/*
 * 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.math3.optim;

import org.apache.commons.math3.exception.TooManyEvaluationsException;
import org.apache.commons.math3.exception.TooManyIterationsException;
import org.apache.commons.math3.util.Incrementor;

/**
 * Base class for implementing optimizers. It contains the boiler-plate code for counting the number
 * of evaluations of the objective function and the number of iterations of the algorithm, and
 * storing the convergence checker. <em>It is not a "user" class.</em>
 *
 * @param <PAIR> Type of the point/value pair returned by the optimization algorithm.
 * @since 3.1
 */
public abstract class BaseOptimizer<PAIR> {
    /** Evaluations counter. */
    protected final Incrementor evaluations;

    /** Iterations counter. */
    protected final Incrementor iterations;

    /** Convergence checker. */
    private final ConvergenceChecker<PAIR> checker;

    /**
     * @param checker Convergence checker.
     */
    protected BaseOptimizer(ConvergenceChecker<PAIR> checker) {
        this(checker, 0, Integer.MAX_VALUE);
    }

    /**
     * @param checker Convergence checker.
     * @param maxEval Maximum number of objective function evaluations.
     * @param maxIter Maximum number of algorithm iterations.
     */
    protected BaseOptimizer(ConvergenceChecker<PAIR> checker, int maxEval, int maxIter) {
        this.checker = checker;

        evaluations = new Incrementor(maxEval, new MaxEvalCallback());
        iterations = new Incrementor(maxIter, new MaxIterCallback());
    }

    /**
     * Gets the maximal number of function evaluations.
     *
     * @return the maximal number of function evaluations.
     */
    public int getMaxEvaluations() {
        return evaluations.getMaximalCount();
    }

    /**
     * Gets the number of evaluations of the objective function. The number of evaluations
     * corresponds to the last call to the {@code optimize} method. It is 0 if the method has not
     * been called yet.
     *
     * @return the number of evaluations of the objective function.
     */
    public int getEvaluations() {
        return evaluations.getCount();
    }

    /**
     * Gets the maximal number of iterations.
     *
     * @return the maximal number of iterations.
     */
    public int getMaxIterations() {
        return iterations.getMaximalCount();
    }

    /**
     * Gets the number of iterations performed by the algorithm. The number iterations corresponds
     * to the last call to the {@code optimize} method. It is 0 if the method has not been called
     * yet.
     *
     * @return the number of evaluations of the objective function.
     */
    public int getIterations() {
        return iterations.getCount();
    }

    /**
     * Gets the convergence checker.
     *
     * @return the object used to check for convergence.
     */
    public ConvergenceChecker<PAIR> getConvergenceChecker() {
        return checker;
    }

    /**
     * Stores data and performs the optimization.
     *
     * <p>The list of parameters is open-ended so that sub-classes can extend it with arguments
     * specific to their concrete implementations.
     *
     * <p>When the method is called multiple times, instance data is overwritten only when actually
     * present in the list of arguments: when not specified, data set in a previous call is retained
     * (and thus is optional in subsequent calls).
     *
     * <p>Important note: Subclasses <em>must</em> override {@link
     * #parseOptimizationData(OptimizationData[])} if they need to register their own options; but
     * then, they <em>must</em> also call {@code super.parseOptimizationData(optData)} within that
     * method.
     *
     * @param optData Optimization data. This method will register the following data:
     *     <ul>
     *       <li>{@link MaxEval}
     *       <li>{@link MaxIter}
     *     </ul>
     *
     * @return a point/value pair that satisfies the convergence criteria.
     * @throws TooManyEvaluationsException if the maximal number of evaluations is exceeded.
     * @throws TooManyIterationsException if the maximal number of iterations is exceeded.
     */
    public PAIR optimize(OptimizationData... optData)
            throws TooManyEvaluationsException, TooManyIterationsException {
        // Parse options.
        parseOptimizationData(optData);

        // Reset counters.
        evaluations.resetCount();
        iterations.resetCount();
        // Perform optimization.
        return doOptimize();
    }

    /**
     * Performs the optimization.
     *
     * @return a point/value pair that satisfies the convergence criteria.
     * @throws TooManyEvaluationsException if the maximal number of evaluations is exceeded.
     * @throws TooManyIterationsException if the maximal number of iterations is exceeded.
     */
    public PAIR optimize() throws TooManyEvaluationsException, TooManyIterationsException {
        // Reset counters.
        evaluations.resetCount();
        iterations.resetCount();
        // Perform optimization.
        return doOptimize();
    }

    /**
     * Performs the bulk of the optimization algorithm.
     *
     * @return the point/value pair giving the optimal value of the objective function.
     */
    protected abstract PAIR doOptimize();

    /**
     * Increment the evaluation count.
     *
     * @throws TooManyEvaluationsException if the allowed evaluations have been exhausted.
     */
    protected void incrementEvaluationCount() throws TooManyEvaluationsException {
        evaluations.incrementCount();
    }

    /**
     * Increment the iteration count.
     *
     * @throws TooManyIterationsException if the allowed iterations have been exhausted.
     */
    protected void incrementIterationCount() throws TooManyIterationsException {
        iterations.incrementCount();
    }

    /**
     * Scans the list of (required and optional) optimization data that characterize the problem.
     *
     * @param optData Optimization data. The following data will be looked for:
     *     <ul>
     *       <li>{@link MaxEval}
     *       <li>{@link MaxIter}
     *     </ul>
     */
    protected void parseOptimizationData(OptimizationData... optData) {
        // The existing values (as set by the previous call) are reused if
        // not provided in the argument list.
        for (OptimizationData data : optData) {
            if (data instanceof MaxEval) {
                evaluations.setMaximalCount(((MaxEval) data).getMaxEval());
                continue;
            }
            if (data instanceof MaxIter) {
                iterations.setMaximalCount(((MaxIter) data).getMaxIter());
                continue;
            }
        }
    }

    /** Defines the action to perform when reaching the maximum number of evaluations. */
    private static class MaxEvalCallback implements Incrementor.MaxCountExceededCallback {
        /**
         * {@inheritDoc}
         *
         * @throws TooManyEvaluationsException
         */
        public void trigger(int max) {
            throw new TooManyEvaluationsException(max);
        }
    }

    /** Defines the action to perform when reaching the maximum number of evaluations. */
    private static class MaxIterCallback implements Incrementor.MaxCountExceededCallback {
        /**
         * {@inheritDoc}
         *
         * @throws TooManyIterationsException
         */
        public void trigger(int max) {
            throw new TooManyIterationsException(max);
        }
    }
}