/*
 * Copyright Terracotta, 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.ehcache.clustered.lock.server;

import java.util.Set;
import java.util.concurrent.CopyOnWriteArraySet;

import org.ehcache.clustered.common.internal.lock.LockMessaging;
import org.ehcache.clustered.common.internal.lock.LockMessaging.HoldType;
import org.ehcache.clustered.common.internal.lock.LockMessaging.LockOperation;
import org.ehcache.clustered.common.internal.lock.LockMessaging.LockTransition;

import org.terracotta.entity.ActiveServerEntity;
import org.terracotta.entity.ClientCommunicator;
import org.terracotta.entity.ClientDescriptor;
import org.terracotta.entity.MessageCodecException;
import org.terracotta.entity.PassiveSynchronizationChannel;

/**
 *
 * @author cdennis
 */
class VoltronReadWriteLockActiveEntity implements ActiveServerEntity<LockOperation, LockTransition> {

  private final ClientCommunicator communicator;

  private final Set<ClientDescriptor> releaseListeners = new CopyOnWriteArraySet<ClientDescriptor>();
  private final Set<ClientDescriptor> sharedHolders = new CopyOnWriteArraySet<ClientDescriptor>();

  private ClientDescriptor exclusiveHolder;

  public VoltronReadWriteLockActiveEntity(ClientCommunicator communicator) {
    this.communicator = communicator;
  }

  @Override
  public LockTransition invoke(ClientDescriptor client, LockOperation message) {
    switch (message.getOperation()) {
      case TRY_ACQUIRE: return tryAcquire(client, message.getHoldType());
      case ACQUIRE: return acquire(client, message.getHoldType());
      case RELEASE: return release(client, message.getHoldType());
      default: throw new AssertionError();
    }
  }

  @Override
  public void connected(ClientDescriptor client) {
    //nothing to do
  }

  @Override
  public void disconnected(ClientDescriptor client) {
    releaseListeners.remove(client);
    if (client.equals(exclusiveHolder)) {
      release(client, HoldType.WRITE);
    } else if (sharedHolders.contains(client)) {
      release(client, HoldType.READ);
    }
  }

  @Override
  public void handleReconnect(ClientDescriptor client, byte[] reconnectData) {
    if (reconnectData.length == 0) {
      releaseListeners.add(client);
    } else {
      try {
        if (!invoke(client, LockMessaging.codec().decodeMessage(reconnectData)).isAcquired()) {
          throw new IllegalStateException("Unexpected lock acquisition failure during reconnect");
        }
      } catch (MessageCodecException ex) {
        throw new AssertionError(ex);
      }
    }
  }

  @Override
  public void synchronizeKeyToPassive(PassiveSynchronizationChannel<LockOperation> syncChannel, int concurrencyKey) {
    //nothing to synchronize
  }

  private LockTransition tryAcquire(ClientDescriptor client, HoldType holdType) {
    if (exclusiveHolder != null) {
      return LockMessaging.empty();
    } else {
      switch (holdType) {
        case READ:
          sharedHolders.add(client);
          return acquired(client);
        case WRITE:
          if (sharedHolders.isEmpty()) {
            exclusiveHolder = client;
            return acquired(client);
          } else {
            return LockMessaging.empty();
          }
        default:
          throw new AssertionError();
      }
    }
  }

  private LockTransition acquire(ClientDescriptor client, HoldType holdType) {
    if (exclusiveHolder != null) {
      return waiting(client);
    } else {
      switch (holdType) {
        case READ:
          sharedHolders.add(client);
          return acquired(client);
        case WRITE:
          if (sharedHolders.isEmpty()) {
            exclusiveHolder = client;
            return acquired(client);
          } else {
            return waiting(client);
          }
        default:
          throw new AssertionError();
      }
    }
  }

  private LockTransition release(ClientDescriptor client, HoldType holdType) {
    switch (holdType) {
      case READ:
        if (sharedHolders.remove(client)) {
          if (sharedHolders.isEmpty()) {
            notifyReleaseListeners();
          }
          return LockMessaging.released();
        } else {
          return LockMessaging.empty();
        }
      case WRITE:
        if (client.equals(exclusiveHolder)) {
          exclusiveHolder = null;
          notifyReleaseListeners();
          return LockMessaging.released();
        } else {
          return LockMessaging.empty();
        }
      default:
        throw new AssertionError();
    }
  }

  @Override
  public void createNew() {
    //nothing to do
  }

  @Override
  public void loadExisting() {
    //nothing to do
  }

  @Override
  public void destroy() {
    //nothing to do
  }

  private LockTransition acquired(ClientDescriptor client) {
    releaseListeners.remove(client);
    return LockMessaging.acquired();
  }

  private LockTransition waiting(ClientDescriptor client) {
    releaseListeners.add(client);
    return LockMessaging.empty();
  }

  private void notifyReleaseListeners() {
    for (ClientDescriptor client : releaseListeners) {
      try {
        communicator.sendNoResponse(client, LockMessaging.released());
      } catch (MessageCodecException e) {
        throw new AssertionError(e);
      }
    }
  }
}