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/*
 * Copyright 2017 Baidu, 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.
 */
package com.baidu.aip.util;

import com.baidu.aip.exception.AipException;

import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;
import java.io.UnsupportedEncodingException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class SignUtil {
    private static final char[] DIGITS;

    public static String hmacSha256(String key, String data) throws AipException {
        try {
            Mac mac = Mac.getInstance("HmacSHA256");
            SecretKeySpec signingKey = new SecretKeySpec(key.getBytes(),
                    mac.getAlgorithm());
            mac.init(signingKey);
            return encodeHex(mac.doFinal(data.getBytes()));
        } catch (Exception e) {
            e.printStackTrace();
            throw new AipException(-1, "Fail to generate HMAC-SHA256 signature");
        }
    }

    public static String md5(String data, String charset) {
        try {
            byte[] msg = data.getBytes(charset);
            MessageDigest md = MessageDigest.getInstance("MD5");
            return encodeHex(md.digest(msg));
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        }
        return null;
    }

    private static String encodeHex(byte[] data) {
        int l = data.length;
        char[] out = new char[l << 1];
        int i = 0;

        for (int j = 0; i < l; ++i) {
            out[j++] = DIGITS[(240 & data[i]) >>> 4];
            out[j++] = DIGITS[15 & data[i]];
        }

        return new String(out);
    }

    static {
        DIGITS = new char[]{'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'};
    }
}