/*
    * Licensed to the Apache Software Foundation (ASF) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * The ASF licenses this file to You under the Apache License, Version 2.0
    * (the "License"); you may not use this file except in compliance with
    * the License.  You may obtain a copy of the License at
    *
    *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.apache.commons.configuration2.event;
  
  import java.util.Collection;
  import java.util.Collections;
  import java.util.LinkedList;
  import java.util.List;
  
  /**
   * <p>
   * A base class for objects that can generate configuration events.
   * </p>
   * <p>
   * This class implements functionality for managing a set of event listeners that can be notified when an event occurs.
   * It can be extended by configuration classes that support the event mechanism. In this case these classes only need to
   * call the {@code fireEvent()} method when an event is to be delivered to the registered listeners.
   * </p>
   * <p>
   * Adding and removing event listeners can happen concurrently to manipulations on a configuration that cause events.
   * The operations are synchronized.
   * </p>
   * <p>
   * With the {@code detailEvents} property the number of detail events can be controlled. Some methods in configuration
   * classes are implemented in a way that they call other methods that can generate their own events. One example is the
   * {@code setProperty()} method that can be implemented as a combination of {@code clearProperty()} and
   * {@code addProperty()}. With {@code detailEvents} set to <strong>true</strong>, all involved methods will generate events (i.e.
   * listeners will receive property set events, property clear events, and property add events). If this mode is turned
   * off (which is the default), detail events are suppressed, so only property set events will be received. Note that the
   * number of received detail events may differ for different configuration implementations.
   * {@link org.apache.commons.configuration2.BaseHierarchicalConfiguration BaseHierarchicalConfiguration} for instance
   * has a custom implementation of {@code setProperty()}, which does not generate any detail events.
   * </p>
   * <p>
   * In addition to &quot;normal&quot; events, error events are supported. Such events signal an internal problem that
   * occurred during access of properties. They are handled via the regular {@link EventListener} interface, but there are
   * special event types defined by {@link ConfigurationErrorEvent}. The {@code fireError()} method can be used by derived
   * classes to send notifications about errors to registered observers.
   * </p>
   *
   * @since 1.3
   */
  public class BaseEventSource implements EventSource {
  
      /** The list for managing registered event listeners. */
      private EventListenerList eventListeners;
  
      /** A lock object for guarding access to the detail events counter. */
      private final Object lockDetailEventsCount = new Object();
  
      /** A counter for the detail events. */
      private int detailEvents;
  
      /**
       * Creates a new instance of {@code BaseEventSource}.
       */
      public BaseEventSource() {
          initListeners();
      }
  
      @Override
      public <T extends Event> void addEventListener(final EventType<T> eventType, final EventListener<? super T> listener) {
          eventListeners.addEventListener(eventType, listener);
      }
  
      /**
       * Helper method for checking the current counter for detail events. This method checks whether the counter is greater
       * than the passed in limit.
       *
       * @param limit the limit to be compared to
       * @return <strong>true</strong> if the counter is greater than the limit, <strong>false</strong> otherwise
       */
      private boolean checkDetailEvents(final int limit) {
          synchronized (lockDetailEventsCount) {
              return detailEvents > limit;
          }
      }
  
      /**
       * Removes all registered error listeners.
       *
       * @since 1.4
       */
      public void clearErrorListeners() {
          eventListeners.getRegistrationsForSuperType(ConfigurationErrorEvent.ANY).forEach(eventListeners::removeEventListener);
     }
 
     /**
      * Removes all registered event listeners.
      */
     public void clearEventListeners() {
         eventListeners.clear();
     }
 
     /**
      * Overrides the {@code clone()} method to correctly handle so far registered event listeners. This implementation ensures that the clone will have empty
      * event listener lists, i.e. the listeners registered at an {@code BaseEventSource} object will not be copied.
      *
      * @return the cloned object
      * @throws CloneNotSupportedException if the object's class does not support the {@code Cloneable} interface. Subclasses that override the {@code clone}
      *                                    method can also throw this exception to indicate that an instance cannot be cloned.
      * @since 1.4
      */
     @Override
     protected Object clone() throws CloneNotSupportedException {
         final BaseEventSource copy = (BaseEventSource) super.clone();
         copy.initListeners();
         return copy;
     }
 
     /**
      * Copies all event listener registrations maintained by this object to the specified {@code BaseEventSource} object.
      *
      * @param source the target source for the copy operation (must not be <strong>null</strong>)
      * @throws IllegalArgumentException if the target source is <strong>null</strong>
      * @since 2.0
      */
     public void copyEventListeners(final BaseEventSource source) {
         if (source == null) {
             throw new IllegalArgumentException("Target event source must not be null!");
         }
         source.eventListeners.addAll(eventListeners);
     }
 
