/*
    * #%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;
     }
 
 }