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SRI International's AIC Symbolic Manipulation and Evaluation Library (for Java 1.8+)
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/*
 * Copyright (c) 2013, SRI International
 * All rights reserved.
 * Licensed under the The BSD 3-Clause License;
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at:
 * 
 * http://opensource.org/licenses/BSD-3-Clause
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 
 * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 * 
 * Redistributions in binary form must reproduce the above copyright
 * notice, this list of conditions and the following disclaimer in the
 * documentation and/or other materials provided with the distribution.
 * 
 * Neither the name of the aic-expresso nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, 
 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES 
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, 
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package com.sri.ai.grinder.library.number;

import com.google.common.annotations.Beta;
import com.sri.ai.expresso.api.Expression;
import com.sri.ai.expresso.helper.Expressions;
import com.sri.ai.grinder.api.Context;
import com.sri.ai.grinder.library.FunctorConstants;
import com.sri.ai.grinder.sgdpll.simplifier.api.TopSimplifier;
import com.sri.ai.util.math.Rational;

/**
 * @author braz
 *
 */
@Beta
public class Minus implements TopSimplifier {
	public static String FUNCTOR = FunctorConstants.MINUS;
	
	@Override
	public Expression apply(Expression expression, Context context) {
		return simplify(expression);
	}
	
	static public Expression simplify(Expression expression) {
		Expression result = expression;
		
		Expression first = expression.get(0);
		Expression second = expression.get(1);

		if (Expressions.isNumber(first)) {
			Rational firstValue = first.rationalValue();
			if (Expressions.isNumber(second)) {
				Rational secondValue = second.rationalValue();
				result = Expressions.makeSymbol(firstValue.subtract(secondValue));
			} 
			else if (firstValue.isZero()) {
				result = Expressions.apply("-", second);
			}
		} 
		else if (Expressions.isNumber(second) && second.rationalValue().isZero()) {
			result = first;
		}
			
		return result;
	}
	
	public static Expression make(Expression e1, Expression e2) {
		Expression result = Expressions.apply(FUNCTOR, e1, e2);
		result = simplify(result);
		return result;
	}	
}