/*

 * 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.services;

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;

    }

}