package at.gv.egovernment.moa.id.auth.builder;

import java.io.ByteArrayOutputStream;
import java.security.MessageDigest;

import at.gv.egovernment.moa.id.BuildException;
import at.gv.egovernment.moa.util.Base64Utils;

/**
 * Builder for the SAML artifact, as defined in the 
 * Browser/Artifact profile of SAML.
 * 
 * @author Paul Ivancsics
 * @version $Id$
 */
public class SAMLArtifactBuilder {

  /**
   * Constructor for SAMLArtifactBuilder.
   */
  public SAMLArtifactBuilder() {
    super();
  }
  
  /**
   * Builds the SAML artifact, encoded BASE64.
   * <ul>
   * <li><code>TypeCode</code>: <code>0x0001</code>.</li>
   * <li><code>SourceID</code>: SHA-1 hash of the authURL</li>
   * <li><code>AssertionHandle</code>: SHA-1 hash of the <code>MOASessionID</code></li>
   * </ul>
   * @param authURL URL auf the MOA-ID Auth component to be used for construction 
   *                 of <code>SourceID</code>
   * @param sessionID <code>MOASessionID</code> to be used for construction 
   *                   of <code>AssertionHandle</code>
   * @return the 42-byte SAML artifact, encoded BASE64
   */
  public String build(String authURL, String sessionID) throws BuildException {
		try {
			MessageDigest md = MessageDigest.getInstance("SHA-1");
	  	byte[] sourceID = md.digest(authURL.getBytes());
	  	byte[] assertionHandle = md.digest(sessionID.getBytes());
			ByteArrayOutputStream out = new ByteArrayOutputStream(42);
			out.write(0);
			out.write(1);
			out.write(sourceID, 0, 20);
			out.write(assertionHandle, 0, 20);
			byte[] samlArtifact = out.toByteArray();
  		String samlArtifactBase64 = Base64Utils.encode(samlArtifact);
			return samlArtifactBase64;
  	}
		catch (Throwable ex) {
			throw new BuildException(
				"builder.00", 
				new Object[] {"SAML Artifact, MOASessionID=" + sessionID, ex.toString()}, 
				ex);
		}
  }

}