// Copyright 2009 The Apache Software Foundation

 //

 // Licensed 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.tapestry5.corelib.base;

 import org.apache.tapestry5.BindingConstants;

 import org.apache.tapestry5.Block;

 import org.apache.tapestry5.ComponentResources;

 import org.apache.tapestry5.MarkupWriter;

 import org.apache.tapestry5.annotations.Parameter;

 import org.apache.tapestry5.annotations.SupportsInformalParameters;

 import org.apache.tapestry5.ioc.annotations.Inject;

 /**

  * Base class for {@link org.apache.tapestry5.corelib.components.If} and {@link org.apache.tapestry5.corelib.components.Unless}.

  * Will render its body or the block from its else parameter.  If it renders anything and it has an element name, then

  * it renders the element and its informal parameters.

  */

 @SupportsInformalParameters

 public abstract class AbstractConditional

 {

     @Inject

     private ComponentResources resources;

     /**

      * Performs the test via the parameters; return true to render the body of the component, false to render the else

      * block (or nothing).

      *

      * @return true to render body

      */

     protected abstract boolean test();

     /**

      * An alternate {@link org.apache.tapestry5.Block} to render if {@link #test()} is false. The default, null, means

      * render nothing in that situation.

      */

     @Parameter(name = "else", defaultPrefix = BindingConstants.LITERAL)

     private Block elseBlock;

     private boolean renderTag;

     /**

      * Returns null if the {@link #test()} is true, which allows normal rendering (of the body). If the test parameter

      * is false, returns the else parameter (this may also be null).

      */

     Object beginRender(MarkupWriter writer)

     {

         Block toRender = test() ? resources.getBody() : elseBlock;

         String elementName = resources.getElementName();

         renderTag = toRender != null && elementName != null;

         if (renderTag)

         {

             writer.element(elementName);

             resources.renderInformalParameters(writer);

         }

         return toRender;

     }

     /**

      * If {@link #test()} is true, then the body is rendered, otherwise not. The component does not have a template or

      * do any other rendering besides its body.

      */

     boolean beforeRenderBody()

     {

         return false;

     }

     void afterRenderBody(MarkupWriter writer)

     {

         if (renderTag)

             writer.end();

     }

 }