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/*
 *
 * Copyright (c) 2013 - 2017 Lijun Liao
 *
 * 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 org.xipki.security;

import java.io.UnsupportedEncodingException;
import java.nio.ByteBuffer;
import java.util.concurrent.TimeUnit;

import org.bouncycastle.crypto.Digest;
import org.bouncycastle.crypto.digests.SHA1Digest;
import org.bouncycastle.operator.RuntimeOperatorException;
import org.xipki.common.concurrent.ConcurrentBagEntry;
import org.xipki.common.concurrent.ConcurrentBag;
import org.xipki.common.util.ParamUtil;

/**
 * @author Lijun Liao
 * @since 2.0.0
 */

public class FpIdCalculator {

    private static final int PARALLELISM = 50;

    private static final ConcurrentBag> MDS = getMD5MessageDigests();

    private FpIdCalculator() {
    }

    private static ConcurrentBag> getMD5MessageDigests() {
        ConcurrentBag> mds = new ConcurrentBag<>();
        for (int i = 0; i < PARALLELISM; i++) {
            Digest md = new SHA1Digest();
            mds.add(new ConcurrentBagEntry<>(md));
        }
        return mds;
    }

    /**
     * Hash the data.getBytes("UTF-8") and returns the first 8 bytes of the hash value.
     * @param data data over which the hash value is calculated.
     * @return long represented of the first 8 bytes
     */
    public static long hash(final String data) {
        ParamUtil.requireNonNull("data", data);
        byte[] encoded;
        try {
            encoded = data.getBytes("UTF-8");
        } catch (UnsupportedEncodingException ex) {
            encoded = data.getBytes();
        }
        return hash(encoded);
    }

    /**
     * Hash the data and returns the first 8 bytes of the hash value.
     * @param data data over which the hash value is calculated.
     * @return long represented of the first 8 bytes
     */
    public static long hash(final byte[] data) {
        ParamUtil.requireNonNull("data", data);

        ConcurrentBagEntry md0 = null;
        for (int i = 0; i < 3; i++) {
            try {
                md0 = MDS.borrow(10, TimeUnit.SECONDS);
                break;
            } catch (InterruptedException ex) { // CHECKSTYLE:SKIP
            }
        }

        if (md0 == null) {
            throw new RuntimeOperatorException("could not get idle MessageDigest");
        }

        try {
            Digest md = md0.value();
            md.reset();
            md.update(data, 0, data.length);
            byte[] bytes = new byte[md.getDigestSize()];
            md.doFinal(bytes, 0);

            return bytesToLong(bytes);
        } finally {
            MDS.requite(md0);
        }
    }

    private static long bytesToLong(final byte[] bytes) {
        ByteBuffer buffer = ByteBuffer.allocate(8);
        buffer.put(bytes, 0, 8);
        buffer.flip(); //need flip
        return buffer.getLong();
    }

}