/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.commons.math.optimization.linear;

import java.util.Collection;

import org.apache.commons.math.MaxIterationsExceededException;
import org.apache.commons.math.optimization.GoalType;
import org.apache.commons.math.optimization.OptimizationException;
import org.apache.commons.math.optimization.RealPointValuePair;

/**
 * Base class for implementing linear optimizers.
 * <p>
 * This base class handles the boilerplate methods associated to thresholds
 * settings and iterations counters.
 * </p>
 * 
 * @version $Revision$ $Date$
 * @since 2.0
 *
 */
public abstract class AbstractLinearOptimizer implements LinearOptimizer {

	/** Default maximal number of iterations allowed. */
	public static final int DEFAULT_MAX_ITERATIONS = 100;

	/** Maximal number of iterations allowed. */
	private int maxIterations;

	/** Number of iterations already performed. */
	private int iterations;

	/** Linear objective function. */
	protected LinearObjectiveFunction f;

	/** Linear constraints. */
	protected Collection<LinearConstraint> constraints;

	/**
	 * Type of optimization goal: either {@link GoalType#MAXIMIZE} or
	 * {@link GoalType#MINIMIZE}.
	 */
	protected GoalType goalType;

	/** Whether to restrict the variables to non-negative values. */
	protected boolean restrictToNonNegative;

	/**
	 * Simple constructor with default settings.
	 * <p>
	 * The maximal number of evaluation is set to its default value.
	 * </p>
	 */
	protected AbstractLinearOptimizer() {
		setMaxIterations(DEFAULT_MAX_ITERATIONS);
	}

	/** {@inheritDoc} */
	public void setMaxIterations(int maxIterations) {
		this.maxIterations = maxIterations;
	}

	/** {@inheritDoc} */
	public int getMaxIterations() {
		return maxIterations;
	}

	/** {@inheritDoc} */
	public int getIterations() {
		return iterations;
	}

	/**
	 * Increment the iterations counter by 1.
	 * 
	 * @exception OptimizationException
	 *                if the maximal number of iterations is exceeded
	 */
	protected void incrementIterationsCounter() throws OptimizationException {
		if (++iterations > maxIterations) {
			throw new OptimizationException(new MaxIterationsExceededException(maxIterations));
		}
	}

	/** {@inheritDoc} */
	public RealPointValuePair optimize(final LinearObjectiveFunction f, final Collection<LinearConstraint> constraints,
			final GoalType goalType, final boolean restrictToNonNegative) throws OptimizationException {

		// store linear problem characteristics
		this.f = f;
		this.constraints = constraints;
		this.goalType = goalType;
		this.restrictToNonNegative = restrictToNonNegative;

		iterations = 0;

		// solve the problem
		return doOptimize();

	}

	/**
	 * Perform the bulk of optimization algorithm.
	 * 
	 * @return the point/value pair giving the optimal value for objective
	 *         function
	 * @exception OptimizationException
	 *                if no solution fulfilling the constraints can be found in
	 *                the allowed number of iterations
	 */
	abstract protected RealPointValuePair doOptimize() throws OptimizationException;

}