/*
 * Copyright (C) 2009 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 android.backup;

import android.annotation.SdkConstant;
import android.annotation.SdkConstant.SdkConstantType;
import android.app.Service;
import android.backup.IBackupService;
import android.content.Intent;
import android.os.IBinder;
import android.os.ParcelFileDescriptor;
import android.os.RemoteException;
import android.util.Log;

/**
 * This is the central interface between an application and Android's
 * settings backup mechanism.
 * 
 * In order to use the backup service, your application must implement a
 * subclass of BackupService, and declare an intent filter
 * in the application manifest specifying that your BackupService subclass
 * handles the {@link BackupService#SERVICE_ACTION} intent action.  For example:
 * 
 * <pre class="prettyprint">
 *      &lt;!-- Use the class "MyBackupService" to perform backups for my app --&gt;
 *      &lt;service android:name=".MyBackupService"&gt;
 *          &lt;intent-filter&gt;
 *              &lt;action android:name="android.backup.BackupService.SERVICE" /&gt;
 *          &lt;/intent-filter&gt;
 *      &lt;/service&gt;</pre>
 * 
 * @hide pending API solidification
 */

public abstract class BackupService extends Service {
    /**
     * Service Action: Participate in the backup infrastructure.  Applications
     * that wish to use the Android backup mechanism must provide an exported
     * subclass of BackupService and give it an {@link android.content.IntentFilter
     * IntentFilter} that accepts this action. 
     */
    @SdkConstant(SdkConstantType.SERVICE_ACTION)
    public static final String SERVICE_ACTION = "android.backup.BackupService.SERVICE";

    /**
     * The application is being asked to write any data changed since the
     * last time it performed a backup operation.  The state data recorded
     * during the last backup pass is provided in the oldState file descriptor.
     * If oldState is null, no old state is available and the application should perform
     * a full backup.  In both cases, a representation of the final backup state after
     * this pass should be written to the file pointed to by the newStateFd file descriptor.
     *
     * @param oldState An open, read-only ParcelFileDescriptor pointing to the last backup
     *                 state provided by the application.  May be null, in which
     *                 case no prior state is being provided and the application should
     *                 perform a full backup.
     * @param data An open, read/write ParcelFileDescriptor pointing to the backup data
     *             destination.  Typically the application will use backup helper
     *             classes to write to this file.
     * @param newState An open, read/write ParcelFileDescriptor pointing to an empty
     *                 file.  The application should record the final backup state
     *                 here after writing the requested data to dataFd.
     */
    public abstract void onBackup(ParcelFileDescriptor oldState, BackupDataOutput data,
             ParcelFileDescriptor newState);
    
    /**
     * The application is being restored from backup, and should replace any
     * existing data with the contents of the backup.  The backup data is
     * provided in the file pointed to by the dataFd file descriptor.  Once
     * the restore is finished, the application should write a representation
     * of the final state to the newStateFd file descriptor, 
     *
     * @param data An open, read-only ParcelFileDescriptor pointing to a full snapshot
     *             of the application's data.
     * @param newState An open, read/write ParcelFileDescriptor pointing to an empty
     *                 file.  The application should record the final backup state
     *                 here after restoring its data from dataFd.
     */
    public abstract void onRestore(ParcelFileDescriptor /* TODO: BackupDataInput */ data, ParcelFileDescriptor newState);


    // ----- Core implementation -----
    
    /**
     * Returns the private interface called by the backup system.  Applications will
     * not typically override this.
     */
    public IBinder onBind(Intent intent) {
        if (intent.getAction().equals(SERVICE_ACTION)) {
            return mBinder;
        }
        return null;
    }

    private final IBinder mBinder = new BackupServiceBinder().asBinder();

    // ----- IBackupService binder interface -----
    private class BackupServiceBinder extends IBackupService.Stub {
        public void doBackup(ParcelFileDescriptor oldState,
                ParcelFileDescriptor data,
                ParcelFileDescriptor newState) throws RemoteException {
            // !!! TODO - real implementation; for now just invoke the callbacks directly
            Log.v("BackupServiceBinder", "doBackup() invoked");
            BackupDataOutput output = new BackupDataOutput(BackupService.this,
                    data.getFileDescriptor());
            try {
                BackupService.this.onBackup(oldState, output, newState);
            } catch (RuntimeException ex) {
                Log.d("BackupService", "onBackup ("
                        + BackupService.this.getClass().getName() + ") threw", ex);
                throw ex;
            }
        }

        public void doRestore(ParcelFileDescriptor data,
                ParcelFileDescriptor newState) throws RemoteException {
            // !!! TODO - real implementation; for now just invoke the callbacks directly
            Log.v("BackupServiceBinder", "doRestore() invoked");
            BackupService.this.onRestore(data, newState);
        }
    }
}