/*
 * Copyright 2002-2017 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
 *
 *      https://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.springframework.expression.spel.support;

import java.lang.reflect.Array;
import java.lang.reflect.Method;
import java.util.List;

import org.springframework.core.MethodParameter;
import org.springframework.core.convert.TypeDescriptor;
import org.springframework.expression.EvaluationException;
import org.springframework.expression.TypeConverter;
import org.springframework.expression.spel.SpelEvaluationException;
import org.springframework.util.Assert;
import org.springframework.util.ClassUtils;
import org.springframework.util.CollectionUtils;
import org.springframework.util.MethodInvoker;

/**
 * Utility methods used by the reflection resolver code to discover the appropriate
 * methods/constructors and fields that should be used in expressions.
 *
 * @author Andy Clement
 * @author Juergen Hoeller
 * @since 3.0
 */
public class ReflectionHelper {

        /**
         * Compare argument arrays and return information about whether they match.
         * A supplied type converter and conversionAllowed flag allow for matches to take
         * into account that a type may be transformed into a different type by the converter.
         * @param expectedArgTypes the types the method/constructor is expecting
         * @param suppliedArgTypes the types that are being supplied at the point of invocation
         * @param typeConverter a registered type converter
         * @return a MatchInfo object indicating what kind of match it was,
         * or {@code null} if it was not a match
         */
        static ArgumentsMatchInfo compareArguments(
                        List<TypeDescriptor> expectedArgTypes, List<TypeDescriptor> suppliedArgTypes, TypeConverter typeConverter) {

                Assert.isTrue(expectedArgTypes.size() == suppliedArgTypes.size(),
                                "Expected argument types and supplied argument types should be arrays of same length");

                ArgumentsMatchKind match = ArgumentsMatchKind.EXACT;
                for (int i = 0; i < expectedArgTypes.size() && match != null; i++) {
                        TypeDescriptor suppliedArg = suppliedArgTypes.get(i);
                        TypeDescriptor expectedArg = expectedArgTypes.get(i);
                        if (!expectedArg.equals(suppliedArg)) {
                                // The user may supply null - and that will be ok unless a primitive is expected
                                if (suppliedArg == null) {
                                        if (expectedArg.isPrimitive()) {
                                                match = null;
                                        }
                                }
                                else {
                                        if (suppliedArg.isAssignableTo(expectedArg)) {
                                                if (match != ArgumentsMatchKind.REQUIRES_CONVERSION) {
                                                        match = ArgumentsMatchKind.CLOSE;
                                                }
                                        }
                                        else if (typeConverter.canConvert(suppliedArg, expectedArg)) {
                                                match = ArgumentsMatchKind.REQUIRES_CONVERSION;
                                        }
                                        else {
                                                match = null;
                                        }
                                }
                        }
                }
                return (match != null ? new ArgumentsMatchInfo(match) : null);
        }

        /**
         * Based on {@link MethodInvoker#getTypeDifferenceWeight(Class[], Object[])} but operates on TypeDescriptors.
         */
        public static int getTypeDifferenceWeight(List<TypeDescriptor> paramTypes, List<TypeDescriptor> argTypes) {
                int result = 0;
                for (int i = 0; i < paramTypes.size(); i++) {
                        TypeDescriptor paramType = paramTypes.get(i);
                        TypeDescriptor argType = (i < argTypes.size() ? argTypes.get(i) : null);
                        if (argType == null) {
                                if (paramType.isPrimitive()) {
                                        return Integer.MAX_VALUE;
                                }
                        }
                        else {
                                Class<?> paramTypeClazz = paramType.getType();
                                if (!ClassUtils.isAssignable(paramTypeClazz, argType.getType())) {
                                        return Integer.MAX_VALUE;
                                }
                                if (paramTypeClazz.isPrimitive()) {
                                        paramTypeClazz = Object.class;
                                }
                                Class<?> superClass = argType.getType().getSuperclass();
                                while (superClass != null) {
                                        if (paramTypeClazz.equals(superClass)) {
                                                result = result + 2;
                                                superClass = null;
                                        }
                                        else if (ClassUtils.isAssignable(paramTypeClazz, superClass)) {
                                                result = result + 2;
                                                superClass = superClass.getSuperclass();
                                        }
                                        else {
                                                superClass = null;
                                        }
                                }
                                if (paramTypeClazz.isInterface()) {
                                        result = result + 1;
                                }
                        }
                }
                return result;
        }

