/*
 * Copyright 2013-2016 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 * Portions copyright 2006-2009 James Murty. Please see LICENSE.txt
 * for applicable license terms and NOTICE.txt for applicable notices.
 *
 * Licensed under the Apache License, Version 2.0 (the "License").
 * You may not use this file except in compliance with the License.
 * A copy of the License is located at
 *
 *  http://aws.amazon.com/apache2.0
 *
 * or in the "license" file accompanying this file. This file 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 com.amazonaws.services.s3.internal;

import com.amazonaws.internal.SdkFilterInputStream;

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

/**
 * Common base class used to wrap an InputStream with a cipher input stream to
 * encrypt it, and handles resets by attempting to reset on the original,
 * unencrypted data InputStream, and recreate an identical Cipher and identical
 * CipherInputStream on the original data.
 * <p>
 * It's repeatable if and only if the underlying unencryptedDataStream is
 * repeatable - if the underlying input stream is not repeatable and you're
 * going to buffer to make it repeatable anyways, it makes more sense to do so
 * after wrapping in this object, so we buffer the encrypted data and don't have
 * to bother re-encrypting on retry.
 * <p>
 * This stream <em>only</em> supports being marked before the first call to
 * {@code read} or {@code skip}, since it's not possible to rewind the
 * encryption state of a {@code CipherInputStream} to an arbitrary point. If you
 * call {@code mark} after calling {@code read} or {@code skip}, it will throw
 * an {@code UnsupportedOperationException}.
 */
public abstract class AbstractRepeatableCipherInputStream<T>
        extends SdkFilterInputStream {
    private final T cipherFactory;
    private final InputStream unencryptedDataStream;
    private boolean hasBeenAccessed;

    /**
     * Constructs a new repeatable cipher input stream using the specified
     * InputStream as the source data, and the CipherFactory for building Cipher
     * objects.
     *
     * @param input The original, unencrypted data stream. This stream should be
     *            markable/resetable in order for this class to work correctly.
     * @param cipherInputStream The cipher input stream wrapping the original
     *            input stream
     * @param cipherFactory The factory used for creating identical cipher
     *            objects when this stream is reset and a new CipherInputStream
     *            is needed.
     */
    protected AbstractRepeatableCipherInputStream(final InputStream input,
            final FilterInputStream cipherInputStream,
            final T cipherFactory) {
        super(cipherInputStream);
        this.unencryptedDataStream = input;
        this.cipherFactory = cipherFactory;
    }

    @Override
    public boolean markSupported() {
        abortIfNeeded();
        return unencryptedDataStream.markSupported();
    }

    @Override
    public void mark(final int readlimit) {
        abortIfNeeded();
        if (hasBeenAccessed) {
            throw new UnsupportedOperationException(
                    "Marking is only supported before your first call to "
                            + "read or skip.");
        }

        unencryptedDataStream.mark(readlimit);
    }

    @Override
    public void reset() throws IOException {
        abortIfNeeded();
        unencryptedDataStream.reset();
        in = createCipherInputStream(unencryptedDataStream, cipherFactory);
        hasBeenAccessed = false;
    }

    @Override
    public int read() throws IOException {
        hasBeenAccessed = true;
        return super.read();
    }

    @Override
    public int read(final byte[] b) throws IOException {
        hasBeenAccessed = true;
        return super.read(b);
    }

    @Override
    public int read(final byte[] b, final int off, final int len)
            throws IOException {

        hasBeenAccessed = true;
        return super.read(b, off, len);
    }

    @Override
    public long skip(final long n) throws IOException {
        hasBeenAccessed = true;
        return super.skip(n);
    }

    protected abstract FilterInputStream createCipherInputStream(
            InputStream unencryptedDataStream, T cipherFactory);
}