/**
    * This file Copyright (c) 2003-2010 Magnolia International
    * Ltd.  (http://www.magnolia-cms.com). All rights reserved.
    *
    *
    * This file is dual-licensed under both the Magnolia
    * Network Agreement and the GNU General Public License.
    * You may elect to use one or the other of these licenses.
    *
   * This file is distributed in the hope that it will be
   * useful, but AS-IS and WITHOUT ANY WARRANTY; without even the
   * implied warranty of MERCHANTABILITY or FITNESS FOR A
   * PARTICULAR PURPOSE, TITLE, or NONINFRINGEMENT.
   * Redistribution, except as permitted by whichever of the GPL
   * or MNA you select, is prohibited.
   *
   * 1. For the GPL license (GPL), you can redistribute and/or
   * modify this file under the terms of the GNU General
   * Public License, Version 3, as published by the Free Software
   * Foundation.  You should have received a copy of the GNU
   * General Public License, Version 3 along with this program;
   * if not, write to the Free Software Foundation, Inc., 51
   * Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * 2. For the Magnolia Network Agreement (MNA), this file
   * and the accompanying materials are made available under the
   * terms of the MNA which accompanies this distribution, and
   * is available at http://www.magnolia-cms.com/mna.html
   *
   * Any modifications to this file must keep this entire header
   * intact.
   *
   */
  package info.magnolia.cms.security;
  
  import javax.security.auth.Subject;
  import java.util.Collection;
  import java.util.Map;
  
  
  /**
   * A {@link UserManager} delegating to a set of user managers. The first user manager which does not
   * through an {@link UnsupportedOperationException} will be used.
   * @author gjoseph
   * @version $Revision: $ ($Author: $)
   */
  public class DelegatingUserManager implements UserManager {
      private final Map<String, UserManager> delegates;
  
      /**
       * @param delegates <String realm, UserManager delegate>
       */
      public DelegatingUserManager(Map<String, UserManager> delegates) {
          this.delegates = delegates;
      }
  
      public User createUser(final String name, final String pw) throws UnsupportedOperationException {
          final Op<User> op = new Op<User>() {
              public User delegate(UserManager um) {
                  return um.createUser(name, pw);
              }
          };
          return delegateUntilSupported(op);
      }
  
      public void changePassword(User user, String newPassword) throws UnsupportedOperationException {
          throw new UnsupportedOperationException("Please use a specific instance of UserManager to do this.");
      }
  
      public User getAnonymousUser() {
          return delegateUntilSupported(new Op<User>() {
              public User delegate(UserManager um) {
                  return um.getAnonymousUser();
              }
          });
      }
  
      public User getSystemUser() {
          return delegateUntilSupported(new Op<User>() {
              public User delegate(UserManager um) {
                  return um.getSystemUser();
              }
          });
      }
  
      public User getUser(final String name) throws UnsupportedOperationException {
          return delegateUntilNotNull(new Op<User>() {
              public User delegate(UserManager um) {
                  return um.getUser(name);
              }
          });
      }
  
      public User getUser(final Subject subject) throws UnsupportedOperationException {
          return delegateUntilNotNull(new Op<User>() {
              public User delegate(UserManager um) {
                  return um.getUser(subject);
              }
          });
     }
 
     // TODO : this should maybe aggregate results, but ExternalUserManager throws an UnsupportedOperationException
     // TODO : also not that this is seemingly never used (or maybe through reflection or other ide-search unfriendly mechanisms)
     public Collection<User> getAllUsers() throws UnsupportedOperationException {
         return delegateUntilSupported(new Op<Collection<User>>() {
             public Collection<User> delegate(UserManager um) {
                 return um.getAllUsers();
             }
         });
     }
 
     private <RT> RT delegateUntilSupported(Op<RT> op) {
         for (String realmName : delegates.keySet()) {
             final UserManager um = delegates.get(realmName);
             try {
                 return op.delegate(um);
             } catch (UnsupportedOperationException e) {
                 // try the next delegate
             }
         }
         throw new UnsupportedOperationException("None of the delegate UserManager supports this operation.");
     }
 
     private <RT> RT delegateUntilNotNull(Op<RT> op) {
         for (String realmName : delegates.keySet()) {
             final UserManager um = delegates.get(realmName);
             final RT result = op.delegate(um);
             if (result != null) {
                 return result;
             }
         }
         return null;
     }
 
     private interface Op<RT> {
         RT delegate(UserManager um);
     }
 }