package com.atlassian.plugin.manager;
   
   import com.atlassian.plugin.ModuleDescriptor;
   import com.atlassian.plugin.PluginAccessor;
   import com.atlassian.plugin.event.PluginEventListener;
   import com.atlassian.plugin.event.PluginEventManager;
   import com.atlassian.plugin.event.events.PluginDisabledEvent;
   import com.atlassian.plugin.tracker.PluginModuleTracker;
   import com.atlassian.plugin.cache.ConcurrentCacheFactory;
  import com.google.common.base.Function;
  import com.google.common.cache.Cache;
  import com.google.common.cache.CacheBuilder;
  import com.google.common.cache.CacheLoader;
  
  import java.util.List;
  
  import static com.atlassian.plugin.tracker.DefaultPluginModuleTracker.create;
  import static com.google.common.base.Preconditions.checkNotNull;
  import static com.google.common.collect.ImmutableList.copyOf;
  
  /**
   * A caching decorator which caches {@link #getEnabledModuleDescriptorsByClass(Class)} on {@link com.atlassian.plugin.PluginAccessor} interface.
   *
   * @since 2.7.0
   */
  public final class EnabledModuleCachingPluginAccessor extends ForwardingPluginAccessor implements PluginAccessor
  {
      private final PluginEventManager pluginEventManager;
      private final Cache<Class<ModuleDescriptor<Object>>, PluginModuleTracker<Object, ModuleDescriptor<Object>>> cache;
  
      public EnabledModuleCachingPluginAccessor(final PluginAccessor delegate, final PluginEventManager pluginEventManager)
      {
          super(delegate);
          this.pluginEventManager = checkNotNull(pluginEventManager);
          this.pluginEventManager.register(this);
          this.cache = new DefaultPluginModuleTrackerCacheFactory().createCache();
      }
  
      public EnabledModuleCachingPluginAccessor(final PluginAccessor delegate, final PluginEventManager pluginEventManager, final ConcurrentCacheFactory<Class<ModuleDescriptor<Object>>, PluginModuleTracker<Object, ModuleDescriptor<Object>>> pluginModuleTrackerCacheFactory)
      {
          super(delegate);
          this.pluginEventManager = checkNotNull(pluginEventManager);
          this.pluginEventManager.register(this);
          this.cache = pluginModuleTrackerCacheFactory.createCache();
      }
  
  
      @Override
      public <D extends ModuleDescriptor<?>> List<D> getEnabledModuleDescriptorsByClass(final Class<D> descriptorClazz)
      {
          return copyOf(descriptors(descriptorClazz));
      }
  
      /**
       * Clears the enabled module cache when any plugin is disabled.  The cache already has weak keys and values, but this
       * ensures old modules are never returned from disabled plugins.
       *
       * @param event The plugin disabled event
       */
      @PluginEventListener
      public void onPluginDisable(PluginDisabledEvent event)
      {
          cache.invalidateAll();
      }
  
      /**
       * Cache implementation.
       */
      @SuppressWarnings("unchecked")
      <D> Iterable<D> descriptors(final Class<D> moduleDescriptorClass)
      {
          PluginModuleTracker<Object, ModuleDescriptor<Object>> tracker = cache.getUnchecked((Class<ModuleDescriptor<Object>>) moduleDescriptorClass);
          return (Iterable<D>) tracker.getModuleDescriptors();
      }
  
      private class DefaultPluginModuleTrackerCacheFactory implements ConcurrentCacheFactory<Class<ModuleDescriptor<Object>>, PluginModuleTracker<Object, ModuleDescriptor<Object>>>
      {
          @Override
          public Cache<Class<ModuleDescriptor<Object>>, PluginModuleTracker<Object, ModuleDescriptor<Object>>> createCache()
          {
              return CacheBuilder.newBuilder().weakKeys().weakValues().build(CacheLoader.from(new PluginModuleTrackerFactory()));
          }
      }
  
      private class PluginModuleTrackerFactory implements Function<Class<ModuleDescriptor<Object>>, PluginModuleTracker<Object, ModuleDescriptor<Object>>>
      {
          public PluginModuleTracker<Object, ModuleDescriptor<Object>> apply(final Class<ModuleDescriptor<Object>> moduleDescriptorClass)
          {
              return create(delegate, pluginEventManager, moduleDescriptorClass);
          }
      }
  }