/*
    * 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.netty.handler.codec.http.websocketx.extensions;
  
  import io.netty.handler.codec.http.HttpHeaderNames;
  import io.netty.handler.codec.http.HttpHeaderValues;
  import io.netty.handler.codec.http.HttpHeaders;
  
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  import java.util.Map.Entry;
  import java.util.regex.Matcher;
  import java.util.regex.Pattern;
  
  public final class WebSocketExtensionUtil {
  
      private static final String EXTENSION_SEPARATOR = ",";
      private static final String PARAMETER_SEPARATOR = ";";
      private static final char PARAMETER_EQUAL = '=';
  
      private static final Pattern PARAMETER = Pattern.compile("^([^=]+)(=[\\\"]?([^\\\"]+)[\\\"]?)?$");
  
      static boolean isWebsocketUpgrade(HttpHeaders headers) {
          //this contains check does not allocate an iterator, and most requests are not upgrades
          //so we do the contains check first before checking for specific values
          return headers.contains(HttpHeaderNames.UPGRADE) &&
                  headers.containsValue(HttpHeaderNames.CONNECTION, HttpHeaderValues.UPGRADE, true) &&
                  headers.contains(HttpHeaderNames.UPGRADE, HttpHeaderValues.WEBSOCKET, true);
      }
  
      public static List<WebSocketExtensionData> extractExtensions(String extensionHeader) {
          String[] rawExtensions = extensionHeader.split(EXTENSION_SEPARATOR);
          if (rawExtensions.length > 0) {
              List<WebSocketExtensionData> extensions = new ArrayList<WebSocketExtensionData>(rawExtensions.length);
              for (String rawExtension : rawExtensions) {
                  String[] extensionParameters = rawExtension.split(PARAMETER_SEPARATOR);
                  String name = extensionParameters[0].trim();
                  Map<String, String> parameters;
                  if (extensionParameters.length > 1) {
                      parameters = new HashMap<String, String>(extensionParameters.length - 1);
                      for (int i = 1; i < extensionParameters.length; i++) {
                          String parameter = extensionParameters[i].trim();
                          Matcher parameterMatcher = PARAMETER.matcher(parameter);
                          if (parameterMatcher.matches() && parameterMatcher.group(1) != null) {
                              parameters.put(parameterMatcher.group(1), parameterMatcher.group(3));
                          }
                      }
                  } else {
                      parameters = Collections.emptyMap();
                  }
                  extensions.add(new WebSocketExtensionData(name, parameters));
              }
              return extensions;
          } else {
              return Collections.emptyList();
          }
      }
  
      static String computeMergeExtensionsHeaderValue(String userDefinedHeaderValue,
                                                      List<WebSocketExtensionData> extraExtensions) {
          List<WebSocketExtensionData> userDefinedExtensions =
            userDefinedHeaderValue != null ?
              extractExtensions(userDefinedHeaderValue) :
              Collections.<WebSocketExtensionData>emptyList();
  
          for (WebSocketExtensionData userDefined: userDefinedExtensions) {
              WebSocketExtensionData matchingExtra = null;
              int i;
              for (i = 0; i < extraExtensions.size(); i ++) {
                  WebSocketExtensionData extra = extraExtensions.get(i);
                  if (extra.name().equals(userDefined.name())) {
                      matchingExtra = extra;
                      break;
                  }
              }
              if (matchingExtra == null) {
                  extraExtensions.add(userDefined);
              } else {
                  // merge with higher precedence to user defined parameters
                  Map<String, String> mergedParameters = new HashMap<String, String>(matchingExtra.parameters());
                  mergedParameters.putAll(userDefined.parameters());
                  extraExtensions.set(i, new WebSocketExtensionData(matchingExtra.name(), mergedParameters));
              }
         }
 
         StringBuilder sb = new StringBuilder(150);
 
         for (WebSocketExtensionData data: extraExtensions) {
             sb.append(data.name());
             for (Entry<String, String> parameter : data.parameters().entrySet()) {
                 sb.append(PARAMETER_SEPARATOR);
                 sb.append(parameter.getKey());
                 if (parameter.getValue() != null) {
                     sb.append(PARAMETER_EQUAL);
                     sb.append(parameter.getValue());
                 }
             }
             sb.append(EXTENSION_SEPARATOR);
         }
 
         if (!extraExtensions.isEmpty()) {
             sb.setLength(sb.length() - EXTENSION_SEPARATOR.length());
         }
 
         return sb.toString();
     }
 
     private WebSocketExtensionUtil() {
         // Unused
     }
 }