Add "Allow black theme" feature flag

libraries/compound/src/main/kotlin/io/element/android/compound/theme/Theme.kt

@@ -20,6 +20,10 @@ enum class Theme {
     Light,
 }
 
+private fun Theme.coerceBlackTheme(allowBlackTheme: Boolean): Theme {
+    return if (this == Theme.Black && !allowBlackTheme) Theme.Dark else this
+}
+
 @Composable
 fun Theme.isDark(): Boolean {
     return when (this) {
@@ -29,9 +33,9 @@ fun Theme.isDark(): Boolean {
     }
 }
 
-fun Flow<String?>.mapToTheme(): Flow<Theme> = map {
+fun Flow<String?>.mapToTheme(allowBlackTheme: Boolean = true): Flow<Theme> = map {
     when (it) {
         null -> Theme.System
         else -> Theme.valueOf(it)
-    }
+    }.coerceBlackTheme(allowBlackTheme)
 }

libraries/compound/src/test/kotlin/io/element/android/compound/theme/ThemeTest.kt

@@ -15,6 +15,7 @@ import app.cash.molecule.RecompositionMode
 import app.cash.molecule.moleculeFlow
 import app.cash.turbine.test
 import com.google.common.truth.Truth.assertThat
+import kotlinx.coroutines.flow.flowOf
 import kotlinx.coroutines.test.runTest
 import org.junit.Test
 
@@ -72,4 +73,14 @@ class ThemeTest {
             assertThat(awaitItem()).isTrue()
         }
     }
+
+    @Test
+    fun `mapToTheme falls back to dark when black theme is disabled`() = runTest {
+        flowOf(Theme.Black.name)
+            .mapToTheme(allowBlackTheme = false)
+            .test {
+                assertThat(awaitItem()).isEqualTo(Theme.Dark)
+                awaitComplete()
+            }
+    }
 }

libraries/designsystem/build.gradle.kts

@@ -38,6 +38,7 @@ dependencies {
     implementation(projects.libraries.androidutils)
     implementation(projects.libraries.architecture)
     implementation(projects.libraries.core)
+    implementation(projects.libraries.featureflag.api)
     implementation(projects.libraries.preferences.api)
     implementation(projects.libraries.testtags)
     implementation(projects.libraries.uiStrings)

libraries/designsystem/src/main/kotlin/io/element/android/libraries/designsystem/theme/ElementThemeApp.kt

@@ -22,6 +22,8 @@ import io.element.android.compound.theme.mapToTheme
 import io.element.android.compound.tokens.generated.SemanticColors
 import io.element.android.libraries.core.meta.BuildMeta
 import io.element.android.libraries.core.meta.BuildType
+import io.element.android.libraries.featureflag.api.FeatureFlagService
+import io.element.android.libraries.featureflag.api.FeatureFlags
 import io.element.android.libraries.preferences.api.store.AppPreferencesStore
 
 val LocalBuildMeta = staticCompositionLocalOf {
@@ -53,15 +55,18 @@ val LocalBuildMeta = staticCompositionLocalOf {
 @Composable
 fun ElementThemeApp(
     appPreferencesStore: AppPreferencesStore,
+    featureFlagService: FeatureFlagService,
     compoundLight: SemanticColors,
     compoundDark: SemanticColors,
     buildMeta: BuildMeta,
     content: @Composable () -> Unit,
 ) {
+    val isBlackThemeAllowed by remember {
+        featureFlagService.isFeatureEnabledFlow(FeatureFlags.AllowBlackTheme)
+    }.collectAsState(initial = false)
     val theme by remember {
-        appPreferencesStore.getThemeFlow().mapToTheme()
-    }
-        .collectAsState(initial = Theme.System)
+        appPreferencesStore.getThemeFlow().mapToTheme(allowBlackTheme = isBlackThemeAllowed)
+    }.collectAsState(initial = Theme.System)
     LaunchedEffect(theme) {
         AppCompatDelegate.setDefaultNightMode(
             when (theme) {

libraries/featureflag/api/src/main/kotlin/io/element/android/libraries/featureflag/api/FeatureFlags.kt

@@ -147,6 +147,13 @@ enum class FeatureFlags(
         defaultValue = { false },
         isFinished = false,
     ),
+    AllowBlackTheme(
+        key = "feature.allow_black_theme",
+        title = "Allow black theme",
+        description = "Allow selecting the black appearance theme for battery saving on OLED.",
+        defaultValue = { false },
+        isFinished = false,
+    ),
     LiveLocationSharing(
         key = "feature.liveLocationSharing",
         title = "Live location sharing",