content: /*
   * Symphony - A modern community (forum/BBS/SNS/blog) platform written in Java.
   * Copyright (C) 2012-present, b3log.org
   *
   * This program is free software: you can redistribute it and/or modify
   * it under the terms of the GNU Affero General Public License as published by
   * the Free Software Foundation, either version 3 of the License, or
   * (at your option) any later version.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU Affero General Public License for more details.
   *
   * You should have received a copy of the GNU Affero General Public License
   * along with this program.  If not, see <https://www.gnu.org/licenses/>.
   */
  package org.b3log.symphony.cache;
  
  import org.b3log.latke.ioc.Inject;
  import org.b3log.latke.ioc.Singleton;
  import org.b3log.symphony.service.DomainQueryService;
  import org.b3log.symphony.util.JSONs;
  import org.json.JSONObject;
  
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.List;
  import java.util.concurrent.locks.ReadWriteLock;
  import java.util.concurrent.locks.ReentrantReadWriteLock;
  
  /**
   * Domain cache.
   *
   * @author <a href="http://88250.b3log.org">Liang Ding</a>
   * @version 1.0.2.3, Aug 31, 2018
   * @since 1.4.0
   */
  @Singleton
  public class DomainCache {
  
      /**
       * Domains.
       */
      private static final List<JSONObject> DOMAINS = new ArrayList<>();
  
      /**
       * Lock.
       */
      private static final ReadWriteLock LOCK = new ReentrantReadWriteLock();
  
      /**
       * Domain query service.
       */
      @Inject
      private DomainQueryService domainQueryService;
  
      /**
       * Gets domains with the specified fetch size.
       *
       * @param fetchSize the specified fetch size
       * @return domains
       */
      public List<JSONObject> getDomains(final int fetchSize) {
          LOCK.readLock().lock();
          try {
              if (DOMAINS.isEmpty()) {
                  return Collections.emptyList();
              }
  
              final int end = fetchSize >= DOMAINS.size() ? DOMAINS.size() : fetchSize;
  
              return JSONs.clone(DOMAINS.subList(0, end));
          } finally {
              LOCK.readLock().unlock();
          }
      }
  
      /**
       * Loads domains.
       */
      public void loadDomains() {
          LOCK.writeLock().lock();
          try {
              DOMAINS.clear();
              DOMAINS.addAll(domainQueryService.getMostTagNaviDomains(Integer.MAX_VALUE));
          } finally {
              LOCK.writeLock().unlock();
          }
      }
  }
  