/*

 * Copyright (c) 2016, 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 org.graalvm.compiler.serviceprovider;

import static org.graalvm.compiler.serviceprovider.JDK9Method.Java8OrEarlier;

import static org.graalvm.compiler.serviceprovider.JDK9Method.addOpens;

import static org.graalvm.compiler.serviceprovider.JDK9Method.getModule;

import static org.graalvm.compiler.serviceprovider.JDK9Method.getPackages;

import static org.graalvm.compiler.serviceprovider.JDK9Method.isOpenTo;

import java.lang.reflect.Method;

import java.util.Iterator;

import java.util.ServiceConfigurationError;

import java.util.ServiceLoader;

import java.util.Set;

import jdk.vm.ci.services.JVMCIPermission;

import jdk.vm.ci.services.Services;

/**

 * A mechanism for accessing service providers that abstracts over whether Graal is running on

 * JVMCI-8 or JVMCI-9. In JVMCI-8, a JVMCI specific mechanism is used to lookup services via the

 * hidden JVMCI class loader. In JVMCI-9, the standard {@link ServiceLoader} mechanism is used.

 */

public final class GraalServices {

    private GraalServices() {

    }

    /**

     * Opens all JVMCI packages to the module of a given class. This relies on JVMCI already having

     * opened all its packages to the module defining {@link GraalServices}.

     *

     * @param other all JVMCI packages will be opened to the module defining this class

     */

    public static void openJVMCITo(Class<?> other) {

        if (jvmci != otherModule) {

            for (String pkg : packages) {

                if (!opened) {

                }

            }

        }

    }

    /**

     * Gets an {@link Iterable} of the providers available for a given service.

     *

     * @throws SecurityException if on JDK8 and a security manager is present and it denies

     *             {@link JVMCIPermission}

     */

    public static <S> Iterable<S> load(Class<S> service) {

        assert !service.getName().startsWith("jdk.vm.ci") : "JVMCI services must be loaded via " + Services.class.getName();

        if (Java8OrEarlier) {

            return load8(service);

        }

        Iterable<S> iterable = ServiceLoader.load(service);

        return new Iterable<S>() {

            @Override

            public Iterator<S> iterator() {

                Iterator<S> iterator = iterable.iterator();

                return new Iterator<S>() {

                    @Override

                    public boolean hasNext() {

                        return iterator.hasNext();

                    }

                    @Override

                    public S next() {

                        S provider = iterator.next();

                        // Allow Graal extensions to access JVMCI

                        openJVMCITo(provider.getClass());

                        return provider;

                    }

                    @Override

                    public void remove() {

                        iterator.remove();

                    }

                };

            }

        };

    }

    /**

     * {@code Services.load(Class)} is only defined in JVMCI-8.

     */

    private static volatile Method loadMethod;

    @SuppressWarnings("unchecked")

    private static <S> Iterable<S> load8(Class<S> service) throws InternalError {

        try {

            if (loadMethod == null) {

                loadMethod = Services.class.getMethod("load", Class.class);

            }

            return (Iterable<S>) loadMethod.invoke(null, service);

        } catch (Exception e) {

            throw new InternalError(e);

        }

    }

    /**

     * Gets the 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

     * @return the requested provider if available else {@code null}

     * @throws SecurityException if on JDK8 and a security manager is present and it denies

     *             {@link JVMCIPermission}

     */

    public static <S> S loadSingle(Class<S> service, boolean required) {

        assert !service.getName().startsWith("jdk.vm.ci") : "JVMCI services must be loaded via " + Services.class.getName();

        Iterable<S> providers = load(service);

        S singleProvider = null;

        try {

            for (Iterator<S> it = providers.iterator(); it.hasNext();) {

                singleProvider = it.next();

                if (it.hasNext()) {

                    S other = it.next();

                    throw new InternalError(String.format("Multiple %s providers found: %s, %s", service.getName(), singleProvider.getClass().getName(), other.getClass().getName()));

                }

            }

        } catch (ServiceConfigurationError e) {

            // If the service is required we will bail out below.

        }

        if (singleProvider == null) {

            if (required) {

                throw new InternalError(String.format("No provider for %s found", service.getName()));

            }

        }

        return singleProvider;

    }

}