package us.codecraft.webmagic.scheduler;
   
   import java.util.concurrent.BlockingQueue;
   import java.util.concurrent.LinkedBlockingQueue;
   
   import us.codecraft.webmagic.Request;
   import us.codecraft.webmagic.Site;
   import us.codecraft.webmagic.Task;
   
  /**
   * Basic Scheduler implementation.<br>
   * Store urls to fetch in LinkedBlockingQueue and remove duplicate urls by HashMap.
   *
   * Note: if you use this {@link QueueScheduler}
   * with {@link Site#getCycleRetryTimes()} enabled, you may encountered dead-lock
   * when the queue is full.
   *
   * @author code4crafter@gmail.com <br>
   * @since 0.1.0
   */
  public class QueueScheduler extends DuplicateRemovedScheduler implements MonitorableScheduler {
  
      private final BlockingQueue<Request> queue;
  
      public QueueScheduler() {
          this.queue = new LinkedBlockingQueue<>();
      }
  
      /**
       * Creates a {@code QueueScheduler} with the given (fixed) capacity.
       *
       * @param capacity the capacity of this queue,
       * see {@link LinkedBlockingQueue#LinkedBlockingQueue(int)}
       * @since 0.8.0
       */
      public QueueScheduler(int capacity) {
          this.queue = new LinkedBlockingQueue<>(capacity);
      }
  
      @Override
      public void pushWhenNoDuplicate(Request request, Task task) {
          logger.trace("Remaining capacity: {}", this.queue.remainingCapacity());
  
          try {
              queue.put(request);
          } catch (InterruptedException e) {
              Thread.currentThread().interrupt();
          }
      }
  
      @Override
      public Request poll(Task task) {
          return queue.poll();
      }
  
      @Override
      public int getLeftRequestsCount(Task task) {
          return queue.size();
      }
  
      @Override
      public int getTotalRequestsCount(Task task) {
          return getDuplicateRemover().getTotalRequestsCount(task);
      }
  }