ClassMap

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.maven.model.interpolation.reflection;

import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.Hashtable;
import java.util.Map;

/**
 * A cache of introspection information for a specific class instance.
 * Keys {@link Method} objects by a concatenation of the
 * method name and the names of classes that make up the parameters.
 */
class ClassMap {
    private static final class CacheMiss {}

    private static final CacheMiss CACHE_MISS = new CacheMiss();

    private static final Object OBJECT = new Object();

    /**
     * Class passed into the constructor used to as
     * the basis for the Method map.
     */
    private final Class<?> clazz;

    /**
     * Cache of Methods, or CACHE_MISS, keyed by method
     * name and actual arguments used to find it.
     */
    private final Map<String, Object> methodCache = new Hashtable<>();

    private MethodMap methodMap = new MethodMap();

    /**
     * Standard constructor
     * @param clazz The class.
     */
    ClassMap(Class<?> clazz) {
        this.clazz = clazz;
        populateMethodCache();
    }

    /**
     * @return the class object whose methods are cached by this map.
     */
    Class<?> getCachedClass() {
        return clazz;
    }

    /**
     * <p>Find a Method using the methodKey provided.</p>
     * <p>Look in the methodMap for an entry. If found,
     * it'll either be a CACHE_MISS, in which case we
     * simply give up, or it'll be a Method, in which
     * case, we return it.</p>
     * <p>If nothing is found, then we must actually go
     * and introspect the method from the MethodMap.</p>
     * @param name Method name.
     * @param params Method parameters.
     * @return The found method.
     * @throws MethodMap.AmbiguousException in case of duplicate methods.
     */
    public Method findMethod(String name, Object... params) throws MethodMap.AmbiguousException {
        String methodKey = makeMethodKey(name, params);
        Object cacheEntry = methodCache.get(methodKey);

        if (cacheEntry == CACHE_MISS) {
            return null;
        }

        if (cacheEntry == null) {
            try {
                cacheEntry = methodMap.find(name, params);
            } catch (MethodMap.AmbiguousException ae) {
                // that's a miss :)
                methodCache.put(methodKey, CACHE_MISS);
                throw ae;
            }

            if (cacheEntry == null) {
                methodCache.put(methodKey, CACHE_MISS);
            } else {
                methodCache.put(methodKey, cacheEntry);
            }
        }

        // Yes, this might just be null.
        return (Method) cacheEntry;
    }

    /**
     * Populate the Map of direct hits. These
     * are taken from all the public methods
     * that our class provides.
     */
    private void populateMethodCache() {
        // get all publicly accessible methods
        Method[] methods = getAccessibleMethods(clazz);

        // map and cache them
        for (Method method : methods) {
            // now get the 'public method', the method declared by a
            // public interface or class (because the actual implementing
            // class may be a facade...)

            Method publicMethod = getPublicMethod(method);

            // it is entirely possible that there is no public method for
            // the methods of this class (i.e. in the facade, a method
            // that isn't on any of the interfaces or superclass
            // in which case, ignore it.  Otherwise, map and cache
            if (publicMethod != null) {
                methodMap.add(publicMethod);
                methodCache.put(makeMethodKey(publicMethod), publicMethod);
            }
        }
    }

    /**
     * Make a methodKey for the given method using
     * the concatenation of the name and the
     * types of the method parameters.
     */
    private String makeMethodKey(Method method) {
        Class<?>[] parameterTypes = method.getParameterTypes();

        StringBuilder methodKey = new StringBuilder(method.getName());

        for (Class<?> parameterType : parameterTypes) {
            // If the argument type is primitive then we want
            // to convert our primitive type signature to the
            // corresponding Object type so introspection for
            // methods with primitive types will work correctly.
            if (parameterType.isPrimitive()) {
                if (parameterType.equals(Boolean.TYPE)) {
                    methodKey.append("java.lang.Boolean");
                } else if (parameterType.equals(Byte.TYPE)) {
                    methodKey.append("java.lang.Byte");
                } else if (parameterType.equals(Character.TYPE)) {
                    methodKey.append("java.lang.Character");
                } else if (parameterType.equals(Double.TYPE)) {
                    methodKey.append("java.lang.Double");
                } else if (parameterType.equals(Float.TYPE)) {
                    methodKey.append("java.lang.Float");
                } else if (parameterType.equals(Integer.TYPE)) {
                    methodKey.append("java.lang.Integer");
                } else if (parameterType.equals(Long.TYPE)) {
                    methodKey.append("java.lang.Long");
                } else if (parameterType.equals(Short.TYPE)) {
                    methodKey.append("java.lang.Short");
                }
            } else {
                methodKey.append(parameterType.getName());
            }
        }

        return methodKey.toString();
    }

    private static String makeMethodKey(String method, Object... params) {
        StringBuilder methodKey = new StringBuilder().append(method);

        for (Object param : params) {
            Object arg = param;

            if (arg == null) {
                arg = OBJECT;
            }

            methodKey.append(arg.getClass().getName());
        }

        return methodKey.toString();
    }

    /**
     * Retrieves public methods for a class. In case the class is not
     * public, retrieves methods with same signature as its public methods
     * from public superclasses and interfaces (if they exist). Basically
     * upcasts every method to the nearest acccessible method.
     */
    private static Method[] getAccessibleMethods(Class<?> clazz) {
        Method[] methods = clazz.getMethods();

