/*

 * Copyright (c) 2016, 2019, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code 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 General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 */

package java.util.random;

import java.util.function.Function;

import java.util.Map;

import java.util.Objects;

import java.util.ServiceLoader;

import java.util.ServiceLoader.Provider;

import java.util.stream.Collectors;

import java.util.stream.Stream;

import java.util.stream.StreamSupport;

/**

 * This is a factory class for generating random number generators of a specific

 * catagory and algorithm.

 */

public class RandomGeneratorFactory<T> {

    /**

     * Instance provider class of random number algorithm.

     */

    private final Provider<T> provider;

    /**

     * Map of provider classes.

     */

    private static Map<String, Provider<RandomGenerator>> providerMap;

    /**

     * Private constructor.

     *

     * @param provider  Provider class to wrap.

     */

    private RandomGeneratorFactory(Provider<T> provider) {

        this.provider = provider;

    }

    /**

     * Returns the provider map, lazily constructing map on first call.

     *

     * @return Map of provider classes.

     */

    private static Map<String, Provider<RandomGenerator>> getProviderMap() {

        if (providerMap == null) {

            synchronized (RandomGeneratorFactory.class) {

                if (providerMap == null) {

                    providerMap =

                        ServiceLoader

                            .load(RandomGenerator.class)

                            .stream()

                            .filter(p -> !p.type().isInterface())

                            .collect(Collectors.toMap(p -> p.type().getSimpleName().toUpperCase(),

                                    Function.identity()));

                }

            }

        }

        return providerMap;

    }

    private static Provider<RandomGenerator> findProvider(String name, Class<? extends RandomGenerator> category)

            throws IllegalArgumentException {

        Map<String, Provider<RandomGenerator>> pm = getProviderMap();

        Provider<RandomGenerator> provider = pm.get(name.toUpperCase());

        if (provider == null || provider.type().isAssignableFrom(category)) {

            throw new IllegalArgumentException(name + " is an unknown random number generator");

        }

        return provider;

    }

    /**

     * Returns a {@link RandomGenerator} that utilizes the {@code name} algorithm.

     *

     * @param name  Name of random number algorithm to use

     * @param category Sub-interface of {@link RandomGenerator} to type check

     * @param <T> Sub-interface of {@link RandomGenerator} to produce

     * @return An instance of {@link RandomGenerator}

     * @throws IllegalArgumentException when either the name or category is null

     */

    static <T> T of(String name, Class<? extends RandomGenerator> category)

            throws IllegalArgumentException {

        @SuppressWarnings("unchecked")

        T uncheckedRandomGenerator = (T)findProvider(name, category).get();

        return uncheckedRandomGenerator;

    }

    /**

     * Returns a {@link RandomGeneratorFactory} that will produce instances

     * of {@link RandomGenerator} that utilizes the {@code name} algorithm.

     *

     * @param name  Name of random number algorithm to use

     * @param category Sub-interface of {@link RandomGenerator} to type check

     * @param <T> Sub-interface of {@link RandomGenerator} to produce

     * @return Factory of {@link RandomGenerator}

     * @throws IllegalArgumentException when either the name or category is null

     */

    static <T> RandomGeneratorFactory<T> factoryOf(String name, Class<? extends RandomGenerator> category)

            throws IllegalArgumentException {

        @SuppressWarnings("unchecked")

        Provider<T> uncheckedProvider = (Provider<T>)findProvider(name, category);

        return new RandomGeneratorFactory<T>(uncheckedProvider);

    }

    /**

     * Create an instance of {@link RandomGenerator}.

     *

     * @return Instance of {@link RandomGenerator}.

     */

    public T create() {

        return provider.get();

    }

}