/*
    * 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.
   */
  package org.apache.commons.scxml2;
  
  import java.io.Serializable;
  import java.util.Arrays;
  import java.util.Collections;
  import java.util.HashMap;
  import java.util.HashSet;
  import java.util.Map;
  import java.util.Set;
  
  /**
   * The SCXMLSystemContext is used as a read only Context wrapper
   * and provides the SCXML (read only) system variables which are injected via the unwrapped {@link #getContext()}.
   *
   * @see <a href="http://www.w3.org/TR/scxml/#SystemVariables">http://www.w3.org/TR/scxml/#SystemVariables</a>
   */
  public class SCXMLSystemContext implements Context, Serializable {
  
      /**
       * Serial version UID.
       */
      private static final long serialVersionUID = 1L;
  
      /**
       * The protected system variables names as defined in the SCXML specification
       * @see <a href="http://www.w3.org/TR/scxml/#SystemVariables">http://www.w3.org/TR/scxml/#SystemVariables</a>
       */
      public static final String EVENT_KEY = "_event";
      public static final String SESSIONID_KEY = "_sessionid";
      public static final String SCXML_NAME_KEY = "_name";
      public static final String IOPROCESSORS_KEY = "_ioprocessors";
      public static final String X_KEY = "_x";
  
      /** The Commons SCXML internal {@link #getPlatformVariables() platform variable key} holding the current SCXML
       * status instance **/
      public static final String STATUS_KEY = "status";
  
      /**
       * The set of protected system variables names
       */
      private static final Set<String> PROTECTED_NAMES = new HashSet<String>(Arrays.asList(
              new String[] {EVENT_KEY, SESSIONID_KEY, SCXML_NAME_KEY, IOPROCESSORS_KEY, X_KEY}
      ));
  
      /**
       * The wrapped system context
       */
  
      private Context systemContext;
  
      /**
       * The auto-generated next sessionId prefixed ID
       * @see #generateSessionId()
       */
      private long nextSessionSequenceId;
  
      /**
       * Initialize or replace systemContext
       * @param systemContext the system context to set
       * @throws java.lang.NullPointerException if systemContext == null
       */
      void setSystemContext(Context systemContext) {
          if (this.systemContext != null) {
              // replace systemContext
              systemContext.getVars().putAll(this.systemContext.getVars());
          }
          else {
              // create Platform variables map
              systemContext.setLocal(X_KEY, new HashMap<String, Object>());
          }
          this.systemContext = systemContext;
          this.protectedVars = Collections.unmodifiableMap(systemContext.getVars());
      }
  
      /**
       * The unmodifiable wrapped variables map from the wrapped system context
       */
      private Map<String, Object> protectedVars;
  
      public SCXMLSystemContext(Context systemContext) {
          setSystemContext(systemContext);
      }
  
     public String generateSessionId() {
         return getContext().get(SESSIONID_KEY) + "-" + nextSessionSequenceId++;
     }
 
     @Override
     public void set(final String name, final Object value) {
         if (PROTECTED_NAMES.contains(name)) {
             throw new UnsupportedOperationException();
         }
         // non-protected variables are set on the parent of the system context (e.g. root context)
         systemContext.getParent().set(name, value);
     }
 
     @Override
     public void setLocal(final String name, final Object value) {
         throw new UnsupportedOperationException();
     }
 
     @Override
     public Object get(final String name) {
         return systemContext.get(name);
     }
 
     @Override
     public boolean has(final String name) {
         return systemContext.has(name);
     }
 
     @Override
     public boolean hasLocal(final String name) {
         return systemContext.hasLocal(name);
     }
 
     @Override
     public Map<String, Object> getVars() {
         return protectedVars;
     }
 
     @Override
     public void reset() {
         throw new UnsupportedOperationException();
     }
 
     @Override
     public Context getParent() {
         return systemContext.getParent();
     }
 
     @Override
     public SCXMLSystemContext getSystemContext() {
         return this;
     }
 
     /**
      * @return The Platform specific system variables map stored under the {@link #X_KEY _x} root system variable
      */
     @SuppressWarnings("unchecked")
     public Map<String, Object> getPlatformVariables() {
         return (Map<String, Object>)get(X_KEY);
     }
 
     /**
      * @return Returns the wrapped (modifiable) system context
      */
     Context getContext() {
         return systemContext;
     }
 }