/*
 * Copyright (C) 2015 Red Hat, Inc. and/or its affiliates.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.jboss.errai.databinding.client;

/**
 * A partial implementation of {@link PropertyChangeUnsubscribeHandle} that only
 * allows {@link PropertyChangeUnsubscribeHandle#unsubscribe()} to be called
 * once.
 *
 * @author Max Barkley <mbarkley@redhat.com>
 */
public abstract class OneTimeUnsubscribeHandle implements PropertyChangeUnsubscribeHandle {

  private boolean unsubscribed = false;

  @Override
  public void unsubscribe() {
    if (unsubscribed) {
      throw new RuntimeException("Can only call unsubscribe once.");
    } else {
      try {
        doUnsubscribe();
      } finally {
        unsubscribed = true;
      }
    }
  }

  /**
   * This method is guaranteed to only be called the first time
   * {@link OneTimeUnsubscribeHandle#unsubscribe()} is called.
   *
   * @see PropertyChangeUnsubscribeHandle#unsubscribe()
   */
  public abstract void doUnsubscribe();

}
