/*
 * Copyright 2001,2004 The Apache Software Foundation.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.commons.jexl.util.introspection;

import java.util.Map;
import java.util.Set;
import java.util.HashMap;
import java.util.HashSet;

import java.lang.reflect.Method;

/**
 * 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
 * 
 * @since 1.0
 * @author <a href="mailto:jvanzyl@apache.org">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: IntrospectorBase.java 398464 2006-04-30 23:50:43Z dion $
 */
public class IntrospectorBase {
    /**
     * Holds the method maps for the classes we know about, keyed by Class
     * object.
     */
    protected Map classMethodMaps = new HashMap();

    /**
     * Holds the qualified class names for the classes we hold in the
     * classMethodMaps hash.
     */
    protected Set cachedClassNames = new HashSet();

    /**
     * Gets the method defined by <code>name</code> and <code>params</code>
     * for the Class <code>c</code>.
     * 
     * @param c Class in which the method search is taking place
     * @param name Name of the method being searched for
     * @param params An array of Objects (not Classes) that describe the the
     *            parameters
     * 
     * @return The desired Method object.
     * @throws Exception on any logical error.
     */
    public 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 we don't have this, check to see if we have it by name. if so,
             * then we have a classloader change so dump our caches.
             */

            if (classMap == null) {
                if (cachedClassNames.contains(c.getName())) {
                    /*
                     * we have a map for a class with same name, but not this
                     * class we are looking at. This implies a classloader
                     * change, so dump
                     */
                    clearCache();
                }

                classMap = createClassMap(c);
            }
        }

        return classMap.findMethod(name, params);
    }

    /**
     * Creates a class map for specific class and registers it in the cache.
     * Also adds the qualified name to the name->class map for later Classloader
     * change detection.
     * @param c class.
     * @return a {@link ClassMap}
     */
    protected ClassMap createClassMap(Class c) {
        ClassMap classMap = new ClassMap(c);
        classMethodMaps.put(c, classMap);
        cachedClassNames.add(c.getName());

        return classMap;
    }

    /**
     * Clears the classmap and classname caches.
     */
    protected void clearCache() {
        /*
         * since we are synchronizing on this object, we have to clear it rather
         * than just dump it.
         */
        classMethodMaps.clear();

        /*
         * for speed, we can just make a new one and let the old one be GC'd
         */
        cachedClassNames = new HashSet();
    }
}
