package com.atlassian.plugin.web.descriptors;
   
   import com.atlassian.plugin.PluginParseException;
   import com.atlassian.plugin.elements.ResourceDescriptor;
   import com.atlassian.plugin.hostcontainer.HostContainer;
   import com.atlassian.plugin.module.ModuleFactory;
   import com.atlassian.plugin.web.model.EmbeddedTemplateWebPanel;
   import com.atlassian.plugin.web.model.ResourceTemplateWebPanel;
   import com.atlassian.plugin.web.model.WebPanel;
  import com.google.common.base.Preconditions;
  import com.google.common.base.Predicate;
  import com.google.common.base.Supplier;
  import com.google.common.collect.Iterables;
  import org.apache.commons.lang.StringUtils;
  
  import java.util.Iterator;
  
  /**
   * Produces {@link Supplier} objects that in turn produce {@link WebPanel}
   * instances.
   * <br>
   * This class exists to simplify the {@link DefaultWebPanelModuleDescriptor} and
   * make it more testable.
   *
   * @since   2.6.0
   */
  class WebPanelSupplierFactory
  {
      private final WebPanelModuleDescriptor webPanelModuleDescriptor;
      private final HostContainer hostContainer;
      private final ModuleFactory moduleFactory;
  
      public WebPanelSupplierFactory(
          WebPanelModuleDescriptor webPanelModuleDescriptor,
          HostContainer hostContainer, ModuleFactory moduleFactory)
      {
          this.webPanelModuleDescriptor = webPanelModuleDescriptor;
          this.hostContainer = hostContainer;
          this.moduleFactory = moduleFactory;
      }
  
      public Supplier<WebPanel> build(final String moduleClassName)
      {
          if (moduleClassName != null)
          {
              // If a classname is specified return the WebPanel for that class
              return new Supplier<WebPanel>()
              {
                  public WebPanel get()
                  {
                      return moduleFactory.createModule(moduleClassName, webPanelModuleDescriptor);
                  }
              };
          }
  
          final ResourceDescriptor resource = getRequiredViewResource();
          final String filename = resource.getLocation();
          if (StringUtils.isNotEmpty(filename))
          {
              // If a resource file is specified it is the template for the panel.
              return new Supplier<WebPanel>()
              {
                  public WebPanel get()
                  {
                      final ResourceTemplateWebPanel panel = hostContainer.create(ResourceTemplateWebPanel.class);
                      panel.setResourceFilename(filename);
                      panel.setResourceType(getRequiredResourceType(resource));
                      panel.setPlugin(webPanelModuleDescriptor.getPlugin());
                      return panel;
                  }
              };
          }
  
          // If no resource file is specified the panel template must be
          // embedded.
          final String body = Preconditions.checkNotNull(resource.getContent());
          return new Supplier<WebPanel>()
          {
              public WebPanel get()
              {
                  final EmbeddedTemplateWebPanel panel = hostContainer.create(EmbeddedTemplateWebPanel.class);
                  panel.setTemplateBody(body);
                  panel.setResourceType(getRequiredResourceType(resource));
                  panel.setPlugin(webPanelModuleDescriptor.getPlugin());
                  return panel;
              }
          };
      }
  
      /**
       * @return the (first) resource with attribute <code>name="view"</code>
       * @throws PluginParseException when no resources with name "view" were
       *             found.
       */
      private ResourceDescriptor getRequiredViewResource() throws PluginParseException
      {
          final Iterable<ResourceDescriptor> resources = Iterables.filter(webPanelModuleDescriptor.getResourceDescriptors(), new Predicate<ResourceDescriptor>()
          {
              public boolean apply(final ResourceDescriptor input)
             {
                 return "view".equals(input.getName());
             }
         });
         final Iterator<ResourceDescriptor> iterator = resources.iterator();
         if (!iterator.hasNext())
         {
             throw new PluginParseException("Required resource with name 'view' does not exist.");
         }
         else
         {
             return iterator.next();
         }
     }
 
     private String getRequiredResourceType(final ResourceDescriptor resource)
     {
         final String type = resource.getType();
         if (StringUtils.isEmpty(type))
         {
             throw new PluginParseException("Resource element is lacking a type attribute.");
         }
         else
         {
             return type;
         }
     }
 }