/*
 * 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
 *
 *      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.springframework.expression.spel.support;

import java.lang.reflect.Array;
import java.lang.reflect.Executable;
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.lang.Nullable;
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
	 */
	@Nullable
	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);
			// 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 (!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;
				}
			}
		}
		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
	 */
	@Nullable
	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);
			TypeDescriptor elementDesc = varargsDesc.getElementTypeDescriptor();
			Assert.state(elementDesc != null, "No element type");
			Class<?> varargsParamType = elementDesc.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.getParameterCount() - 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 executable 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, Executable executable,
			@Nullable Integer varargsPosition) throws EvaluationException {

		boolean conversionOccurred = false;
		if (varargsPosition == null) {
			for (int i = 0; i < arguments.length; i++) {
				TypeDescriptor targetType = new TypeDescriptor(MethodParameter.forExecutable(executable, 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.forExecutable(executable, i));
				Object argument = arguments[i];
				arguments[i] = converter.convertValue(argument, TypeDescriptor.forObject(argument), targetType);
				conversionOccurred |= (argument != arguments[i]);
			}
			MethodParameter methodParam = MethodParameter.forExecutable(executable, 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();
				Assert.state(targetType != null, "No element type");
				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, @Nullable 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;
		}
	}

}
