/*
    * 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.buffer.api.BufferAllocator;
  import io.netty5.channel.internal.DelegatingChannelHandlerContext;
  import io.netty5.util.Resource;
  import io.netty5.util.Send;
  import io.netty5.channel.ChannelFutureListeners;
  import io.netty5.channel.ChannelHandlerContext;
  import io.netty5.util.concurrent.Future;
  
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.List;
  
  import static io.netty5.handler.codec.http.HttpResponseStatus.SWITCHING_PROTOCOLS;
  import static io.netty5.handler.codec.http.HttpVersion.HTTP_1_1;
  import static io.netty5.util.AsciiString.containsAllContentEqualsIgnoreCase;
  import static io.netty5.util.AsciiString.containsContentEqualsIgnoreCase;
  import static io.netty5.util.internal.StringUtil.COMMA;
  import static java.util.Objects.requireNonNull;
  
  /**
   * A server-side handler that receives HTTP requests and optionally performs a protocol switch if
   * the requested protocol is supported. Once an upgrade is performed, this handler removes itself
   * from the pipeline.
   */
  public class HttpServerUpgradeHandler<C extends HttpContent<C>> extends HttpObjectAggregator<C> {
  
      /**
       * The source codec that is used in the pipeline initially.
       */
      public interface SourceCodec {
          /**
           * 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 {
          /**
           * Gets all protocol-specific headers required by this protocol for a successful upgrade.
           * Any supplied header will be required to appear in the {@link HttpHeaderNames#CONNECTION} header as well.
           */
          Collection<CharSequence> requiredUpgradeHeaders();
  
          /**
           * Prepares the {@code upgradeHeaders} for a protocol update based upon the contents of {@code upgradeRequest}.
           * This method returns a boolean value to proceed or abort the upgrade in progress. If {@code false} is
           * returned, the upgrade is aborted and the {@code upgradeRequest} will be passed through the inbound pipeline
           * as if no upgrade was performed. If {@code true} is returned, the upgrade will proceed to the next
           * step which invokes {@link #upgradeTo}. When returning {@code true}, you can add headers to
           * the {@code upgradeHeaders} so that they are added to the 101 Switching protocols response.
           */
          boolean prepareUpgradeResponse(ChannelHandlerContext ctx, FullHttpRequest upgradeRequest,
                                      HttpHeaders upgradeHeaders);
  
          /**
           * 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 upgradeRequest the request that triggered the upgrade to this protocol.
           */
          void upgradeTo(ChannelHandlerContext ctx, FullHttpRequest upgradeRequest);
      }
  
      /**
       * Creates a new {@link UpgradeCodec} for the requested protocol name.
       */
      public interface UpgradeCodecFactory {
          /**
           * Invoked by {@link HttpServerUpgradeHandler} for all the requested protocol names in the order of
           * the client preference. The first non-{@code null} {@link UpgradeCodec} returned by this method
           * will be selected.
           *
           * @return a new {@link UpgradeCodec}, or {@code null} if the specified protocol name is not supported
           */
          UpgradeCodec newUpgradeCodec(CharSequence protocol);
      }
  
      /**
       * User event that is fired to notify about the completion of an HTTP upgrade
      * to another protocol. Contains the original upgrade request so that the response
      * (if required) can be sent using the new protocol.
      */
     public static final class UpgradeEvent implements Resource<UpgradeEvent> {
         private final CharSequence protocol;
         private final FullHttpRequest upgradeRequest;
 
         UpgradeEvent(CharSequence protocol, FullHttpRequest upgradeRequest) {
             this.protocol = protocol;
             this.upgradeRequest = upgradeRequest;
         }
 
         /**
          * The protocol that the channel has been upgraded to.
          */
         public CharSequence protocol() {
             return protocol;
         }
 
         /**
          * Gets the request that triggered the protocol upgrade.
          */
         public FullHttpRequest upgradeRequest() {
             return upgradeRequest;
         }
 
         @Override
         public Send<UpgradeEvent> send() {
             return upgradeRequest.send().map(UpgradeEvent.class, req -> new UpgradeEvent(protocol, req));
         }
 
         public UpgradeEvent copy() {
             return new UpgradeEvent(protocol, upgradeRequest.copy());
         }
 
         @Override
         public void close() {
             upgradeRequest.close();
         }
 
         @Override
         public boolean isAccessible() {
             return upgradeRequest.isAccessible();
         }
 
         @Override
         public UpgradeEvent touch(Object hint) {
             upgradeRequest.touch(hint);
             return this;
         }
 
         @Override
         public String toString() {
             return "UpgradeEvent [protocol=" + protocol + ", upgradeRequest=" + upgradeRequest + ']';
         }
     }
 
     private final SourceCodec sourceCodec;
     private final UpgradeCodecFactory upgradeCodecFactory;
     private final boolean validateHeaders;
     private boolean handlingUpgrade;
 
