fix: stack unpositioned subtitle cues so simultaneous subtitles do not overlap

feature/player/src/main/java/dev/anilbeesetti/nextplayer/feature/player/extensions/CueExtensions.kt

@@ -0,0 +1,20 @@
+package dev.anilbeesetti.nextplayer.feature.player.extensions
+
+import androidx.media3.common.text.Cue
+
+fun List<Cue>.stackUnpositionedCues(): List<Cue> {
+    if (size <= 1) return this
+
+    var nextLine = -1
+    return map { cue ->
+        val text = cue.text
+        if (cue.line != Cue.DIMEN_UNSET || text == null) {
+            cue
+        } else {
+            cue.buildUpon()
+                .setLine(nextLine.toFloat(), Cue.LINE_TYPE_NUMBER)
+                .build()
+                .also { nextLine -= text.count { it == '\n' } + 1 }
+        }
+    }
+}

feature/player/src/main/java/dev/anilbeesetti/nextplayer/feature/player/state/CuesState.kt

@@ -10,6 +10,7 @@ import androidx.media3.common.Player
 import androidx.media3.common.listen
 import androidx.media3.common.text.Cue
 import androidx.media3.common.util.UnstableApi
+import dev.anilbeesetti.nextplayer.feature.player.extensions.stackUnpositionedCues
 
 @UnstableApi
 @Composable
@@ -26,10 +27,10 @@ class CuesState(
         private set
 
     suspend fun observe() {
-        cues = player.currentCues.cues
+        cues = player.currentCues.cues.stackUnpositionedCues()
         player.listen { events ->
             if (events.contains(Player.EVENT_CUES)) {
-                cues = player.currentCues.cues
+                cues = player.currentCues.cues.stackUnpositionedCues()
             }
         }
     }

feature/player/src/test/java/dev/anilbeesetti/nextplayer/feature/player/extensions/CueExtensionsTest.kt

@@ -0,0 +1,71 @@
+package dev.anilbeesetti.nextplayer.feature.player.extensions
+
+import androidx.media3.common.text.Cue
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertSame
+import org.junit.Test
+
+class CueExtensionsTest {
+
+    @Test
+    fun `empty cue list remains empty`() {
+        assertEquals(emptyList<Cue>(), emptyList<Cue>().stackUnpositionedCues())
+    }
+
+    @Test
+    fun `single unpositioned cue remains unchanged`() {
+        val cue = textCue("only cue")
+
+        val result = listOf(cue).stackUnpositionedCues()
+
+        assertSame(cue, result.single())
+        assertEquals(Cue.DIMEN_UNSET, result.single().line)
+    }
+
+    @Test
+    fun `two unpositioned cues are stacked from the bottom`() {
+        val result = listOf(textCue("first"), textCue("second")).stackUnpositionedCues()
+
+        assertEquals(-1f, result[0].line)
+        assertEquals(Cue.LINE_TYPE_NUMBER, result[0].lineType)
+        assertEquals(-2f, result[1].line)
+        assertEquals(Cue.LINE_TYPE_NUMBER, result[1].lineType)
+    }
+
+    @Test
+    fun `multiline lower cue offsets the cue above by its rendered line count`() {
+        val result = listOf(textCue("a\nb"), textCue("above")).stackUnpositionedCues()
+
+        assertEquals(-1f, result[0].line)
+        assertEquals(-3f, result[1].line)
+    }
+
+    @Test
+    fun `explicitly positioned cue remains unchanged while siblings are stacked`() {
+        val first = textCue("first")
+        val positioned = Cue.Builder()
+            .setText("positioned")
+            .setLine(0.25f, Cue.LINE_TYPE_FRACTION)
+            .build()
+        val second = textCue("second")
+
+        val result = listOf(first, positioned, second).stackUnpositionedCues()
+
+        assertEquals(-1f, result[0].line)
+        assertSame(positioned, result[1])
+        assertEquals(0.25f, result[1].line)
+        assertEquals(Cue.LINE_TYPE_FRACTION, result[1].lineType)
+        assertEquals(-2f, result[2].line)
+    }
+
+    @Test
+    fun `stacking preserves cue text identity`() {
+        val cue = textCue("styled")
+
+        val result = listOf(cue, textCue("second")).stackUnpositionedCues()
+
+        assertSame(cue.text, result[0].text)
+    }
+
+    private fun textCue(text: CharSequence): Cue = Cue.Builder().setText(text).build()
+}