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/PlaybackManager.swift

@@ -106,6 +106,7 @@ final class PlaybackManager: StemEngineListener, @unchecked Sendable {
     @ObservationIgnored private let eq: EqController
     @ObservationIgnored private(set) var engine: StemEngine!
     @ObservationIgnored private let queueFile: URL
+    @ObservationIgnored private let songMixFile: URL
 
     private(set) var queue: [QueueItem] = []
     private(set) var index = -1
@@ -121,6 +122,11 @@ final class PlaybackManager: StemEngineListener, @unchecked Sendable {
     private(set) var waveform: Waveform?
     private(set) var durationMs: Int64 = 0
     private(set) var message: AppMessage?
+    /// Mixes saved for single songs (by rating key), put back whenever that song starts.
+    private(set) var songMixes: [String: [String: StemSetting]] = [:]
+    /// Karaoke mode: vocals out on every song, lyrics on Now Playing.
+    private(set) var karaoke = false
+    @ObservationIgnored private var preKaraokeMix: [String: StemSetting]?
 
     @ObservationIgnored private var listeners: [UUID: () -> Void] = [:]
     @ObservationIgnored private var messageListeners: [UUID: (String) -> Void] = [:]
@@ -148,6 +154,8 @@ final class PlaybackManager: StemEngineListener, @unchecked Sendable {
         self.cache = cache
         self.eq = eq
         queueFile = dir.appendingPathComponent("queue.json")
+        songMixFile = dir.appendingPathComponent("song-mixes.json")
+        songMixes = (try? JSONDecoder().decode([String: [String: StemSetting]].self, from: Data(contentsOf: songMixFile))) ?? [:]
         master = settings.masterVolume
         engine = StemEngine(listener: self)
         eq.onParams = { [weak self] p in self?.engine.eqParams = p }
@@ -405,6 +413,42 @@ final class PlaybackManager: StemEngineListener, @unchecked Sendable {
         pushMix()
     }
 
+    /// The mix a song starts with: karaoke if that's on, else the song's saved mix, else cleared (or kept, per settings).
+    private func startMix(_ t: Track) -> [String: StemSetting] {
+        if karaoke { return Self.karaokeMix }
+        return songMixes[t.ratingKey] ?? (settings.keepStemMix ? mix : [:])
+    }
+
+    private static let karaokeMix = ["vocals": StemSetting(muted: true)]
+
+    /// Turning it off puts back the song's saved mix, or the one from before, unless the mix was changed meanwhile.
+    func setKaraoke(_ on: Bool) {
+        guard on != karaoke else { return }
+        karaoke = on
+        if on {
+            preKaraokeMix = mix
+            applyMix(Self.karaokeMix)
+        } else {
+            if MixPresets.normalized(mix) == Self.karaokeMix { applyMix(songMix ?? preKaraokeMix ?? [:]) }
+            preKaraokeMix = nil
+            changed()
+        }
+    }
+
+    var songMix: [String: StemSetting]? { current.flatMap { songMixes[$0.track.ratingKey] } }
+
+    func saveSongMix() { setSongMix(MixPresets.normalized(mix)) }
+    func forgetSongMix() { setSongMix(nil) }
+
+    private func setSongMix(_ m: [String: StemSetting]?) {
+        guard let key = current?.track.ratingKey else { return }
+        songMixes[key] = m
+        let all = songMixes, file = songMixFile
+        DispatchQueue.global(qos: .utility).async {
+            if let data = try? JSONEncoder().encode(all) { try? data.write(to: file, options: .atomic) }
+        }
+    }
+
     private func editMix(_ name: String, _ f: (inout StemSetting) -> Void) {
         var s = mix[name] ?? StemSetting()
         f(&s)
@@ -462,7 +506,7 @@ final class PlaybackManager: StemEngineListener, @unchecked Sendable {
         if play && !activateSession() { return }
         playWhenReady = play
         buffering = true
-        if !settings.keepStemMix { mix = [:] }
+        mix = startMix(item.track)
         changed()
         save()
         loadTask = Task { @MainActor [weak self] in
@@ -635,7 +679,7 @@ final class PlaybackManager: StemEngineListener, @unchecked Sendable {
         guard let item = current else { return }
         durationMs = item.track.durationMs
         waveform = nil
-        if !settings.keepStemMix { mix = [:] }
+        mix = startMix(item.track)
         source = currentEntry != nil ? .Stems : .Original
         stemNames = Stems.sort(currentEntry?.stems.map(\.name) ?? ["mix"])
         pushMix()