/*
    * 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.util.Map;
  import java.util.concurrent.ConcurrentHashMap;
  
  import org.apache.commons.scxml2.env.groovy.GroovyEvaluator;
  import org.apache.commons.scxml2.env.javascript.JSEvaluator;
  import org.apache.commons.scxml2.env.jexl.JexlEvaluator;
  import org.apache.commons.scxml2.env.minimal.MinimalEvaluator;
  import org.apache.commons.scxml2.env.xpath.XPathEvaluator;
  import org.apache.commons.scxml2.model.ModelException;
  import org.apache.commons.scxml2.model.SCXML;
  import static org.apache.commons.scxml2.Evaluator.DEFAULT_DATA_MODEL;
  
  /**
   * A static singleton factory for {@link EvaluatorProvider}s by supported SCXML datamodel type.
   * <p>
   *  The EvaluatorFactory is used to automatically create an {@link Evaluator} instance for an SCXML
   *  statemachine when none has been pre-defined and configured for the {@link SCXMLExecutor}.
   * </p>
   * <p>
   *  The builtin supported providers are:
   *  <ul>
   *      <li>no or empty datamodel (default) or datamodel="jexl": {@link JexlEvaluator.JexlEvaluatorProvider}</li>
   *      <li>datamodel="ecmascript": {@link JSEvaluator.JSEvaluatorProvider}</li>
   *      <li>datamodel="groovy": {@link GroovyEvaluator.GroovyEvaluatorProvider}</li>
   *      <li>datamodel="xpath": {@link XPathEvaluator.XPathEvaluatorProvider}</li>
   *      <li>datamodel="null": {@link MinimalEvaluator.MinimalEvaluatorProvider}</li>
   *  </ul>
   *  </p>
   *  <p>
   *  For adding additional or overriding the builtin Evaluator implementations use
   *  {@link #registerEvaluatorProvider(EvaluatorProvider)} or {@link #unregisterEvaluatorProvider(String)}.
   *  </p>
   *  <p>
   *  The default provider can be overridden using the {@link #setDefaultProvider(EvaluatorProvider)} which will
   *  register the provider under the {@link Evaluator#DEFAULT_DATA_MODEL} ("") value for the datamodel.<br/>
   *  Note: this is <em>not</em> the same as datamodel="null"!
   * </p>
   */
  public class EvaluatorFactory {
  
      private static EvaluatorFactory INSTANCE = new EvaluatorFactory();
  
      private final Map<String, EvaluatorProvider> providers = new ConcurrentHashMap<String, EvaluatorProvider>();
  
      private EvaluatorFactory() {
          providers.put(XPathEvaluator.SUPPORTED_DATA_MODEL, new XPathEvaluator.XPathEvaluatorProvider());
          providers.put(JSEvaluator.SUPPORTED_DATA_MODEL, new JSEvaluator.JSEvaluatorProvider());
          providers.put(GroovyEvaluator.SUPPORTED_DATA_MODEL, new GroovyEvaluator.GroovyEvaluatorProvider());
          providers.put(JexlEvaluator.SUPPORTED_DATA_MODEL, new JexlEvaluator.JexlEvaluatorProvider());
          providers.put(MinimalEvaluator.SUPPORTED_DATA_MODEL, new MinimalEvaluator.MinimalEvaluatorProvider());
          providers.put(DEFAULT_DATA_MODEL, providers.get(JexlEvaluator.SUPPORTED_DATA_MODEL));
      }
  
      public static void setDefaultProvider(EvaluatorProvider defaultProvider) {
          INSTANCE.providers.put(DEFAULT_DATA_MODEL, defaultProvider);
      }
  
      @SuppressWarnings("unused")
      public static EvaluatorProvider getDefaultProvider() {
          return INSTANCE.providers.get(DEFAULT_DATA_MODEL);
      }
  
      @SuppressWarnings("unused")
      public static EvaluatorProvider getEvaluatorProvider(String datamodelName) {
          return INSTANCE.providers.get(datamodelName == null ? DEFAULT_DATA_MODEL : datamodelName);
      }
  
      @SuppressWarnings("unused")
      public static void registerEvaluatorProvider(EvaluatorProvider provider) {
          INSTANCE.providers.put(provider.getSupportedDatamodel(), provider);
      }
  
      @SuppressWarnings("unused")
      public static void unregisterEvaluatorProvider(String datamodelName) {
          INSTANCE.providers.remove(datamodelName == null ? DEFAULT_DATA_MODEL : datamodelName);
      }
  
      /**
       * Returns a dedicated Evaluator instance for a specific SCXML document its documentmodel.
       * <p>If no SCXML document is provided a default Evaluator will be returned.</p>
       * @param document The document to return a dedicated Evaluator for. May be null to retrieve the default Evaluator.
      * @return a new and not sharable Evaluator instance for the provided document, or a default Evaluator otherwise
      * @throws ModelException If the SCXML document datamodel is not supported.
      */
     public static Evaluator getEvaluator(SCXML document) throws ModelException {
         String datamodelName = document != null ? document.getDatamodelName() : null;
         EvaluatorProvider provider = INSTANCE.providers.get(datamodelName == null ? DEFAULT_DATA_MODEL : datamodelName);
         if (provider == null) {
             throw new ModelException("Unsupported SCXML document datamodel \""+(datamodelName)+"\"");
         }
         return document != null ? provider.getEvaluator(document) : provider.getEvaluator();
     }
 }