/*
 * 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.app.backup;

import android.compat.annotation.UnsupportedAppUsage;

import java.io.IOException;
import java.io.InputStream;

/**
 * Provides an {@link java.io.InputStream}-like interface for accessing an
 * entity's data during a restore operation. Used by {@link BackupHelper} classes within the {@link
 * BackupAgentHelper} mechanism.
 * <p>
 * When {@link BackupHelper#restoreEntity(BackupDataInputStream) BackupHelper.restoreEntity()}
 * is called, the current entity's header has already been read from the underlying
 * {@link BackupDataInput}.  The entity's key string and total data size are available
 * through this class's {@link #getKey()} and {@link #size()} methods, respectively.
 * <p class="note">
 * <strong>Note:</strong> The caller should take care not to seek or close the underlying data
 * source, nor read more than {@link #size()} bytes from the stream.</p>
 *
 * @see BackupAgentHelper
 * @see BackupHelper
 */
public class BackupDataInputStream extends InputStream {

    @UnsupportedAppUsage
    String key;
    @UnsupportedAppUsage
    int dataSize;

    BackupDataInput mData;
    byte[] mOneByte;

    /** @hide */
    BackupDataInputStream(BackupDataInput data) {
        mData = data;
    }

    /**
     * Read one byte of entity data from the stream, returning it as
     * an integer value.  If more than {@link #size()} bytes of data
     * are read from the stream, the output of this method is undefined.
     *
     * @return The byte read, or undefined if the end of the stream has been reached.
     */
    public int read() throws IOException {
        byte[] one = mOneByte;
        if (mOneByte == null) {
            one = mOneByte = new byte[1];
        }
        mData.readEntityData(one, 0, 1);
        return one[0];
    }

    /**
     * Read up to {@code size} bytes of data into a byte array, beginning at position
     * {@code offset} within the array.
     *
     * @param b Byte array into which the data will be read
     * @param offset The data will be stored in {@code b} beginning at this index
     *   within the array.
     * @param size The number of bytes to read in this operation.  If insufficient
     *   data exists within the entity to fulfill this request, only as much data
     *   will be read as is available.
     * @return The number of bytes of data read, or zero if all of the entity's
     *   data has already been read.
     */
    public int read(byte[] b, int offset, int size) throws IOException {
        return mData.readEntityData(b, offset, size);
    }

    /**
     * Read enough entity data into a byte array to fill the array.
     *
     * @param b Byte array to fill with data from the stream.  If the stream does not
     *   have sufficient data to fill the array, then the contents of the remainder of
     *   the array will be undefined.
     * @return The number of bytes of data read, or zero if all of the entity's
     *   data has already been read.
     */
    public int read(byte[] b) throws IOException {
        return mData.readEntityData(b, 0, b.length);
    }

    /**
     * Report the key string associated with this entity within the backup data set.
     *
     * @return The key string for this entity, equivalent to calling
     *   {@link BackupDataInput#getKey()} on the underlying {@link BackupDataInput}.
     */
    public String getKey() {
        return this.key;
    }

    /**
     * Report the total number of bytes of data available for the current entity.
     *
     * @return The number of data bytes available, equivalent to calling
     *   {@link BackupDataInput#getDataSize()} on the underlying {@link BackupDataInput}.
     */
    public int size() {
        return this.dataSize;
    }
}