/*
 * 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.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Hashtable;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;

/**
 * 
 * @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:Christoph.Reck@dlr.de">Christoph Reck</a>
 * @author <a href="mailto:geirm@optonline.net">Geir Magnusson Jr.</a>
 * @author <a href="mailto:szegedia@freemail.hu">Attila Szegedi</a>
 * @since 1.0
 * @version $Id: MethodMap.java 398495 2006-05-01 01:33:43Z dion $
 */
public class MethodMap {
    /** whether a method is more specific than a previously compared one. */
    private static final int MORE_SPECIFIC = 0;
    /** whether a method is less specific than a previously compared one. */
    private static final int LESS_SPECIFIC = 1;
    /** A method doesn't match a previously compared one. */
    private static final int INCOMPARABLE = 2;

    /**
     * Keep track of all methods with the same name.
     */
    protected Map methodByNameMap = new Hashtable();

    /**
     * Add a method to a list of methods by name. For a particular class we are
     * keeping track of all the methods with the same name.
     * @param method the method.
     */
    public void add(Method method) {
        String methodName = method.getName();

        List l = get(methodName);

        if (l == null) {
            l = new ArrayList();
            methodByNameMap.put(methodName, l);
        }

        l.add(method);
    }

    /**
     * Return a list of methods with the same name.
     * 
     * @param key The method name.
     * @return List list of methods
     */
    public List get(String key) {
        return (List) methodByNameMap.get(key);
    }

    /**
     * <p>
     * Find a method. Attempts to find the most specific applicable method using
     * the algorithm described in the JLS section 15.12.2 (with the exception
     * that it can't distinguish a primitive type argument from an object type
     * argument, since in reflection primitive type arguments are represented by
     * their object counterparts, so for an argument of type (say)
     * java.lang.Integer, it will not be able to decide between a method that
     * takes int and a method that takes java.lang.Integer as a parameter.
     * </p>
     * 
     * <p>
     * This turns out to be a relatively rare case where this is needed -
     * however, functionality like this is needed.
     * </p>
     * 
     * @param methodName name of method
     * @param args the actual arguments with which the method is called
     * @return the most specific applicable method, or null if no method is
     *         applicable.
     * @throws AmbiguousException if there is more than one maximally specific
     *             applicable method
     */
    public Method find(String methodName, Object[] args) throws AmbiguousException {
        List methodList = get(methodName);

        if (methodList == null) {
            return null;
        }

        int l = args.length;
        Class[] classes = new Class[l];

        for (int i = 0; i < l; ++i) {
            Object arg = args[i];

            /*
             * if we are careful down below, a null argument goes in there so we
             * can know that the null was passed to the method
             */
            classes[i] = arg == null ? null : arg.getClass();
        }

        return getMostSpecific(methodList, classes);
    }

    /**
     * simple distinguishable exception, used when we run across ambiguous
     * overloading.
     */
    public static class AmbiguousException extends Exception {
        /** serialization version id jdk13 generated. */
        static final long serialVersionUID = 8758118091728717367L;
    }

    /**
     * Gets the most specific method from a list.
     * @param methods list of {@link Method methods}
     * @param classes argument types
     * @return the most specific method, or null
     * @throws AmbiguousException if there is more than one specific method
     */
    private static Method getMostSpecific(List methods, Class[] classes) throws AmbiguousException {
        LinkedList applicables = getApplicables(methods, classes);

        if (applicables.isEmpty()) {
            return null;
        }

        if (applicables.size() == 1) {
            return (Method) applicables.getFirst();
        }

        /*
         * This list will contain the maximally specific methods. Hopefully at
         * the end of the below loop, the list will contain exactly one method,
         * (the most specific method) otherwise we have ambiguity.
         */

        LinkedList maximals = new LinkedList();

        for (Iterator applicable = applicables.iterator(); applicable.hasNext();) {
            Method app = (Method) applicable.next();
            Class[] appArgs = app.getParameterTypes();
            boolean lessSpecific = false;

            for (Iterator maximal = maximals.iterator(); !lessSpecific && maximal.hasNext();) {
                Method max = (Method) maximal.next();

                switch (moreSpecific(appArgs, max.getParameterTypes())) {
                    case MORE_SPECIFIC:
                        /*
                         * This method is more specific than the previously
                         * known maximally specific, so remove the old maximum.
                         */
                        maximal.remove();
                        break;

                    case LESS_SPECIFIC:
                        /*
                         * This method is less specific than some of the
                         * currently known maximally specific methods, so we
                         * won't add it into the set of maximally specific
                         * methods
                         */
                        lessSpecific = true;
                        break;
                }
            }

            if (!lessSpecific) {
                maximals.addLast(app);
            }
        }

        if (maximals.size() > 1) {
            // We have more than one maximally specific method
            throw new AmbiguousException();
        }

        return (Method) maximals.getFirst();
    }

    /**
     * Determines which method signature (represented by a class array) is more
     * specific. This defines a partial ordering on the method signatures.
     * 
     * @param c1 first signature to compare
     * @param c2 second signature to compare
     * @return MORE_SPECIFIC if c1 is more specific than c2, LESS_SPECIFIC if c1
     *         is less specific than c2, INCOMPARABLE if they are incomparable.
     */
    private static int moreSpecific(Class[] c1, Class[] c2) {
        boolean c1MoreSpecific = false;
        boolean c2MoreSpecific = false;

        for (int i = 0; i < c1.length; ++i) {
            if (c1[i] != c2[i]) {
                c1MoreSpecific = c1MoreSpecific || isStrictMethodInvocationConvertible(c2[i], c1[i]);
                c2MoreSpecific = c2MoreSpecific || isStrictMethodInvocationConvertible(c1[i], c2[i]);
            }
        }

