/**
 * Copyright 2008 Google Inc.
 *
 * 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.waveprotocol.wave.concurrencycontrol.channel;

import org.waveprotocol.wave.concurrencycontrol.common.ChannelException;
import org.waveprotocol.wave.model.operation.wave.WaveletOperation;
import org.waveprotocol.wave.model.version.HashedVersion;

import java.util.List;


/**
 * A client socket for a wavelet. Sends/receives operations to/from the wave
 * server and transforms (outbound) client operations against (inbound) server
 * operations.
 *
 * An operation channel can operate without network connection to the server by
 * queuing outbound operations until a network connection is established at a
 * later time.
 *
 * If the network connection fails during operation, or the wave server restarts
 * or fails over, a channel will silently try to reconnect and recover (by
 * selectively retransforming and retransmitting relevant client operations) but
 * will notify if recovery fails.
 *
 */
public interface OperationChannel {

  /**
   * A listener for operations being received by a channel.
   */
  public interface Listener {
    /**
     * Invoked when a remote operation received to the channel.
     */
    void onOperationReceived();
  }

  /**
   * Sets the channel listener.
   *
   * @param listener
   */
  void setListener(Listener listener);

  /**
   * Sends client operations to the wave server.
   * If the channel is not connected, the operations are queued.
   *
   * @param operations  client operations to send
   * @throws ChannelException if the channel is corrupt or misused
   */
  void send(WaveletOperation ... operations) throws ChannelException;

  /**
   * Receive (transformed) server operation from the wave server, if any is available.
   *
   * @return the next server operation, if any is received from the server (and makes it
   *         through transformation), null otherwise
   */
  WaveletOperation receive();

  /**
   * Peek at the next (transformed) server operation from the wave server, if any is available.
   *
   * @return the next server operation, if any is received from the server (and makes it
   *         through transformation), null otherwise
   */
  WaveletOperation peek();

  /**
   * Gets the wavelet versions at which this channel could reconnect.
   */
  List<HashedVersion> getReconnectVersions();

  /**
   * @return A dump of the state of cc stack. This is really only used for debugging purposes.
   */
  String getDebugString();
}