     /**
      * Constructs the upgrader with the supported codecs.
      * <p>
      * The handler instantiated by this constructor will reject an upgrade request with non-empty content.
      * It should not be a concern because an upgrade request is most likely a GET request.
      * If you have a client that sends a non-GET upgrade request, please consider using
      * {@link #HttpServerUpgradeHandler(SourceCodec, UpgradeCodecFactory, int)} to specify the maximum
      * length of the content of an upgrade request.
      * </p>
      *
      * @param sourceCodec the codec that is being used initially
      * @param upgradeCodecFactory the factory that creates a new upgrade codec
      *                            for one of the requested upgrade protocols
      */
     public HttpServerUpgradeHandler(SourceCodec sourceCodec, UpgradeCodecFactory upgradeCodecFactory) {
         this(sourceCodec, upgradeCodecFactory, 0);
     }
 
     /**
      * Constructs the upgrader with the supported codecs.
      *
      * @param sourceCodec the codec that is being used initially
      * @param upgradeCodecFactory the factory that creates a new upgrade codec
      *                            for one of the requested upgrade protocols
      * @param maxContentLength the maximum length of the content of an upgrade request
      */
     public HttpServerUpgradeHandler(
             SourceCodec sourceCodec, UpgradeCodecFactory upgradeCodecFactory, int maxContentLength) {
         this(sourceCodec, upgradeCodecFactory, maxContentLength, true);
     }
 
     /**
      * Constructs the upgrader with the supported codecs.
      *
      * @param sourceCodec the codec that is being used initially
      * @param upgradeCodecFactory the factory that creates a new upgrade codec
      *                            for one of the requested upgrade protocols
      * @param maxContentLength the maximum length of the content of an upgrade request
      * @param validateHeaders validate the header names and values of the upgrade response.
      */
     public HttpServerUpgradeHandler(SourceCodec sourceCodec, UpgradeCodecFactory upgradeCodecFactory,
                                     int maxContentLength, boolean validateHeaders) {
         super(maxContentLength);
 
         this.sourceCodec = requireNonNull(sourceCodec, "sourceCodec");
         this.upgradeCodecFactory = requireNonNull(upgradeCodecFactory, "upgradeCodecFactory");
         this.validateHeaders = validateHeaders;
     }
 
     @Override
     protected void decodeAndClose(final ChannelHandlerContext ctx, HttpObject msg)
             throws Exception {
 
         if (!handlingUpgrade) {
             // Not handling an upgrade request yet. Check if we received a new upgrade request.
             if (msg instanceof HttpRequest) {
                 HttpRequest req = (HttpRequest) msg;
                 if (req.headers().contains(HttpHeaderNames.UPGRADE) &&
                     shouldHandleUpgradeRequest(req)) {
                     handlingUpgrade = true;
                 } else {
                     ctx.fireChannelRead(msg);
                     return;
                 }
             } else {
                 ctx.fireChannelRead(msg);
                 return;
             }
         }
 
         FullHttpRequest fullRequest;
         if (msg instanceof FullHttpRequest) {
             fullRequest = (FullHttpRequest) msg;
             tryUpgrade(ctx, fullRequest);
         } else {
             // Call the base class to handle the aggregation of the full request.
             super.decodeAndClose(new DelegatingChannelHandlerContext(ctx) {
                 @Override
                 public ChannelHandlerContext fireChannelRead(Object msg) {
                     // Finished aggregating the full request, get it from the output list.
                     handlingUpgrade = false;
                     tryUpgrade(ctx, (FullHttpRequest) msg);
                     return this;
                 }
             }, msg);
         }
     }
 
     private void tryUpgrade(ChannelHandlerContext ctx, FullHttpRequest request) {
         if (!upgrade(ctx, request)) {
 
             // The upgrade did not succeed, just allow the full request to propagate to the
             // next handler.
             ctx.fireChannelRead(request);
         }
     }
 
     /**
      * Determines whether the specified upgrade {@link HttpRequest} should be handled by this handler or not.
      * This method will be invoked only when the request contains an {@code Upgrade} header.
      * It always returns {@code true} by default, which means any request with an {@code Upgrade} header
      * will be handled. You can override this method to ignore certain {@code Upgrade} headers, for example:
      * <pre>{@code
      * @Override
      * protected boolean isUpgradeRequest(HttpRequest req) {
      *   // Do not handle WebSocket upgrades.
      *   return !req.headers().contains(HttpHeaderNames.UPGRADE, "websocket", false);
      * }
      * }</pre>
      */
     protected boolean shouldHandleUpgradeRequest(HttpRequest req) {
         return true;
     }
 
