Rework the feature flag module.

Fix typo, rename class and interface, add doc, do small refacto, to improve code clarity.

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

@@ -28,7 +28,8 @@ interface FeatureFlagService {
      * @param feature the feature to enable or disable
      * @param enabled true to enable the feature
      *
-     * @return true if the method succeeds, ie if a RuntimeFeatureFlagProvider is registered
+     * @return true if the method succeeds, ie if a [io.element.android.libraries.featureflag.impl.MutableFeatureFlagProvider]
+     * is registered
      */
     suspend fun setFeatureEnabled(feature: Feature, enabled: Boolean): Boolean
 }

libraries/featureflag/impl/src/main/kotlin/io/element/android/libraries/featureflag/impl/DefaultFeatureFlagService.kt

@@ -38,7 +38,7 @@ class DefaultFeatureFlagService @Inject constructor(
     }
 
     override suspend fun setFeatureEnabled(feature: Feature, enabled: Boolean): Boolean {
-        return providers.filterIsInstance(RuntimeFeatureFlagProvider::class.java)
+        return providers.filterIsInstance(MutableFeatureFlagProvider::class.java)
             .sortedBy(FeatureFlagProvider::priority)
             .firstOrNull()
             ?.setFeatureEnabled(feature, enabled)

libraries/featureflag/impl/src/main/kotlin/io/element/android/libraries/featureflag/impl/MutableFeatureFlagProvider.kt

@@ -18,6 +18,6 @@ package io.element.android.libraries.featureflag.impl
 
 import io.element.android.libraries.featureflag.api.Feature
 
-interface RuntimeFeatureFlagProvider : FeatureFlagProvider {
+interface MutableFeatureFlagProvider : FeatureFlagProvider {
     suspend fun setFeatureEnabled(feature: Feature, enabled: Boolean)
 }

libraries/featureflag/impl/src/main/kotlin/io/element/android/libraries/featureflag/impl/PreferencesFeatureFlagProvider.kt

@@ -30,12 +30,13 @@ import javax.inject.Inject
 
 private val Context.dataStore: DataStore<Preferences> by preferencesDataStore(name = "elementx_featureflag")
 
-class PreferencesFeatureFlagProvider @Inject constructor(@ApplicationContext context: Context) : RuntimeFeatureFlagProvider {
-
+/**
+ * Note: this will be used only in the nightly and in the debug build.
+ */
+class PreferencesFeatureFlagProvider @Inject constructor(@ApplicationContext context: Context) : MutableFeatureFlagProvider {
     private val store = context.dataStore
 
-    override val priority: Int
-        get() = MEDIUM_PRIORITY
+    override val priority = MEDIUM_PRIORITY
 
     override suspend fun setFeatureEnabled(feature: Feature, enabled: Boolean) {
         store.edit { prefs ->

libraries/featureflag/impl/src/main/kotlin/io/element/android/libraries/featureflag/impl/StaticFeatureFlagProvider.kt

@@ -20,11 +20,14 @@ import io.element.android.libraries.featureflag.api.Feature
 import io.element.android.libraries.featureflag.api.FeatureFlags
 import javax.inject.Inject
 
-class BuildtimeFeatureFlagProvider @Inject constructor() :
+/**
+ * This provider is used for release build.
+ * Change the value return by [isFeatureEnabled] to enable/disable features.
+ */
+class StaticFeatureFlagProvider @Inject constructor() :
     FeatureFlagProvider {
 
-    override val priority: Int
-        get() = LOW_PRIORITY
+    override val priority = LOW_PRIORITY
 
     override suspend fun isFeatureEnabled(feature: Feature): Boolean {
         return if (feature is FeatureFlags) {

libraries/featureflag/impl/src/main/kotlin/io/element/android/libraries/featureflag/impl/di/FeatureFlagModule.kt

@@ -22,7 +22,7 @@ import dagger.Provides
 import dagger.multibindings.ElementsIntoSet
 import io.element.android.libraries.core.meta.BuildType
 import io.element.android.libraries.di.AppScope
-import io.element.android.libraries.featureflag.impl.BuildtimeFeatureFlagProvider
+import io.element.android.libraries.featureflag.impl.StaticFeatureFlagProvider
 import io.element.android.libraries.featureflag.impl.FeatureFlagProvider
 import io.element.android.libraries.featureflag.impl.PreferencesFeatureFlagProvider
 
