/*

 * Copyright (c) 2014, 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 jdk.vm.ci.services;

import java.lang.reflect.InvocationTargetException;

import java.lang.reflect.Method;

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() {

    }

    private static int getJavaSpecificationVersion() {

        String value = System.getProperty("java.specification.version");

        if (value.startsWith("1.")) {

            value = value.substring(2);

        }

        return Integer.parseInt(value);

    }

    /**

     * The integer value corresponding to the value of the {@code java.specification.version} system

     * property after any leading {@code "1."} has been stripped.

     */

    public static final int JAVA_SPECIFICATION_VERSION = getJavaSpecificationVersion();

    // Use reflection so that this compiles on Java 8

    private static final Method getModule;

    private static final Method getPackages;

    private static final Method addUses;

    private static final Method isExported;

    private static final Method addExports;

    static {

        if (JAVA_SPECIFICATION_VERSION >= 9) {

            try {

                getModule = Class.class.getMethod("getModule");

                Class<?> moduleClass = getModule.getReturnType();

                getPackages = moduleClass.getMethod("getPackages");

                addUses = moduleClass.getMethod("addUses", Class.class);

                isExported = moduleClass.getMethod("isExported", String.class, moduleClass);

                addExports = moduleClass.getMethod("addExports", String.class, moduleClass);

            } catch (NoSuchMethodException | SecurityException e) {

                throw new InternalError(e);

            }

        } else {

            getModule = null;

            getPackages = null;

            addUses = null;

            isExported = null;

            addExports = null;

        }

    }

    @SuppressWarnings("unchecked")

    static <T> T invoke(Method method, Object receiver, Object... args) {

        try {

            return (T) method.invoke(receiver, args);

        } catch (IllegalAccessException | IllegalArgumentException | InvocationTargetException e) {

            throw new InternalError(e);

        }

    }

    /**

     * Performs any required security checks and dynamic reconfiguration to allow the module of a

     * given class to access the classes in the JVMCI module.

     *

     * Note: This API uses {@link Class} instead of {@code Module} to provide backwards

     * compatibility for JVMCI clients compiled against a JDK release earlier than 9.

     *

     * @param requestor a class requesting access to the JVMCI module for its module

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

     *             {@link JVMCIPermission}

     */

    public static void exportJVMCITo(Class<?> requestor) {

        SecurityManager sm = System.getSecurityManager();

        if (sm != null) {

            sm.checkPermission(new JVMCIPermission());

        }

        if (JAVA_SPECIFICATION_VERSION >= 9) {

            Object jvmci = invoke(getModule, Services.class);

            Object requestorModule = invoke(getModule, requestor);

            if (jvmci != requestorModule) {

                String[] packages = invoke(getPackages, jvmci);

                for (String pkg : packages) {

                    // Export all JVMCI packages dynamically instead

                    // of requiring a long list of --add-exports

                    // options on the JVM command line.

                    boolean exported = invoke(isExported, jvmci, pkg, requestorModule);

                    if (!exported) {

                        invoke(addExports, jvmci, pkg, requestorModule);

                    }

                }

            }

        }

    }

    /**

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

     *

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

     *             {@link JVMCIPermission}

     */

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

        SecurityManager sm = System.getSecurityManager();

        if (sm != null) {

            sm.checkPermission(new JVMCIPermission());

        }

        if (JAVA_SPECIFICATION_VERSION >= 9) {

            Object jvmci = invoke(getModule, Services.class);

            invoke(addUses, jvmci, service);

        }

        // Restrict JVMCI clients to be on the class path or module path

        return ServiceLoader.load(service, ClassLoader.getSystemClassLoader());

    }

    /**

     * 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

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

     *             {@link JVMCIPermission}

     */

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

        SecurityManager sm = System.getSecurityManager();

        if (sm != null) {

            sm.checkPermission(new JVMCIPermission());

        }

        if (JAVA_SPECIFICATION_VERSION >= 9) {

            Object jvmci = invoke(getModule, Services.class);

            invoke(addUses, jvmci, service);

        }

        // Restrict JVMCI clients to be on the class path or module path

        Iterable<S> providers = ServiceLoader.load(service, ClassLoader.getSystemClassLoader());

        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;

    }

}