/*

 * Copyright (c) 1999, 2014, 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

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package com.sun.naming.internal;

import javax.naming.NamingEnumeration;

import java.io.File;

import java.io.FileInputStream;

import java.io.IOException;

import java.io.InputStream;

import java.net.MalformedURLException;

import java.net.URL;

import java.net.URLClassLoader;

import java.security.AccessController;

import java.security.PrivilegedAction;

import java.security.PrivilegedActionException;

import java.security.PrivilegedExceptionAction;

import java.util.*;

/**

 * VersionHelper was used by JNDI to accommodate differences between

 * JDK 1.1.x and the Java 2 platform. As this is no longer necessary

 * since JNDI's inclusion in the platform, this class currently

 * serves as a set of utilities for performing system-level things,

 * such as class-loading and reading system properties.

 *

 * @author Rosanna Lee

 * @author Scott Seligman

 */

public final class VersionHelper {

    private static final VersionHelper helper = new VersionHelper();

    final static String[] PROPS = new String[]{

        javax.naming.Context.INITIAL_CONTEXT_FACTORY,

        javax.naming.Context.OBJECT_FACTORIES,

        javax.naming.Context.URL_PKG_PREFIXES,

        javax.naming.Context.STATE_FACTORIES,

        javax.naming.Context.PROVIDER_URL,

        javax.naming.Context.DNS_URL,

        // The following shouldn't create a runtime dependence on ldap package.

        javax.naming.ldap.LdapContext.CONTROL_FACTORIES

    };

    public final static int INITIAL_CONTEXT_FACTORY = 0;

    public final static int OBJECT_FACTORIES = 1;

    public final static int URL_PKG_PREFIXES = 2;

    public final static int STATE_FACTORIES = 3;

    public final static int PROVIDER_URL = 4;

    public final static int DNS_URL = 5;

    public final static int CONTROL_FACTORIES = 6;

    private VersionHelper() {} // Disallow anyone from creating one of these.

    public static VersionHelper getVersionHelper() {

        return helper;

    }

    public Class<?> loadClass(String className) throws ClassNotFoundException {

        return loadClass(className, getContextClassLoader());

    }

    /**

     * @param className A non-null fully qualified class name.

     * @param codebase  A non-null, space-separated list of URL strings.

     */

    public Class<?> loadClass(String className, String codebase)

            throws ClassNotFoundException, MalformedURLException {

        ClassLoader parent = getContextClassLoader();

        ClassLoader cl =

                URLClassLoader.newInstance(getUrlArray(codebase), parent);

        return loadClass(className, cl);

    }

    /**

     * Package private.

     * <p>

     * This internal method is used with Thread Context Class Loader (TCCL),

     * please don't expose this method as public.

     */

    Class<?> loadClass(String className, ClassLoader cl)

            throws ClassNotFoundException {

        Class<?> cls = Class.forName(className, true, cl);

        return cls;

    }

    /*

     * Returns a JNDI property from the system properties. Returns

     * null if the property is not set, or if there is no permission

     * to read it.

     */

    String getJndiProperty(int i) {

        PrivilegedAction<String> act = () -> {

            try {

                return System.getProperty(PROPS[i]);

            } catch (SecurityException e) {

                return null;

            }

        };

        return AccessController.doPrivileged(act);

    }

    /*

     * Reads each property in PROPS from the system properties, and

     * returns their values -- in order -- in an array.  For each

     * unset property, the corresponding array element is set to null.

     * Returns null if there is no permission to call System.getProperties().

     */

    String[] getJndiProperties() {

        PrivilegedAction<Properties> act = () -> {

            try {

                return System.getProperties();

            } catch (SecurityException e) {

                return null;

            }

        };

        Properties sysProps = AccessController.doPrivileged(act);

        if (sysProps == null) {

            return null;

        }

        String[] jProps = new String[PROPS.length];

        for (int i = 0; i < PROPS.length; i++) {

            jProps[i] = sysProps.getProperty(PROPS[i]);

        }

        return jProps;

    }

    /*

     * Returns the resource of a given name associated with a particular

     * class (never null), or null if none can be found.