     /**
      * Attempts to upgrade to the protocol(s) identified by the {@link HttpHeaderNames#UPGRADE} header (if provided
      * in the request).
      *
      * @param ctx the context for this handler.
      * @param request the HTTP request.
      * @return {@code true} if the upgrade occurred, otherwise {@code false}.
      */
     private boolean upgrade(final ChannelHandlerContext ctx, final FullHttpRequest request) {
         // Select the best protocol based on those requested in the UPGRADE header.
         final List<CharSequence> requestedProtocols = splitHeader(request.headers().get(HttpHeaderNames.UPGRADE));
         final int numRequestedProtocols = requestedProtocols.size();
         UpgradeCodec upgradeCodec = null;
         CharSequence upgradeProtocol = null;
         for (int i = 0; i < numRequestedProtocols; i ++) {
             final CharSequence p = requestedProtocols.get(i);
             final UpgradeCodec c = upgradeCodecFactory.newUpgradeCodec(p);
             if (c != null) {
                 upgradeProtocol = p;
                 upgradeCodec = c;
                 break;
             }
         }
 
         if (upgradeCodec == null) {
             // None of the requested protocols are supported, don't upgrade.
             return false;
         }
 
         // Make sure the CONNECTION header is present.
         List<String> connectionHeaderValues = request.headers().getAll(HttpHeaderNames.CONNECTION);
 
         if (connectionHeaderValues == null || connectionHeaderValues.isEmpty()) {
             return false;
         }
 
         final StringBuilder concatenatedConnectionValue = new StringBuilder(connectionHeaderValues.size() * 10);
         for (CharSequence connectionHeaderValue : connectionHeaderValues) {
             concatenatedConnectionValue.append(connectionHeaderValue).append(COMMA);
         }
         concatenatedConnectionValue.setLength(concatenatedConnectionValue.length() - 1);
 
         // Make sure the CONNECTION header contains UPGRADE as well as all protocol-specific headers.
         Collection<CharSequence> requiredHeaders = upgradeCodec.requiredUpgradeHeaders();
         List<CharSequence> values = splitHeader(concatenatedConnectionValue);
         if (!containsContentEqualsIgnoreCase(values, HttpHeaderNames.UPGRADE) ||
                 !containsAllContentEqualsIgnoreCase(values, requiredHeaders)) {
             return false;
         }
 
         // Ensure that all required protocol-specific headers are found in the request.
         for (CharSequence requiredHeader : requiredHeaders) {
             if (!request.headers().contains(requiredHeader)) {
                 return false;
             }
         }
 
         // Prepare and send the upgrade response. Wait for this write to complete before upgrading,
         // since we need the old codec in-place to properly encode the response.
         final FullHttpResponse upgradeResponse = createUpgradeResponse(ctx.bufferAllocator(), upgradeProtocol);
         if (!upgradeCodec.prepareUpgradeResponse(ctx, request, upgradeResponse.headers())) {
             return false;
         }
 
         // After writing the upgrade response we immediately prepare the
         // pipeline for the next protocol to avoid a race between completion
         // of the write future and receiving data before the pipeline is
         // restructured.
         Future<Void> writeComplete = ctx.writeAndFlush(upgradeResponse);
         // Perform the upgrade to the new protocol.
         sourceCodec.upgradeFrom(ctx);
         upgradeCodec.upgradeTo(ctx, request);
 
         // Notify that the upgrade has occurred.
         ctx.fireChannelInboundEvent(new UpgradeEvent(upgradeProtocol, request));
 
         // Remove this handler from the pipeline.
         ctx.pipeline().remove(HttpServerUpgradeHandler.this);
 
         // Add the listener last to avoid firing upgrade logic after
         // the channel is already closed since the listener may fire
         // immediately if the write failed eagerly.
         writeComplete.addListener(ctx.channel(), ChannelFutureListeners.CLOSE_ON_FAILURE);
         return true;
     }
 
     /**
      * Creates the 101 Switching Protocols response message.
      */
     private FullHttpResponse createUpgradeResponse(BufferAllocator allocator, CharSequence upgradeProtocol) {
         DefaultFullHttpResponse res = new DefaultFullHttpResponse(
                 HTTP_1_1, SWITCHING_PROTOCOLS, allocator.allocate(0), validateHeaders);
         res.headers().add(HttpHeaderNames.CONNECTION, HttpHeaderValues.UPGRADE);
         res.headers().add(HttpHeaderNames.UPGRADE, upgradeProtocol);
         return res;
     }
 
     /**
      * Splits a comma-separated header value. The returned set is case-insensitive and contains each
      * part with whitespace removed.
      */
     private static List<CharSequence> splitHeader(CharSequence header) {
         final StringBuilder builder = new StringBuilder(header.length());
         final List<CharSequence> protocols = new ArrayList<>(4);
         for (int i = 0; i < header.length(); ++i) {
             char c = header.charAt(i);
             if (Character.isWhitespace(c)) {
                 // Don't include any whitespace.
                 continue;
             }
             if (c == ',') {
                 // Add the string and reset the builder for the next protocol.
                 protocols.add(builder.toString());
                 builder.setLength(0);
             } else {
                 builder.append(c);
             }
         }
 
         // Add the last protocol
         if (builder.length() > 0) {
             protocols.add(builder.toString());
         }
 
         return protocols;
     }
 }