        // Short circuit for the (hopefully) majority of cases where the
        // clazz is public
        if (Modifier.isPublic(clazz.getModifiers())) {
            return methods;
        }

        // No luck - the class is not public, so we're going the longer way.
        MethodInfo[] methodInfos = new MethodInfo[methods.length];
        for (int i = methods.length; i-- > 0; ) {
            methodInfos[i] = new MethodInfo(methods[i]);
        }

        int upcastCount = getAccessibleMethods(clazz, methodInfos, 0);

        // Reallocate array in case some method had no accessible counterpart.
        if (upcastCount < methods.length) {
            methods = new Method[upcastCount];
        }

        int j = 0;
        for (MethodInfo methodInfo : methodInfos) {
            if (methodInfo.upcast) {
                methods[j++] = methodInfo.method;
            }
        }
        return methods;
    }

    /**
     * Recursively finds a match for each method, starting with the class, and then
     * searching the superclass and interfaces.
     *
     * @param clazz       Class to check
     * @param methodInfos array of methods we are searching to match
     * @param upcastCount current number of methods we have matched
     * @return count of matched methods
     */
    private static int getAccessibleMethods(Class<?> clazz, MethodInfo[] methodInfos, int upcastCount) {
        int l = methodInfos.length;

        // if this class is public, then check each of the currently
        // 'non-upcasted' methods to see if we have a match
        if (Modifier.isPublic(clazz.getModifiers())) {
            for (int i = 0; i < l && upcastCount < l; ++i) {
                try {
                    MethodInfo methodInfo = methodInfos[i];
                    if (!methodInfo.upcast) {
                        methodInfo.tryUpcasting(clazz);
                        upcastCount++;
                    }
                } catch (NoSuchMethodException e) {
                    // Intentionally ignored - it means it wasn't found in the current class
                }
            }

            /*
             *  Short circuit if all methods were upcast
             */

            if (upcastCount == l) {
                return upcastCount;
            }
        }

        // Examine superclass
        Class<?> superclazz = clazz.getSuperclass();
        if (superclazz != null) {
            upcastCount = getAccessibleMethods(superclazz, methodInfos, upcastCount);

            // Short circuit if all methods were upcast
            if (upcastCount == l) {
                return upcastCount;
            }
        }

        // Examine interfaces. Note we do it even if superclazz == null.
        // This is redundant as currently java.lang.Object does not implement
        // any interfaces, however nothing guarantees it will not in the future.
        Class<?>[] interfaces = clazz.getInterfaces();
        for (int i = interfaces.length; i-- > 0; ) {
            upcastCount = getAccessibleMethods(interfaces[i], methodInfos, upcastCount);

            // Short circuit if all methods were upcast
            if (upcastCount == l) {
                return upcastCount;
            }
        }

        return upcastCount;
    }

    /**
     * For a given method, retrieves its publicly accessible counterpart.
     * This method will look for a method with same name
     * and signature declared in a public superclass or implemented interface of this
     * method's declaring class. This counterpart method is publicly callable.
     *
     * @param method a method whose publicly callable counterpart is requested.
     * @return the publicly callable counterpart method. Note that if the parameter
     *         method is itself declared by a public class, this method is an identity
     *         function.
     */
    private static Method getPublicMethod(Method method) {
        Class<?> clazz = method.getDeclaringClass();

        // Short circuit for (hopefully the majority of) cases where the declaring
        // class is public.
        if ((clazz.getModifiers() & Modifier.PUBLIC) != 0) {
            return method;
        }

        return getPublicMethod(clazz, method.getName(), method.getParameterTypes());
    }

    /**
     * Looks up the method with specified name and signature in the first public
     * superclass or implemented interface of the class.
     *
     * @param clazz      the class whose method is sought
     * @param name       the name of the method
     * @param paramTypes the classes of method parameters
     */
    private static Method getPublicMethod(Class<?> clazz, String name, Class<?>... paramTypes) {
        // if this class is public, then try to get it
        if ((clazz.getModifiers() & Modifier.PUBLIC) != 0) {
            try {
                return clazz.getMethod(name, paramTypes);
            } catch (NoSuchMethodException e) {
                // If the class does not have the method, then neither its superclass
                // nor any of its interfaces has it so quickly return null.
                return null;
            }
        }

        //  try the superclass
        Class<?> superclazz = clazz.getSuperclass();

        if (superclazz != null) {
            Method superclazzMethod = getPublicMethod(superclazz, name, paramTypes);

            if (superclazzMethod != null) {
                return superclazzMethod;
            }
        }

        // and interfaces
        Class<?>[] interfaces = clazz.getInterfaces();

        for (Class<?> anInterface : interfaces) {
            Method interfaceMethod = getPublicMethod(anInterface, name, paramTypes);

            if (interfaceMethod != null) {
                return interfaceMethod;
            }
        }

        return null;
    }

    /**
     * Used for the iterative discovery process for public methods.
     */
    private static final class MethodInfo {
        Method method;

        String name;

        Class<?>[] parameterTypes;

        boolean upcast;

        MethodInfo(Method method) {
            this.method = null;
            name = method.getName();
            parameterTypes = method.getParameterTypes();
            upcast = false;
        }

        void tryUpcasting(Class<?> clazz) throws NoSuchMethodException {
            method = clazz.getMethod(name, parameterTypes);
            name = null;
            parameterTypes = null;
            upcast = true;
        }
    }
}