refactor: optimize album color scheme generation and caching

app/src/main/java/com/theveloper/pixelplay/presentation/viewmodel/ThemeStateHolder.kt

@@ -22,7 +22,6 @@ import kotlinx.coroutines.flow.update
 import kotlinx.coroutines.launch
 import javax.inject.Inject
 import javax.inject.Singleton
-import java.util.concurrent.ConcurrentHashMap
 
 @Singleton
 class ThemeStateHolder @Inject constructor(
@@ -139,30 +138,56 @@ class ThemeStateHolder @Inject constructor(
         32, 0.75f, true
     ) {
         override fun removeEldestEntry(eldest: MutableMap.MutableEntry<String, MutableStateFlow<ColorSchemePair?>>?): Boolean {
-            return size > 30
+            return size > 96
         }
     }
 
-    private val pendingAlbumColorSchemeRequests = ConcurrentHashMap.newKeySet<String>()
+    private val emptyAlbumColorScheme = MutableStateFlow<ColorSchemePair?>(null).asStateFlow()
+    private val pendingAlbumColorSchemeLock = Any()
+    private val pendingAlbumColorSchemeTargets = mutableMapOf<String, MutableSet<MutableStateFlow<ColorSchemePair?>>>()
 
     private fun requestAlbumColorSchemeGeneration(
         uriString: String,
         targetFlow: MutableStateFlow<ColorSchemePair?>
     ) {
-        if (!pendingAlbumColorSchemeRequests.add(uriString)) return
+        if (uriString.isBlank()) return
+
+        val shouldStartRequest = synchronized(pendingAlbumColorSchemeLock) {
+            val existingTargets = pendingAlbumColorSchemeTargets[uriString]
+            if (existingTargets != null) {
+                existingTargets.add(targetFlow)
+                false
+            } else {
+                pendingAlbumColorSchemeTargets[uriString] = mutableSetOf(targetFlow)
+                true
+            }
+        }
+
+        if (!shouldStartRequest) return
+
+        val requestScope = scope
+        if (requestScope == null) {
+            synchronized(pendingAlbumColorSchemeLock) {
+                pendingAlbumColorSchemeTargets.remove(uriString)
+            }
+            return
+        }
 
-        scope?.launch(Dispatchers.IO) {
+        requestScope.launch(Dispatchers.IO) {
+            var scheme: ColorSchemePair? = null
             try {
-                val scheme = colorSchemeProcessor.getOrGenerateColorScheme(
+                scheme = colorSchemeProcessor.getOrGenerateColorScheme(
                     albumArtUri = uriString,
                     paletteStyle = currentPaletteStyle,
                     colorAccuracyLevel = currentPaletteAccuracy
                 )
-                targetFlow.value = scheme
             } catch (_: Exception) {
                 // Ignore or log
             } finally {
-                pendingAlbumColorSchemeRequests.remove(uriString)
+                val targets = synchronized(pendingAlbumColorSchemeLock) {
+                    pendingAlbumColorSchemeTargets.remove(uriString)?.toList().orEmpty()
+                }
+                targets.forEach { it.value = scheme }
             }
         }
     }
@@ -171,6 +196,8 @@ class ThemeStateHolder @Inject constructor(
         uriString: String,
         eager: Boolean = true
     ): StateFlow<ColorSchemePair?> {
+        if (uriString.isBlank()) return emptyAlbumColorScheme
+
         val existingFlow = individualAlbumColorSchemes[uriString]
         if (existingFlow != null) {
             if (eager && existingFlow.value == null) {
@@ -190,6 +217,8 @@ class ThemeStateHolder @Inject constructor(
     }
 
     fun ensureAlbumColorScheme(uriString: String) {
+        if (uriString.isBlank()) return
+
         val targetFlow = individualAlbumColorSchemes[uriString]
             ?: MutableStateFlow<ColorSchemePair?>(null).also { individualAlbumColorSchemes[uriString] = it }
 
@@ -276,7 +305,9 @@ class ThemeStateHolder @Inject constructor(
             level >= ComponentCallbacks2.TRIM_MEMORY_RUNNING_CRITICAL ||
             level >= ComponentCallbacks2.TRIM_MEMORY_COMPLETE
         ) {
-            pendingAlbumColorSchemeRequests.clear()
+            synchronized(pendingAlbumColorSchemeLock) {
+                pendingAlbumColorSchemeTargets.clear()
+            }
         }
     }