//
   //  ========================================================================
   //  Copyright (c) 1995-2015 Mort Bay Consulting Pty. Ltd.
   //  ------------------------------------------------------------------------
   //  All rights reserved. This program and the accompanying materials
   //  are made available under the terms of the Eclipse Public License v1.0
   //  and Apache License v2.0 which accompanies this distribution.
   //
   //      The Eclipse Public License is available at
  //      http://www.eclipse.org/legal/epl-v10.html
  //
  //      The Apache License v2.0 is available at
  //      http://www.opensource.org/licenses/apache2.0.php
  //
  //  You may elect to redistribute this code under either of these licenses.
  //  ========================================================================
  //
  
  package org.eclipse.jetty.client;
  
  import java.util.concurrent.atomic.AtomicReference;
  
  import org.eclipse.jetty.client.api.Connection;
  import org.eclipse.jetty.client.api.Request;
  import org.eclipse.jetty.util.Promise;
  
  public abstract class MultiplexHttpDestination<C extends Connection> extends HttpDestination implements Promise<Connection>
  {
      private final AtomicReference<ConnectState> connect = new AtomicReference<>(ConnectState.DISCONNECTED);
      private C connection;
  
      protected MultiplexHttpDestination(HttpClient client, Origin origin)
      {
          super(client, origin);
      }
  
      @Override
      public void send()
      {
          while (true)
          {
              ConnectState current = connect.get();
              switch (current)
              {
                  case DISCONNECTED:
                  {
                      if (!connect.compareAndSet(current, ConnectState.CONNECTING))
                          break;
                      newConnection(this);
                      return;
                  }
                  case CONNECTING:
                  {
                      // Waiting to connect, just return
                      return;
                  }
                  case CONNECTED:
                  {
                      if (process(connection))
                          break;
                      return;
                  }
                  default:
                  {
                      abort(new IllegalStateException("Invalid connection state " + current));
                      return;
                  }
              }
          }
      }
  
      @Override
      @SuppressWarnings("unchecked")
      public void succeeded(Connection result)
      {
          C connection = this.connection = (C)result;
          if (connect.compareAndSet(ConnectState.CONNECTING, ConnectState.CONNECTED))
          {
              process(connection);
          }
          else
          {
              connection.close();
              failed(new IllegalStateException());
          }
      }
  
      @Override
      public void failed(Throwable x)
      {
          connect.set(ConnectState.DISCONNECTED);
          abort(x);
      }
  
      protected boolean process(final C connection)
      {
          HttpClient client = getHttpClient();
          final HttpExchange exchange = getHttpExchanges().poll();
          if (LOG.isDebugEnabled())
             LOG.debug("Processing {} on {}", exchange, connection);
         if (exchange == null)
             return false;
 
         final Request request = exchange.getRequest();
         Throwable cause = request.getAbortCause();
         if (cause != null)
         {
             if (LOG.isDebugEnabled())
                 LOG.debug("Aborted before processing {}: {}", exchange, cause);
             // It may happen that the request is aborted before the exchange
             // is created. Aborting the exchange a second time will result in
             // a no-operation, so we just abort here to cover that edge case.
             exchange.abort(cause);
         }
         else
         {
             send(connection, exchange);
         }
         return true;
     }
 
     @Override
     public void close()
     {
         super.close();
         C connection = this.connection;
         if (connection != null)
             connection.close();
     }
 
     @Override
     public void close(Connection connection)
     {
         super.close(connection);
         while (true)
         {
             ConnectState current = connect.get();
             if (connect.compareAndSet(current, ConnectState.DISCONNECTED))
             {
                 if (getHttpClient().isRemoveIdleDestinations())
                     getHttpClient().removeDestination(this);
                 break;
             }
         }
     }
 
     protected abstract void send(C connection, HttpExchange exchange);
 
     private enum ConnectState
     {
         DISCONNECTED, CONNECTING, CONNECTED
     }
 }