Implement a in-memory cache for user avatar colors.

libraries/designsystem/src/main/kotlin/io/element/android/libraries/designsystem/colors/AvatarColors.kt

@@ -16,9 +16,8 @@
 
 package io.element.android.libraries.designsystem.colors
 
-import androidx.compose.runtime.Composable
+import androidx.collection.LruCache
 import androidx.compose.ui.graphics.Color
-import io.element.android.libraries.theme.ElementTheme
 import io.element.android.libraries.theme.colors.avatarColorsDark
 import io.element.android.libraries.theme.colors.avatarColorsLight
 
@@ -27,18 +26,37 @@ data class AvatarColors(
     val foreground: Color,
 )
 
-@Composable
-fun avatarColors(userId: String): AvatarColors {
-    val hash = userId.toHash()
-    val colors = if (ElementTheme.isLightTheme) {
-        avatarColorsLight[hash]
-    } else {
-        avatarColorsDark[hash]
+object AvatarColorsProvider {
+    private val cache = LruCache<String, AvatarColors>(200)
+    private var currentThemeIsLight = true
+
+    fun provide(id: String, isLightTheme: Boolean): AvatarColors {
+        if (currentThemeIsLight != isLightTheme) {
+            currentThemeIsLight = isLightTheme
+            cache.evictAll()
+        }
+        val valueFromCache = cache.get(id)
+        return if (valueFromCache != null) {
+            valueFromCache
+        } else {
+            val colors = avatarColors(id, isLightTheme)
+            cache.put(id, colors)
+            colors
+        }
+    }
+
+    private fun avatarColors(id: String, isLightTheme: Boolean): AvatarColors {
+        val hash = id.toHash()
+        val colors = if (isLightTheme) {
+            avatarColorsLight[hash]
+        } else {
+            avatarColorsDark[hash]
+        }
+        return AvatarColors(
+            background = colors.first,
+            foreground = colors.second,
+        )
     }
-    return AvatarColors(
-        background = colors.first,
-        foreground = colors.second,
-    )
 }
 
 internal fun String.toHash(): Int {

libraries/designsystem/src/main/kotlin/io/element/android/libraries/designsystem/components/avatar/Avatar.kt

@@ -33,7 +33,7 @@ import androidx.compose.ui.unit.dp
 import androidx.compose.ui.unit.sp
 import coil.compose.AsyncImage
 import io.element.android.libraries.designsystem.colors.AvatarColors
-import io.element.android.libraries.designsystem.colors.avatarColors
+import io.element.android.libraries.designsystem.colors.AvatarColorsProvider
 import io.element.android.libraries.designsystem.preview.ElementThemedPreview
 import io.element.android.libraries.designsystem.preview.PreviewGroup
 import io.element.android.libraries.designsystem.preview.debugPlaceholderAvatar
@@ -53,7 +53,7 @@ fun Avatar(
         .size(avatarData.size.dp)
         .clip(CircleShape)
     if (avatarData.url.isNullOrBlank()) {
-        val avatarColors = initialAvatarColors ?: avatarColors(avatarData.id)
+        val avatarColors = initialAvatarColors ?: AvatarColorsProvider.provide(avatarData.id, ElementTheme.isLightTheme)
         InitialsAvatar(
             avatarData = avatarData,
             avatarColors = avatarColors,

libraries/designsystem/src/main/kotlin/io/element/android/libraries/designsystem/components/avatar/UserAvatarPreview.kt

@@ -24,10 +24,11 @@ import androidx.compose.runtime.Composable
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.unit.dp
-import io.element.android.libraries.designsystem.colors.avatarColors
+import io.element.android.libraries.designsystem.colors.AvatarColorsProvider
 import io.element.android.libraries.designsystem.preview.DayNightPreviews
 import io.element.android.libraries.designsystem.preview.ElementPreview
 import io.element.android.libraries.designsystem.theme.components.Text
+import io.element.android.libraries.theme.ElementTheme
 import io.element.android.libraries.theme.colors.avatarColorsLight
 
 @DayNightPreviews
@@ -43,7 +44,7 @@ internal fun UserAvatarPreview() = ElementPreview {
                 verticalAlignment = Alignment.CenterVertically,
             ) {
                 // Note: it's OK, since the hash of "0" is 0, the hash of "1" is 1, etc.
-                Avatar(anAvatarData(), initialAvatarColors = avatarColors("$it"))
+                Avatar(anAvatarData(), initialAvatarColors = AvatarColorsProvider.provide("$it", ElementTheme.isLightTheme))
                 Text(text = "Color index $it")
             }
         }