/*
 * Copyright (C) 2014 University of Dundee & Open Microscopy Environment.
 * All rights reserved.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

package ome.util.checksum;

import java.io.File;
import java.nio.ByteBuffer;

import com.google.common.hash.HashCode;

/**
 * Trivial checksum provider whose hash is simply the number of bytes that were put into the calculation.
 * 
 * @author m.t.b.carroll@dundee.ac.uk
 * @since 5.0.3
 */
public class FileSizeChecksumProviderImpl implements ChecksumProvider {
    private long size = 0;
    private boolean isChecksumCalculated = false;

    @Override
    public ChecksumProvider putBytes(byte[] byteArray) {
        verifyState();

        size += byteArray.length;
        return this;
    }

    @Override
    public ChecksumProvider putBytes(byte[] byteArray, int offset, int length) {
        verifyState();

        /* provide bounds exception specified by method documentation */
        @SuppressWarnings("unused")
        final byte start = byteArray[offset];
        @SuppressWarnings("unused")
        final byte end = byteArray[offset + length - 1];

        size += length;
        return this;
    }

    @Override
    public ChecksumProvider putBytes(ByteBuffer byteBuffer) {
        verifyState();

        if (!byteBuffer.hasArray()) {
            throw new IllegalArgumentException("Supplied ByteBuffer has " +
                    "inaccessible array.");
        }

        size += byteBuffer.limit() - byteBuffer.position();
        return this;
    }

    @Override
    public ChecksumProvider putFile(String filePath) {
        verifyState();

        size = new File(filePath).length();
        return this;
    }

    @Override
    public byte[] checksumAsBytes() {
        isChecksumCalculated = true;
        /* use Guava hash code to match the other algorithms */
        return HashCode.fromLong(size).asBytes();
    }

    @Override
    public String checksumAsString() {
        isChecksumCalculated = true;
        return HashCode.fromLong(size).toString();
    }

    private void verifyState() {
        if (isChecksumCalculated) {
            throw new IllegalStateException("Checksum state already set. " +
                    "Mutation illegal.");
        }
    }
}