feat: refactor out MusicPlayerEngine

app/src/main/java/at/lockstep/player/pasada/LibPasada.java

@@ -0,0 +1,75 @@
+package at.lockstep.player.pasada;
+
+/**
+ * JNI entry point for libpasada. Used by {@link at.lockstep.player.playback.engine.PasadaMusicPlayerEngine};
+ * {@link at.lockstep.player.playback.PlaybackService} still defaults to
+ * {@link at.lockstep.player.playback.engine.ExoPlayerMusicPlayerEngine} until the native library is ready.
+ *
+ * <p>Native state machine: LOADED → INITIALIZED → PLAYING ↔ PAUSED → FINISHED → STOPPED
+ *
+ * <p>Call {@link #loadNative()} once before any other method once the {@code pasada} shared
+ * library is added via CMake (step 3).
+ */
+public final class LibPasada {
+
+    private static boolean loaded;
+
+    private LibPasada() {}
+
+    /** Loads {@code libpasada.so}. Safe to call multiple times. */
+    public static synchronized void loadNative() {
+        if (loaded) {
+            return;
+        }
+        System.loadLibrary("pasada");
+        loaded = true;
+    }
+
+    /** Called each time a run/playlist session starts (Oboe silent, buffers ready). */
+    public static native void init();
+
+    /** Submit one accelerometer sample (m/s²); may be called from a sensor thread. */
+    public static native void feedAccel(float x, float y, float z, long timestampNanos);
+
+    /**
+     * Open MP3 from an already-open file descriptor and begin adaptive playback.
+     *
+     * @param fd open read FD (Java retains ownership; do not close until track changes)
+     * @param offset start offset within the FD (0 for whole file)
+     * @param length byte length from offset ({@code -1} if unknown / to EOF)
+     */
+    public static native void play(int fd, long offset, long length);
+
+    /** PLAYING → PAUSED (silent output, graph kept alive). */
+    public static native void pause();
+
+    /** PAUSED → PLAYING (same track, same decode position, same FD). */
+    public static native void resume();
+
+    /** Tear down Oboe for this run segment → STOPPED. */
+    public static native void stop();
+
+    /**
+     * Milliseconds from the start of the current track — same timebase as ExoPlayer
+     * {@code getCurrentPosition()}. Safe to poll from background threads.
+     */
+    public static native long getCurrentPositionMs();
+
+    /** Track duration in ms, or {@code 0} if not yet known. */
+    public static native long getDurationMs();
+
+    /** Whether adapted audio is actively being output (not paused, not finished). */
+    public static native boolean isPlaying();
+
+    /** Current native state; see {@link PasadaState}. */
+    public static native int getState();
+
+    /** Seek within the current track. */
+    public static native void seekTo(long positionMs);
+
+    /** Runtime metrics / last error string for logging and debug UI. */
+    public static native String getDiagnostics();
+
+    /** Register listener for async events raised from the audio/native thread. */
+    public static native void setPlaybackListener(PasadaPlaybackListener listener);
+}