/*
    * Copyright 2014 The Netty Project
    *
    * The Netty Project 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:
    *
    * https://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.
   */
  package io.netty5.handler.codec.http;
  
  import io.netty5.channel.internal.DelegatingChannelHandlerContext;
  import io.netty5.util.Send;
  import io.netty5.channel.ChannelHandlerContext;
  import io.netty5.util.AsciiString;
  import io.netty5.util.concurrent.Future;
  
  import java.util.Collection;
  import java.util.LinkedHashSet;
  import java.util.Set;
  
  import static io.netty5.handler.codec.http.HttpResponseStatus.SWITCHING_PROTOCOLS;
  import static java.util.Objects.requireNonNull;
  
  /**
   * Client-side handler for handling an HTTP upgrade handshake to another protocol. When the first
   * HTTP request is sent, this handler will add all appropriate headers to perform an upgrade to the
   * new protocol. If the upgrade fails (i.e. response is not 101 Switching Protocols), this handler
   * simply removes itself from the pipeline. If the upgrade is successful, upgrades the pipeline to
   * the new protocol.
   */
  public class HttpClientUpgradeHandler<C extends HttpContent<C>> extends HttpObjectAggregator<C> {
  
      /**
       * User events that are fired to notify about upgrade status.
       */
      public enum UpgradeEvent {
          /**
           * The Upgrade request was sent to the server.
           */
          UPGRADE_ISSUED,
  
          /**
           * The Upgrade to the new protocol was successful.
           */
          UPGRADE_SUCCESSFUL,
  
          /**
           * The Upgrade was unsuccessful due to the server not issuing
           * with a 101 Switching Protocols response.
           */
          UPGRADE_REJECTED
      }
  
      /**
       * The source codec that is used in the pipeline initially.
       */
      public interface SourceCodec {
  
          /**
           * Removes or disables the encoder of this codec so that the {@link UpgradeCodec} can send an initial greeting
           * (if any).
           */
          void prepareUpgradeFrom(ChannelHandlerContext ctx);
  
          /**
           * Removes this codec (i.e. all associated handlers) from the pipeline.
           */
          void upgradeFrom(ChannelHandlerContext ctx);
      }
  
      /**
       * A codec that the source can be upgraded to.
       */
      public interface UpgradeCodec {
          /**
           * Returns the name of the protocol supported by this codec, as indicated by the {@code 'UPGRADE'} header.
           */
          CharSequence protocol();
  
          /**
           * Sets any protocol-specific headers required to the upgrade request. Returns the names of
           * all headers that were added. These headers will be used to populate the CONNECTION header.
           */
          Collection<CharSequence> setUpgradeHeaders(ChannelHandlerContext ctx, HttpRequest upgradeRequest);
  
          /**
           * Performs an HTTP protocol upgrade from the source codec. This method is responsible for
           * adding all handlers required for the new protocol.
           *
           * @param ctx the context for the current handler.
           * @param upgradeResponse the 101 Switching Protocols response that indicates that the server
           *            has switched to this protocol.
           */
         void upgradeTo(ChannelHandlerContext ctx, Send<FullHttpResponse> upgradeResponse) throws Exception;
     }
 
     private final SourceCodec sourceCodec;
     private final UpgradeCodec upgradeCodec;
     private boolean upgradeRequested;
 
     /**
      * Constructs the client upgrade handler.
      *
      * @param sourceCodec the codec that is being used initially.
      * @param upgradeCodec the codec that the client would like to upgrade to.
      * @param maxContentLength the maximum length of the aggregated content.
      */
     public HttpClientUpgradeHandler(SourceCodec sourceCodec, UpgradeCodec upgradeCodec,
                                     int maxContentLength) {
         super(maxContentLength);
         requireNonNull(sourceCodec, "sourceCodec");
         requireNonNull(upgradeCodec, "upgradeCodec");
         this.sourceCodec = sourceCodec;
         this.upgradeCodec = upgradeCodec;
     }
 
     @Override
     public Future<Void> write(ChannelHandlerContext ctx, Object msg) {
         if (!(msg instanceof HttpRequest)) {
             return ctx.write(msg);
         }
 
         if (upgradeRequested) {
             return ctx.newFailedFuture(new IllegalStateException(
                     "Attempting to write HTTP request with upgrade in progress"));
         }
 
         upgradeRequested = true;
         setUpgradeRequestHeaders(ctx, (HttpRequest) msg);
 
