PreferenceDataStoreFactory.kt

/*
 * Copyright 2022 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.Storage
import androidx.datastore.core.handlers.ReplaceFileCorruptionHandler
import kotlinx.coroutines.CoroutineScope
import kotlinx.coroutines.SupervisorJob
import kotlin.jvm.JvmOverloads
import okio.Path

expect object PreferenceDataStoreFactory {

    /**
     * Create an instance of [DataStore]. 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 storage The storage object defines where and how the preferences will be stored.
     * @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.
     * 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(
        storage: Storage<Preferences>,
        corruptionHandler: ReplaceFileCorruptionHandler<Preferences>? = null,
        migrations: List<DataMigration<Preferences>> = listOf(),
        scope: CoroutineScope = CoroutineScope(ioDispatcher() + SupervisorJob()),
    ): DataStore<Preferences>

    /**
     * Create an instance of [DataStore] using an okio Path. 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 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.
     * 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 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. File will be created if it doesn't exist.
     *
     * @return a new DataStore instance with the provided configuration
     */
    @JvmOverloads
    public fun createWithPath(
        corruptionHandler: ReplaceFileCorruptionHandler<Preferences>? = null,
        migrations: List<DataMigration<Preferences>> = listOf(),
        scope: CoroutineScope = CoroutineScope(ioDispatcher() + SupervisorJob()),
        produceFile: () -> Path,
    ): DataStore<Preferences>
}

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
        }
    }
}