        /**
         * Compare argument arrays and return information about whether they match.
         * A supplied type converter and conversionAllowed flag allow for matches to
         * take into account that a type may be transformed into a different type by the
         * converter. This variant of compareArguments also allows for a varargs match.
         * @param expectedArgTypes the types the method/constructor is expecting
         * @param suppliedArgTypes the types that are being supplied at the point of invocation
         * @param typeConverter a registered type converter
         * @return a MatchInfo object indicating what kind of match it was,
         * or {@code null} if it was not a match
         */
        static ArgumentsMatchInfo compareArgumentsVarargs(
                        List<TypeDescriptor> expectedArgTypes, List<TypeDescriptor> suppliedArgTypes, TypeConverter typeConverter) {

                Assert.isTrue(!CollectionUtils.isEmpty(expectedArgTypes),
                                "Expected arguments must at least include one array (the varargs parameter)");
                Assert.isTrue(expectedArgTypes.get(expectedArgTypes.size() - 1).isArray(),
                                "Final expected argument should be array type (the varargs parameter)");

                ArgumentsMatchKind match = ArgumentsMatchKind.EXACT;

                // Check up until the varargs argument:

                // Deal with the arguments up to 'expected number' - 1 (that is everything but the varargs argument)
                int argCountUpToVarargs = expectedArgTypes.size() - 1;
                for (int i = 0; i < argCountUpToVarargs && match != null; i++) {
                        TypeDescriptor suppliedArg = suppliedArgTypes.get(i);
                        TypeDescriptor expectedArg = expectedArgTypes.get(i);
                        if (suppliedArg == null) {
                                if (expectedArg.isPrimitive()) {
                                        match = null;
                                }
                        }
                        else {
                                if (!expectedArg.equals(suppliedArg)) {
                                        if (suppliedArg.isAssignableTo(expectedArg)) {
                                                if (match != ArgumentsMatchKind.REQUIRES_CONVERSION) {
                                                        match = ArgumentsMatchKind.CLOSE;
                                                }
                                        }
                                        else if (typeConverter.canConvert(suppliedArg, expectedArg)) {
                                                match = ArgumentsMatchKind.REQUIRES_CONVERSION;
                                        }
                                        else {
                                                match = null;
                                        }
                                }
                        }
                }

                // If already confirmed it cannot be a match, then return
                if (match == null) {
                        return null;
                }

                if (suppliedArgTypes.size() == expectedArgTypes.size() &&
                                expectedArgTypes.get(expectedArgTypes.size() - 1).equals(
                                                suppliedArgTypes.get(suppliedArgTypes.size() - 1))) {
                        // Special case: there is one parameter left and it is an array and it matches the varargs
                        // expected argument - that is a match, the caller has already built the array. Proceed with it.
                }
                else {
                        // Now... we have the final argument in the method we are checking as a match and we have 0
                        // or more other arguments left to pass to it.
                        TypeDescriptor varargsDesc = expectedArgTypes.get(expectedArgTypes.size() - 1);
                        Class<?> varargsParamType = varargsDesc.getElementTypeDescriptor().getType();

                        // All remaining parameters must be of this type or convertible to this type
                        for (int i = expectedArgTypes.size() - 1; i < suppliedArgTypes.size(); i++) {
                                TypeDescriptor suppliedArg = suppliedArgTypes.get(i);
                                if (suppliedArg == null) {
                                        if (varargsParamType.isPrimitive()) {
                                                match = null;
                                        }
                                }
                                else {
                                        if (varargsParamType != suppliedArg.getType()) {
                                                if (ClassUtils.isAssignable(varargsParamType, suppliedArg.getType())) {
                                                        if (match != ArgumentsMatchKind.REQUIRES_CONVERSION) {
                                                                match = ArgumentsMatchKind.CLOSE;
                                                        }
                                                }
                                                else if (typeConverter.canConvert(suppliedArg, TypeDescriptor.valueOf(varargsParamType))) {
                                                        match = ArgumentsMatchKind.REQUIRES_CONVERSION;
                                                }
                                                else {
                                                        match = null;
                                                }
                                        }
                                }
                        }
                }

