/*

 * Copyright (c) 2016, 2018, 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 static jdk.vm.ci.services.Services.IS_BUILDING_NATIVE_IMAGE;

import static jdk.vm.ci.services.Services.IS_IN_NATIVE_IMAGE;

import java.util.ArrayList;

import java.util.List;

import java.util.ServiceLoader;

/**

 * Service-provider class for the runtime to locate providers of JVMCI services where the latter are

 * not in packages exported by the JVMCI module. As part of instantiating a

 * {@link JVMCIServiceLocator}, all JVMCI packages will be opened to the module defining the class

 * of the instantiated object.

 *

 * While the {@link #getProvider(Class)} method can be used directly, it's usually easier to use

 * {@link #getProviders(Class)}.

 */

public abstract class JVMCIServiceLocator {

    private static Void checkPermission() {

        SecurityManager sm = System.getSecurityManager();

        if (sm != null) {

            sm.checkPermission(new JVMCIPermission());

        }

        return null;

    }

    @SuppressWarnings("unused")

    private JVMCIServiceLocator(Void ignore) {

    }

    /**

     * Creates a capability for accessing JVMCI. Once successfully instantiated, JVMCI opens all its

     * packages to the module defining the type of this object.

     *

     * @throws SecurityException if a security manager has been installed and it denies

     *             {@link JVMCIPermission}

     */

    protected JVMCIServiceLocator() {

        this(checkPermission());

        Services.checkJVMCIEnabled();

        Services.openJVMCITo(getClass().getModule());

    }

    /**

     * Gets the provider of the service defined by {@code service} or {@code null} if this object

     * does not have a provider for {@code service}.

     */

    protected abstract <S> S getProvider(Class<S> service);

    private static volatile List<JVMCIServiceLocator> cachedLocators;

    private static Iterable<JVMCIServiceLocator> getJVMCIServiceLocators() {

        Iterable<JVMCIServiceLocator> result = cachedLocators;

        if (result != null) {

            return result;

        }

        result = ServiceLoader.load(JVMCIServiceLocator.class, ClassLoader.getSystemClassLoader());

        if (IS_BUILDING_NATIVE_IMAGE) {

            ArrayList<JVMCIServiceLocator> l = new ArrayList<>();

            for (JVMCIServiceLocator locator: result) {

                l.add(locator);

            }

            l.trimToSize();

            cachedLocators = l;

            return l;

        }

        return result;

    }

    /**

     * Gets the providers of the service defined by {@code service} by querying the available

     * {@link JVMCIServiceLocator} providers.

     *

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

     *             {@link JVMCIPermission}

     */

    public static <S> List<S> getProviders(Class<S> service) {

        Services.checkJVMCIEnabled();

        SecurityManager sm = System.getSecurityManager();

        if (sm != null) {

            sm.checkPermission(new JVMCIPermission());

        }

        List<S> providers = new ArrayList<>();

        for (JVMCIServiceLocator access : getJVMCIServiceLocators()) {

            S provider = access.getProvider(service);

            if (provider != null) {

                providers.add(provider);

            }

        }

        return providers;

    }

}