/**
 * Copyright (C) 2010-2017 Gordon Fraser, Andrea Arcuri and EvoSuite
 * contributors
 *
 * This file is part of EvoSuite.
 *
 * EvoSuite 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 3.0 of the License, or
 * (at your option) any later version.
 *
 * EvoSuite 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 Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with EvoSuite. If not, see <http://www.gnu.org/licenses/>.
 */
package org.evosuite.symbolic.solver;

import java.io.IOException;
import java.util.Collection;
import java.util.HashMap;

import org.evosuite.symbolic.expr.Constraint;

public final class SolverCache {

	/**
	 * 
	 * @param solver
	 * @param constraints
	 * @return 
	 */
	public SolverResult solve(Solver solver, Collection<Constraint<?>> constraints) {
		if (hasCachedResult(constraints)) {
			SolverResult cached_solution = getCachedResult();
			return cached_solution;
		}

		SolverResult solverResult;
		try {
			solverResult = solver.solve(constraints);
			if (solverResult.isUNSAT()) {
				addUNSAT(constraints, solverResult);
			} else {
				addSAT(constraints, solverResult);
			}
		} catch (SolverTimeoutException | IOException | SolverParseException | SolverEmptyQueryException
				| SolverErrorException e) {
			solverResult = null;
		}

		return solverResult;

	}

	private static final SolverCache instance = new SolverCache();

	private HashMap<Collection<Constraint<?>>, SolverResult> cached_solver_results = new HashMap<Collection<Constraint<?>>, SolverResult>();
	private int cached_sat_result_count = 0;
	private int cached_unsat_result_count = 0;

	public int getNumberOfUNSATs() {
		return cached_unsat_result_count;
	}

	public int getNumberOfSATs() {
		return cached_sat_result_count;
	}

	private int number_of_accesses = 0;
	private int number_of_hits = 0;

	private SolverCache() {
		/* empty constructor */
	}

	public static SolverCache getInstance() {
		return instance;
	}

	private void addUNSAT(Collection<Constraint<?>> unsat_constraints, SolverResult unsatResult) {
		cached_solver_results.put(unsat_constraints, unsatResult);
		cached_unsat_result_count++;
	}

	private void addSAT(Collection<Constraint<?>> sat_constraints, SolverResult satResult) {
		cached_solver_results.put(sat_constraints, satResult);
		cached_sat_result_count++;
	}

	private boolean valid_cached_solution = false;
	private SolverResult cached_solution = null;

	private boolean hasCachedResult(Collection<Constraint<?>> constraints) {
		number_of_accesses++;

		if (this.cached_solver_results.containsKey(constraints)) {
			valid_cached_solution = true;
			cached_solution = this.cached_solver_results.get(constraints);
			number_of_hits++;
			return true;
		} else {
			valid_cached_solution = false;
			return false;
		}
	}

	public double getHitRate() {
		return (double) this.number_of_hits / (double) this.number_of_accesses;
	}

	/**
	 * If not in cache returns IllegalArgumentException()
	 * 
	 * @param constraints
	 * @return
	 */
	public SolverResult getCachedResult() {

		if (valid_cached_solution == false) {
			throw new IllegalArgumentException("The constraint is not cached!");
		}

		valid_cached_solution = false;
		return this.cached_solution;
	}

}