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Stochastice Performance Logic is a formalism for capturing performance assumptions. It is, for example, possible to capture assumption that newer version of a function bar is faster than the previous version or that library foobar is faster than library barfoo when rendering antialiased text. The purpose of this framework is to allow evaluation of SPL formulas inside Java applications.

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/*
 * Copyright 2015 Charles University in Prague
 * Copyright 2015 Vojtech Horky
 * 
 * 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 cz.cuni.mff.d3s.spl.formula;

import cz.cuni.mff.d3s.spl.Result;
import cz.cuni.mff.d3s.spl.data.DataSource;
import cz.cuni.mff.d3s.spl.interpretation.ComparisonResult;
import cz.cuni.mff.d3s.spl.interpretation.Interpretation;

import java.util.HashSet;
import java.util.NoSuchElementException;
import java.util.Set;

/** Formula node: actual comparison of a data set with a constant.
*
*/
public class ComparisonWithConst implements Formula {
	/* Internally, we always assume SOURCE OP CONST */
	
	private DataSource source;
	private final String sourceName;
	private final double constant;
	private final Comparison.Operator operator;
	private Interpretation interpretation;
	
	public ComparisonWithConst(String leftVariable, double rightConstant, Comparison.Operator op) {
		sourceName = leftVariable;
		constant = rightConstant;
		operator = op;
	}
	
	@Override
	public void setInterpretation(Interpretation interpretation) {
		this.interpretation = interpretation;
	}

	@Override
	public void bind(String variable, DataSource data) {
		if (sourceName.equals(variable)) {
			source = data;
		} else {
			throw new NoSuchElementException(String.format(
					"Uknown variable %s in comparison.", variable));
		}
	}

	@Override
	public Result evaluate(double significanceLevel) {
		if (source == null) {
			// TODO: throw exception?
			return Result.CANNOT_COMPUTE;
		}
		
		ComparisonResult result = interpretation.compare(source.makeSnapshot(), constant);
		
		ComparisonResult.Relation rel = result.get(significanceLevel);
		
		return Comparison.relationToResult(operator, rel);
	}

	@Override
	public Set getVariables() {
		Set variables = new HashSet<>();
		variables.add(sourceName);
		return variables;
	}

}