     /**
      * Creates a {@code ConfigurationErrorEvent} object based on the passed in parameters. This is called by
      * {@code fireError()} if it decides that an event needs to be generated.
      *
      * @param type the event's type
      * @param opType the operation type related to this error
      * @param propName the name of the affected property (can be <strong>null</strong>)
      * @param propValue the value of the affected property (can be <strong>null</strong>)
      * @param ex the {@code Throwable} object that caused this error event
      * @return the event object
      */
     protected ConfigurationErrorEvent createErrorEvent(final EventType<? extends ConfigurationErrorEvent> type, final EventType<?> opType,
         final String propName, final Object propValue, final Throwable ex) {
         return new ConfigurationErrorEvent(this, type, opType, propName, propValue, ex);
     }
 
     /**
      * Creates a {@code ConfigurationEvent} object based on the passed in parameters. This method is called by
      * {@code fireEvent()} if it decides that an event needs to be generated.
      *
      * @param type the event's type
      * @param propName the name of the affected property (can be <strong>null</strong>)
      * @param propValue the value of the affected property (can be <strong>null</strong>)
      * @param before the before update flag
      * @param <T> the type of the event to be created
      * @return the newly created event object
      */
     protected <T extends ConfigurationEvent> ConfigurationEvent createEvent(final EventType<T> type, final String propName, final Object propValue,
         final boolean before) {
         return new ConfigurationEvent(this, type, propName, propValue, before);
     }
 
     /**
      * Creates an error event object and delivers it to all registered error listeners of a matching type.
      *
      * @param eventType the event's type
      * @param operationType the type of the failed operation
      * @param propertyName the name of the affected property (can be <strong>null</strong>)
      * @param propertyValue the value of the affected property (can be <strong>null</strong>)
      * @param cause the {@code Throwable} object that caused this error event
      * @param <T> the event type
      */
     public <T extends ConfigurationErrorEvent> void fireError(final EventType<T> eventType, final EventType<?> operationType, final String propertyName,
         final Object propertyValue, final Throwable cause) {
         final EventListenerList.EventListenerIterator<T> iterator = eventListeners.getEventListenerIterator(eventType);
         if (iterator.hasNext()) {
             final ConfigurationErrorEvent event = createErrorEvent(eventType, operationType, propertyName, propertyValue, cause);
             while (iterator.hasNext()) {
                 iterator.invokeNext(event);
             }
         }
     }
 
     /**
      * Creates an event object and delivers it to all registered event listeners. The method checks first if sending an
      * event is allowed (making use of the {@code detailEvents} property), and if listeners are registered.
      *
      * @param type the event's type
      * @param propName the name of the affected property (can be <strong>null</strong>)
      * @param propValue the value of the affected property (can be <strong>null</strong>)
      * @param before the before update flag
      * @param <T> the type of the event to be fired
      */
     protected <T extends ConfigurationEvent> void fireEvent(final EventType<T> type, final String propName, final Object propValue, final boolean before) {
         if (checkDetailEvents(-1)) {
             final EventListenerList.EventListenerIterator<T> it = eventListeners.getEventListenerIterator(type);
             if (it.hasNext()) {
                 final ConfigurationEvent event = createEvent(type, propName, propValue, before);
                 while (it.hasNext()) {
                     it.invokeNext(event);
                 }
             }
         }
     }
 
     /**
      * Gets a list with all {@code EventListenerRegistrationData} objects currently contained for this event source. This
      * method allows access to all registered event listeners, independent on their type.
      *
      * @return a list with information about all registered event listeners
      */
     public List<EventListenerRegistrationData<?>> getEventListenerRegistrations() {
         return eventListeners.getRegistrations();
     }
 
     /**
      * Gets a collection with all event listeners of the specified event type that are currently registered at this
      * object.
      *
      * @param eventType the event type object
      * @param <T> the event type
      * @return a collection with the event listeners of the specified event type (this collection is a snapshot of the
      *         currently registered listeners; it cannot be manipulated)
      */
     public <T extends Event> Collection<EventListener<? super T>> getEventListeners(final EventType<T> eventType) {
         final List<EventListener<? super T>> result = new LinkedList<>();
         eventListeners.getEventListeners(eventType).forEach(result::add);
         return Collections.unmodifiableCollection(result);
     }
 
     /**
      * Initializes the collections for storing registered event listeners.
      */
     private void initListeners() {
         eventListeners = new EventListenerList();
     }
 
     /**
      * Returns a flag whether detail events are enabled.
      *
      * @return a flag if detail events are generated
      */
     public boolean isDetailEvents() {
         return checkDetailEvents(0);
     }
 
     @Override
     public <T extends Event> boolean removeEventListener(final EventType<T> eventType, final EventListener<? super T> listener) {
         return eventListeners.removeEventListener(eventType, listener);
     }
 
     /**
      * Determines whether detail events should be generated. If enabled, some methods can generate multiple update events.
      * Note that this method records the number of calls, i.e. if for instance {@code setDetailEvents(false)} was called
      * three times, you will have to invoke the method as often to enable the details.
      *
      * @param enable a flag if detail events should be enabled or disabled
      */
     public void setDetailEvents(final boolean enable) {
         synchronized (lockDetailEventsCount) {
             if (enable) {
                 detailEvents++;
             } else {
                 detailEvents--;
             }
         }
     }
 }