         // Continue writing the request.
         Future<Void> f = ctx.write(msg);
 
         // Notify that the upgrade request was issued.
         ctx.fireChannelInboundEvent(UpgradeEvent.UPGRADE_ISSUED);
         // Now we wait for the next HTTP response to see if we switch protocols.
         return f;
     }
 
     @Override
     protected void decode(final ChannelHandlerContext ctx, HttpObject msg)
             throws Exception {
         FullHttpResponse response = null;
         try {
             if (!upgradeRequested) {
                 throw new IllegalStateException("Read HTTP response without requesting protocol switch");
             }
 
             if (msg instanceof HttpResponse) {
                 HttpResponse rep = (HttpResponse) msg;
                 if (!SWITCHING_PROTOCOLS.equals(rep.status())) {
                     // The server does not support the requested protocol, just remove this handler
                     // and continue processing HTTP.
                     // NOTE: not releasing the response since we're letting it propagate to the
                     // next handler.
                     ctx.fireChannelInboundEvent(UpgradeEvent.UPGRADE_REJECTED);
                     ctx.fireChannelRead(msg);
                     removeThisHandler(ctx);
                     return;
                 }
             }
 
             if (msg instanceof FullHttpResponse) {
                 response = (FullHttpResponse) msg;
 
                 tryUpgrade(ctx, response);
             } else {
                 // Call the base class to handle the aggregation of the full request.
                 super.decode(new DelegatingChannelHandlerContext(ctx) {
                     @Override
                     public ChannelHandlerContext fireChannelRead(Object msg) {
                         FullHttpResponse response = (FullHttpResponse) msg;
                         tryUpgrade(ctx, response);
                         return this;
                     }
                 }, msg);
             }
 
         } catch (Throwable t) {
             if (response != null && response.isAccessible()) {
                 response.close();
             }
             ctx.fireChannelExceptionCaught(t);
             removeThisHandler(ctx);
         }
     }
 
     private void tryUpgrade(ChannelHandlerContext ctx, FullHttpResponse response) {
         try (response) {
             CharSequence upgradeHeader = response.headers().get(HttpHeaderNames.UPGRADE);
             if (upgradeHeader != null && !AsciiString.contentEqualsIgnoreCase(upgradeCodec.protocol(), upgradeHeader)) {
                 throw new IllegalStateException(
                         "Switching Protocols response with unexpected UPGRADE protocol: " + upgradeHeader);
             }
 
             // Upgrade to the new protocol.
             sourceCodec.prepareUpgradeFrom(ctx);
             upgradeCodec.upgradeTo(ctx, response.send());
 
             // Notify that the upgrade to the new protocol completed successfully.
             ctx.fireChannelInboundEvent(UpgradeEvent.UPGRADE_SUCCESSFUL);
 
             // We guarantee UPGRADE_SUCCESSFUL event will be arrived at the next handler
             // before http2 setting frame and http response.
             sourceCodec.upgradeFrom(ctx);
             removeThisHandler(ctx);
         } catch (Throwable t) {
             ctx.fireChannelExceptionCaught(t);
             removeThisHandler(ctx);
         }
     }
 
     private static void removeThisHandler(ChannelHandlerContext ctx) {
         ctx.pipeline().remove(ctx.name());
     }
 
     /**
      * Adds all upgrade request headers necessary for an upgrade to the supported protocols.
      */
     private void setUpgradeRequestHeaders(ChannelHandlerContext ctx, HttpRequest request) {
         // Set the UPGRADE header on the request.
         request.headers().set(HttpHeaderNames.UPGRADE, upgradeCodec.protocol());
 
         // Add all protocol-specific headers to the request.
         Set<CharSequence> connectionParts = new LinkedHashSet<>(2);
         connectionParts.addAll(upgradeCodec.setUpgradeHeaders(ctx, request));
 
         // Set the CONNECTION header from the set of all protocol-specific headers that were added.
         StringBuilder builder = new StringBuilder();
         for (CharSequence part : connectionParts) {
             builder.append(part);
             builder.append(',');
         }
         builder.append(HttpHeaderValues.UPGRADE);
         request.headers().add(HttpHeaderNames.CONNECTION, builder.toString());
     }
 }