package com.atlassian.plugin.eventlistener.descriptors;
   
   import com.atlassian.event.api.EventPublisher;
   import com.atlassian.plugin.Permissions;
   import com.atlassian.plugin.Plugin;
   import com.atlassian.plugin.PluginParseException;
   import com.atlassian.plugin.RequirePermission;
   import com.atlassian.plugin.descriptors.AbstractModuleDescriptor;
   import com.atlassian.plugin.module.ModuleFactory;
  import io.atlassian.util.concurrent.LazyReference;
  import org.dom4j.Element;
  
  import javax.annotation.Nonnull;
  
  @RequirePermission(Permissions.EXECUTE_JAVA)
  public class EventListenerModuleDescriptor extends AbstractModuleDescriptor<Object> {
  
      /**
       * This is fallback property in case if registration by module descriptor somehow failed to work.
       * <p>
       * It will restore old behaviour when registration happening by module.
       */
      static final String FALLBACK_MODE = "EventListenerModuleDescriptor.Fallback.Mode";
  
      private final EventPublisher eventPublisher;
  
      private LazyReference<Object> moduleObj = new LazyReference<Object>() {
          @Override
          protected Object create() throws Exception {
              return moduleFactory.createModule(moduleClassName, EventListenerModuleDescriptor.this);
          }
      };
  
      public EventListenerModuleDescriptor(ModuleFactory moduleFactory, EventPublisher eventPublisher) {
          super(moduleFactory);
          this.eventPublisher = eventPublisher;
      }
  
      @Override
      public void init(@Nonnull Plugin plugin, @Nonnull Element element) throws PluginParseException {
          super.init(plugin, element);
          checkPermissions();
      }
  
      @Override
      public Object getModule() {
          return moduleObj.get();
      }
  
      @Override
      public void enabled() {
          super.enabled();
  
          if (Boolean.getBoolean(FALLBACK_MODE)) {
              eventPublisher.register(getModule());
          } else {
              eventPublisher.register(this);
          }
      }
  
      public void disabled() {
          if (Boolean.getBoolean(FALLBACK_MODE)) {
              eventPublisher.unregister(getModule());
          } else {
              eventPublisher.unregister(this);
          }
  
          super.disabled();
      }
  }