        if (c1MoreSpecific) {
            if (c2MoreSpecific) {
                /*
                 * Incomparable due to cross-assignable arguments (i.e.
                 * foo(String, Object) vs. foo(Object, String))
                 */

                return INCOMPARABLE;
            }

            return MORE_SPECIFIC;
        }

        if (c2MoreSpecific) {
            return LESS_SPECIFIC;
        }

        /*
         * Incomparable due to non-related arguments (i.e. foo(Runnable) vs.
         * foo(Serializable))
         */

        return INCOMPARABLE;
    }

    /**
     * Returns all methods that are applicable to actual argument types.
     * 
     * @param methods list of all candidate methods
     * @param classes the actual types of the arguments
     * @return a list that contains only applicable methods (number of formal
     *         and actual arguments matches, and argument types are assignable
     *         to formal types through a method invocation conversion).
     */
    private static LinkedList getApplicables(List methods, Class[] classes) {
        LinkedList list = new LinkedList();

        for (Iterator imethod = methods.iterator(); imethod.hasNext();) {
            Method method = (Method) imethod.next();

            if (isApplicable(method, classes)) {
                list.add(method);
            }

        }
        return list;
    }

    /**
     * Returns true if the supplied method is applicable to actual argument
     * types.
     * @param method the method to check
     * @param classes possible argument types
     * @return true if the arguments are applicable to the method.
     */
    private static boolean isApplicable(Method method, Class[] classes) {
        Class[] methodArgs = method.getParameterTypes();

        if (methodArgs.length != classes.length) {
            return false;
        }

        for (int i = 0; i < classes.length; ++i) {
            if (!isMethodInvocationConvertible(methodArgs[i], classes[i])) {
                return false;
            }
        }

        return true;
    }

    /**
     * Determines whether a type represented by a class object is convertible to
     * another type represented by a class object using a method invocation
     * conversion, treating object types of primitive types as if they were
     * primitive types (that is, a Boolean actual parameter type matches boolean
     * primitive formal type). This behavior is because this method is used to
     * determine applicable methods for an actual parameter list, and primitive
     * types are represented by their object duals in reflective method calls.
     * 
     * @param formal the formal parameter type to which the actual parameter
     *            type should be convertible
     * @param actual the actual parameter type.
     * @return true if either formal type is assignable from actual type, or
     *         formal is a primitive type and actual is its corresponding object
     *         type or an object type of a primitive type that can be converted
     *         to the formal type.
     */
    private static boolean isMethodInvocationConvertible(Class formal, Class actual) {
        /*
         * if it's a null, it means the arg was null
         */
        if (actual == null && !formal.isPrimitive()) {
            return true;
        }

        /*
         * Check for identity or widening reference conversion
         */

        if (actual != null && formal.isAssignableFrom(actual)) {
            return true;
        }

        /*
         * Check for boxing with widening primitive conversion. Note that actual
         * parameters are never primitives.
         */

        if (formal.isPrimitive()) {
            if (formal == Boolean.TYPE && actual == Boolean.class) {
                return true;
            }
            if (formal == Character.TYPE && actual == Character.class) {
                return true;
            }
            if (formal == Byte.TYPE && actual == Byte.class) {
                return true;
            }
            if (formal == Short.TYPE && (actual == Short.class || actual == Byte.class)) {
                return true;
            }
            if (formal == Integer.TYPE && (actual == Integer.class || actual == Short.class || actual == Byte.class)) {
                return true;
            }
            if (formal == Long.TYPE
                && (actual == Long.class || actual == Integer.class || actual == Short.class || actual == Byte.class)) {
                return true;
            }
            if (formal == Float.TYPE
                && (actual == Float.class || actual == Long.class || actual == Integer.class 
                    || actual == Short.class || actual == Byte.class)) {
                return true;
            }
            if (formal == Double.TYPE
                && (actual == Double.class || actual == Float.class || actual == Long.class || actual == Integer.class
                    || actual == Short.class || actual == Byte.class)) {
                return true;
            }
        }

        return false;
    }

    /**
     * Determines whether a type represented by a class object is convertible to
     * another type represented by a class object using a method invocation
     * conversion, without matching object and primitive types. This method is
     * used to determine the more specific type when comparing signatures of
     * methods.
     * 
     * @param formal the formal parameter type to which the actual parameter
     *            type should be convertible
     * @param actual the actual parameter type.
     * @return true if either formal type is assignable from actual type, or
     *         formal and actual are both primitive types and actual can be
     *         subject to widening conversion to formal.
     */
    private static boolean isStrictMethodInvocationConvertible(Class formal, Class actual) {
        /*
         * we shouldn't get a null into, but if so
         */
        if (actual == null && !formal.isPrimitive()) {
            return true;
        }

        /*
         * Check for identity or widening reference conversion
         */

        if (formal.isAssignableFrom(actual)) {
            return true;
        }

        /*
         * Check for widening primitive conversion.
         */

        if (formal.isPrimitive()) {
            if (formal == Short.TYPE && (actual == Byte.TYPE)) {
                return true;
            }
            if (formal == Integer.TYPE && (actual == Short.TYPE || actual == Byte.TYPE)) {
                return true;
            }
            if (formal == Long.TYPE && (actual == Integer.TYPE || actual == Short.TYPE || actual == Byte.TYPE)) {
                return true;
            }
            if (formal == Float.TYPE
                && (actual == Long.TYPE || actual == Integer.TYPE || actual == Short.TYPE || actual == Byte.TYPE)) {
                return true;
            }
            if (formal == Double.TYPE
                && (actual == Float.TYPE || actual == Long.TYPE || actual == Integer.TYPE || actual == Short.TYPE 
                    || actual == Byte.TYPE)) {
                return true;
            }
        }
        return false;
    }
}
