Android: Use android.media.MediaPlayer for BGM playback

Playlist is written to <gamedir>/playlist.txt during installation
("cdrom_device" in .xsys35rc is not used).
Files that match /(\d+)\.(wav|mp3|ogg)$/ are recognized as BGM files
(digits represent a track number). Note that this convention is the same
as Kichikuou on Web.

android/app/src/main/java/io/github/kichikuou/xsystem35/GameActivity.kt

@@ -17,16 +17,39 @@
 */
 package io.github.kichikuou.xsystem35
 
+import android.media.MediaPlayer
+import android.os.Bundle
+import android.util.Log
 import org.libsdl.app.SDLActivity
 import java.io.File
+import java.io.IOException
 
 // Intent for this activity must have two extras:
 // - EXTRA_GAME_ROOT (string): A path to the game installation.
 // - EXTRA_TITLE_FILE (string): A file to which the game title will be written.
+// - EXTRA_PLAYLIST_FILE (string): A path to the BGM playlist file.
 class GameActivity : SDLActivity() {
     companion object {
         const val EXTRA_GAME_ROOT = "GAME_ROOT"
         const val EXTRA_TITLE_FILE = "TITLE_FILE"
+        const val EXTRA_PLAYLIST_FILE = "PLAYLIST_FILE"
+    }
+
+    private lateinit var player: BGMPlayer
+
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        player = BGMPlayer(intent.getStringExtra(EXTRA_PLAYLIST_FILE))
+    }
+
+    override fun onStop() {
+        super.onStop()
+        player.onStop()
+    }
+
+    override fun onResume() {
+        super.onResume()
+        player.onResume()
     }
 
     override fun getLibraries(): Array<String> {
@@ -44,4 +67,71 @@ class GameActivity : SDLActivity() {
             return
         intent.getStringExtra(EXTRA_TITLE_FILE)?.let { File(it).writeText(str) }
     }
+
+    // These functions are called in the SDL thread by JNI.
+    @Suppress("unused") fun cddaStart(track: Int, loop: Int) = player.cddaStart(track, loop)
+    @Suppress("unused") fun cddaStop() = player.cddaStop()
+    @Suppress("unused") fun cddaCurrentPosition(): Int = player.cddaCurrentPosition()
 }
+
+private class BGMPlayer(playlistPath: String?) {
+    private val playlist = playlistPath?.let {
+        try {
+            File(it).readLines()
+        } catch (e: IOException) {
+            Log.e("loadPlaylist", "Cannot load $playlistPath", e)
+            null
+        }
+    } ?: emptyList()
+    private var currentTrack = 0
+    private val player = MediaPlayer()
+    private var playerPaused = false
+
+    fun cddaStart(track: Int, loop: Int) {
+        val f = playlist.elementAtOrNull(track)
+        if (f.isNullOrEmpty()) {
+            Log.w("cddaStart", "No playlist entry for track $track")
+            return
+        }
+        Log.v("cddaStart", f)
+        try {
+            player.apply {
+                reset()
+                setDataSource(f)
+                isLooping = loop == 0
+                prepare()
+                start()
+            }
+            currentTrack = track
+        } catch (e: IOException) {
+            Log.e("cddaStart", "Cannot play $f", e)
+            player.reset()
+        }
+    }
+
+    fun cddaStop() {
+        if (currentTrack > 0 && player.isPlaying)
+            player.stop()
+    }
+
+    fun cddaCurrentPosition(): Int {
+        if (currentTrack == 0)
+            return 0
+        val frames = player.currentPosition * 75 / 1000
+        return currentTrack or (frames shl 8)
+    }
+
+    fun onStop() {
+        if (currentTrack > 0 && player.isPlaying) {
+            player.pause()
+            playerPaused = true
+        }
+    }
+
+    fun onResume() {
+        if (playerPaused) {
+            player.start()
+            playerPaused = false
+        }
+    }
+}

android/app/src/main/java/io/github/kichikuou/xsystem35/LauncherActivity.kt

@@ -117,6 +117,7 @@ class LauncherActivity : ListActivity(), AdapterView.OnItemLongClickListener {
         i.setClass(applicationContext, GameActivity::class.java)
         i.putExtra(GameActivity.EXTRA_GAME_ROOT, gameRoot.path)
         i.putExtra(GameActivity.EXTRA_TITLE_FILE, File(path, GameManager.TITLE_FILE).path)
+        i.putExtra(GameActivity.EXTRA_PLAYLIST_FILE, File(path, GameManager.PLAYLIST_FILE).path)
         startActivity(i)
     }
 
@@ -151,6 +152,7 @@ class ProgressDialogFragment : DialogFragment() {
 private class GameManager(private val rootDir: File) {
     companion object {
         const val TITLE_FILE = "title.txt"
+        const val PLAYLIST_FILE = "playlist.txt"
     }
 
     data class Entry(val path: File, val title: String)
@@ -193,6 +195,7 @@ private class GameManager(private val rootDir: File) {
 
     private fun extractFiles(input: InputStream, outDir: File, handler: Handler) {
         try {
+            val playlistWriter = PlaylistWriter()
             val zip = if (Build.VERSION.SDK_INT >= 24) {
                 ZipInputStream(input.buffered(), Charset.forName("Shift_JIS"))
             } else {
@@ -200,7 +203,7 @@ private class GameManager(private val rootDir: File) {
             }
             while (true) {
                 val zipEntry = zip.nextEntry ?: break
-                Log.d("extractFiles", zipEntry.name)
+                Log.v("extractFiles", zipEntry.name)
                 val path = File(outDir, zipEntry.name)
                 if (zipEntry.isDirectory)
                     continue
@@ -209,8 +212,10 @@ private class GameManager(private val rootDir: File) {
                 val output = FileOutputStream(path).buffered()
                 zip.copyTo(output)
                 output.close()
+                playlistWriter.maybeAdd(path.path)
             }
             zip.close()
+            playlistWriter.write(outDir)
             handler.sendMessage(handler.obtainMessage(SUCCESS, outDir))
         } catch (e: UTFDataFormatException) {
             // Attempted to read Shift_JIS zip in Android < 7
@@ -220,6 +225,24 @@ private class GameManager(private val rootDir: File) {
             handler.sendMessage(handler.obtainMessage(FAILURE, R.string.zip_extraction_error))
         }
     }
+
+    private class PlaylistWriter {
+        private val audioRegex = """.*?(\d+)\.(wav|mp3|ogg)""".toRegex(RegexOption.IGNORE_CASE)
+        private val audioFiles: Array<String?> = arrayOfNulls(100)
+
+        fun maybeAdd(path: String) {
+            audioRegex.matchEntire(path)?.let {
+                val track = it.groupValues[1].toInt()
+                if (track < audioFiles.size)
+                    audioFiles[track] = path
+            }
+        }
+
+        fun write(outDir: File) {
+            val text = audioFiles.joinToString("\n") { it ?: "" }.trimEnd('\n')
+            File(outDir, PLAYLIST_FILE).writeText(text)
+        }
+    }
 }
 
 private fun findGameRoot(path: File): File? {