package us.codecraft.webmagic.proxy;
   
   import us.codecraft.webmagic.Page;
   import us.codecraft.webmagic.Request;
   import us.codecraft.webmagic.Task;
   
   import java.util.ArrayList;
   import java.util.Collections;
   import java.util.List;
  import java.util.concurrent.atomic.AtomicInteger;
  
  /**
   * A simple ProxyProvider. Provide proxy as round-robin without heartbeat and error check. It can be used when all proxies are stable.
   * @author code4crafter@gmail.com
   *         Date: 17/4/16
   *         Time: 10:18
   * @since 0.7.0
   */
  public class SimpleProxyProvider implements ProxyProvider {
  
      private final List<Proxy> proxies;
  
      private final AtomicInteger pointer;
  
      public SimpleProxyProvider(List<Proxy> proxies) {
          this(proxies, new AtomicInteger(-1));
      }
  
      private SimpleProxyProvider(List<Proxy> proxies, AtomicInteger pointer) {
          this.proxies = proxies;
          this.pointer = pointer;
      }
  
      public static SimpleProxyProvider from(Proxy... proxies) {
          List<Proxy> proxiesTemp = new ArrayList<Proxy>(proxies.length);
          for (Proxy proxy : proxies) {
              proxiesTemp.add(proxy);
          }
          return new SimpleProxyProvider(Collections.unmodifiableList(proxiesTemp));
      }
  
      @Override
      public void returnProxy(Proxy proxy, Page page, Task task) {
          //Donothing
      }
  
      @Override
      public Proxy getProxy(Request request, Task task) {
          return proxies.get(incrForLoop());
      }
  
      private int incrForLoop() {
          int p = pointer.incrementAndGet();
          int size = proxies.size();
          if (p < size) {
              return p;
          }
          while (!pointer.compareAndSet(p, p % size)) {
              p = pointer.get();
          }
          return p % size;
      }
  
  }