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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
 * 
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 * modification, are permitted provided that the following conditions
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 * 
 * Redistributions of source code must retain the above copyright
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 * 
 * Redistributions in binary form must reproduce the above copyright
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 * documentation and/or other materials provided with the distribution.
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 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
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package com.sri.ai.grinder.sgdpllt.theory.differencearithmetic;

import static com.sri.ai.expresso.helper.Expressions.INFINITY;
import static com.sri.ai.expresso.helper.Expressions.apply;
import static com.sri.ai.grinder.sgdpllt.library.FunctorConstants.GREATER_THAN;
import static com.sri.ai.grinder.sgdpllt.library.FunctorConstants.LESS_THAN;
import static com.sri.ai.util.Util.iterator;
import static com.sri.ai.util.Util.list;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import com.google.common.annotations.Beta;
import com.sri.ai.expresso.api.Expression;
import com.sri.ai.expresso.api.Type;
import com.sri.ai.expresso.type.IntegerExpressoType;
import com.sri.ai.expresso.type.IntegerInterval;
import com.sri.ai.grinder.sgdpllt.api.Context;
import com.sri.ai.grinder.sgdpllt.api.Theory;
import com.sri.ai.grinder.sgdpllt.library.number.UnaryMinus;
import com.sri.ai.grinder.sgdpllt.theory.numeric.AbstractSingleVariableNumericConstraint;

/**
 * A difference arithmetic single-variable constraint solver.
 *
 * @author braz
 *
 */
@Beta
public class SingleVariableDifferenceArithmeticConstraint extends AbstractSingleVariableNumericConstraint {

	private static final long serialVersionUID = 1L;
	
	public SingleVariableDifferenceArithmeticConstraint(
			Expression variable,
			boolean propagateAllLiteralsWhenVariableIsBound,
			Theory theory) {
		
		super(variable, propagateAllLiteralsWhenVariableIsBound, theory);
	}

	private SingleVariableDifferenceArithmeticConstraint(
			Expression variable,
			ArrayList positiveNormalizedAtoms,
			ArrayList negativeNormalizedAtoms,
			List externalLiterals,
			boolean propagateAllLiteralsWhenVariableIsBound,
			Theory theory) {
		
		super(variable, positiveNormalizedAtoms, negativeNormalizedAtoms, externalLiterals, propagateAllLiteralsWhenVariableIsBound, theory);
	}

	public SingleVariableDifferenceArithmeticConstraint(SingleVariableDifferenceArithmeticConstraint other) {
		super(other);
	}

	@Override
	public SingleVariableDifferenceArithmeticConstraint clone() {
		SingleVariableDifferenceArithmeticConstraint result = new SingleVariableDifferenceArithmeticConstraint(this);
		return result;
	}

	@Override
	protected SingleVariableDifferenceArithmeticConstraint makeSimplification(ArrayList positiveNormalizedAtoms, ArrayList negativeNormalizedAtoms, List externalLiterals) {
		// no special bookkeeping to be retained in simplifications, so we just make a new constraint.
		SingleVariableDifferenceArithmeticConstraint result = new SingleVariableDifferenceArithmeticConstraint(getVariable(), positiveNormalizedAtoms, negativeNormalizedAtoms, externalLiterals, getPropagateAllLiteralsWhenVariableIsBound(), getTheory());
		return result;
	}

	@Override
	protected Expression isolateVariable(Expression atom, Context context) {
		Expression result = DifferenceArithmeticUtil.isolateVariable(getVariable(), atom);
		return result;
	}

	@Override
	/**
	 * Returns empty-range iterator; only implicit literals in these theories
	 * are from bounds, but those result in negative normalized implicit atoms, not positive.
	 */
	protected Iterator getImplicitPositiveNormalizedAtomsIterator(Context context) {
		return iterator();
	}

	List cachedImplicitNegativeNormalizedAtoms;
	@Override
	/**
	 * Returns iterator ranging over implicit normalized atoms representing variable bounds.
	 */
	protected Iterator getImplicitNegativeNormalizedAtomsIterator(Context context) {
		if (cachedImplicitNegativeNormalizedAtoms == null) {
			IntegerInterval interval = getType(context);
			Expression nonStrictLowerBound = interval.getNonStrictLowerBound();
			Expression nonStrictUpperBound = interval.getNonStrictUpperBound();
			cachedImplicitNegativeNormalizedAtoms = list();
			if (!nonStrictLowerBound.equals("unknown") && !nonStrictLowerBound.equals(UnaryMinus.make(INFINITY))) {
				cachedImplicitNegativeNormalizedAtoms.add(apply(LESS_THAN, getVariable(), nonStrictLowerBound));
				// this is the negation of variable >= nonStrictLowerBound. We need to use a negative normalized atom because applications of >= are not considered normalized atoms
			}
			if (!nonStrictUpperBound.equals("unknown") && !nonStrictUpperBound.equals(INFINITY)) {
				cachedImplicitNegativeNormalizedAtoms.add(apply(GREATER_THAN, getVariable(), nonStrictUpperBound));
				// this is the negation of variable <= nonStrictUpperBound. We need to use a negative normalized atom because applications of <= are not considered normalized atoms
			}
		}
		return cachedImplicitNegativeNormalizedAtoms.iterator();
	}

	private IntegerInterval cachedType;
	
	/**
	 * Returns the {@link IntegerInterval} type of the constraint's variable.
	 * @param context
	 * @return
	 */
	public IntegerInterval getType(Context context) {
		if (cachedType == null) {
			Expression variableTypeExpression = getVariableTypeExpression(context);
			Type type = context.getTypeFromTypeExpression(variableTypeExpression);
			if (type instanceof IntegerExpressoType) {
				cachedType = new IntegerInterval("-infinity..infinity");
				// represents Integer as integer interval for uniformity
			}
			else {
				cachedType = (IntegerInterval) type;
			}
		}
		return cachedType ;
	}

	@Override
	public boolean variableIsIntegerTyped() {
		return true;
	}
}