NavidromeApp/iOS/Views/Lyrics/LyricsManager.swift

import Foundation
import Combine

// ──────────────────────────────────────────────────────────────────────
// LyricsManager.swift
// Orchestrates lyrics loading, line/word tracking during playback,
// and the source priority pipeline (embedded > lrc > cache > LRCLIB).
//
// Performance: line tracking uses binary search (O(log n)).
// Word tracking only runs when the lyrics view is visible.
// No @Published on per-frame properties — views use TimelineView.
// ──────────────────────────────────────────────────────────────────────

final class LyricsManager: ObservableObject {
    static let shared = LyricsManager()
    
    // MARK: - Published State (low-frequency updates)
    
    /// The loaded lyrics for the current song. Nil = no lyrics available.
    @Published var currentLyrics: LyricsData?
    
    /// Whether lyrics are currently being fetched.
    @Published var isLoading = false
    
    /// The current line index — updated ~every 0.5s from the sync timer.
    @Published var currentLineIndex: Int = 0
    
    /// Whether the lyrics overlay is visible in Now Playing.
    @Published var isLyricsVisible = false
    
    // MARK: - Non-Published State (polled per-frame by views)
    
    /// Current word index within the active line. Updated per-frame when visible.
    /// NOT @Published — views read this from TimelineView/Canvas to avoid SwiftUI thrash.
    var currentWordIndex: Int = 0
    
    /// The current playback time — snapshot for word-level tracking.
    var lastSyncedTime: Double = 0
    
    // MARK: - Private
    
    private var currentSongId: String?
    private var currentArtist: String?
    private var currentTitle: String?
    
    private init() {}
    
    // MARK: - Song Changed
    
    /// Call when a new song starts playing. Kicks off the lyrics fetch pipeline.
    func songChanged(songId: String, artist: String, title: String, path: String?, duration: Double) {
        // Skip if same song
        guard songId != currentSongId else { return }
        currentSongId = songId
        currentArtist = artist
        currentTitle = title
        currentLineIndex = 0
        currentWordIndex = 0
        lastSyncedTime = 0
        
        // Check local cache first (instant, no network)
        if let cached = LyricsCache.shared.get(artist: artist, title: title) {
            currentLyrics = cached
            DebugLogger.shared.log("Lyrics: loaded from cache (\(cached.lines.count) lines)", category: "Lyrics")
            return
        }
        
        // Fetch async from companion API
        isLoading = true
        Task {
            await fetchLyrics(artist: artist, title: title, path: path, duration: duration)
        }
    }
    
    /// Clear lyrics when playback stops.
    func clear() {
        currentSongId = nil
        currentArtist = nil
        currentTitle = nil
        currentLyrics = nil
        currentLineIndex = 0
        currentWordIndex = 0
        lastSyncedTime = 0
        isLyricsVisible = false
    }
    
    // MARK: - Time Sync (called from AudioPlayer's sync timer)
    
    /// Update the current line based on playback time. Call every ~0.5s.
    /// Uses binary search for O(log n) lookup.
    func syncToTime(_ time: Double) {
        lastSyncedTime = time
        guard let lyrics = currentLyrics, !lyrics.lines.isEmpty else { return }
        
        let newIndex = findLineIndex(at: time, in: lyrics.lines)
        if newIndex != currentLineIndex {
            currentLineIndex = newIndex
        }
        
        // Update word index if we have word-level data
        if isLyricsVisible,
           newIndex < lyrics.lines.count,
           let words = lyrics.lines[newIndex].words {
            currentWordIndex = findWordIndex(at: time, in: words)
        }
    }
    
    /// Fine-grained word tracking — call per-frame from TimelineView when visible.
    /// Returns the word progress (0.0–1.0) within the current word for gradient fill.
    func wordProgress(at time: Double) -> (lineIndex: Int, wordIndex: Int, wordFraction: Double) {
        guard let lyrics = currentLyrics, !lyrics.lines.isEmpty else {
            return (0, 0, 0)
        }
        
        let lineIdx = findLineIndex(at: time, in: lyrics.lines)
        let line = lyrics.lines[lineIdx]
        
        guard let words = line.words, !words.isEmpty else {
            return (lineIdx, 0, 0)
        }
        
        let wordIdx = findWordIndex(at: time, in: words)
        let word = words[min(wordIdx, words.count - 1)]
        let wordDuration = word.endTime - word.startTime
        let fraction: Double
        if wordDuration > 0 {
            fraction = min(max((time - word.startTime) / wordDuration, 0), 1)
        } else {
            fraction = time >= word.startTime ? 1 : 0
        }
        
        return (lineIdx, wordIdx, fraction)
    }
    
    /// The text of the current line, for the mini player ticker.
    var currentLineText: String? {
        guard let lyrics = currentLyrics, !lyrics.lines.isEmpty,
              currentLineIndex < lyrics.lines.count else { return nil }
        return lyrics.lines[currentLineIndex].text
    }
    
    // MARK: - Manual Lyrics Import
    
    /// Import lyrics from LRC text (pasted or from search result).
    func importLRC(_ lrc: String, source: String = "lrclib") {
        let lines = LRCParser.parse(lrc)
        let data = LyricsData(lines: lines, source: source, hasSynced: true)
        currentLyrics = data
        
        if let artist = currentArtist, let title = currentTitle {
            LyricsCache.shared.store(data, artist: artist, title: title)
        }
    }
    