                return (match != null ? new ArgumentsMatchInfo(match) : null);
        }


        // TODO could do with more refactoring around argument handling and varargs
        /**
         * Convert a supplied set of arguments into the requested types. If the parameterTypes are related to
         * a varargs method then the final entry in the parameterTypes array is going to be an array itself whose
         * component type should be used as the conversion target for extraneous arguments. (For example, if the
         * parameterTypes are {Integer, String[]} and the input arguments are {Integer, boolean, float} then both
         * the boolean and float must be converted to strings). This method does *not* repackage the arguments
         * into a form suitable for the varargs invocation - a subsequent call to setupArgumentsForVarargsInvocation handles that.
         * @param converter the converter to use for type conversions
         * @param arguments the arguments to convert to the requested parameter types
         * @param method the target Method
         * @return true if some kind of conversion occurred on the argument
         * @throws SpelEvaluationException if there is a problem with conversion
         */
        public static boolean convertAllArguments(TypeConverter converter, Object[] arguments, Method method)
                        throws SpelEvaluationException {

                Integer varargsPosition = (method.isVarArgs() ? method.getParameterTypes().length - 1 : null);
                return convertArguments(converter, arguments, method, varargsPosition);
        }

        /**
         * Takes an input set of argument values and converts them to the types specified as the
         * required parameter types. The arguments are converted 'in-place' in the input array.
         * @param converter the type converter to use for attempting conversions
         * @param arguments the actual arguments that need conversion
         * @param methodOrCtor the target Method or Constructor
         * @param varargsPosition the known position of the varargs argument, if any
         * ({@code null} if not varargs)
         * @return {@code true} if some kind of conversion occurred on an argument
         * @throws EvaluationException if a problem occurs during conversion
         */
        static boolean convertArguments(TypeConverter converter, Object[] arguments, Object methodOrCtor,
                        Integer varargsPosition) throws EvaluationException {

                boolean conversionOccurred = false;
                if (varargsPosition == null) {
                        for (int i = 0; i < arguments.length; i++) {
                                TypeDescriptor targetType = new TypeDescriptor(MethodParameter.forMethodOrConstructor(methodOrCtor, i));
                                Object argument = arguments[i];
                                arguments[i] = converter.convertValue(argument, TypeDescriptor.forObject(argument), targetType);
                                conversionOccurred |= (argument != arguments[i]);
                        }
                }
                else {
                        // Convert everything up to the varargs position
                        for (int i = 0; i < varargsPosition; i++) {
                                TypeDescriptor targetType = new TypeDescriptor(MethodParameter.forMethodOrConstructor(methodOrCtor, i));
                                Object argument = arguments[i];
                                arguments[i] = converter.convertValue(argument, TypeDescriptor.forObject(argument), targetType);
                                conversionOccurred |= (argument != arguments[i]);
                        }
                        MethodParameter methodParam = MethodParameter.forMethodOrConstructor(methodOrCtor, varargsPosition);
                        if (varargsPosition == arguments.length - 1) {
                                // If the target is varargs and there is just one more argument
                                // then convert it here
                                TypeDescriptor targetType = new TypeDescriptor(methodParam);
                                Object argument = arguments[varargsPosition];
                                TypeDescriptor sourceType = TypeDescriptor.forObject(argument);
                                arguments[varargsPosition] = converter.convertValue(argument, sourceType, targetType);
                                // Three outcomes of that previous line:
                                // 1) the input argument was already compatible (ie. array of valid type) and nothing was done
                                // 2) the input argument was correct type but not in an array so it was made into an array
                                // 3) the input argument was the wrong type and got converted and put into an array
                                if (argument != arguments[varargsPosition] &&
                                                !isFirstEntryInArray(argument, arguments[varargsPosition])) {
                                        conversionOccurred = true; // case 3
                                }
                        }
                        else {
                                // Convert remaining arguments to the varargs element type
                                TypeDescriptor targetType = new TypeDescriptor(methodParam).getElementTypeDescriptor();
                                for (int i = varargsPosition; i < arguments.length; i++) {
                                        Object argument = arguments[i];
                                        arguments[i] = converter.convertValue(argument, TypeDescriptor.forObject(argument), targetType);
                                        conversionOccurred |= (argument != arguments[i]);
                                }
                        }
                }
                return conversionOccurred;
        }