     */

    InputStream getResourceAsStream(Class<?> c, String name) {

        return AccessController.doPrivileged(act);

    }

    /*

     * Returns an input stream for a file in <java.home>/conf,

     * or null if it cannot be located or opened.

     *

     * @param filename  The file name, sans directory.

     */

    InputStream getJavaHomeConfStream(String filename) {

        PrivilegedAction<InputStream> act = () -> {

            try {

                String javahome = System.getProperty("java.home");

                if (javahome == null) {

                    return null;

                }

                String pathname = javahome + File.separator +

                        "conf" + File.separator + filename;

                return new FileInputStream(pathname);

            } catch (Exception e) {

                return null;

            }

        };

        return AccessController.doPrivileged(act);

    }

    /*

     * Returns an enumeration (never null) of InputStreams of the

     * resources of a given name associated with a particular class

     * loader.  Null represents the bootstrap class loader in some

     * Java implementations.

     */

    NamingEnumeration<InputStream> getResources(ClassLoader cl,

                                                String name) throws IOException {

        Enumeration<URL> urls;

        PrivilegedExceptionAction<Enumeration<URL>> act = () ->

                (cl == null)

                        ? ClassLoader.getSystemResources(name)

                        : cl.getResources(name);

        try {

            urls = AccessController.doPrivileged(act);

        } catch (PrivilegedActionException e) {

            throw (IOException) e.getException();

        }

        return new InputStreamEnumeration(urls);

    }

    /**

     * Package private.

     * <p>

     * This internal method returns Thread Context Class Loader (TCCL),

     * if null, returns the system Class Loader.

     * <p>

     * Please don't expose this method as public.

     * @throws SecurityException if the class loader is not accessible

     */

    ClassLoader getContextClassLoader() {

        PrivilegedAction<ClassLoader> act = () -> {

            ClassLoader loader = Thread.currentThread().getContextClassLoader();

            if (loader == null) {

                // Don't use bootstrap class loader directly!

                loader = ClassLoader.getSystemClassLoader();

            }

            return loader;

        };

        return AccessController.doPrivileged(act);

    }

    private static URL[] getUrlArray(String codebase)

            throws MalformedURLException {

        // Parse codebase into separate URLs

        StringTokenizer parser = new StringTokenizer(codebase);

        List<String> list = new ArrayList<>();

        while (parser.hasMoreTokens()) {

            list.add(parser.nextToken());

        }

        String[] url = new String[list.size()];

        for (int i = 0; i < url.length; i++) {

            url[i] = list.get(i);

        }

        URL[] urlArray = new URL[url.length];

        for (int i = 0; i < urlArray.length; i++) {

            urlArray[i] = new URL(url[i]);

        }

        return urlArray;

    }

    /**

     * Given an enumeration of URLs, an instance of this class represents

     * an enumeration of their InputStreams.  Each operation on the URL

     * enumeration is performed within a doPrivileged block.

     * This is used to enumerate the resources under a foreign codebase.

     * This class is not MT-safe.

     */

    private class InputStreamEnumeration implements

            NamingEnumeration<InputStream> {

        private final Enumeration<URL> urls;

        private InputStream nextElement;

        InputStreamEnumeration(Enumeration<URL> urls) {

            this.urls = urls;

        }

        /*

         * Returns the next InputStream, or null if there are no more.

         * An InputStream that cannot be opened is skipped.

         */

        private InputStream getNextElement() {

            PrivilegedAction<InputStream> act = () -> {

                while (urls.hasMoreElements()) {

                    try {

                        return urls.nextElement().openStream();

                    } catch (IOException e) {

                        // skip this URL

                    }

                }

                return null;

            };

            return AccessController.doPrivileged(act);

        }

        public boolean hasMore() {

            if (nextElement != null) {

                return true;

            }

            nextElement = getNextElement();

            return (nextElement != null);

        }

        public boolean hasMoreElements() {

            return hasMore();

        }

        public InputStream next() {

            if (hasMore()) {

                InputStream res = nextElement;

                nextElement = null;

                return res;

            } else {

                throw new NoSuchElementException();

            }

        }

        public InputStream nextElement() {

            return next();

        }

        public void close() {

        }

    }

}