    /// Import plain (unsynced) lyrics.
    func importPlain(_ text: String, source: String = "manual") {
        let lines = text.components(separatedBy: .newlines)
            .enumerated()
            .filter { !$0.element.trimmingCharacters(in: .whitespaces).isEmpty }
            .map { LyricLine(id: $0.offset, startTime: 0, endTime: nil, text: $0.element, words: nil) }
        
        let data = LyricsData(lines: lines, source: source, hasSynced: false)
        currentLyrics = data
        
        if let artist = currentArtist, let title = currentTitle {
            LyricsCache.shared.store(data, artist: artist, title: title)
        }
    }
    
    /// Update lyrics after timing editor saves (replaces current with new timestamps).
    func updateTimedLyrics(_ lines: [LyricLine]) {
        let data = LyricsData(lines: lines, source: "manual", hasSynced: true)
        currentLyrics = data
        
        if let artist = currentArtist, let title = currentTitle {
            LyricsCache.shared.store(data, artist: artist, title: title)
        }
    }
    
    // MARK: - Private: Fetch Pipeline
    
    private func fetchLyrics(artist: String, title: String, path: String?, duration: Double) async {
        let service = LyricsService.shared
        
        // 1. On-device: read embedded lyrics from downloaded file
        if let songId = currentSongId {
            if let response = await service.readEmbedded(songId: songId) {
                if let synced = response.syncedLyrics, !synced.isEmpty {
                    let lines = LRCParser.parse(synced)
                    let data = LyricsData(lines: lines, source: "embedded", hasSynced: true)
                    await MainActor.run { self.currentLyrics = data; self.isLoading = false }
                    LyricsCache.shared.store(data, artist: artist, title: title)
                    DebugLogger.shared.log("Lyrics: embedded in local file (\(lines.count) lines)", category: "Lyrics")
                    return
                } else if let plain = response.plainLyrics, !plain.isEmpty {
                    await MainActor.run { self.importPlain(plain, source: "embedded"); self.isLoading = false }
                    DebugLogger.shared.log("Lyrics: plain text embedded in local file", category: "Lyrics")
                    return
                }
            }
        }
        
        // 2. LRCLIB direct from iOS (no companion needed)
        do {
            let response = try await service.fetch(artist: artist, title: title, duration: duration)
            if let synced = response.syncedLyrics, !synced.isEmpty {
                let lines = LRCParser.parse(synced)
                let data = LyricsData(lines: lines, source: "lrclib", hasSynced: true)
                await MainActor.run { self.currentLyrics = data; self.isLoading = false }
                LyricsCache.shared.store(data, artist: artist, title: title)
                DebugLogger.shared.log("Lyrics: LRCLIB direct (synced, \(lines.count) lines)", category: "Lyrics")
                return
            } else if let plain = response.plainLyrics, !plain.isEmpty {
                await MainActor.run { self.importPlain(plain, source: "lrclib"); self.isLoading = false }
                DebugLogger.shared.log("Lyrics: LRCLIB direct (plain text)", category: "Lyrics")
                return
            }
        } catch {
            DebugLogger.shared.log("Lyrics: LRCLIB direct failed: \(error.localizedDescription)", category: "Lyrics")
        }
        
        // 3. Companion API fallback (reads server-side embedded tags + .lrc sidecars)
        if CompanionSettings.shared.isEnabled, let path = path {
            do {
                let api = CompanionAPIService.shared
                let response = try await api.fetchLyricsForPath(relativePath: path)
                if let synced = response.syncedLyrics, !synced.isEmpty {
                    let lines = LRCParser.parse(synced)
                    let data = LyricsData(lines: lines, source: response.source ?? "companion", hasSynced: true)
                    await MainActor.run { self.currentLyrics = data; self.isLoading = false }
                    LyricsCache.shared.store(data, artist: artist, title: title)
                    DebugLogger.shared.log("Lyrics: companion fallback (\(response.source ?? "?"), \(lines.count) lines)", category: "Lyrics")
                    return
                } else if let plain = response.plainLyrics, !plain.isEmpty {
                    await MainActor.run { self.importPlain(plain, source: response.source ?? "companion"); self.isLoading = false }
                    return
                }
            } catch {
                DebugLogger.shared.log("Lyrics: companion fallback failed: \(error.localizedDescription)", category: "Lyrics")
            }
        }
        
        await MainActor.run {
            self.currentLyrics = nil
            self.isLoading = false
        }
        DebugLogger.shared.log("Lyrics: none found for \(artist) — \(title)", category: "Lyrics")
    }
    
    // MARK: - Binary Search
    
    /// Find the active line index at a given time. O(log n).
    private func findLineIndex(at time: Double, in lines: [LyricLine]) -> Int {
        var lo = 0, hi = lines.count - 1
        while lo <= hi {
            let mid = (lo + hi) / 2
            if lines[mid].startTime <= time {
                lo = mid + 1
            } else {
                hi = mid - 1
            }
        }
        return max(hi, 0)
    }
    
    /// Find the active word index at a given time. O(log n).
    private func findWordIndex(at time: Double, in words: [LyricWord]) -> Int {
        var lo = 0, hi = words.count - 1
        while lo <= hi {
            let mid = (lo + hi) / 2
            if words[mid].startTime <= time {
                lo = mid + 1
            } else {
                hi = mid - 1
            }
        }
        return max(hi, 0)
    }
}