/*

 * Copyright (c) 2005, 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.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * 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

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 */

package javax.tools;

import java.lang.reflect.InvocationTargetException;

import java.lang.reflect.Method;

import java.security.AccessController;

import java.security.PrivilegedAction;

import java.util.Iterator;

import java.util.ServiceConfigurationError;

import java.util.ServiceLoader;

/**

 * Provides methods for locating tool providers, for example,

 * providers of compilers.  This class complements the

 * functionality of {@link java.util.ServiceLoader}.

 *

 * @author Peter von der Ahé

 * @since 1.6

 */

public class ToolProvider {

    private static final String systemJavaCompilerModule = "jdk.compiler";

    private static final String systemJavaCompilerName   = "com.sun.tools.javac.api.JavacTool";

    /**

     * Returns the Java™ programming language compiler provided

     * with this platform.

     * <p>The file manager returned by calling

     * {@link JavaCompiler#getStandardFileManager getStandardFileManager}

     * on this compiler supports paths provided by any

     * {@linkplain java.nio.file.FileSystem filesystem}.</p>

     * @return the compiler provided with this platform or

     * {@code null} if no compiler is provided

     * @implNote This implementation returns the compiler provided

     * by the {@code jdk.compiler} module if that module is available,

     */

    public static JavaCompiler getSystemJavaCompiler() {

        return getSystemTool(JavaCompiler.class,

                systemJavaCompilerModule, systemJavaCompilerName);

    }

    private static final String systemDocumentationToolModule = "jdk.javadoc";

    private static final String systemDocumentationToolName = "jdk.javadoc.internal.api.JavadocTool";

    /**

     * Returns the Java™ programming language documentation tool provided

     * with this platform.

     * <p>The file manager returned by calling

     * {@link DocumentationTool#getStandardFileManager getStandardFileManager}

     * on this tool supports paths provided by any

     * {@linkplain java.nio.file.FileSystem filesystem}.</p>

     * @return the documentation tool provided with this platform or

     * {@code null} if no documentation tool is provided

     * @implNote This implementation returns the tool provided

     * by the {@code jdk.javadoc} module if that module is available,

     */

    public static DocumentationTool getSystemDocumentationTool() {

        return getSystemTool(DocumentationTool.class,

                systemDocumentationToolModule, systemDocumentationToolName);

    }

    /**

     */

    public static ClassLoader getSystemToolClassLoader() {

    }

    private static final boolean useLegacy;

    static {

        Class<?> c = null;

        try {

            c = Class.forName("java.lang.reflect.Module");

        } catch (Throwable t) {

        }

        useLegacy = (c == null);

    }

    /**

     * Get an instance of a system tool using the service loader.

     * @implNote         By default, this returns the implementation in the specified module.

     *                   For limited backward compatibility, if this code is run on an older version

     *                   of the Java platform that does not support modules, this method will

     *                   try and create an instance of the named class. Note that implies the

     *                   class must be available on the system class path.

     * @param <T>        the interface of the tool

     * @param clazz      the interface of the tool

     * @param moduleName the name of the module containing the desired implementation

     * @param className  the class name of the desired implementation

     * @return the specified implementation of the tool

     */

    private static <T> T getSystemTool(Class<T> clazz, String moduleName, String className) {

        if (useLegacy) {

            try {

                return Class.forName(className, true, ClassLoader.getSystemClassLoader()).

                    asSubclass(clazz).getConstructor().newInstance();

            } catch (ReflectiveOperationException e) {

                throw new Error(e);

            }

        }

        try {

            ServiceLoader<T> sl = ServiceLoader.load(clazz, ClassLoader.getSystemClassLoader());

            for (Iterator<T> iter = sl.iterator(); iter.hasNext(); ) {

                T tool = iter.next();

                if (matches(tool, moduleName))

                    return tool;

            }

        } catch (ServiceConfigurationError e) {

            throw new Error(e);

        }

        return null;

    }

    /**

     * Determine if this is the desired tool instance.

     * @param <T>        the interface of the tool

     * @param tool       the instance of the tool

     * @param moduleName the name of the module containing the desired implementation

     * @return true if and only if the tool matches the specified criteria

     */

    private static <T> boolean matches(T tool, String moduleName) {

        PrivilegedAction<Boolean> pa = () -> {

            // for now, use reflection to implement

            //      return moduleName.equals(tool.getClass().getModule().getName());

            try {

                Method getModuleMethod = Class.class.getDeclaredMethod("getModule");

                Object toolModule = getModuleMethod.invoke(tool.getClass());

                Method getNameMethod = toolModule.getClass().getDeclaredMethod("getName");

                String toolModuleName = (String) getNameMethod.invoke(toolModule);

                return moduleName.equals(toolModuleName);

            } catch (InvocationTargetException | NoSuchMethodException | IllegalAccessException e) {

                return false;

            }

        };

        return AccessController.doPrivileged(pa);

    }

}