/*

 * Copyright (c) 2004, 2013, 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.xml.xpath;

import java.io.File;

import java.lang.reflect.Method;

import java.lang.reflect.Modifier;

import java.net.URL;

import java.security.AccessControlContext;

import java.security.AccessController;

import java.security.PrivilegedAction;

import java.util.Properties;

import java.util.ServiceConfigurationError;

import java.util.ServiceLoader;

/**

 * Implementation of {@link XPathFactory#newInstance(String)}.

 *

 * @author <a href="Kohsuke.Kawaguchi@Sun.com">Kohsuke Kawaguchi</a>

 * @since 1.5

 */

class XPathFactoryFinder  {

    private static final String DEFAULT_PACKAGE = "com.sun.org.apache.xpath.internal";

    private static final SecuritySupport ss = new SecuritySupport() ;

    /** debug support code. */

    private static boolean debug = false;

    static {

        // Use try/catch block to support applets

        try {

            debug = ss.getSystemProperty("jaxp.debug") != null;

        } catch (Exception unused) {

            debug = false;

        }

    }

    /**

     * <p>Cache properties for performance.</p>

     */

    private static final Properties cacheProps = new Properties();

    /**

     * <p>First time requires initialization overhead.</p>

     */

    private volatile static boolean firstTime = true;

    /**

     * <p>Conditional debug printing.</p>

     *

     * @param msg to print

     */

    private static void debugPrintln(String msg) {

        if (debug) {

            System.err.println("JAXP: " + msg);

        }

    }

    /**

     * <p><code>ClassLoader</code> to use to find <code>XPathFactory</code>.</p>

     */

    private final ClassLoader classLoader;

    /**

     * <p>Constructor that specifies <code>ClassLoader</code> to use

     * to find <code>XPathFactory</code>.</p>

     *

     * @param loader

     *      to be used to load resource and {@link XPathFactory}

     *      implementations during the resolution process.

     *      If this parameter is null, the default system class loader

     *      will be used.

     */

    public XPathFactoryFinder(ClassLoader loader) {

        this.classLoader = loader;

        if( debug ) {

            debugDisplayClassLoader();

        }

    }

    private void debugDisplayClassLoader() {

        try {

            if( classLoader == ss.getContextClassLoader() ) {

                debugPrintln("using thread context class loader ("+classLoader+") for search");

                return;

            }

        } catch( Throwable unused ) {

             // getContextClassLoader() undefined in JDK1.1

        }

        if( classLoader==ClassLoader.getSystemClassLoader() ) {

            debugPrintln("using system class loader ("+classLoader+") for search");

            return;

        }

        debugPrintln("using class loader ("+classLoader+") for search");

    }

    /**

     * <p>Creates a new {@link XPathFactory} object for the specified

     * object model.</p>

     *

     * @param uri

     *       Identifies the underlying object model.

     *

     * @return <code>null</code> if the callee fails to create one.

     *

     * @throws NullPointerException

     *      If the parameter is null.

     */

    public XPathFactory newFactory(String uri) throws XPathFactoryConfigurationException {

        if (uri == null) {

            throw new NullPointerException();

        }

        XPathFactory f = _newFactory(uri);

        if (f != null) {

            debugPrintln("factory '" + f.getClass().getName() + "' was found for " + uri);

        } else {

            debugPrintln("unable to find a factory for " + uri);

        }

        return f;

    }

    /**

     * <p>Lookup a {@link XPathFactory} for the given object model.</p>

     *

     * @param uri identifies the object model.

     *

     * @return {@link XPathFactory} for the given object model.

