/*

 * Copyright (c) 2005, 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.  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.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,

     * and {@code null} otherwise.

     */

    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,

     * and {@code null} otherwise.

     */

    public static DocumentationTool getSystemDocumentationTool() {

        return getSystemTool(DocumentationTool.class,

                systemDocumentationToolModule, systemDocumentationToolName);

    }

    /**

     * Returns a class loader that may be used to load system tools,

     * or {@code null} if no such special loader is provided.

     * @implSpec This implementation always returns {@code null}.

     * @deprecated This method is subject to removal in a future version of

     * Java SE.

     * Use the {@link java.util.spi.ToolProvider system tool provider} or

     * {@link java.util.ServiceLoader service loader} mechanisms to

     * locate system tools as well as user-installed tools.

     * @return a class loader, or {@code null}

     */

    @Deprecated(since="9")

    public static ClassLoader getSystemToolClassLoader() {

        return 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) {

        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 = () -> {

            Module toolModule = tool.getClass().getModule();

            String toolModuleName = toolModule.getName();

            return toolModuleName.equals(moduleName);

        };

        return AccessController.doPrivileged(pa);

    }

}