feat(settings): add settings management with DataStore integration

core/src/main/java/hu/bbara/purefin/settings/SettingOption.kt

@@ -0,0 +1,21 @@
+package hu.bbara.purefin.settings
+
+sealed interface SettingOption<T> {
+    val key: String
+    val defaultValue: T
+}
+
+data class NumberSetting(
+    override val key: String,
+    override val defaultValue: Double
+) : SettingOption<Double>
+
+data class BooleanSetting(
+    override val key: String,
+    override val defaultValue: Boolean
+) : SettingOption<Boolean>
+
+data class StringSetting(
+    override val key: String,
+    override val defaultValue: String
+) : SettingOption<String>

core/src/main/java/hu/bbara/purefin/settings/SettingsModule.kt

@@ -0,0 +1,41 @@
+package hu.bbara.purefin.settings
+
+import android.content.Context
+import androidx.datastore.core.DataStore
+import androidx.datastore.core.DataStoreFactory
+import androidx.datastore.core.handlers.ReplaceFileCorruptionHandler
+import androidx.datastore.dataStoreFile
+import dagger.Module
+import dagger.Provides
+import dagger.hilt.InstallIn
+import dagger.hilt.android.qualifiers.ApplicationContext
+import dagger.hilt.components.SingletonComponent
+import hu.bbara.purefin.model.Settings
+import javax.inject.Singleton
+
+@Module
+@InstallIn(SingletonComponent::class)
+class SettingsModule {
+
+    @Provides
+    @Singleton
+    fun provideSettingsDataStore(
+        @ApplicationContext context: Context
+    ): DataStore<Settings> {
+        return DataStoreFactory.create(
+            serializer = SettingsSerializer,
+            produceFile = { context.dataStoreFile("settings.json") },
+            corruptionHandler = ReplaceFileCorruptionHandler(
+                produceNewData = { SettingsSerializer.defaultValue }
+            )
+        )
+    }
+
+    @Provides
+    @Singleton
+    fun provideSettingsRepository(
+        settingsDataStore: DataStore<Settings>
+    ): SettingsRepository {
+        return SettingsRepository(settingsDataStore)
+    }
+}

core/src/main/java/hu/bbara/purefin/settings/SettingsRepository.kt

@@ -0,0 +1,56 @@
+package hu.bbara.purefin.settings
+
+import androidx.datastore.core.DataStore
+import hu.bbara.purefin.model.Settings
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.distinctUntilChanged
+import kotlinx.coroutines.flow.map
+import javax.inject.Inject
+
+class SettingsRepository @Inject constructor(
+    private val settingsDataStore: DataStore<Settings>
+) {
+    val settings: Flow<Settings> = settingsDataStore.data
+
+    fun value(option: NumberSetting): Flow<Double> {
+        return settings
+            .map { it.numberSettings[option.key] ?: option.defaultValue }
+            .distinctUntilChanged()
+    }
+
+    fun value(option: BooleanSetting): Flow<Boolean> {
+        return settings
+            .map { it.booleanSettings[option.key] ?: option.defaultValue }
+            .distinctUntilChanged()
+    }
+
+    fun value(option: StringSetting): Flow<String> {
+        return settings
+            .map { it.stringSettings[option.key] ?: option.defaultValue }
+            .distinctUntilChanged()
+    }
+
+    suspend fun set(option: NumberSetting, value: Double) {
+        settingsDataStore.updateData { current ->
+            current.copy(
+                numberSettings = current.numberSettings + (option.key to value)
+            )
+        }
+    }
+
+    suspend fun set(option: BooleanSetting, value: Boolean) {
+        settingsDataStore.updateData { current ->
+            current.copy(
+                booleanSettings = current.booleanSettings + (option.key to value)
+            )
+        }
+    }
+
+    suspend fun set(option: StringSetting, value: String) {
+        settingsDataStore.updateData { current ->
+            current.copy(
+                stringSettings = current.stringSettings + (option.key to value)
+            )
+        }
+    }
+}

core/src/main/java/hu/bbara/purefin/settings/SettingsSerializer.kt

@@ -0,0 +1,31 @@
+package hu.bbara.purefin.settings
+
+import androidx.datastore.core.CorruptionException
+import androidx.datastore.core.Serializer
+import hu.bbara.purefin.model.Settings
+import kotlinx.serialization.SerializationException
+import kotlinx.serialization.json.Json
+import java.io.InputStream
+import java.io.OutputStream
+
+object SettingsSerializer : Serializer<Settings> {
+    override val defaultValue: Settings
+        get() = Settings()
+
+    override suspend fun readFrom(input: InputStream): Settings {
+        try {
+            return Json.decodeFromString<Settings>(
+                input.readBytes().decodeToString()
+            )
+        } catch (serialization: SerializationException) {
+            throw CorruptionException("Unable to read Settings", serialization)
+        }
+    }
+
+    override suspend fun writeTo(t: Settings, output: OutputStream) {
+        output.write(
+            Json.encodeToString(Settings.serializer(), t)
+                .encodeToByteArray()
+        )
+    }
+}