/*
 * Copyright 2012 LinkedIn Corp.
 * 
 * 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 azkaban.utils.cache;

import java.util.HashSet;
import java.util.Set;

public class CacheManager {
  // Thread that expires caches at
  // Every 30 sec by default.
  private static final long UPDATE_FREQUENCY = 30000;

  private long updateFrequency = UPDATE_FREQUENCY;
  private Set<Cache> caches;
  private static CacheManager manager = null;
  private final CacheManagerThread updaterThread;

  private boolean activeExpiry = false;

  public static CacheManager getInstance() {
    if (manager == null) {
      manager = new CacheManager();
    }

    return manager;
  }

  private CacheManager() {
    updaterThread = new CacheManagerThread();
    caches = new HashSet<Cache>();

    updaterThread.start();
  }

  public static void setUpdateFrequency(long updateFreqMs) {
    manager.internalUpdateFrequency(updateFreqMs);
  }

  public static void shutdown() {
    manager.internalShutdown();
  }

  public Cache createCache() {
    Cache cache = new Cache(manager);
    manager.internalAddCache(cache);
    return cache;
  }

  public void removeCache(Cache cache) {
    manager.internalRemoveCache(cache);
  }

  private void internalUpdateFrequency(long updateFreq) {
    updateFrequency = updateFreq;
    updaterThread.interrupt();
  }

  private void internalAddCache(Cache cache) {
    caches.add(cache);
    updaterThread.interrupt();
  }

  private void internalRemoveCache(Cache cache) {
    caches.remove(cache);
  }

  private synchronized void internalShutdown() {
    updaterThread.shutdown();
  }

  /* package */synchronized void update() {
    boolean activeExpiry = false;
    for (Cache cache : caches) {
      if (cache.getExpireTimeToIdle() > 0 || cache.getExpireTimeToLive() > 0) {
        activeExpiry = true;
        break;
      }
    }

    if (this.activeExpiry != activeExpiry && activeExpiry) {
      this.activeExpiry = activeExpiry;
      updaterThread.interrupt();
    }
  }

  private class CacheManagerThread extends Thread {
    private boolean shutdown = false;

    public void run() {
      while (!shutdown) {
        if (activeExpiry) {
          for (Cache cache : caches) {
            cache.expireCache();
          }

          synchronized (this) {
            try {
              wait(updateFrequency);
            } catch (InterruptedException e) {
            }
          }
        } else {
          synchronized (this) {
            try {
              wait();
            } catch (InterruptedException e) {
            }
          }
        }
      }
    }

    public void shutdown() {
      this.shutdown = true;
      updaterThread.interrupt();
    }
  }
}
