iOS 1.0.4: per-song saved mixes, karaoke mode with synced lyrics

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

ios/Stemify/Playback/Lyrics.swift

@@ -0,0 +1,86 @@
+import Foundation
+
+struct LyricLine: Hashable {
+    let ms: Int64
+    let text: String
+}
+
+struct Lyrics {
+    var lines: [LyricLine] = []
+    /// False for plain lyrics, which have no timings (every [ms] is 0).
+    var synced = false
+    var instrumental = false
+}
+
+/// Lyrics from LRCLIB (lrclib.net), synced when it has them. Hits are cached on disk by track,
+/// misses only until the app restarts.
+actor LyricsSource {
+    static let shared = LyricsSource()
+
+    private struct Record: Codable {
+        var syncedLyrics: String?
+        var plainLyrics: String?
+        var instrumental: Bool?
+        var duration: Double?
+    }
+
+    private let dir: URL
+    private var misses: Set<String> = []
+
+    private init() {
+        dir = FileManager.default.urls(for: .cachesDirectory, in: .userDomainMask)[0].appendingPathComponent("lyrics", isDirectory: true)
+        try? FileManager.default.createDirectory(at: dir, withIntermediateDirectories: true)
+    }
+
+    /// Nil when LRCLIB has nothing for this song or couldn't be reached.
+    func lyrics(_ t: Track) async -> Lyrics? {
+        let file = dir.appendingPathComponent(t.ratingKey.replacingOccurrences(of: "/", with: "_") + ".json")
+        if let data = try? Data(contentsOf: file), let r = try? JSONDecoder().decode(Record.self, from: data) { return Self.parse(r) }
+        if misses.contains(t.ratingKey) { return nil }
+        let secs = Double(t.durationMs) / 1000
+        var rec = await get("get", ["track_name": t.title, "artist_name": t.artist, "album_name": t.album, "duration": String(Int(secs.rounded()))])
+            .flatMap { try? JSONDecoder().decode(Record.self, from: $0) }
+        if rec == nil, let data = await get("search", ["track_name": t.title, "artist_name": t.artist]),
+           let found = try? JSONDecoder().decode([Record].self, from: data) {
+            // Closest length first, so a live or extended version doesn't win.
+            let close = found.filter { abs(($0.duration ?? 0) - secs) < 8 || secs <= 0 }
+            rec = close.first { $0.syncedLyrics?.isEmpty == false } ?? close.first { $0.plainLyrics?.isEmpty == false } ?? close.first
+        }
+        guard let rec else {
+            misses.insert(t.ratingKey)
+            return nil
+        }
+        if let data = try? JSONEncoder().encode(rec) { try? data.write(to: file, options: .atomic) }
+        return Self.parse(rec)
+    }
+
+    private func get(_ path: String, _ query: [String: String]) async -> Data? {
+        var c = URLComponents(string: "https://lrclib.net/api/\(path)")!
+        c.queryItems = query.map { URLQueryItem(name: $0.key, value: $0.value) }
+        var req = URLRequest(url: c.url!, timeoutInterval: 10)
+        req.setValue("Stemify iOS (https://git.iamchrisama.com/cdnutter/stemify)", forHTTPHeaderField: "User-Agent")
+        guard let (data, resp) = try? await URLSession.shared.data(for: req), (resp as? HTTPURLResponse)?.statusCode == 200 else { return nil }
+        return data
+    }
+
+    private static let stamp = #/\[(\d+):(\d+(?:\.\d+)?)\]/#
+
+    /// LRC: each line starts with one or more [mm:ss.xx] stamps.
+    private static func parse(_ r: Record) -> Lyrics {
+        if let lrc = r.syncedLyrics, !lrc.isEmpty {
+            var lines: [LyricLine] = []
+            for raw in lrc.split(separator: "\n", omittingEmptySubsequences: false) {
+                let stamps = raw.matches(of: stamp)
+                guard let last = stamps.last else { continue }
+                let text = raw[last.range.upperBound...].trimmingCharacters(in: .whitespaces)
+                for m in stamps {
+                    let ms = (Int64(m.output.1) ?? 0) * 60_000 + Int64((Double(m.output.2) ?? 0) * 1000)
+                    lines.append(LyricLine(ms: ms, text: text))
+                }
+            }
+            return Lyrics(lines: lines.sorted { $0.ms < $1.ms }, synced: true)
+        }
+        let plain = (r.plainLyrics ?? "").split(separator: "\n", omittingEmptySubsequences: false).map { LyricLine(ms: 0, text: String($0)) }
+        return Lyrics(lines: plain.count > 1 || plain.first?.text.isEmpty == false ? plain : [], instrumental: r.instrumental == true)
+    }
+}