/*
 * Copyright (c) Thomas Parker, 2016.
 * 
 * This program 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 2.1 of the License, or (at your option)
 * any later version.
 * 
 * This program 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 this library; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA
 */
package pcgen.cdom.formula;

import java.util.List;

import pcgen.base.formula.base.VariableID;
import pcgen.base.formula.inst.SimpleVariableStore;
import pcgen.base.util.HashMapToList;

/**
 * A MonitorableVariableStore is a WriteableVariableStore that allows
 * VariableListener objects to listen for changes to the variables within this
 * VariableStore.
 */
public class MonitorableVariableStore extends SimpleVariableStore
{

	/**
	 * The listeners, identified by which VariableID they are listening to.
	 */
	private final HashMapToList<VariableID<?>, VariableListener<?>> listenerList =
			new HashMapToList<>();

	/**
	 * Adds a VariableListener for the given VariableID.
	 * 
	 * @param varID
	 *            The VariableID for which the given VariableListener wishes to
	 *            receive VariableChangeEvents
	 * @param listener
	 *            The VariableListener that will listen for changes to the given
	 *            VariableID
	 */
	public <T> void addVariableListener(VariableID<T> varID,
		VariableListener<T> listener)
	{
		listenerList.addToListFor(varID, listener);
	}

	/**
	 * Adds a VariableListener from the given VariableID.
	 * 
	 * @param varID
	 *            The VariableID for which the given VariableListener is to be
	 *            removed from the listener list
	 * @param listener
	 *            The VariableListener to be removed from the listener list for
	 *            the given VariableID
	 */
	public <T> void removeVariableListener(VariableID<T> varID,
		VariableListener<T> listener)
	{
		listenerList.removeFromListFor(varID, listener);
	}

	@Override
	public <T> T put(VariableID<T> varID, T value)
	{
		T old = super.put(varID, value);
		if (!value.equals(old))
		{
			fireVariableChanged(varID, old, value);
		}
		return old;
	}

	/**
	 * Fires a VariableChangeEvent to the VariableListeners subscribed to the
	 * given VariableID.
	 * 
	 * @param varID
	 *            The VariableID indicating which variable changed
	 * @param old
	 *            The previous value of the variable prior to the change
	 * @param value
	 *            The (current and) new value of the variable after the change
	 */
	public <T> void fireVariableChanged(VariableID<T> varID, T old, T value)
	{
		List<VariableListener<?>> listeners = listenerList.getListFor(varID);
		VariableChangeEvent vcEvent = null;
		if (listeners != null)
		{
			for (VariableListener<?> listener : listeners)
			{
				// Lazily create event
				if (vcEvent == null)
				{
					vcEvent = new VariableChangeEvent<>(this, varID, old, value);
				}
				listener.variableChanged(vcEvent);
			}
		}
	}

}