/*
    * Kuali Coeus, a comprehensive research administration system for higher education.
    * 
    * Copyright 2005-2015 Kuali, Inc.
    * 
    * This program is free software: you can redistribute it and/or modify
    * it under the terms of the GNU Affero General Public License as
    * published by the Free Software Foundation, either version 3 of the
    * License, or (at your option) any later version.
   * 
   * This program 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 Affero General Public License for more details.
   * 
   * You should have received a copy of the GNU Affero General Public License
   * along with this program.  If not, see <http://www.gnu.org/licenses/>.
   */
  package org.kuali.coeus.s2sgen.impl.hash;
  
  import org.apache.xml.security.algorithms.MessageDigestAlgorithm;
  import org.apache.xml.security.c14n.CanonicalizationException;
  import org.apache.xml.security.c14n.Canonicalizer;
  import org.apache.xml.security.c14n.InvalidCanonicalizerException;
  import org.apache.xml.security.signature.XMLSignatureException;
  import org.apache.xml.security.utils.Base64;
  import org.apache.xml.security.utils.DigesterOutputStream;
  import org.kuali.coeus.s2sgen.api.core.S2SException;
  import org.kuali.coeus.s2sgen.impl.util.XPathExecutor;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  import org.w3c.dom.Document;
  import org.w3c.dom.Node;
  
  import javax.xml.transform.TransformerException;
  
  /**
   * This is a convenience object that simplifies the hashing processing to one
   * method call.
   * 
   * @author David Wong
   */
  public class GrantApplicationHash {
  
  	private static final Logger log = LoggerFactory.getLogger(GrantApplicationHash.class
              .getName());
  
  	static java.security.MessageDigest messageDigester = null;
  
  	static {
  		org.apache.xml.security.Init.init();
  		try {
  			messageDigester = java.security.MessageDigest.getInstance("SHA-1");
  		} catch (Exception ex) {
  			log.error(
  					"Unable to get instance of java.security.MessageDigester",
  					ex);
  		}
  	}
  
  	/**
  	 * Added private constructor to prevent creation by user.
  	 */
  	private GrantApplicationHash() {
  
  	}
  
  	/**
  	 * Computes the hash value for the Grants.gov application XML.
  	 * 
  	 * @param xml
  	 *            The Grants.gov application XML.
  	 * @return The SHA-1 hash value of &lt;grant:forms&gt; tag inside the
  	 *         application XML.
  	 * @throws Exception
  	 *             When the XML cannot be parsed.
  	 */
  	public final static String computeGrantFormsHash(String xml) throws S2SException {
  		GrantApplicationXpath xpath;
          try {
              xpath = new GrantApplicationXpath(xml);
              return _hash(xpath);
          }catch (Exception e) {
              log.error(e.getMessage(), e);
              throw new S2SException(e.getMessage(),e);
          }
  	}
  
  	/**
  	 * Computes the hash of an binary attachment.
  	 * 
  	 * @param attachment
  	 * @return The SHA-1 hash value of the attachment byte array.
  	 * @throws Exception
  	 */
  	public final static String computeAttachmentHash(byte[] attachment) {
  
  		byte[] rawDigest = messageDigester.digest(attachment);
  
 		return Base64.encode(rawDigest);
 
 	}
 
 	/**
 	 * Computes the hash value for the Grants.gov application XML.
 	 * 
 	 * @param xpath
 	 *            An xpath object holding the Grants.gov application XML.
 	 * @return The SHA-1 hash value of &lt;grant:forms&gt; tag inside the
 	 *         application XML.
 	 * @throws Exception
 	 *             When the XML cannot be parsed.
 	 */
 	public final static String computeGrantFormsHash(GrantApplicationXpath xpath)
 			throws Exception {
 		return _hash(xpath);
 	}
 
 	/**
 	 * Computes the hash value for the Grants.gov application XML.
 	 * 
 	 * @param xml
 	 *            The Grants.gov application XML.
 	 * @return The SHA-1 hash value of &lt;grant:forms&gt; tag inside the
 	 *         application XML.
 	 * @throws Exception
 	 *             When the XML cannot be parsed.
 	 */
 	public final static String computeGrantFormsHash(Document xml) throws Exception {
 		XPathExecutor executor = new XPathExecutor(null);
 		executor.setDoc(xml);
 		GrantApplicationXpath xpath = new GrantApplicationXpath(null);
 		xpath.setExecutor(executor);
 		return _hash(xpath);
 	}
 
 	private static String _hash(GrantApplicationXpath xpath)
 			throws TransformerException, XMLSignatureException,
 			InvalidCanonicalizerException, CanonicalizationException {
 		Node formsNode = xpath.getFormsNode();
 		DigesterOutputStream digester = _createDigesterOutputStream(xpath
 				.getExecutor().getDoc());
 		Canonicalizer canonicalizer = Canonicalizer
 				.getInstance(Canonicalizer.ALGO_ID_C14N_EXCL_OMIT_COMMENTS);
 		canonicalizer.setWriter(digester);
 		canonicalizer.canonicalizeSubtree(formsNode);
 		byte[] hash = digester.getDigestValue();
 		return Base64.encode(hash);
 	}
 
 	private static DigesterOutputStream _createDigesterOutputStream(Document doc)
 			throws XMLSignatureException {
 		DigesterOutputStream stream = null;
 		if (doc != null) {
 			stream = new DigesterOutputStream(MessageDigestAlgorithm
 					.getInstance(doc,
 							MessageDigestAlgorithm.ALGO_ID_DIGEST_SHA1));
 		}
 		return stream;
 	}
 }