/*
 * Copyright 2020 Red Hat, Inc. and/or its affiliates.
 *
 * 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 org.optaplanner.core.config.solver;

import java.util.Random;

import javax.xml.bind.annotation.XmlEnum;

import org.optaplanner.core.api.solver.Solver;
import org.optaplanner.core.impl.heuristic.move.Move;
import org.optaplanner.core.impl.score.director.InnerScoreDirector;

/**
 * The environment mode also allows you to detect common bugs in your implementation.
 * <p>
 * Also, a {@link Solver} has a single {@link Random} instance.
 * Some optimization algorithms use the {@link Random} instance a lot more than others.
 * For example simulated annealing depends highly on random numbers,
 * while tabu search only depends on it to deal with score ties.
 * This environment mode influences the seed of that {@link Random} instance.
 */
@XmlEnum
public enum EnvironmentMode {
    /**
     * This mode turns on all assertions
     * to fail-fast on a bug in a {@link Move} implementation, a constraint, the engine itself or something else
     * at a horrible performance cost.
     * <p>
     * This mode is reproducible (see {@link #REPRODUCIBLE} mode).
     * <p>
     * This mode is intrusive because it calls the {@link InnerScoreDirector#calculateScore()} more frequently
     * than a non assert mode.
     * <p>
     * This mode is horribly slow.
     */
    FULL_ASSERT,
    /**
     * This mode turns on several assertions (but not all of them)
     * to fail-fast on a bug in a {@link Move} implementation, a constraint, the engine itself or something else
     * at an overwhelming performance cost.
     * <p>
     * This mode is reproducible (see {@link #REPRODUCIBLE} mode).
     * <p>
     * This mode is non-intrusive, unlike {@link #FULL_ASSERT} and {@link #FAST_ASSERT}.
     * <p>
     * This mode is horribly slow.
     */
    NON_INTRUSIVE_FULL_ASSERT,
    /**
     * This mode turns on several assertions (but not all of them)
     * to fail-fast on a bug in a {@link Move} implementation, a constraint rule, the engine itself or something else
     * at a reasonable performance cost (in development at least).
     * <p>
     * This mode is reproducible (see {@link #REPRODUCIBLE} mode).
     * <p>
     * This mode is intrusive because it calls the {@link InnerScoreDirector#calculateScore()} more frequently
     * than a non assert mode.
     * <p>
     * This mode is slow.
     */
    FAST_ASSERT,
    /**
     * The reproducible mode is the default mode because it is recommended during development.
     * In this mode, 2 runs on the same computer will execute the same code in the same order.
     * They will also yield the same result, except if they use a time based termination
     * and they have a sufficiently large difference in allocated CPU time.
     * This allows you to benchmark new optimizations (such as a new {@link Move} implementation) fairly
     * and reproduce bugs in your code reliably.
     * <p>
     * Warning: some code can disrupt reproducibility regardless of this mode. See the reference manual for more info.
     * <p>
     * In practice, this mode uses the default random seed,
     * and it also disables certain concurrency optimizations (such as work stealing).
     */
    REPRODUCIBLE,
    /**
     * The non reproducible mode is equally fast or slightly faster than {@link #REPRODUCIBLE}.
     * <p>
     * The random seed is different on every run, which makes it more robust against an unlucky random seed.
     * An unlucky random seed gives a bad result on a certain data set with a certain solver configuration.
     * Note that in most use cases the impact of the random seed is relatively low on the result.
     * An occasional bad result is far more likely to be caused by another issue (such as a score trap).
     * <p>
     * In multithreaded scenarios, this mode allows the use of work stealing and other non deterministic speed tricks.
     */
    NON_REPRODUCIBLE;

    public boolean isAsserted() {
        switch (this) {
            case FULL_ASSERT:
            case NON_INTRUSIVE_FULL_ASSERT:
            case FAST_ASSERT:
                return true;
            case REPRODUCIBLE:
            case NON_REPRODUCIBLE:
                return false;
            default:
                throw new IllegalStateException("The environmentMode (" + this + ") is not implemented.");
        }
    }

    public boolean isNonIntrusiveFullAsserted() {
        switch (this) {
            case FULL_ASSERT:
            case NON_INTRUSIVE_FULL_ASSERT:
                return true;
            case FAST_ASSERT:
            case REPRODUCIBLE:
            case NON_REPRODUCIBLE:
                return false;
            default:
                throw new IllegalStateException("The environmentMode (" + this + ") is not implemented.");
        }
    }

    public boolean isIntrusiveFastAsserted() {
        switch (this) {
            case FULL_ASSERT:
            case FAST_ASSERT:
                return true;
            case NON_INTRUSIVE_FULL_ASSERT:
            case REPRODUCIBLE:
            case NON_REPRODUCIBLE:
                return false;
            default:
                throw new IllegalStateException("The environmentMode (" + this + ") is not implemented.");
        }
    }

    public boolean isReproducible() {
        switch (this) {
            case FULL_ASSERT:
            case NON_INTRUSIVE_FULL_ASSERT:
            case FAST_ASSERT:
            case REPRODUCIBLE:
                return true;
            case NON_REPRODUCIBLE:
                return false;
            default:
                throw new IllegalStateException("The environmentMode (" + this + ") is not implemented.");
        }
    }

}
