refactor: extract playback timing and subtitle index calculations into separate flows in PlayerViewModel

shared/src/commonMain/kotlin/fr/ajaury/gwenedeg/player/ui/viewmodel/PlayerViewModel.kt

@@ -24,6 +24,7 @@ import kotlinx.coroutines.flow.combine
 import kotlinx.coroutines.flow.flatMapLatest
 import kotlinx.coroutines.flow.flow
 import kotlinx.coroutines.flow.flowOf
+import kotlinx.coroutines.flow.map
 import kotlinx.coroutines.flow.stateIn
 import kotlinx.coroutines.launch
 import kotlin.time.Duration.Companion.milliseconds
@@ -59,24 +60,36 @@ class PlayerViewModel(
             }
         }
 
+    private val currentSubtitleIndex = combine(
+        subtitle,
+        currentPosition,
+    ) { subtitle, currentPosition ->
+        getCurrentSubtitleIndex(
+            subtitle = subtitle,
+            progressMs = currentPosition.inWholeMilliseconds,
+        )
+    }
+
+    private val playbackTiming = currentPosition.map { currentPosition ->
+        PlaybackTiming(
+            positionMs = currentPosition.inWholeMilliseconds,
+            durationMs = audioPlayer.duration.inWholeMilliseconds,
+        )
+    }
+
     val uiState: StateFlow<PlayerUiState> = combine(
         recordTitle,
         playbackState,
-        currentPosition,
+        playbackTiming,
         subtitle,
-    ) { recordTitle, playbackState, currentPosition, subtitle ->
+        currentSubtitleIndex,
+    ) { recordTitle, playbackState, playbackTiming, subtitle, currentSubtitleIndex ->
         PlayerUiState(
             recordTitle = recordTitle,
             playbackState = playbackState,
-            playbackTiming = PlaybackTiming(
-                positionMs = currentPosition.inWholeMilliseconds,
-                durationMs = audioPlayer.duration.inWholeMilliseconds,
-            ),
+            playbackTiming = playbackTiming,
             subtitleLines = subtitle.lines,
-            currentSubtitleIndex = getCurrentSubtitleIndex(
-                subtitle = subtitle,
-                progressMs = currentPosition.inWholeMilliseconds,
-            ),
+            currentSubtitleIndex = currentSubtitleIndex,
         )
     }.stateIn(
         scope = viewModelScope,