     */

    private XPathFactory _newFactory(String uri) throws XPathFactoryConfigurationException {

        XPathFactory xpathFactory = null;

        String propertyName = SERVICE_CLASS.getName() + ":" + uri;

        // system property look up

        try {

            debugPrintln("Looking up system property '"+propertyName+"'" );

            String r = ss.getSystemProperty(propertyName);

            if(r!=null) {

                debugPrintln("The value is '"+r+"'");

                xpathFactory = createInstance(r, true);

                if (xpathFactory != null) {

                    return xpathFactory;

                }

            } else

                debugPrintln("The property is undefined.");

        } catch( Throwable t ) {

            if( debug ) {

                debugPrintln("failed to look up system property '"+propertyName+"'" );

                t.printStackTrace();

            }

        }

        String javah = ss.getSystemProperty( "java.home" );

        String configFile = javah + File.separator +

        "lib" + File.separator + "jaxp.properties";

        // try to read from $java.home/lib/jaxp.properties

        try {

            if(firstTime){

                synchronized(cacheProps){

                    if(firstTime){

                        File f=new File( configFile );

                        firstTime = false;

                        if(ss.doesFileExist(f)){

                            debugPrintln("Read properties file " + f);

                            cacheProps.load(ss.getFileInputStream(f));

                        }

                    }

                }

            }

            final String factoryClassName = cacheProps.getProperty(propertyName);

            debugPrintln("found " + factoryClassName + " in $java.home/jaxp.properties");

            if (factoryClassName != null) {

                xpathFactory = createInstance(factoryClassName, true);

                if(xpathFactory != null){

                    return xpathFactory;

                }

            }

        } catch (Exception ex) {

            if (debug) {

                ex.printStackTrace();

            }

        }

        // Try with ServiceLoader

        assert xpathFactory == null;

        xpathFactory = findServiceProvider(uri);

        // The following assertion should always be true.

        // Uncomment it, recompile, and run with -ea in case of doubts:

        // assert xpathFactory == null || xpathFactory.isObjectModelSupported(uri);

        if (xpathFactory != null) {

            return xpathFactory;

        }

        // platform default

        if(uri.equals(XPathFactory.DEFAULT_OBJECT_MODEL_URI)) {

            debugPrintln("attempting to use the platform default W3C DOM XPath lib");

            return createInstance("com.sun.org.apache.xpath.internal.jaxp.XPathFactoryImpl", true);

        }

        debugPrintln("all things were tried, but none was found. bailing out.");

        return null;

    }

    /** <p>Create class using appropriate ClassLoader.</p>

     *

     * @param className Name of class to create.

     * @return Created class or <code>null</code>.

     */

    private Class<?> createClass(String className) {

        Class clazz;

        // make sure we have access to restricted packages

        boolean internal = false;

        if (System.getSecurityManager() != null) {

            if (className != null && className.startsWith(DEFAULT_PACKAGE)) {

                internal = true;

            }

        }

        // use approprite ClassLoader

        try {

            if (classLoader != null && !internal) {

                    clazz = Class.forName(className, false, classLoader);

            } else {

                    clazz = Class.forName(className);

            }

        } catch (Throwable t) {

            if(debug) {

                t.printStackTrace();

            }

            return null;

        }

        return clazz;

    }

    /**

     * <p>Creates an instance of the specified and returns it.</p>

     *

     * @param className

     *      fully qualified class name to be instantiated.

     *

     * @return null

     *      if it fails. Error messages will be printed by this method.

     */

    XPathFactory createInstance( String className )

            throws XPathFactoryConfigurationException

    {

        return createInstance( className, false );

    }

    XPathFactory createInstance( String className, boolean useServicesMechanism  )

            throws XPathFactoryConfigurationException

    {

        XPathFactory xPathFactory = null;

        debugPrintln("createInstance(" + className + ")");

        // get Class from className

        Class<?> clazz = createClass(className);

        if (clazz == null) {

            debugPrintln("failed to getClass(" + className + ")");

            return null;

        }

        debugPrintln("loaded " + className + " from " + which(clazz));

        // instantiate Class as a XPathFactory

        try {

            if (!useServicesMechanism) {

                xPathFactory = newInstanceNoServiceLoader(clazz);

            }

            if (xPathFactory == null) {

                xPathFactory = (XPathFactory) clazz.newInstance();

            }

        } catch (ClassCastException classCastException) {

                debugPrintln("could not instantiate " + clazz.getName());

                if (debug) {

                        classCastException.printStackTrace();

                }

                return null;

        } catch (IllegalAccessException illegalAccessException) {

                debugPrintln("could not instantiate " + clazz.getName());

                if (debug) {

                        illegalAccessException.printStackTrace();

                }

                return null;

        } catch (InstantiationException instantiationException) {

                debugPrintln("could not instantiate " + clazz.getName());

                if (debug) {

                        instantiationException.printStackTrace();

                }

                return null;

        }

        return xPathFactory;

    }

    /**

     * Try to construct using newXPathFactoryNoServiceLoader

     *   method if available.

