/*
    * ====================================================================
    * 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.nio.support;
  
  import java.io.IOException;
  import java.nio.ByteBuffer;
  import java.util.List;
  
  import org.apache.hc.core5.annotation.Contract;
  import org.apache.hc.core5.annotation.ThreadingBehavior;
  import org.apache.hc.core5.http.EntityDetails;
  import org.apache.hc.core5.http.Header;
  import org.apache.hc.core5.http.HeaderElements;
  import org.apache.hc.core5.http.HttpException;
  import org.apache.hc.core5.http.HttpHeaders;
  import org.apache.hc.core5.http.HttpRequest;
  import org.apache.hc.core5.http.HttpResponse;
  import org.apache.hc.core5.http.HttpStatus;
  import org.apache.hc.core5.http.message.BasicClassicHttpResponse;
  import org.apache.hc.core5.http.message.BasicHttpResponse;
  import org.apache.hc.core5.http.nio.AsyncDataConsumer;
  import org.apache.hc.core5.http.nio.AsyncEntityProducer;
  import org.apache.hc.core5.http.nio.AsyncFilterChain;
  import org.apache.hc.core5.http.nio.AsyncFilterHandler;
  import org.apache.hc.core5.http.nio.CapacityChannel;
  import org.apache.hc.core5.http.nio.entity.AsyncEntityProducers;
  import org.apache.hc.core5.http.protocol.HttpContext;
  import org.apache.hc.core5.net.URIAuthority;
  
  /**
   * Abstract asynchronous HTTP request filter that implements standard HTTP authentication handshake.
   *
   * @param <T> authorization token representation.
   *
   * @since 5.0
   */
  @Contract(threading = ThreadingBehavior.STATELESS)
  public abstract class AbstractAsyncServerAuthFilter<T> implements AsyncFilterHandler {
  
      private final boolean respondImmediately;
  
      protected AbstractAsyncServerAuthFilter(final boolean respondImmediately) {
          this.respondImmediately = respondImmediately;
      }
  
      /**
       * Parses authorization header value into an authentication token sent by the client
       * as a response to an authentication challenge.
       *
       * @param authorizationValue the authorization header value.
       * @param context the actual execution context.
       * @return authorization token
       */
      protected abstract T parseChallengeResponse(String authorizationValue, HttpContext context) throws HttpException;
  
      /**
       * Authenticates the client using the authentication token sent by the client
       * as a response to an authentication challenge.
       *
       * @param challengeResponse the authentication token sent by the client
       *                          as a response to an authentication challenge.
       * @param authority the URI authority.
       * @param requestUri the request URI.
       * @param context the actual execution context.
       * @return {@code true} if the client could be successfully authenticated {@code false} otherwise.
       */
      protected abstract boolean authenticate(T challengeResponse, URIAuthority authority, String requestUri, HttpContext context);
  
      /**
       * Generates an authentication challenge in case of unsuccessful authentication.
       *
       * @param challengeResponse the authentication token sent by the client
       *                          as a response to an authentication challenge
       *                          or {@code null} if the client has not sent any.
       * @param authority the URI authority.
      * @param requestUri the request URI.
      * @param context the actual execution context.
      * @return an authorization challenge value.
      */
     protected abstract String generateChallenge(T challengeResponse, URIAuthority authority, String requestUri, HttpContext context);
 
     /**
      * Generates response body for UNAUTHORIZED response.
      *
      * @param unauthorized the response to return as a result of authentication failure.
      * @return the response content entity.
      */
     protected AsyncEntityProducer generateResponseContent(final HttpResponse unauthorized) {
         return AsyncEntityProducers.create("Unauthorized");
     }
 
     @Override
     public final AsyncDataConsumer handle(
             final HttpRequest request,
             final EntityDetails entityDetails,
             final HttpContext context,
             final AsyncFilterChain.ResponseTrigger responseTrigger,
             final AsyncFilterChain chain) throws HttpException, IOException {
         final Header h = request.getFirstHeader(HttpHeaders.AUTHORIZATION);
         final T challengeResponse = h != null ? parseChallengeResponse(h.getValue(), context) : null;
 
         final URIAuthority authority = request.getAuthority();
         final String requestUri = request.getRequestUri();
 
         final boolean authenticated = authenticate(challengeResponse, authority, requestUri, context);
         final Header expect = request.getFirstHeader(HttpHeaders.EXPECT);
         final boolean expectContinue = expect != null && HeaderElements.CONTINUE.equalsIgnoreCase(expect.getValue());
 
         if (authenticated) {
             if (expectContinue) {
                 responseTrigger.sendInformation(new BasicClassicHttpResponse(HttpStatus.SC_CONTINUE));
             }
             return chain.proceed(request, entityDetails, context, responseTrigger);
         }
         final HttpResponse unauthorized = new BasicHttpResponse(HttpStatus.SC_UNAUTHORIZED);
         unauthorized.addHeader(HttpHeaders.WWW_AUTHENTICATE, generateChallenge(challengeResponse, authority, requestUri, context));
         final AsyncEntityProducer responseContentProducer = generateResponseContent(unauthorized);
         if (respondImmediately || expectContinue || entityDetails == null) {
             responseTrigger.submitResponse(unauthorized, responseContentProducer);
             return null;
         }
         return new AsyncDataConsumer() {
 
             @Override
             public void updateCapacity(final CapacityChannel capacityChannel) throws IOException {
                 capacityChannel.update(Integer.MAX_VALUE);
             }
 
             @Override
             public void consume(final ByteBuffer src) throws IOException {
             }
 
             @Override
             public void streamEnd(final List<? extends Header> trailers) throws HttpException, IOException {
                 responseTrigger.submitResponse(unauthorized, responseContentProducer);
             }
 
             @Override
             public void releaseResources() {
                 if (responseContentProducer != null) {
                     responseContentProducer.releaseResources();
                 }
             }
 
         };
     }
 
 }