/*************************GO-LICENSE-START*********************************
 * Copyright 2014 ThoughtWorks, Inc.
 *
 * 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.
 *************************GO-LICENSE-END***********************************/

package com.thoughtworks.go.util;

import java.io.IOException;
import java.io.InputStream;
import java.security.MessageDigest;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

import com.thoughtworks.go.util.pool.DigestObjectPools;
import org.apache.commons.codec.binary.Hex;

/**
 * A replacement for org.apache.commons.codec.digest.DigestUtils , with the MessageDigest Instance cached.
 * <p/>
 * This is to avoid the block on the call below which causes performance bottle necks.
 * java.security.Provider.getService(String, String)
 * <p/>
 * http://groups.google.com/group/spymemcached/browse_thread/thread/146bd39fa95cce6a
 */
public class CachedDigestUtils {

    private static final int STREAM_BUFFER_LENGTH = 1024;
    private static DigestObjectPools objectPools = new DigestObjectPools();
    private static ConcurrentMap<String, String> shaDigestCache = new ConcurrentHashMap<>();

    public static String sha256Hex(String string) {
        if (shaDigestCache.containsKey(string)) {
            return shaDigestCache.get(string);
        }

        String digest = compute(string, DigestObjectPools.SHA_256);
        shaDigestCache.putIfAbsent(string, digest);
        return digest;
    }

    public static String md5Hex(String string) {
        return compute(string, DigestObjectPools.MD_5);
    }

    public static String md5Hex(final InputStream data) throws IOException {
        return objectPools.computeDigest(DigestObjectPools.MD_5, new DigestObjectPools.DigestOperation() {
            public String perform(MessageDigest digest) throws IOException {
                byte[] buffer = new byte[STREAM_BUFFER_LENGTH];
                int read = data.read(buffer, 0, STREAM_BUFFER_LENGTH);

                while (read > -1) {
                    digest.update(buffer, 0, read);
                    read = data.read(buffer, 0, STREAM_BUFFER_LENGTH);
                }
                return Hex.encodeHexString(digest.digest());
            }
        });
    }

    private static String compute(final String string, String algorithm) {
        return objectPools.computeDigest(algorithm, new DigestObjectPools.DigestOperation() {

            public String perform(MessageDigest digest) {
                digest.update(org.apache.commons.codec.binary.StringUtils.getBytesUtf8(string));
                return Hex.encodeHexString(digest.digest());
            }
        });
    }
}