/*
    * Copyright (C) 2015, Google Inc. and others
    *
    * This program and the accompanying materials are made available under the
    * terms of the Eclipse Distribution License v. 1.0 which is available at
    * https://www.eclipse.org/org/documents/edl-v10.php.
    *
    * SPDX-License-Identifier: BSD-3-Clause
    */
  package org.eclipse.jgit.transport;
  
  import static java.nio.charset.StandardCharsets.ISO_8859_1;
  import static java.nio.charset.StandardCharsets.UTF_8;
  
  import java.security.InvalidKeyException;
  import java.security.NoSuchAlgorithmException;
  
  import javax.crypto.Mac;
  import javax.crypto.spec.SecretKeySpec;
  
  import org.eclipse.jgit.lib.Repository;
  import org.eclipse.jgit.transport.PushCertificate.NonceStatus;
  
  /**
   * The nonce generator which was first introduced to git-core.
   *
   * @since 4.0
   */
  public class HMACSHA1NonceGenerator implements NonceGenerator {
  
  	private Mac mac;
  
  	/**
  	 * Constructor for HMACSHA1NonceGenerator.
  	 *
  	 * @param seed
  	 *            seed the generator
  	 * @throws java.lang.IllegalStateException
  	 */
  	public HMACSHA1NonceGenerator(String seed) throws IllegalStateException {
  		try {
  			byte[] keyBytes = seed.getBytes(ISO_8859_1);
  			SecretKeySpec signingKey = new SecretKeySpec(keyBytes, "HmacSHA1"); //$NON-NLS-1$
  			mac = Mac.getInstance("HmacSHA1"); //$NON-NLS-1$
  			mac.init(signingKey);
  		} catch (InvalidKeyException | NoSuchAlgorithmException e) {
  			throw new IllegalStateException(e);
  		}
  	}
  
  	/** {@inheritDoc} */
  	@Override
  	public synchronized String createNonce(Repository repo, long timestamp)
  			throws IllegalStateException {
  		String input = repo.getIdentifier() + ":" + String.valueOf(timestamp); //$NON-NLS-1$
  		byte[] rawHmac = mac.doFinal(input.getBytes(UTF_8));
  		return Long.toString(timestamp) + "-" + toHex(rawHmac); //$NON-NLS-1$
  	}
  
  	/** {@inheritDoc} */
  	@Override
  	public NonceStatus verify(String received, String sent,
  			Repository db, boolean allowSlop, int slop) {
  		if (received.isEmpty()) {
  			return NonceStatus.MISSING;
  		} else if (sent.isEmpty()) {
  			return NonceStatus.UNSOLICITED;
  		} else if (received.equals(sent)) {
  			return NonceStatus.OK;
  		}
  
  		if (!allowSlop) {
  			return NonceStatus.BAD;
  		}
  
  		/* nonce is concat(<seconds-since-epoch>, "-", <hmac>) */
  		int idxSent = sent.indexOf('-');
  		int idxRecv = received.indexOf('-');
  		if (idxSent == -1 || idxRecv == -1) {
  			return NonceStatus.BAD;
  		}
  
  		String signedStampStr = received.substring(0, idxRecv);
  		String advertisedStampStr = sent.substring(0, idxSent);
  		long signedStamp;
  		long advertisedStamp;
  		try {
  			signedStamp = Long.parseLong(signedStampStr);
  			advertisedStamp = Long.parseLong(advertisedStampStr);
  		} catch (IllegalArgumentException e) {
  			return NonceStatus.BAD;
  		}
  
  		// what we would have signed earlier
  		String expect = createNonce(db, signedStamp);
  
  		if (!expect.equals(received)) {
  			return NonceStatus.BAD;
  		}
 
 		long nonceStampSlop = Math.abs(advertisedStamp - signedStamp);
 
 		if (nonceStampSlop <= slop) {
 			return NonceStatus.OK;
 		}
 		return NonceStatus.SLOP;
 	}
 
 	private static final String HEX = "0123456789ABCDEF"; //$NON-NLS-1$
 
 	private static String toHex(byte[] bytes) {
 		StringBuilder builder = new StringBuilder(2 * bytes.length);
 		for (byte b : bytes) {
 			builder.append(HEX.charAt((b & 0xF0) >> 4));
 			builder.append(HEX.charAt(b & 0xF));
 		}
 		return builder.toString();
 	}
 }