/*
 * Copyright (c) 2003, 2005, 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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 * questions.
 */

package javax.xml.validation;

import java.io.File;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.net.URL;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Properties;
import java.util.ServiceConfigurationError;
import java.util.ServiceLoader;

/**
 * Implementation of {@link SchemaFactory#newInstance(String)}.
 *
 * @author <a href="Kohsuke.Kawaguchi@Sun.com">Kohsuke Kawaguchi</a>
 * @version $Revision: 1.8 $, $Date: 2010-11-01 04:36:13 $
 * @since 1.5
 */
class SchemaFactoryFinder {

    private static final String DEFAULT_IMPL_NAME = "com.sun.org.apache.xerces.internal.jaxp.validation.XMLSchemaFactory";
    /**
     * debug support code.
     */
    private static boolean debug = false;
    /**
     * <p> Take care of restrictions imposed by java security model </p>
     */
    private static SecuritySupport ss = new SecuritySupport();
    /**
     * <p>Cache properties for performance.</p>
     */
    private static Properties cacheProps = new Properties();
    /**
     * <p>First time requires initialization overhead.</p>
     */
    private static volatile boolean firstTime = true;

    static {
        // Use try/catch block to support applets
        try {
            debug = ss.getSystemProperty("jaxp.debug") != null;
        } catch (Exception _) {
            debug = false;
        }
    }

    /**
     * <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>SchemaFactory</code>.</p>
     */
    private final ClassLoader classLoader;

    /**
     * <p>Constructor that specifies
     * <code>ClassLoader</code> to use to find
     * <code>SchemaFactory</code>.</p>
     *
     * @param loader to be used to load resource, {@link SchemaFactory}, and
     * {@link SchemaFactoryLoader} implementations during the resolution
     * process. If this parameter is null, the default system class loader will
     * be used.
     */
    public SchemaFactoryFinder(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 SchemaFactory} object for the specified schema
     * language.</p>
     *
     * @param schemaLanguage See {@link SchemaFactory Schema Language} table
     * in <code>SchemaFactory</code> for the list of available schema languages.
     *
     * @return <code>null</code> if the callee fails to create one.
     *
     * @throws NullPointerException If the <code>schemaLanguage</code> parameter
     * is null.
     */
    public SchemaFactory newFactory(String schemaLanguage)
            throws FactoryConfigurationError {
        if (schemaLanguage == null) {
            throw new NullPointerException();
        }
        SchemaFactory f = _newFactory(schemaLanguage);
        if (f != null) {
            debugPrintln("factory '" + f.getClass().getName() + "' was found for " + schemaLanguage);
        } else {
            debugPrintln("unable to find a factory for " + schemaLanguage);
        }
        return f;
    }

    /**
     * <p>Lookup a
     * <code>SchemaFactory</code> for the given
     * <code>schemaLanguage</code>.</p>
     *
     * @param schemaLanguage Schema language to
     * lookup <code>SchemaFactory</code> for.
     *
     * @return <code>SchemaFactory</code> for the
     * given <code>schemaLanguage</code>.
     */
    private SchemaFactory _newFactory(String schemaLanguage)
            throws FactoryConfigurationError {
        SchemaFactory sf;

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

        // system property look up
        try {
            debugPrintln("Looking up system property '" + propertyName + "'");
            String r = ss.getSystemProperty(propertyName);
            if (r != null) {
                debugPrintln("The value is '" + r + "'");
                sf = createInstance(r, true);
                if (sf != null) {
                    return sf;
                }
            } 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) {
                sf = createInstance(factoryClassName, true);
                if (sf != null) {
                    return sf;
                }
            }
        } catch (Exception ex) {
            if (debug) {
                ex.printStackTrace();
            }
        }


        // try finding a service provider
        sf = findServiceProvider(schemaLanguage, DEFAULT_IMPL_NAME);
        if (sf != null) {
            return sf;
        }

        // platform default
        if (schemaLanguage.equals("http://www.w3.org/2001/XMLSchema")) {
            debugPrintln("attempting to use the platform default XML Schema validator");
            return createInstance(DEFAULT_IMPL_NAME, 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;

        // 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.
     */
    SchemaFactory createInstance(String className) {
        return createInstance(className, false);
    }

    SchemaFactory createInstance(String className, boolean useServicesMechanism) {
        SchemaFactory schemaFactory = 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 SchemaFactory
        try {
            if (!useServicesMechanism) {
                schemaFactory = (SchemaFactory) newInstanceNoServiceLoader(clazz);
            }
            if (schemaFactory == null) {
                schemaFactory = (SchemaFactory) 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 schemaFactory;
    }

    /**
     * Try to construct using newTransformerFactoryNoServiceLoader method if
     * available.
     */
    private static Object newInstanceNoServiceLoader(
            Class<?> providerClass) {
        // Retain maximum compatibility if no security manager.
        if (System.getSecurityManager() == null) {
            return null;
        }
        try {
            Method creationMethod =
                    providerClass.getDeclaredMethod(
                    "newXMLSchemaFactoryNoServiceLoader");
            return creationMethod.invoke(null, null);
        } catch (NoSuchMethodException exc) {
            return null;
        } catch (Exception exc) {
            return null;
        }
    }


    /*
     * Try to find a provider using Service Loader
     *
     * @return instance of provider class if found or null
     */
    private SchemaFactory findServiceProvider(final String schemaLanguage, final String fallbackClassName)
            throws FactoryConfigurationError {
        try {
            return (SchemaFactory) AccessController.doPrivileged(new PrivilegedAction() {
                public SchemaFactory run() {
                    SchemaFactory defaultProvider = null;
                    for (SchemaFactory schemaFactory : ServiceLoader.load(SchemaFactory.class, classLoader)) {
                        if (schemaFactory.getClass().getName().equals(fallbackClassName)) {
                            defaultProvider = schemaFactory;
                        } else {
                            if (isSchemaSupported(schemaFactory, schemaLanguage)) {
                                return schemaFactory;
                            }
                        }
                    }
                    if (defaultProvider != null) {
                        return defaultProvider;
                    }
                    return null;
                }
            });
        } catch (ServiceConfigurationError e) {
            throw new FactoryConfigurationError(e.getMessage(), (Exception) e.getCause());
        }
    }

    /**
     * <p>Test if the specified schemas are supported by the provider.</p>
     *
     * @param schemaFactory a Schema factory provider.
     * @param schemaLanguage Schema Language to support.
     *
     * @return <code>true</code> if the Schema Language is supported by the
     * provider.
     */
    private static boolean isSchemaSupported(SchemaFactory schemaFactory, String schemaLanguage) {
        final Class[] stringClassArray = {"".getClass()};
        final Object[] schemaLanguageObjectArray = {schemaLanguage};
        final String isSchemaLanguageSupportedMethod = "isSchemaLanguageSupported";

        // does this Class support desired Schema?
        try {
            Method isSchemaLanguageSupported = schemaFactory.getClass().getMethod(isSchemaLanguageSupportedMethod, stringClassArray);
            Boolean supported = (Boolean) isSchemaLanguageSupported.invoke(schemaFactory, schemaLanguageObjectArray);
            if (supported.booleanValue()) {
                return true;
            }
        } catch (NoSuchMethodException noSuchMethodException) {
        } catch (IllegalAccessException illegalAccessException) {
        } catch (InvocationTargetException invocationTargetException) {
        }

        return false;
    }
    private static final Class SERVICE_CLASS = SchemaFactory.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;
        }
    }
}