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/**
    This file is part of coinbase-pro-client.

    coinbase-pro-client is free software: you can redistribute it and/or modify
    it under the terms of the GNU Lesser General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    Foobar 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 Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public License
    along with coinbase-pro-client.  If not, see .
 */
package org.erc.coinbase.pro.rest;

import java.util.Base64;
import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;

import org.erc.coinbase.pro.exceptions.SignatureException;

/**
 * Signature
 * The CB-ACCESS-SIGN header is generated by creating a sha256 HMAC.
 * 
 * The base64-decoded secret key on the string: 
 * 	timestamp + method + requestPath + body and base64-encode the output.
 * 
 * The timestamp value is the same as the CB-ACCESS-TIMESTAMP header.
 *
 */
final class Signature {

	/** The signature MAC Instance. */
	private Mac sha256 = null;
	
	/**
	 * Instantiates a new signature.
	 *
	 * @param secretKey	the secret key
	 * @throws SignatureException	the signature exception
	 */
	public Signature(String secretKey) throws SignatureException {
		byte[] secretDecoded = Base64.getDecoder().decode(secretKey);
		try {
			sha256 = Mac.getInstance("HmacSHA256");
			sha256.init(new SecretKeySpec(secretDecoded, sha256.getAlgorithm()));
		} catch (Exception e) {
			 throw new SignatureException("Cannot set up authentication headers.",e);
		}
	}
	
	/**
	 * Sign.
	 *
	 * @param requestPath	the request path
	 * @param method	the HTTP method
	 * @param body	the body
	 * @param timestamp	the timestamp (Execution TS)
	 * @return the result sing string
	 * @throws SignatureException	the signature exception
	 */
	public String sign(String requestPath, String method, String body, Long timestamp) throws SignatureException {
        try {
            String prehash = timestamp + method.toUpperCase() + requestPath + body;
            return Base64.getEncoder().encodeToString(sha256.doFinal(prehash.getBytes()));
        } catch (Exception  e) {
            throw new SignatureException("Cannot set up authentication headers.",e);
        }
	}

}