/*

  * #%L

  * JavaHg parent POM

  * %%

  * Copyright (C) 2011 aragost Trifork ag

  * %%

  * Permission is hereby granted, free of charge, to any person obtaining a copy

  * of this software and associated documentation files (the "Software"), to deal

  * in the Software without restriction, including without limitation the rights

  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell

  * copies of the Software, and to permit persons to whom the Software is

  * furnished to do so, subject to the following conditions:

  * 

  * The above copyright notice and this permission notice shall be included in

  * all copies or substantial portions of the Software.

  * 

  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE

  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER

  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,

  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN

  * THE SOFTWARE.

  * #L%

  */

 package com.aragost.javahg.internals;

 import java.util.Collection;

 import java.util.List;

 import java.util.concurrent.ExecutionException;

 import com.aragost.javahg.MercurialExtension;

 import com.aragost.javahg.log.Logger;

 import com.aragost.javahg.log.LoggerFactory;

 import com.google.common.cache.CacheBuilder;

 import com.google.common.cache.CacheLoader;

 import com.google.common.cache.LoadingCache;

 import com.google.common.collect.Lists;

 /**

  * This is a singleton to manage Mercurial extensions.

  * <p>

  * To use a Mercurial extension with JavaHg there has to be an

  * implementation of {@link MercurialExtension}. Call the process()

  * method with this class to enable an extension.

  */

 public class ExtensionManager {

     private static final Logger LOG = LoggerFactory.getLogger(ExtensionManager.class);

     private static final ExtensionManager INSTANCE = new ExtensionManager();

     private CacheLoader<Class<? extends MercurialExtension>, MercurialExtension> createExtInstance = new CacheLoader<Class<? extends MercurialExtension>, MercurialExtension>() {

         public MercurialExtension load(Class<? extends MercurialExtension> klass) {

             MercurialExtension instance = null;

             try {

                 instance = klass.newInstance();

             } catch (InstantiationException e) {

                 throw Utils.asRuntime(e);

             } catch (IllegalAccessException e) {

                 throw Utils.asRuntime(e);

             }

             try {

                 instance.initialize();

             } catch (Exception e) {

                 LOG.error("Initialization of {} failed", klass);

                 LOG.error("The extension will be used anyway");

                 LOG.error("Exception: {}", e);

             }

             return instance;

         }

     };

     private LoadingCache<Class<? extends MercurialExtension>, MercurialExtension> extInstances = CacheBuilder.newBuilder().build(

             createExtInstance);

     public static ExtensionManager getInstance() {

         return INSTANCE;

     }

     /**

      * Enable the Mercurial extension for the classes.

      * 

      * @param classes

      * @return list of command line flags needed to enable the

      *         extensions

      */

     public List<String> process(Collection<Class<? extends MercurialExtension>> classes) {

         List<String> result = Lists.newArrayList();

         for (Class<? extends MercurialExtension> k : classes) {

             MercurialExtension ext;

             try {

                 ext = this.extInstances.get(k);

             } catch (ExecutionException e) {

                 throw Utils.asRuntime(e);

             }

             String path = ext.getPath();

             if (path == null) {

                 path = "";

             }

             result.add("--config");

             result.add("extensions." + ext.getName() + "=" + path);

         }

         return result;

     }

 }