/*
 * Units of Measurement Reference Implementation
 * Copyright (c) 2005-2020, Jean-Marie Dautelle, Werner Keil, Otavio Santana.
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions
 *    and the following disclaimer in the documentation and/or other materials provided with the distribution.
 *
 * 3. Neither the name of JSR-385, Indriya nor the names of their contributors may be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
 * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package tech.units.indriya.spi;

import javax.measure.Quantity;
import javax.measure.spi.FormatService;
import javax.measure.spi.QuantityFactory;
import javax.measure.spi.ServiceProvider;
import javax.measure.spi.SystemOfUnitsService;
import javax.measure.spi.UnitFormatService;

import tech.units.indriya.quantity.DefaultQuantityFactory;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.ServiceLoader;
import java.util.concurrent.ConcurrentHashMap;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * This class extends the {@link javax.measure.spi.ServiceProvider} class and hereby uses the JDK {@link java.util.ServiceLoader} to load the required
 * services.
 *
 * @author Werner Keil
 * @version 1.2
 * @since 2.0
 */
public abstract class AbstractServiceProvider extends ServiceProvider implements Comparable<ServiceProvider> {
    
        /**
     * List of services loaded, per class.
     */
    @SuppressWarnings("rawtypes")
    private final Map<Class, List<Object>> servicesLoaded = new ConcurrentHashMap<>();

    private static final Comparator<Object> SERVICE_COMPARATOR = AbstractServiceProvider::compareServices;

    @SuppressWarnings("rawtypes")
    private final Map<Class, QuantityFactory> QUANTITY_FACTORIES = new ConcurrentHashMap<>();

    /**
     * Loads and registers services.
     *
     * @param serviceType
     *            The service type.
     * @param <T>
     *            the concrete type.
     * @return the items found, never {@code null}.
     */
    protected <T> List<T> getServices(final Class<T> serviceType) {
        @SuppressWarnings("unchecked")
        List<T> found = (List<T>) servicesLoaded.get(serviceType);
        if (found != null) {
            return found;
        }
        return loadServices(serviceType);
    }

    protected <T> T getService(Class<T> serviceType) {
        List<T> services = getServices(serviceType);
        if (services.isEmpty()) {
            return null;
        }
        return services.get(0);
    }

    private static int compareServices(Object o1, Object o2) {
        int prio1 = 0;
        int prio2 = 0;
        if (prio1 < prio2) {
            return 1;
        }
        if (prio2 < prio1) {
            return -1;
        }
        return o2.getClass().getSimpleName().compareTo(o1.getClass().getSimpleName());
    }

    /**
     * Loads and registers services.
     *
     * @param serviceType
     *            The service type.
     * @param <T>
     *            the concrete type.
     * @return the items found, never {@code null}.
     */
    private <T> List<T> loadServices(final Class<T> serviceType) {
        List<T> services = new ArrayList<>();
        try {
            for (T t : ServiceLoader.load(serviceType)) {
                services.add(t);
            }
            Collections.sort(services, SERVICE_COMPARATOR);
            @SuppressWarnings("unchecked")
            final List<T> previousServices = (List<T>) servicesLoaded.putIfAbsent(serviceType, (List<Object>) services);
            return Collections.unmodifiableList(previousServices != null ? previousServices : services);
        } catch (Exception e) {
            Logger.getLogger(AbstractServiceProvider.class.getName()).log(Level.WARNING, "Error loading services of type " + serviceType, e);
            Collections.sort(services, SERVICE_COMPARATOR);
            return services;
        }
    }

    @Override
    public int compareTo(ServiceProvider o) {
        return Integer.compare(getPriority(), o.getPriority());
    }

    @Override
    public SystemOfUnitsService getSystemOfUnitsService() {
        return getService(SystemOfUnitsService.class);
    }

    @Override
    public UnitFormatService getUnitFormatService() {
        return getService(UnitFormatService.class);
    }

    @Override
    public FormatService getFormatService() {
        return getService(FormatService.class);
    }

    /**
     * Return a factory for this quantity
     * 
     * @param quantity
     *            the quantity type
     * @return the {@link QuantityFactory}
     * @throws NullPointerException if quantity is {@code null}
     */
    @Override
    @SuppressWarnings("unchecked")
    public final <Q extends Quantity<Q>> QuantityFactory<Q> getQuantityFactory(Class<Q> quantity) {
        Objects.requireNonNull(quantity);
        if (!QUANTITY_FACTORIES.containsKey(quantity)) {
            synchronized (QUANTITY_FACTORIES) {
                QUANTITY_FACTORIES.put(quantity, DefaultQuantityFactory.getInstance(quantity));
            }
        }
        return QUANTITY_FACTORIES.get(quantity);
    }

    @Override
    public abstract String toString();
}