/**********************************************
    * Copyright (C) 2010 Lukas Laag
    * This file is part of lib-gwt-svg.
    * 
    * libgwtsvg is free software: you can redistribute it and/or modify
    * it under the terms of the GNU Lesser General Public License as published by
    * the Free Software Foundation, either version 3 of the License, or
    * (at your option) any later version.
    * 
   * libgwtsvg is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU Lesser General Public License for more details.
   * 
   * You should have received a copy of the GNU Lesser General Public License
   * along with libgwtsvg.  If not, see http://www.gnu.org/licenses/
   **********************************************/
  /*
   * Copyright 2011 Google Inc.
   * 
   * Licensed 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.vectomatic.dom.svg.impl;
  
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.HashMap;
  import java.util.HashSet;
  import java.util.List;
  import java.util.ListIterator;
  import java.util.Map;
  import java.util.Set;
  
  import org.vectomatic.dom.svg.OMElement;
  import org.vectomatic.dom.svg.utils.DOMHelper;
  
  import com.google.gwt.dom.client.Element;
  import com.google.gwt.event.dom.client.DomEvent;
  import com.google.gwt.event.shared.EventBus;
  import com.google.gwt.event.shared.EventHandler;
  import com.google.gwt.event.shared.GwtEvent;
  import com.google.gwt.event.shared.GwtEvent.Type;
  import com.google.gwt.event.shared.HandlerRegistration;
  import com.google.web.bindery.event.shared.Event;
  import com.google.web.bindery.event.shared.UmbrellaException;
  
  /**
   * Implementation of {@link EventBus} which invokes
   * {@link org.vectomatic.dom.svg.utils.DOMHelper#unbindEventListener(Element, String)}
   * on DOM element sources when they no longer have any event registered handlers
   * for the corresponding event type.
   */
  public class DOMEventBus extends EventBus {
  	private interface Command {
  		void execute();
  	}
  
  	private int firingDepth = 0;
  
  	/**
  	 * Add and remove operations received during dispatch.
  	 */
  	private List<Command> deferredDeltas;
  
  	/**
  	 * Map of event type to map of event source to list of their handlers.
  	 */
  	private final Map<Event.Type<?>, Map<Object, List<?>>> map = new HashMap<Event.Type<?>, Map<Object, List<?>>>();
  
  	@Override
  	public <H extends EventHandler> HandlerRegistration addHandler(Type<H> type, H handler) {
  	    return doAdd(type, null, handler);
  	}
  
  	@Override
  	public <H extends EventHandler> HandlerRegistration addHandlerToSource(Type<H> type, Object source, H handler) {
  		if (source == null) {
  			throw new NullPointerException("Cannot add a handler with a null source");
  		}
  		return doAdd(type, source, handler);
  	}
  
  	@Override
  	public void fireEvent(GwtEvent<?> event) {
  	    doFire(event, null);
  	}
  
  	@Override
  	public void fireEventFromSource(GwtEvent<?> event, Object source) {
 		if (source == null) {
 			throw new NullPointerException("Cannot fire from a null source");
 		}
 		doFire(event, source);
 	}
 	
 
 	@Override
 	public <H> HandlerRegistration addHandlerToSource(final Event.Type<H> type,
 			final Object source, final H handler) {
 		if (source == null) {
 			throw new NullPointerException("Cannot add a handler with a null source");
 		}
 		return doAdd(type, source, handler);
 	}
 
 	protected <H> void doRemove(Event.Type<H> type, Object source, H handler) {
 		if (firingDepth > 0) {
 			enqueueRemove(type, source, handler);
 		} else {
 			doRemoveNow(type, source, handler);
 		}
 	}
 
 	protected <H> H getHandler(Event.Type<H> type, int index) {
 		assert index < getHandlerCount(type) : "handlers for "
 				+ type.getClass() + " have size: " + getHandlerCount(type)
 				+ " so do not have a handler at index: " + index;
 
 		List<H> l = getHandlerList(type, null);
 		return l.get(index);
 	}
 
 	protected int getHandlerCount(Event.Type<?> eventKey) {
 		return getHandlerList(eventKey, null).size();
 	}
 
 	protected boolean isEventHandled(Event.Type<?> eventKey) {
 		return map.containsKey(eventKey);
 	}
 
 	private void defer(Command command) {
 		if (deferredDeltas == null) {
 			deferredDeltas = new ArrayList<Command>();
 		}
 		deferredDeltas.add(command);
 	}
 
 	private <H> HandlerRegistration doAdd(final Event.Type<H> type,
 			final Object source, final H handler) {
 		if (type == null) {
 			throw new NullPointerException(
 					"Cannot add a handler with a null type");
 		}
 		if (handler == null) {
 			throw new NullPointerException("Cannot add a null handler");
 		}
 
