/* ConditionImpl.java

	Purpose:
		
	Description:
		
	History:
		Thu Jun  2 22:41:20     2005, Created by tomyeh

Copyright (C) 2005 Potix Corporation. All Rights Reserved.

{{IS_RIGHT
	This program is distributed under LGPL Version 2.1 in the hope that
	it will be useful, but WITHOUT ANY WARRANTY.
}}IS_RIGHT
*/
package org.zkoss.zk.ui.util;

import org.zkoss.zk.ui.Component;
import org.zkoss.zk.ui.Page;
import org.zkoss.zk.xel.Evaluator;
import org.zkoss.zk.xel.ExValue;

/**
 * An utility to simplify the implementation of {@link Condition}.
 * Note: it doesn't implement {@link Condition}.
 *
 * @author tomyeh
 */
public class ConditionImpl implements java.io.Serializable {
	private static final long serialVersionUID = 20060622L;

	private ExValue _if;
	private ExValue _unless;

	/** Returns an instance of Condition, or null if both ifc and unless
	 * are empty.
	 * In other words, it is useful if you use null or empty to denote true.
	 */
	public static ConditionImpl getInstance(String ifc, String unless) {
		if ((ifc == null || ifc.length() == 0) && (unless == null || unless.length() == 0))
			return null;
		return new ConditionImpl(ifc, unless);
	}

	/** Construct.
	 * In most cases, use {@link #getInstance} instead of this constructor.
	 */
	public ConditionImpl(String ifc, String unless) {
		setIf(ifc);
		setUnless(unless);
	}

	/** Sets the if condition.
	 * @see #isEffective
	 * @param cond the condition.
	 * Note: If null (not specified), it is considered effective.
	 */
	public void setIf(String cond) {
		_if = cond != null && cond.length() > 0 ? new ExValue(cond, Boolean.TYPE) : null;
	}

	/** Sets the unless condition.
	 * @see #isEffective
	 * @param cond the condition.
	 * Note: If null (not specified), it is considered ineffective.
	 */
	public void setUnless(String cond) {
		_unless = cond != null && cond.length() > 0 ? new ExValue(cond, Boolean.TYPE) : null;
	}

	/** Used to evaluate whether it is effective.
	 *
	 * @param eval the evaluator to evaluate this condition
	 * @param comp used as the self variable. Ignored if null.
	 * @since 3.0.0
	 */
	public boolean isEffective(Evaluator eval, Component comp) {
		return (_if == null || ((Boolean) _if.getValue(eval, comp)).booleanValue())
				&& (_unless == null || !((Boolean) _unless.getValue(eval, comp)).booleanValue());
	}

	/** Used to evaluate whether it is effective.
	 *
	 * @param eval the evaluator to evaluate this condition
	 * @param page used as the self variable. Ignored if null.
	 * @since 3.0.0
	 */
	public boolean isEffective(Evaluator eval, Page page) {
		return (_if == null || ((Boolean) _if.getValue(eval, page)).booleanValue())
				&& (_unless == null || !((Boolean) _unless.getValue(eval, page)).booleanValue());
	}
}