/*

 * Copyright 2004-2005 Sun Microsystems, Inc.  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.  Sun designates this

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

 * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

 * CA 95054 USA or visit www.sun.com if you need additional information or

 * have any questions.

 */

package javax.xml.xpath;

import java.io.BufferedReader;

import java.io.File;

import java.io.FileInputStream;

import java.io.IOException;

import java.io.InputStream;

import java.io.InputStreamReader;

import java.lang.reflect.Method;

import java.lang.reflect.InvocationTargetException;

import java.net.URL;

import java.util.ArrayList;

import java.util.Enumeration;

import java.util.Iterator;

import java.util.NoSuchElementException;

import java.util.Properties;

/**

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

 *

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

 * @since 1.5

 */

class XPathFactoryFinder  {

    private static 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 _) {

            debug = false;

        }

    }

    /**

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

     */

        private static Properties cacheProps = new Properties();

        /**

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

         */

        private 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, {@link XPathFactory}, and

     *      {@link SchemaFactoryLoader} 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 _ ) {

            ; // 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

     * schema language.</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) {

        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) {

        XPathFactory xpathFactory;

        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);

                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";

        String factoryClassName = null ;

        // 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));

                        }

                    }

                }

            }

            factoryClassName = cacheProps.getProperty(propertyName);

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

            if (factoryClassName != null) {

                xpathFactory = createInstance(factoryClassName);

                if(xpathFactory != null){

                    return xpathFactory;

                }

            }

        } catch (Exception ex) {

            if (debug) {

                ex.printStackTrace();

            }

        }

        // try META-INF/services files

        Iterator sitr = createServiceFileIterator();

        while(sitr.hasNext()) {

            URL resource = (URL)sitr.next();

            debugPrintln("looking into " + resource);

            try {

                xpathFactory = loadFromService(uri, resource.toExternalForm(),

                                                ss.getURLInputStream(resource));

                if (xpathFactory != null) {

                    return xpathFactory;

                }

            } catch(IOException e) {

                if( debug ) {

                    debugPrintln("failed to read "+resource);

                    e.printStackTrace();

                }

            }

        }

        // 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");

        }

        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;

            // use approprite ClassLoader

            try {

                    if (classLoader != null) {

                            clazz = classLoader.loadClass(className);

                    } 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 instanciated.

     *

     * @return null

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

     */

    XPathFactory createInstance( String className ) {

        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 {

                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;

    }

    /**

     * <p>Look up a value in a property file.</p>

     *

     * <p>Set <code>debug</code> to <code>true</code> to trace property evaluation.</p>

     *

     * @param objectModel URI of object model to support.

     * @param inputName Name of <code>InputStream</code>.

     * @param in <code>InputStream</code> of properties.

     *

     * @return <code>XPathFactory</code> as determined by <code>keyName</code> value or <code>null</code> if there was an error.

     *

     * @throws IOException If IO error reading from <code>in</code>.

     */

    private XPathFactory loadFromService(

            String objectModel,

            String inputName,

            InputStream in)

            throws IOException {

            XPathFactory xPathFactory = null;

            final Class[] stringClassArray = {"".getClass()};

            final Object[] objectModelObjectArray = {objectModel};

            final String isObjectModelSupportedMethod = "isObjectModelSupported";

            debugPrintln("Reading " + inputName);

            // read from InputStream until a match is found

            BufferedReader configFile = new BufferedReader(new InputStreamReader(in));

            String line = null;

            while ((line = configFile.readLine()) != null) {

                    // '#' is comment char

                    int comment = line.indexOf("#");

                    switch (comment) {

                            case -1: break; // no comment

                            case 0: line = ""; break; // entire line is a comment

                            default: line = line.substring(0, comment); break; // trim comment

                    }

                    // trim whitespace

                    line = line.trim();

                    // any content left on line?

                    if (line.length() == 0) {

                            continue;

                    }

                    // line content is now the name of the class

                    Class clazz = createClass(line);

                    if (clazz == null) {

                            continue;

                    }

                    // create an instance of the Class

                    try {

                            xPathFactory = (XPathFactory) clazz.newInstance();

                    } catch (ClassCastException classCastExcpetion) {

                            xPathFactory = null;

                            continue;

                    } catch (InstantiationException instantiationException) {

                            xPathFactory = null;

                            continue;

                    } catch (IllegalAccessException illegalAccessException) {

                            xPathFactory = null;

                            continue;

                    }

                    // does this Class support desired object model?

                    try {

                            Method isObjectModelSupported = clazz.getMethod(isObjectModelSupportedMethod, stringClassArray);

                            Boolean supported = (Boolean) isObjectModelSupported.invoke(xPathFactory, objectModelObjectArray);

                            if (supported.booleanValue()) {

                                    break;

                            }

                    } catch (NoSuchMethodException noSuchMethodException) {

                    } catch (IllegalAccessException illegalAccessException) {

                    } catch (InvocationTargetException invocationTargetException) {

                    }

                    xPathFactory = null;

            }

            // clean up

            configFile.close();

            // return new instance of XPathFactory or null

            return xPathFactory;

    }

    /** Iterator that lazily computes one value and returns it. */

    private static abstract class SingleIterator implements Iterator {

        private boolean seen = false;

        public final void remove() { throw new UnsupportedOperationException(); }

        public final boolean hasNext() { return !seen; }

        public final Object next() {

            if(seen)    throw new NoSuchElementException();

            seen = true;

            return value();

        }

        protected abstract Object value();

    }

    /**

     * Looks up a value in a property file

     * while producing all sorts of debug messages.

     *

     * @return null

     *      if there was an error.

     */

    private XPathFactory loadFromProperty( String keyName, String resourceName, InputStream in )

        throws IOException {

        debugPrintln("Reading "+resourceName );

        Properties props = new Properties();

        props.load(in);

        in.close();

        String factoryClassName = props.getProperty(keyName);

        if(factoryClassName != null){

            debugPrintln("found "+keyName+" = " + factoryClassName);

            return createInstance(factoryClassName);

        } else {

            debugPrintln(keyName+" is not in the property file");

            return null;

        }

    }

    /**

     * Returns an {@link Iterator} that enumerates all

     * the META-INF/services files that we care.

     */

    private Iterator createServiceFileIterator() {

        if (classLoader == null) {

            return new SingleIterator() {

                protected Object value() {

                    ClassLoader classLoader = XPathFactoryFinder.class.getClassLoader();

                    return ss.getResourceAsURL(classLoader, SERVICE_ID);

                    //return (ClassLoader.getSystemResource( SERVICE_ID ));

                }

            };

        } else {

            try {

                //final Enumeration e = classLoader.getResources(SERVICE_ID);

                final Enumeration e = ss.getResources(classLoader, SERVICE_ID);

                if(!e.hasMoreElements()) {

                    debugPrintln("no "+SERVICE_ID+" file was found");

                }

                // wrap it into an Iterator.

                return new Iterator() {

                    public void remove() {

                        throw new UnsupportedOperationException();

                    }

                    public boolean hasNext() {

                        return e.hasMoreElements();

                    }

                    public Object next() {

                        return e.nextElement();

                    }

                };

            } catch (IOException e) {

                debugPrintln("failed to enumerate resources "+SERVICE_ID);

                if(debug)   e.printStackTrace();

                return new ArrayList().iterator();  // empty iterator

            }

        }

    }

    private static final Class SERVICE_CLASS = XPathFactory.class;

    private static final String SERVICE_ID = "META-INF/services/" + SERVICE_CLASS.getName();

    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;

        }

    }

}