/*
 * Copyright (c) 2014, 2015, 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.
 *
 * 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
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */
package jdk.vm.ci.service;

import java.util.Formatter;
import java.util.Iterator;
import java.util.ServiceConfigurationError;
import java.util.ServiceLoader;

/**
 * A mechanism for accessing service providers via JVMCI.
 */
public final class Services {

    private Services() {
    }

    /**
     * Gets an {@link Iterable} of the JVMCI providers available for a given service.
     */
    public static <S> Iterable<S> load(Class<S> service) {
        return ServiceLoader.load(service);
    }

    /**
     * Gets the JVMCI provider for a given service for which at most one provider must be available.
     *
     * @param service the service whose provider is being requested
     * @param required specifies if an {@link InternalError} should be thrown if no provider of
     *            {@code service} is available
     */
    public static <S> S loadSingle(Class<S> service, boolean required) {
        Iterable<S> providers = ServiceLoader.load(service);
        S singleProvider = null;
        try {
            for (Iterator<S> it = providers.iterator(); it.hasNext();) {
                singleProvider = it.next();
                if (it.hasNext()) {
                    throw new InternalError(String.format("Multiple %s providers found", service.getName()));
                }
            }
        } catch (ServiceConfigurationError e) {
            // If the service is required we will bail out below.
        }
        if (singleProvider == null && required) {
            String javaHome = System.getProperty("java.home");
            String vmName = System.getProperty("java.vm.name");
            Formatter errorMessage = new Formatter();
            errorMessage.format("The VM does not expose required service %s.%n", service.getName());
            errorMessage.format("Currently used Java home directory is %s.%n", javaHome);
            errorMessage.format("Currently used VM configuration is: %s", vmName);
            throw new UnsupportedOperationException(errorMessage.toString());
        }
        return singleProvider;
    }
}