PreferenceDataStoreFactory.kt

/*
 * Copyright 2020 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package androidx.datastore.preferences.core

import androidx.datastore.core.CorruptionException
import androidx.datastore.core.DataMigration
import androidx.datastore.core.DataStore
import androidx.datastore.core.DataStoreFactory
import androidx.datastore.core.handlers.ReplaceFileCorruptionHandler
import kotlinx.coroutines.CoroutineScope
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.SupervisorJob
import java.io.File

/**
 * Public factory for creating PreferenceDataStore instances.
 */
public object PreferenceDataStoreFactory {
    /**
     * Create an instance of SingleProcessDataStore. Never create more than one instance of
     * DataStore for a given file; doing so can break all DataStore functionality. You should
     * consider managing your DataStore instance as a singleton.
     *
     * @param produceFile Function which returns the file that the new DataStore will act on.
     * The function must return the same path every time. No two instances of PreferenceDataStore
     * should act on the same file at the same time. The file must have the extension
     * preferences_pb.
     * @param corruptionHandler The corruptionHandler is invoked if DataStore encounters a
     * [CorruptionException] when attempting to read data. CorruptionExceptions are thrown by
     * serializers when data cannot be de-serialized.
     * @param migrations are run before any access to data can occur. Each producer and migration
     * may be run more than once whether or not it already succeeded (potentially because another
     * migration failed or a write to disk failed.)
     * @param scope The scope in which IO operations and transform functions will execute.
     * @param produceFile Function which returns the file that the new DataStore will act on.
     * The function must return the same path every time. No two instances of PreferenceDataStore
     * should act on the same file at the same time. The file must have the extension
     * preferences_pb.
     *
     * @return a new DataStore instance with the provided configuration
     */
    @JvmOverloads
    public fun create(
        corruptionHandler: ReplaceFileCorruptionHandler<Preferences>? = null,
        migrations: List<DataMigration<Preferences>> = listOf(),
        scope: CoroutineScope = CoroutineScope(Dispatchers.IO + SupervisorJob()),
        produceFile: () -> File
    ): DataStore<Preferences> {
        val delegate = DataStoreFactory.create(
            serializer = PreferencesSerializer,
            corruptionHandler = corruptionHandler,
            migrations = migrations,
            scope = scope
        ) {
            val file = produceFile()
            check(file.extension == PreferencesSerializer.fileExtension) {
                "File extension for file: $file does not match required extension for" +
                    " Preferences file: ${PreferencesSerializer.fileExtension}"
            }
            file
        }
        return PreferenceDataStore(delegate)
    }
}

internal class PreferenceDataStore(private val delegate: DataStore<Preferences>) :
    DataStore<Preferences> by delegate {
    override suspend fun updateData(transform: suspend (t: Preferences) -> Preferences):
        Preferences {
            return delegate.updateData {
                val transformed = transform(it)
                // Freeze the preferences since any future mutations will break DataStore. If a user
                // tunnels the value out of DataStore and mutates it, this could be problematic.
                // This is a safe cast, since MutablePreferences is the only implementation of
                // Preferences.
                (transformed as MutablePreferences).freeze()
                transformed
            }
        }
}