package org.apache.velocity.util.introspection;

/*
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 2001 The Apache Software Foundation.  All rights
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution, if
 *    any, must include the following acknowlegement:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowlegement may appear in the software itself,
 *    if and wherever such third-party acknowlegements normally appear.
 *
 * 4. The names "The Jakarta Project", "Velocity", and "Apache Software
 *    Foundation" must not be used to endorse or promote products derived
 *    from this software without prior written permission. For written
 *    permission, please contact apache@apache.org.
 *
 * 5. Products derived from this software may not be called "Apache"
 *    nor may "Apache" appear in their names without prior written
 *    permission of the Apache Group.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */

import java.security.*;
import java.util.*;

import java.lang.reflect.Method;
import java.lang.reflect.Modifier;

import org.apache.velocity.util.StringUtils;

/**
 * This basic function of this class is to return a Method
 * object for a particular class given the name of a method
 * and the parameters to the method in the form of an Object[]
 *
 * The first time the Introspector sees a
 * class it creates a class method map for the
 * class in question. Basically the class method map
 * is a Hastable where Method objects are keyed by a
 * concatenation of the method name and the names of
 * classes that make up the parameters.
 *
 * For example, a method with the following signature:
 *
 * public void method(String a, StringBuffer b)
 *
 * would be mapped by the key:
 *
 * "method" + "java.lang.String" + "java.lang.StringBuffer"
 *
 * This mapping is performed for all the methods in a class
 * and stored for
 * @author <a href="mailto:jvanzyl@periapt.com">Jason van Zyl</a>
 * @author <a href="mailto:bob@werken.com">Bob McWhirter</a>
 * @author <a href="mailto:szegedia@freemail.hu">Attila Szegedi</a>
 * @author <a href="mailto:paulo.gaspar@krankikom.de">Paulo Gaspar</a>
 * @version $Id: Introspector.java,v 1.9 2001/03/05 11:48:49 jvanzyl Exp $
 */
public class Introspector
{
    private static final Map classMethodMaps = new HashMap();
    private static final Map classLoaders = new HashMap();
    private static final Map classByName = new HashMap();
    private static boolean canGetClassLoader;

    static
    {
        // Force testing for "getClassLoader" RuntimePermission.
        // This will set canGetClassLoader to appropriate value.
        getClassLoaderPrivileged(new Object().getClass());
    }

    public static Method getMethod(Class c, String name, Object[] params)
        throws Exception
    {
        if (c == null)
        {
            throw new Exception (
                "Introspector.getMethod(): Class method key was null: " + name );
        }

        ClassMap classMap = null;
        synchronized(classMethodMaps)
        {
            classMap = (ClassMap)classMethodMaps.get(c);
            if(null == classMap)
            {
                // Test for class reloads - if some (other)
                // Class was previously introspected with the
                // same qualified name, assume class reloading
                Class cachedClass = (Class)classByName.get(c.getName());
                if (null != cachedClass)
                {
                    // throw away cached info for all classes that
                    // have the same class loader
                    removeEquiloaderClasses(cachedClass);
                }

                // create class map
                classMap = createClassMap(c);
            }
        }

        return classMap.findMethod(name, params);
    }

    /**
     * Creates a class map for specific class, registers it in the
     * cache, maps it by name and associates it with class loader.
     */
    private static ClassMap createClassMap(Class c)
    {
        ClassMap classMap = new ClassMap(c);
        classMethodMaps.put(c, classMap);
        classByName.put(c.getName(), c);
        associateWithClassLoader(c);
        return classMap;
    }

    /**
     * Checks whether the provided object implements a given method.
     *
     *
     * @param object     The object to check.
     * @param methodName The method to check for.
     * @return           Whether the method is implemented.
     */
    public static boolean implementsMethod(Object object, String methodName)
    {
        int m;

        Method[] methods = object.getClass().getMethods();

        for (m = 0 ; m < methods.length ; ++m)
        {
            if (methodName.equals(methods[m].getName()))
            {
                break;
            }
        }

        return (m < methods.length);
    }

    /**
     * Associates the class' qualified name and its class
     * loader. If the Introspector is not granted privilege to
     * access class loaders, does nothing.
     */
    private static void associateWithClassLoader(Class c)
    {
        if(canGetClassLoader)
        {
            ClassLoader cl = getClassLoaderPrivileged(c);
            List classList = (List)classLoaders.get(cl);
            if(classList == null)
            {
                classList = new LinkedList();
                classLoaders.put(cl, classList);
            }
            classList.add(c);
        }
    }

    /**
     * Removes all ClassMap entries from classMethodMaps that
     * are associated with the same class loader as the passed
     * class (removes the ClassMap for the passed class as well).
     * If the Introspector is not granted privilege to access class
     * loaders, clears the entire cache.
     */
    private static void removeEquiloaderClasses(Class c)
    {
        if(canGetClassLoader)
        {
            ClassLoader cl = getClassLoaderPrivileged(c);
            List classList = (List)classLoaders.remove(cl);
            // classList must not be null
            Iterator it = classList.iterator();
            while(it.hasNext())
            {   Class rc = (Class)it.next();
                classMethodMaps.remove(rc);
                classByName.remove(rc.getName());
            }
        }
        else
        {
            classMethodMaps.clear();
            classByName.clear();
        }
    }

    /**
     * Gets a class loader for a class. The code executes in a
     * privileged code block, so it is sufficient to have
     * getClassLoader RuntimePermission on Introspector class.
     * If we didn't execute this in privileged code block, then all
     * classes up the call stack would also need to have this privilege.
     */
    private static ClassLoader getClassLoaderPrivileged(final Class c)
    {
        if(canGetClassLoader)
        {
            return (ClassLoader)AccessController.doPrivileged(
                new PrivilegedAction()
                {
                    public Object run()
                    {
                        if(canGetClassLoader)
                        {
                            try
                            {
                                return c.getClassLoader();
                            }
                            catch(SecurityException e)
                            {
                                // TODO: Use velocity log instead of System.err.
                                System.err.println("Cannot detect class reloads because"
                                   + " Velocity has insufficient privileges. You"
                                   + " should grant getClassLoader runtime permission"
                                   + " to org.apache.velocity.util.introspection.Introspector"
                                   + " in order for it to detect class reloads.");
                                // Flag we can't access class loaders. This
                                // will cause the Introspector to clear the
                                // whole cache when it detects class reloads,
                                // instead of doing it on per-classloader basis.
                                canGetClassLoader = false;
                                return null;
                            }
                        }
                        else
                            return null;
                    }
                });
        }
        else
            return null;
    }
}