/* Copyright © 2013 Matthew Champion

 All rights reserved.

 Redistribution and use in source and binary forms, with or without

 modification, are permitted provided that the following conditions are met:

  * Redistributions of source code must retain the above copyright

       notice, this list of conditions and the following disclaimer.

  * Redistributions in binary form must reproduce the above copyright

       notice, this list of conditions and the following disclaimer in the

       documentation and/or other materials provided with the distribution.

  * Neither the name of mattunderscore.com nor the

       names of its contributors may be used to endorse or promote products

       derived from this software without specific prior written permission.

 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND

 ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED

 WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE

 DISCLAIMED. IN NO EVENT SHALL MATTHEW CHAMPION BE LIABLE FOR ANY

 DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES

 (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;

 LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND

 ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

 (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS

 SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */

 package com.mattunderscore.filter.contentnegotiation.variantsource;

 import java.util.Collections;

 import java.util.List;

 import com.mattunderscore.filter.contentnegotiation.parser.Variant;

 /**

  * Supports caching variant sources by providing a wrapper around them. This will only call the

  * underlying variant source when {@link #isCacheEmpty()} returns true. The cache starts empty and

  * can be cleared. The variant list this returns is unmodifiable.

  * 

  * @author Matt Champion

  * @since 0.2.0

  */

 public final class CachedVariantSource implements VariantSource

 {

     private final VariantSource source;

     private List<Variant> variants;

     /**

      * Constructs a cached version of the variant source.

      * 

      * @param source

      *            Underlying variant source

      * @since 0.2.0

      */

     public CachedVariantSource(VariantSource source)

     {

         this.source = source;

     }

     @Override

     public List<Variant> getVariants() throws VariantSourceException

     {

         if (isCacheEmpty())

         {

             variants = Collections.unmodifiableList(source.getVariants());

         }

         return variants;

     }

     /**

      * Returns true when there are no cached variants.

      * 

      * @return True when there are no cached variants.

      * @since 0.2.0

      */

     public boolean isCacheEmpty()

     {

         return variants == null;

     }

     /**

      * Clears the cache of any variants. The next call to {@link #getVariants()} will cause the

      * underlying source to provide a new list.

      * 

      * @since 0.2.0

      */

     public void clearCache()

     {

         variants = null;

     }

 }