package com.atlassian.plugin.web.descriptors;
   
   import com.atlassian.plugin.util.Assertions;
   import com.atlassian.plugin.web.NoOpContextProvider;
   import org.dom4j.Element;
   
   import com.atlassian.plugin.Plugin;
   import com.atlassian.plugin.PluginParseException;
   import com.atlassian.plugin.loaders.LoaderUtils;
  import com.atlassian.plugin.web.ContextProvider;
  import com.atlassian.plugin.web.WebFragmentHelper;
  import com.atlassian.plugin.web.conditions.ConditionLoadingException;
  
  /**
   * This class is used for constructing
   * {@link com.atlassian.plugin.web.ContextProvider} objects from a module
   * descriptor's XML element. Its functionality is used by both
   * {@link com.atlassian.plugin.web.descriptors.AbstractWebFragmentModuleDescriptor}
   * and
   * {@link com.atlassian.plugin.web.descriptors.DefaultWebPanelModuleDescriptor}.
   * 
   * @since 2.5.0
   */
  class ContextProviderElementParser
  {
      private final WebFragmentHelper webFragmentHelper;
  
      public ContextProviderElementParser(final WebFragmentHelper webFragmentHelper)
      {
          this.webFragmentHelper = webFragmentHelper;
      }
  
      /**
       * @param element the module descriptor's XML element which contains the
       *            nested <context-provider> element.
       * @return the configured {@link ContextProvider} instance, or
       *         <code>null</code> when the descriptor does not contain a
       *         &lt;context-provider> element.
       * @throws PluginParseException
       */
      public ContextProvider makeContextProvider(final Plugin plugin, final Element element) throws PluginParseException
      {
          Assertions.notNull("plugin == null", plugin);
          try
          {
              final Element contextProviderElement = element.element("context-provider");
              if (contextProviderElement == null)
              {
                  return new NoOpContextProvider();
              }
              else
              {
                  final ContextProvider context = webFragmentHelper.loadContextProvider(contextProviderElement.attributeValue("class"), plugin);
                  context.init(LoaderUtils.getParams(contextProviderElement));
                  return context;
              }
          }
          catch (final ClassCastException e)
          {
              throw new PluginParseException("Configured context-provider class does not implement the ContextProvider interface", e);
          }
          catch (final ConditionLoadingException cle)
          {
              throw new PluginParseException("Unable to load the module's display conditions: " + cle.getMessage(), cle);
          }
      }
  }