/*
 * Copyright (c) 2008-2016 Computer Network Information Center (CNIC), Chinese Academy of Sciences.
 * 
 * This file is part of Duckling 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 cn.vlabs.umt.oauth.as.issuer;

import java.security.MessageDigest;
import java.util.UUID;

import cn.vlabs.umt.oauth.common.exception.OAuthSystemException;


/**
 * Exemplar OAuth Token Generator
 *
 *
 *
 */
public class MD5Generator implements ValueGenerator {

    @Override
    public String generateValue() throws OAuthSystemException {
        return generateValue(UUID.randomUUID().toString());
    }

    private static final char[] hexCode = "0123456789abcdef".toCharArray();

    public static String toHexString(byte[] data) {
        if(data == null) {
            return null;
        }
        StringBuilder r = new StringBuilder(data.length*2);
        for ( byte b : data) {
            r.append(hexCode[(b >> 4) & 0xF]);
            r.append(hexCode[(b & 0xF)]);
        }
        return r.toString();
    }

    @Override
    public String generateValue(String param) throws OAuthSystemException {
        try {
            MessageDigest algorithm = MessageDigest.getInstance("MD5");
            algorithm.reset();
            algorithm.update(param.getBytes());
            byte[] messageDigest = algorithm.digest();
            return toHexString(messageDigest);
        } catch (Exception e) {
            throw new OAuthSystemException("OAuth Token cannot be generated.", e);
        }
    }
}