MethodMap

package org.codehaus.plexus.interpolation.reflection;

/* ====================================================================
 *   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.
 * ====================================================================
 */

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;

/**
 * <b>NOTE:</b> This class was copied from plexus-utils, to allow this library
 * to stand completely self-contained.
 * @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>
 */
public class MethodMap {
    private static final int MORE_SPECIFIC = 0;
    private static final int LESS_SPECIFIC = 1;
    private static final int INCOMPARABLE = 2;

    /**
     * Keep track of all methods with the same name.
     */
    Map<String, List<Method>> methodByNameMap = new Hashtable<String, List<Method>>();

    /**
     * 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 {@link Method}
     */
    public void add(Method method) {
        String methodName = method.getName();

        List<Method> l = get(methodName);

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

        l.add(method);
    }

    /**
     * Return a list of methods with the same name.
     *
     * @param key  the key
     * @return list of methods
     */
    public List<Method> get(String key) {
        return 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<Method> 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 {}

    private static Method getMostSpecific(List<Method> methods, Class<?>[] classes) throws AmbiguousException {
        LinkedList<Method> applicables = getApplicables(methods, classes);

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

        if (applicables.size() == 1) {
            return 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<Method> maximals = new LinkedList<Method>();

        for (Method app : applicables) {
            Class<?>[] appArgs = app.getParameterTypes();
            boolean lessSpecific = false;

            for (Iterator<Method> maximal = maximals.iterator(); !lessSpecific && maximal.hasNext(); ) {
                Method max = 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 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<Method> getApplicables(List<Method> methods, Class<?>[] classes) {
        LinkedList<Method> list = new LinkedList<Method>();

        for (Method method : methods) {
            if (isApplicable(method, classes)) {
                list.add(method);
            }
        }
        return list;
    }

    /**
     * Returns true if the supplied method is applicable to actual
     * argument types.
     */
    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) {
                return actual == Boolean.class;
            }
            if (formal == Character.TYPE) {
                return actual == Character.class;
            }
            if (formal == Byte.TYPE) {
                return actual == Byte.class;
            }
            if (formal == Short.TYPE) {
                return actual == Short.class || actual == Byte.class;
            }
            if (formal == Integer.TYPE) {
                return actual == Integer.class || actual == Short.class || actual == Byte.class;
            }
            if (formal == Long.TYPE) {
                return actual == Long.class || actual == Integer.class || actual == Short.class || actual == Byte.class;
            }
            if (formal == Float.TYPE) {
                return actual == Float.class
                        || actual == Long.class
                        || actual == Integer.class
                        || actual == Short.class
                        || actual == Byte.class;
            }
            if (formal == Double.TYPE) {
                return actual == Double.class
                        || actual == Float.class
                        || actual == Long.class
                        || actual == Integer.class
                        || actual == Short.class
                        || actual == Byte.class;
            }
        }

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