@@ -35,14 +35,18 @@ object FeatureFlagModule {
     @ElementsIntoSet
     fun providesFeatureFlagProvider(
         buildType: BuildType,
-        runtimeFeatureFlagProvider: PreferencesFeatureFlagProvider,
-        buildtimeFeatureFlagProvider: BuildtimeFeatureFlagProvider,
+        mutableFeatureFlagProvider: PreferencesFeatureFlagProvider,
+        staticFeatureFlagProvider: StaticFeatureFlagProvider,
     ): Set<FeatureFlagProvider> {
         val providers = HashSet<FeatureFlagProvider>()
-        if (buildType == BuildType.RELEASE) {
-            providers.add(buildtimeFeatureFlagProvider)
-        } else {
-            providers.add(runtimeFeatureFlagProvider)
+        when (buildType) {
+            BuildType.RELEASE -> {
+                providers.add(staticFeatureFlagProvider)
+            }
+            BuildType.NIGHTLY,
+            BuildType.DEBUG -> {
+                providers.add(mutableFeatureFlagProvider)
+            }
         }
         return providers
     }

libraries/featureflag/impl/src/test/kotlin/io/element/android/libraries/featureflag/impl/DefaultFeatureFlagServiceTest.kt

@@ -39,7 +39,7 @@ class DefaultFeatureFlagServiceTest {
 
     @Test
     fun `given service with a runtime provider when set enabled feature is called then it returns true`() = runTest {
-        val featureFlagProvider = FakeRuntimeFeatureFlagProvider(0)
+        val featureFlagProvider = FakeMutableFeatureFlagProvider(0)
         val featureFlagService = DefaultFeatureFlagService(setOf(featureFlagProvider))
         val result = featureFlagService.setFeatureEnabled(FeatureFlags.LocationSharing, true)
         assertThat(result).isEqualTo(true)
@@ -47,7 +47,7 @@ class DefaultFeatureFlagServiceTest {
 
     @Test
     fun `given service with a runtime provider and feature enabled when feature is checked then it returns the correct value`() = runTest {
-        val featureFlagProvider = FakeRuntimeFeatureFlagProvider(0)
+        val featureFlagProvider = FakeMutableFeatureFlagProvider(0)
         val featureFlagService = DefaultFeatureFlagService(setOf(featureFlagProvider))
         featureFlagService.setFeatureEnabled(FeatureFlags.LocationSharing, true)
         assertThat(featureFlagService.isFeatureEnabled(FeatureFlags.LocationSharing)).isEqualTo(true)
@@ -57,11 +57,11 @@ class DefaultFeatureFlagServiceTest {
 
     @Test
     fun `given service with 2 runtime providers when feature is checked then it uses the priority correctly`() = runTest {
-        val lowPriorityfeatureFlagProvider = FakeRuntimeFeatureFlagProvider(LOW_PRIORITY)
-        val highPriorityfeatureFlagProvider = FakeRuntimeFeatureFlagProvider(HIGH_PRIORITY)
-        val featureFlagService = DefaultFeatureFlagService(setOf(lowPriorityfeatureFlagProvider, highPriorityfeatureFlagProvider))
-        lowPriorityfeatureFlagProvider.setFeatureEnabled(FeatureFlags.LocationSharing, false)
-        highPriorityfeatureFlagProvider.setFeatureEnabled(FeatureFlags.LocationSharing, true)
+        val lowPriorityFeatureFlagProvider = FakeMutableFeatureFlagProvider(LOW_PRIORITY)
+        val highPriorityFeatureFlagProvider = FakeMutableFeatureFlagProvider(HIGH_PRIORITY)
+        val featureFlagService = DefaultFeatureFlagService(setOf(lowPriorityFeatureFlagProvider, highPriorityFeatureFlagProvider))
+        lowPriorityFeatureFlagProvider.setFeatureEnabled(FeatureFlags.LocationSharing, false)
+        highPriorityFeatureFlagProvider.setFeatureEnabled(FeatureFlags.LocationSharing, true)
         assertThat(featureFlagService.isFeatureEnabled(FeatureFlags.LocationSharing)).isEqualTo(true)
     }
 }

libraries/featureflag/impl/src/test/kotlin/io/element/android/libraries/featureflag/impl/FakeMutableFeatureFlagProvider.kt

@@ -18,7 +18,7 @@ package io.element.android.libraries.featureflag.impl
 
 import io.element.android.libraries.featureflag.api.Feature
 
-class FakeRuntimeFeatureFlagProvider(override val priority: Int) : RuntimeFeatureFlagProvider {
+class FakeMutableFeatureFlagProvider(override val priority: Int) : MutableFeatureFlagProvider {
 
     private val enabledFeatures = HashMap<String, Boolean>()