     */

    private static XPathFactory newInstanceNoServiceLoader(

         Class<?> providerClass

    ) throws XPathFactoryConfigurationException {

        // Retain maximum compatibility if no security manager.

        if (System.getSecurityManager() == null) {

            return null;

        }

        try {

            Method creationMethod =

                    providerClass.getDeclaredMethod(

                        "newXPathFactoryNoServiceLoader"

                    );

            final int modifiers = creationMethod.getModifiers();

            // Do not call "newXPathFactoryNoServiceLoader" if it's

            // not public static.

            if (!Modifier.isStatic(modifiers) || !Modifier.isPublic(modifiers)) {

                return null;

            }

            // Only calls "newXPathFactoryNoServiceLoader" if it's

            // declared to return an instance of XPathFactory.

            final Class<?> returnType = creationMethod.getReturnType();

            if (SERVICE_CLASS.isAssignableFrom(returnType)) {

                return SERVICE_CLASS.cast(creationMethod.invoke(null, (Object[])null));

            } else {

                // Should not happen since

                // XPathFactoryImpl.newXPathFactoryNoServiceLoader is

                // declared to return XPathFactory.

                throw new ClassCastException(returnType

                            + " cannot be cast to " + SERVICE_CLASS);

            }

        } catch (ClassCastException e) {

            throw new XPathFactoryConfigurationException(e);

        } catch (NoSuchMethodException exc) {

            return null;

        } catch (Exception exc) {

            return null;

        }

    }

    // Call isObjectModelSupportedBy with initial context.

    private boolean isObjectModelSupportedBy(final XPathFactory factory,

            final String objectModel,

            AccessControlContext acc) {

        return AccessController.doPrivileged(new PrivilegedAction<Boolean>() {

                    public Boolean run() {

                        return factory.isObjectModelSupported(objectModel);

                    }

                }, acc);

    }

    /**

     * Finds a service provider subclass of XPathFactory that supports the

     * given object model using the ServiceLoader.

     *

     * @param objectModel URI of object model to support.

     * @return An XPathFactory supporting the specified object model, or null

     *         if none is found.

     * @throws XPathFactoryConfigurationException if a configuration error is found.

     */

    private XPathFactory findServiceProvider(final String objectModel)

            throws XPathFactoryConfigurationException {

        assert objectModel != null;

        // store current context.

        final AccessControlContext acc = AccessController.getContext();

        try {

            return AccessController.doPrivileged(new PrivilegedAction<XPathFactory>() {

                public XPathFactory run() {

                    final ServiceLoader<XPathFactory> loader =

                            ServiceLoader.load(SERVICE_CLASS);

                    for (XPathFactory factory : loader) {

                        // restore initial context to call

                        // factory.isObjectModelSupportedBy

                        if (isObjectModelSupportedBy(factory, objectModel, acc)) {

                            return factory;

                        }

                    }

                    return null; // no factory found.

                }

            });

        } catch (ServiceConfigurationError error) {

            throw new XPathFactoryConfigurationException(error);

        }

    }

    private static final Class<XPathFactory> SERVICE_CLASS = XPathFactory.class;

    private static String which( Class clazz ) {

        return which( clazz.getName(), clazz.getClassLoader() );

    }

    /**

     * <p>Search the specified classloader for the given classname.</p>

     *

     * @param classname the fully qualified name of the class to search for

     * @param loader the classloader to search

     *

     * @return the source location of the resource, or null if it wasn't found

     */

    private static String which(String classname, ClassLoader loader) {

        String classnameAsResource = classname.replace('.', '/') + ".class";

        if( loader==null )  loader = ClassLoader.getSystemClassLoader();

        //URL it = loader.getResource(classnameAsResource);

        URL it = ss.getResourceAsURL(loader, classnameAsResource);

        if (it != null) {

            return it.toString();

        } else {

            return null;

        }

    }

}