 		if (firingDepth > 0) {
 			enqueueAdd(type, source, handler);
 		} else {
 			doAddNow(type, source, handler);
 		}
 
 		return new HandlerRegistration() {
 			public void removeHandler() {
 				doRemove(type, source, handler);
 			}
 		};
 	}
 
 	private <H> void doAddNow(Event.Type<H> type, Object source, H handler) {
 		List<H> l = ensureHandlerList(type, source);
 		l.add(handler);
 	}
 
 	private <H> void doFire(Event<H> event, Object source) {
 		if (event == null) {
 			throw new NullPointerException("Cannot fire null event");
 		}
 		try {
 			firingDepth++;
 
 			if (source != null) {
 				setSourceOfEvent(event, source);
 			}
 
 			List<H> handlers = getDispatchList(event.getAssociatedType(), source);
 			Set<Throwable> causes = null;
 
 			ListIterator<H> it = handlers.listIterator();
 			while (it.hasNext()) {
 				H handler = it.next();
 
 				try {
 					dispatchEvent(event, handler);
 				} catch (Throwable e) {
 					if (causes == null) {
 						causes = new HashSet<Throwable>();
 					}
 					causes.add(e);
 				}
 			}
 
 			if (causes != null) {
 				throw new UmbrellaException(causes);
 			}
 		} finally {
 			firingDepth--;
 			if (firingDepth == 0) {
 				handleQueuedAddsAndRemoves();
 			}
 		}
 	}
 
 	private <H> void doRemoveNow(Event.Type<H> type, Object source, H handler) {
 		List<H> l = getHandlerList(type, source);
 
 		boolean removed = l.remove(handler);
 		assert removed : "redundant remove call";
 		if (removed && l.isEmpty()) {
 			if (type instanceof DomEvent.Type && source instanceof OMElement) {
 				Element elem = ((OMElement)source).getElement();
 				String eventName = ((DomEvent.Type)type).getName();
 				DOMHelper.unbindEventListener(elem, eventName);
 			}
 			prune(type, source);
 		}
 	}
 
 	private <H> void enqueueAdd(final Event.Type<H> type, final Object source, final H handler) {
 		defer(new Command() {
 			public void execute() {
 				doAddNow(type, source, handler);
 			}
 		});
 	}
 
 	private <H> void enqueueRemove(final Event.Type<H> type, final Object source, final H handler) {
 		defer(new Command() {
 			public void execute() {
 				doRemoveNow(type, source, handler);
 			}
 		});
 	}
 
 	private <H> List<H> ensureHandlerList(Event.Type<H> type, Object source) {
 		Map<Object, List<?>> sourceMap = map.get(type);
 		if (sourceMap == null) {
 			sourceMap = new HashMap<Object, List<?>>();
 			map.put(type, sourceMap);
 		}
 
 		// safe, we control the puts.
 		@SuppressWarnings("unchecked")
 		List<H> handlers = (List<H>) sourceMap.get(source);
 		if (handlers == null) {
 			handlers = new ArrayList<H>();
 			sourceMap.put(source, handlers);
 		}
 
 		return handlers;
 	}
 
 	private <H> List<H> getDispatchList(Event.Type<H> type, Object source) {
 		List<H> directHandlers = getHandlerList(type, source);
 		if (source == null) {
 			return directHandlers;
 		}
 
 		List<H> globalHandlers = getHandlerList(type, null);
 
 		List<H> rtn = new ArrayList<H>(directHandlers);
 		rtn.addAll(globalHandlers);
 		return rtn;
 	}
 
 	private <H> List<H> getHandlerList(Event.Type<H> type, Object source) {
 		Map<Object, List<?>> sourceMap = map.get(type);
 		if (sourceMap == null) {
 			return Collections.emptyList();
 		}
 
 		// safe, we control the puts.
 		@SuppressWarnings("unchecked")
 		List<H> handlers = (List<H>) sourceMap.get(source);
 		if (handlers == null) {
 			return Collections.emptyList();
 		}
 
 		return handlers;
 	}
 
 	private void handleQueuedAddsAndRemoves() {
 		if (deferredDeltas != null) {
 			try {
 				for (Command c : deferredDeltas) {
 					c.execute();
 				}
 			} finally {
 				deferredDeltas = null;
 			}
 		}
 	}
 
 	private void prune(Event.Type<?> type, Object source) {
 		Map<Object, List<?>> sourceMap = map.get(type);
 
 		List<?> pruned = sourceMap.remove(source);
 
 		assert pruned != null : "Can't prune what wasn't there";
 		assert pruned.isEmpty() : "Pruned unempty list!";
 
 		if (sourceMap.isEmpty()) {
 			map.remove(type);
 		}
 	}
 
 }