/*
    * ====================================================================
    * Licensed to the Apache Software Foundation (ASF) under one
    * or more contributor license agreements.  See the NOTICE file
    * distributed with this work for additional information
    * regarding copyright ownership.  The ASF licenses this file
    * to you under the Apache License, Version 2.0 (the
    * "License"); you may not use this file except in compliance
    * with the License.  You may obtain a copy of the License at
   *
   *   http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing,
   * software distributed under the License is distributed on an
   * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
   * KIND, either express or implied.  See the License for the
   * specific language governing permissions and limitations
   * under the License.
   * ====================================================================
   *
   * This software consists of voluntary contributions made by many
   * individuals on behalf of the Apache Software Foundation.  For more
   * information on the Apache Software Foundation, please see
   * <http://www.apache.org/>.
   *
   */
  package org.apache.hc.core5.http.io.support;
  
  import java.io.IOException;
  
  import org.apache.hc.core5.annotation.Contract;
  import org.apache.hc.core5.annotation.ThreadingBehavior;
  import org.apache.hc.core5.http.ClassicHttpRequest;
  import org.apache.hc.core5.http.ClassicHttpResponse;
  import org.apache.hc.core5.http.HttpEntity;
  import org.apache.hc.core5.http.HttpException;
  import org.apache.hc.core5.http.HttpResponse;
  import org.apache.hc.core5.http.HttpStatus;
  import org.apache.hc.core5.http.io.HttpFilterChain;
  import org.apache.hc.core5.http.io.HttpFilterHandler;
  import org.apache.hc.core5.http.message.BasicClassicHttpResponse;
  import org.apache.hc.core5.http.support.ExpectSupport;
  import org.apache.hc.core5.http.support.Expectation;
  import org.apache.hc.core5.http.protocol.HttpContext;
  
  /**
   * HttpServerExpectationFilter add support for the Expect-Continue handshake
   * to the request processing pipeline.
   *
   * @since 5.0
   */
  @Contract(threading = ThreadingBehavior.STATELESS)
  public class HttpServerExpectationFilter implements HttpFilterHandler {
  
      /**
       * Verifies the HTTP request and decides whether it meets server expectations and the request
       * processing can continue.
       *
       * @param request the incoming HTTP request.
       * @param context the actual execution context.
       * @return {@code true} if the request meets expectations or {@code false} otherwise.
       */
      protected boolean verify(final ClassicHttpRequest request, final HttpContext context) throws HttpException {
          return true;
      }
  
      /**
       * Generates response content entity for the final HTTP response with an error status
       * representing the cause of expectation failure.
       *
       * @param expectationFailed the final HTTP response.
       * @return the content entity for the final HTTP response with an error status
       *  representing the cause of expectation failure.
       */
      protected HttpEntity generateResponseContent(final HttpResponse expectationFailed) throws HttpException {
          return null;
      }
  
      @Override
      public final void handle(
              final ClassicHttpRequest request,
              final HttpFilterChain.ResponseTrigger responseTrigger,
              final HttpContext context,
              final HttpFilterChain chain) throws HttpException, IOException {
          final Expectation expectation = ExpectSupport.parse(request, request.getEntity());
          if (expectation == Expectation.CONTINUE) {
              final boolean verified = verify(request, context);
              if (verified) {
                  responseTrigger.sendInformation(new BasicClassicHttpResponse(HttpStatus.SC_CONTINUE));
              } else {
                  final ClassicHttpResponse expectationFailed = new BasicClassicHttpResponse(HttpStatus.SC_EXPECTATION_FAILED);
                  final HttpEntity responseContent = generateResponseContent(expectationFailed);
                  expectationFailed.setEntity(responseContent);
                  responseTrigger.submitResponse(expectationFailed);
                  return;
              }
          } else if (expectation == Expectation.UNKNOWN) {
              final ClassicHttpResponse expectationFailed = new BasicClassicHttpResponse(HttpStatus.SC_EXPECTATION_FAILED);
              final HttpEntity responseContent = generateResponseContent(expectationFailed);
             expectationFailed.setEntity(responseContent);
             responseTrigger.submitResponse(expectationFailed);
             return;
         }
         chain.proceed(request, responseTrigger, context);
     }
 }