        /**
         * Check if the supplied value is the first entry in the array represented by the possibleArray value.
         * @param value the value to check for in the array
         * @param possibleArray an array object that may have the supplied value as the first element
         * @return true if the supplied value is the first entry in the array
         */
        private static boolean isFirstEntryInArray(Object value, Object possibleArray) {
                if (possibleArray == null) {
                        return false;
                }
                Class<?> type = possibleArray.getClass();
                if (!type.isArray() || Array.getLength(possibleArray) == 0 ||
                                !ClassUtils.isAssignableValue(type.getComponentType(), value)) {
                        return false;
                }
                Object arrayValue = Array.get(possibleArray, 0);
                return (type.getComponentType().isPrimitive() ? arrayValue.equals(value) : arrayValue == value);
        }

        /**
         * Package up the arguments so that they correctly match what is expected in parameterTypes.
         * For example, if parameterTypes is {@code (int, String[])} because the second parameter
         * was declared {@code String...}, then if arguments is {@code [1,"a","b"]} then it must be
         * repackaged as {@code [1,new String[]{"a","b"}]} in order to match the expected types.
         * @param requiredParameterTypes the types of the parameters for the invocation
         * @param args the arguments to be setup ready for the invocation
         * @return a repackaged array of arguments where any varargs setup has been done
         */
        public static Object[] setupArgumentsForVarargsInvocation(Class<?>[] requiredParameterTypes, Object... args) {
                // Check if array already built for final argument
                int parameterCount = requiredParameterTypes.length;
                int argumentCount = args.length;

                // Check if repackaging is needed...
                if (parameterCount != args.length ||
                                requiredParameterTypes[parameterCount - 1] !=
                                                (args[argumentCount - 1] != null ? args[argumentCount - 1].getClass() : null)) {

                        int arraySize = 0;  // zero size array if nothing to pass as the varargs parameter
                        if (argumentCount >= parameterCount) {
                                arraySize = argumentCount - (parameterCount - 1);
                        }

                        // Create an array for the varargs arguments
                        Object[] newArgs = new Object[parameterCount];
                        System.arraycopy(args, 0, newArgs, 0, newArgs.length - 1);

                        // Now sort out the final argument, which is the varargs one. Before entering this method,
                        // the arguments should have been converted to the box form of the required type.
                        Class<?> componentType = requiredParameterTypes[parameterCount - 1].getComponentType();
                        Object repackagedArgs = Array.newInstance(componentType, arraySize);
                        for (int i = 0; i < arraySize; i++) {
                                Array.set(repackagedArgs, i, args[parameterCount - 1 + i]);
                        }
                        newArgs[newArgs.length - 1] = repackagedArgs;
                        return newArgs;
                }
                return args;
        }


        enum ArgumentsMatchKind {

                /** An exact match is where the parameter types exactly match what the method/constructor is expecting */
                EXACT,

                /** A close match is where the parameter types either exactly match or are assignment-compatible */
                CLOSE,

                /** A conversion match is where the type converter must be used to transform some of the parameter types */
                REQUIRES_CONVERSION
        }


        /**
         * An instance of ArgumentsMatchInfo describes what kind of match was achieved
         * between two sets of arguments - the set that a method/constructor is expecting
         * and the set that are being supplied at the point of invocation. If the kind
         * indicates that conversion is required for some of the arguments then the arguments
         * that require conversion are listed in the argsRequiringConversion array.
         */
        static class ArgumentsMatchInfo {

                private final ArgumentsMatchKind kind;

                ArgumentsMatchInfo(ArgumentsMatchKind kind) {
                        this.kind = kind;
                }

                public boolean isExactMatch() {
                        return (this.kind == ArgumentsMatchKind.EXACT);
                }

                public boolean isCloseMatch() {
                        return (this.kind == ArgumentsMatchKind.CLOSE);
                }

                public boolean isMatchRequiringConversion() {
                        return (this.kind == ArgumentsMatchKind.REQUIRES_CONVERSION);
                }

                @Override
                public String toString() {
                        return "ArgumentMatchInfo: " + this.kind;
                }
        }

}