import java.io.*;
import java.nio.*;
import java.nio.channels.*;

public class RequestHandler implements Handler {
  private ChannelIO channelIO;
  private ByteBuffer requestByteBuffer = null;  //存放HTTP请求的缓冲区

  private boolean requestReceived = false;  //是否已经接收到了所有的HTTP请求
  private Request request = null;  //表示HTTP请求
  private Response response = null;  //表示HTTP响应

  RequestHandler(ChannelIO channelIO) {
    this.channelIO = channelIO;
  }

  /* 
   * 接收HTTP请求，如果已经接收到了所有的HTTP请求数据，就返回true,否则返回false
   */
  private boolean receive(SelectionKey sk) throws IOException {
    ByteBuffer tmp = null;

    if (requestReceived)return true;  //如果已经接收到所有HTTP请求数据，返回true
    
    //如果已经读到通道的末尾，或者已经读到HTTP请求数据的末尾标志“\r\n”，就返回true
    if ((channelIO.read() < 0) || Request.isComplete(channelIO.getReadBuf())) {
      requestByteBuffer = channelIO.getReadBuf();
      return (requestReceived = true);
    }
    return false;
  }

  /*
   * 通过Request类的parse()方法，解析requestByteBuffer中的HTTP请求数据，构造相应的Request对象 
   */
  private boolean parse() throws IOException {
    try {
      request = Request.parse(requestByteBuffer);
      return true;
    } catch (MalformedRequestException x) {  
      //如果HTTP请求的格式不正确，就发送错误信息
      response = new Response(Response.Code.BAD_REQUEST,
                          new StringContent(x));
    }
    return false;
  }

  /*
   * 创建HTTP响应 
   */
  private void build() throws IOException {
    Request.Action action = request.action();
    //仅仅支持GET和HEAD请求方式
    if ((action != Request.Action.GET) &&
            (action != Request.Action.HEAD)){
       response = new Response(Response.Code.METHOD_NOT_ALLOWED,
                          new StringContent("Method Not Allowed"));
    }else{
       response = new Response(Response.Code.OK,
                      new FileContent(request.uri()), action);
    }
  }
  
  /*  接收HTTP请求，发送HTTP响应 */
  public void handle(SelectionKey sk) throws IOException {
    try {
        if (request == null) { //如果还没有接收到HTTP请求的所有数据
            //接收HTTP请求      
            if (!receive(sk))return;
            requestByteBuffer.flip();
     
            //如果成功解析了HTTP请求，就创建一个Response对象
            if (parse())build();
     
            try {
                response.prepare();  //准备HTTP响应的内容
            } catch (IOException x) {
                response.release();  
                response = new Response(Response.Code.NOT_FOUND,
                                  new StringContent(x.getMessage()));
                response.prepare();
            }

            if (send()) {  
               //如果HTTP响应没有发送完毕，则需要注册写就绪事件，
               //以便在写就绪事件发生时继续发送数据
               sk.interestOps(SelectionKey.OP_WRITE);
            } else {
               //如果HTTP响应发送完毕，就断开底层的连接，并且释放Response占用的资源
               channelIO.close();
               response.release();
            }
        } else {  //如果已经接收到HTTP请求的所有数据
            if (!send()) {  //如果HTTP响应发送完毕
              channelIO.close();
              response.release();
            }
        }
    } catch (IOException x) {
        x.printStackTrace();
        channelIO.close();
        if (response !=  null) {
            response.release();
        }
    }
  }

  /* 发送HTTP响应，如果全部发送完毕，就返回false，否则返回true */  
  private boolean send() throws IOException {
    return response.send(channelIO);
  }
}


/****************************************************
 * 作者：孙卫琴                                     *
 * 来源：<<Java网络编程核心技术详解>>                       *
 * 技术支持网址：www.javathinker.net                *
 ***************************************************/
