/*
 * Copyright 2008-2022 Async-IO.org
 *
 * 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.
 */
/**
 * Copyright 2002-2011 the original author or authors.
 *
 * 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.
 */
/**
 * This class is from https://github.com/jhalterman/typetools
 */
package org.atmosphere.wasync.util;

import java.lang.ref.Reference;
import java.lang.ref.WeakReference;
import java.lang.reflect.Array;
import java.lang.reflect.GenericArrayType;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.lang.reflect.TypeVariable;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.WeakHashMap;

/**
 * Enhanced type resolution utilities. Based on org.springframework.core.GenericTypeResolver.
 *
 * @author Jonathan Halterman
 */
public final class TypeResolver {
    private TypeResolver() {
    }

    /** An unknown type. */
    public static final class Unknown {
        private Unknown() {
        }
    }

    /** Cache of type variable/argument pairs */
    private static final Map<Class<?>, Reference<Map<TypeVariable<?>, Type>>> typeVariableCache = Collections.synchronizedMap(new WeakHashMap<Class<?>, Reference<Map<TypeVariable<?>, Type>>>());
    private static boolean cacheEnabled = true;

    /**
     * Enables the internal caching of TypeVariables.
     */
    public static void enableCache() {
        cacheEnabled = true;
    }

    /**
     * Disables the internal caching of TypeVariables.
     */
    public static void disableCache() {
        typeVariableCache.clear();
        cacheEnabled = false;
    }

    /**
     * Returns the raw class representing the type argument for the {@code targetType} resolved
     * upwards from the {@code initialType}. If no arguments can be resolved then
     * {@code Unknown.class} is returned.
     *
     * @param initialType to resolve upwards from
     * @param targetType to resolve arguments for
     * @return type argument for {@code initialType} else {@code null} if no type arguments are
     *         declared
     * @throws IllegalArgumentException if more or less than one type argument is resolved for the
     *           give types
     */
    public static <T, I extends T> Class<?> resolveArgument(Class<I> initialType, Class<T> targetType) {
        return resolveArgument(resolveGenericType(initialType, targetType), initialType);
    }

    /**
     * Resolves the type argument for the {@code genericType} using type variable information from the
     * {@code sourceType}. If {@code genericType} is an instance of class, then {@code genericType} is
     * returned. If no arguments can be resolved then {@code Unknown.class} is returned.
     *
     * @param genericType to resolve upwards from
     * @param targetType to resolve arguments for
     * @return type argument for {@code initialType} else {@code null} if no type arguments are
     *         declared
     * @throws IllegalArgumentException if more or less than one type argument is resolved for the
     *           give types
     */
    public static Class<?> resolveArgument(Type genericType, Class<?> targetType) {
        Class<?>[] arguments = resolveArguments(genericType, targetType);
        if (arguments == null)
            return Unknown.class;

        if (arguments.length != 1)
            throw new IllegalArgumentException("Expected 1 type argument on generic type "
                    + targetType.getName() + " but found " + arguments.length);

        return arguments[0];
    }

    /**
     * Returns an array of raw classes representing type arguments for the {@code targetType} resolved
     * upwards from the {@code initialType}. Arguments for {@code targetType} that cannot be resolved
     * to a Class are returned as {@code Unknown.class}. If no arguments can be resolved then
     * {@code null} is returned.
     *
     * @param initialType to resolve upwards from
     * @param targetType to resolve arguments for
     * @return array of raw classes representing type arguments for {@code initialType} else
     *         {@code null} if no type arguments are declared
     */
    public static <T, I extends T> Class<?>[] resolveArguments(Class<I> initialType,
                                                               Class<T> targetType) {
        return resolveArguments(resolveGenericType(initialType, targetType), initialType);
    }

    /**
     * Resolves the arguments for the {@code genericType} using the type variable information for the
     * {@code targetType}. Returns {@code null} if {@code genericType} is not parameterized or if
     * arguments cannot be resolved.
     */
    public static Class<?>[] resolveArguments(Type genericType, Class<?> targetType) {
        Class<?>[] result = null;

        if (genericType instanceof ParameterizedType) {
            ParameterizedType paramType = (ParameterizedType) genericType;
            Type[] arguments = paramType.getActualTypeArguments();
            result = new Class[arguments.length];
            for (int i = 0; i < arguments.length; i++)
                result[i] = resolveClass(arguments[i], targetType);
        } else if (genericType instanceof TypeVariable) {
            result = new Class[1];
            result[0] = resolveClass(genericType, targetType);
        }

        return result;
    }

    /**
     * Resolves the generic Type for the {@code targetType} by walking the type hierarchy upwards from
     * the {@code initialType}.
     */
    public static Type resolveGenericType(Type initialType, Class<?> targetType) {
        Class<?> rawType;
        if (initialType instanceof ParameterizedType)
            rawType = (Class<?>) ((ParameterizedType) initialType).getRawType();
        else
            rawType = (Class<?>) initialType;

        if (targetType.equals(rawType))
            return initialType;

        Type result;
        if (targetType.isInterface()) {
            for (Type superInterface : rawType.getGenericInterfaces())
                if (superInterface != null && !superInterface.equals(Object.class))
                    if ((result = resolveGenericType(superInterface, targetType)) != null)
                        return result;
        }

