════════════════════════════
    
    private func fetchProfile(for song: Song) async -> SmartDJProfile? {
        guard CompanionSettings.shared.smartDJEnabled else { return nil }
        guard let path = song.path else { return nil }

        // 1. Memory/disk cache
        if let cached = profiles[song.id] { return cached }
        if let cached = SmartDJCache.shared.get(path) {
            profiles[song.id] = cached
            return cached
        }

        // 2. Companion API (server-side analysis)
        if CompanionSettings.shared.isEnabled {
            do {
                let profile = try await api.fetchProfile(relativePath: path)
                profiles[song.id] = profile
                SmartDJCache.shared.store(profile, for: path)
                log("Profile (API): trailing=\(profile.silenceStart ?? 0)s, " +
                    "leading=\(profile.silenceEnd ?? 0)s, " +
                    "LUFS=\(profile.loudnessLUFS ?? 0)")
                return profile
            } catch {
                log("Profile API failed, trying on-device: \(error.localizedDescription)")
            }
        }

        // 3. On-device analysis fallback — for local/downloaded files only.
        // Runs OfflineAudioAnalyzer's combined pass to extract silence boundaries
        // and an approximate integrated loudness in one file read.
        if let localURL = OfflineManager.shared.localURL(for: song.id) {
            if let profile = await analyzeOnDevice(song: song, url: localURL) {
                profiles[song.id] = profile
                SmartDJCache.shared.store(profile, for: path)
                return profile
            }
        }

        return nil
    }

    /// On-device SmartDJ profile extraction using the combined OfflineAudioAnalyzer pass.
    /// Returns silence boundaries and approximate LUFS without requiring Companion API.
    private func analyzeOnDevice(song: Song, url: URL) async -> SmartDJProfile? {
        log("On-device analysis: \(song.title)")
        do {
            let result = try await OfflineAudioAnalyzer.shared.analyzeWithSmartDJ(
                url: url,
                pointsCount: 20,      // minimal for speed — we only need the SmartDJ data
                fps: 15.0,            // low fps = fewer FFT frames = faster
                cutoff: 80,
                extractSmartDJ: true,
                progress: nil
            )
            let profile = SmartDJProfile(
                bpm: nil,
                silenceStart: result.silenceStart,
                silenceEnd: result.silenceEnd,
                loudnessLUFS: result.loudnessLUFS
            )
            log("On-device profile: trailing=\(String(format: "%.2f", result.silenceStart ?? 0))s, " +
                "leading=\(String(format: "%.2f", result.silenceEnd ?? 0))s, " +
                "LUFS≈\(String(format: "%.1f", result.loudnessLUFS ?? 0))")
            return profile
        } catch {
            log("On-device analysis failed: \(error.localizedDescription)")
            return nil
        }
    }
    
    // ═══════════════════════════════════════════════════════
    // MARK: - HELPERS
    // ═══════════════════════════════════════════════════════
    
    func resolveURL(for song: Song) -> URL? {
        if let localURL = OfflineManager.shared.localURL(for: song.id) {
            return localURL
        }
        let quality = StreamingQuality.shared
        return ServerManager.shared.client.streamURL(
            songId: song.id,
            format: quality.format,
            maxBitRate: quality.maxBitRate
        )
    }
    
    private func slotName(_ slot: Slot) -> String {
        slot == .a ? "A" : "B"
    }
    
    private func log(_ msg: String) {
        DebugLogger.shared.log(msg, category: "SmartDJ")
    }
}

// MARK: - Notification
extension Notification.Name {
    static let smartDJNeedsNextTrack = Notification.Name("smartDJNeedsNextTrack")
}