package at.gv.egovernment.moa.spss.api;

import at.gv.egovernment.moa.spss.MOAException;

import org.apache.commons.discovery.tools.DiscoverClass;


import at.gv.egovernment.moa.spss.api.xmlsign.CreateXMLSignatureRequest;
import at.gv.egovernment.moa.spss.api.xmlsign.CreateXMLSignatureResponse;

/**
 * Interface providing functions for signature creation.
 * 
 * @author Patrick Peck
 * @version $Id$
 */
public abstract class SignatureCreationService {

  /** The default implementation class. */
  private static final String DEFAULT_IMPLEMENTATION =
    "at.gv.egovernment.moa.spss.server.invoke.SignatureCreationServiceImpl";
  
  /** The single instance of this class. */  
  private static SignatureCreationService instance = null;

  /**
   * Get an instance of the <code>SignatureCreationService</code>.
   * 
   * @return A concrete instance of the <code>SignatureCreationService</code>.
   */
  public static synchronized SignatureCreationService getInstance() {
    if (instance == null) {
      try {
        DiscoverClass discover = new DiscoverClass();
        instance =
          (SignatureCreationService) discover.newInstance(
            SignatureCreationService.class,
            DEFAULT_IMPLEMENTATION);
      } catch (Exception e) {
        // this can not happen since we provide a valid default 
        // implementation
      }
    }
    return instance;
  }
  
  /**
   * Create an XML signature.
   * 
   * @param request Information on how to create the signature.
   * @return A <code>CreateXMLSignatureResponse</code> containing the 
   * signature.
   * @throws MOAException Error in server side MOA module.
   */
  public abstract CreateXMLSignatureResponse createXMLSignature(CreateXMLSignatureRequest request)
    throws MOAException;
}