        Type superType = rawType.getGenericSuperclass();
        if (superType != null && !superType.equals(Object.class))
            if ((result = resolveGenericType(superType, targetType)) != null)
                return result;

        return null;
    }

    /**
     * Resolves the raw class for the given {@code genericType}, using the type variable information
     * from the {@code targetType}.
     */
    public static Class<?> resolveClass(Type genericType, Class<?> targetType) {
        if (genericType instanceof Class) {
            return (Class<?>) genericType;
        } else if (genericType instanceof ParameterizedType) {
            return resolveClass(((ParameterizedType) genericType).getRawType(), targetType);
        } else if (genericType instanceof GenericArrayType) {
            GenericArrayType arrayType = (GenericArrayType) genericType;
            Class<?> compoment = resolveClass(arrayType.getGenericComponentType(), targetType);
            return Array.newInstance(compoment, 0).getClass();
        } else if (genericType instanceof TypeVariable) {
            TypeVariable<?> variable = (TypeVariable<?>) genericType;
            genericType = getTypeVariableMap(targetType).get(variable);
            genericType = genericType == null ? resolveBound(variable) : resolveClass(genericType,
                    targetType);
        }

        return genericType instanceof Class ? (Class<?>) genericType : Unknown.class;
    }

    private static Map<TypeVariable<?>, Type> getTypeVariableMap(final Class<?> targetType) {
        Reference<Map<TypeVariable<?>, Type>> ref = typeVariableCache.get(targetType);
        Map<TypeVariable<?>, Type> map = ref != null ? ref.get() : null;

        if (map == null) {
            map = new HashMap<TypeVariable<?>, Type>();

            // Populate interfaces
            buildTypeVariableMap(targetType.getGenericInterfaces(), map);

            // Populate super classes and interfaces
            Type genericType = targetType.getGenericSuperclass();
            Class<?> type = targetType.getSuperclass();
            while (type != null && !Object.class.equals(type)) {
                if (genericType instanceof ParameterizedType)
                    buildTypeVariableMap((ParameterizedType) genericType, map);
                buildTypeVariableMap(type.getGenericInterfaces(), map);

                genericType = type.getGenericSuperclass();
                type = type.getSuperclass();
            }

            // Populate enclosing classes
            type = targetType;
            while (type.isMemberClass()) {
                genericType = type.getGenericSuperclass();
                if (genericType instanceof ParameterizedType)
                    buildTypeVariableMap((ParameterizedType) genericType, map);

                type = type.getEnclosingClass();
            }

            if (cacheEnabled)
                typeVariableCache.put(targetType, new WeakReference<Map<TypeVariable<?>, Type>>(map));
        }

        return map;
    }

    /**
     * Populates the {@code map} with with variable/argument pairs for the given {@code types}.
     */
    static void buildTypeVariableMap(final Type[] types, final Map<TypeVariable<?>, Type> map) {
        for (Type type : types) {
            if (type instanceof ParameterizedType) {
                ParameterizedType parameterizedType = (ParameterizedType) type;
                buildTypeVariableMap(parameterizedType, map);
                Type rawType = parameterizedType.getRawType();
                if (rawType instanceof Class)
                    buildTypeVariableMap(((Class<?>) rawType).getGenericInterfaces(), map);
            } else if (type instanceof Class) {
                buildTypeVariableMap(((Class<?>) type).getGenericInterfaces(), map);
            }
        }
    }

    /**
     * Populates the {@code typeVariableMap} with type arguments and parameters for the given
     * {@code type}.
     */
    private static void buildTypeVariableMap(ParameterizedType type,
                                             Map<TypeVariable<?>, Type> typeVariableMap) {
        if (type.getRawType() instanceof Class) {
            TypeVariable<?>[] typeVariables = ((Class<?>) type.getRawType()).getTypeParameters();
            Type[] typeArguments = type.getActualTypeArguments();

            for (int i = 0; i < typeArguments.length; i++) {
                TypeVariable<?> variable = typeVariables[i];
                Type typeArgument = typeArguments[i];

                if (typeArgument instanceof Class) {
                    typeVariableMap.put(variable, typeArgument);
                } else if (typeArgument instanceof GenericArrayType) {
                    typeVariableMap.put(variable, typeArgument);
                } else if (typeArgument instanceof ParameterizedType) {
                    typeVariableMap.put(variable, typeArgument);
                } else if (typeArgument instanceof TypeVariable) {
                    TypeVariable<?> typeVariableArgument = (TypeVariable<?>) typeArgument;
                    Type resolvedType = typeVariableMap.get(typeVariableArgument);
                    if (resolvedType == null)
                        resolvedType = resolveBound(typeVariableArgument);
                    typeVariableMap.put(variable, resolvedType);
                }
            }
        }
    }

    /**
     * Resolves the first bound for the {@code typeVariable}, returning {@code Unknown.class} if none
     * can be resolved.
     */
    public static Type resolveBound(TypeVariable<?> typeVariable) {
        Type[] bounds = typeVariable.getBounds();
        if (bounds.length == 0)
            return Unknown.class;

        Type bound = bounds[0];
        if (bound instanceof TypeVariable)
            bound = resolveBound((TypeVariable<?>) bound);

        return bound == Object.class ? Unknown.class : bound;
    }
}
