/*
 * Copyright 2002-2018 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.Method;
import java.lang.reflect.Modifier;
import java.lang.reflect.Proxy;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;

import org.springframework.core.BridgeMethodResolver;
import org.springframework.core.MethodParameter;
import org.springframework.core.convert.TypeDescriptor;
import org.springframework.expression.AccessException;
import org.springframework.expression.EvaluationContext;
import org.springframework.expression.EvaluationException;
import org.springframework.expression.MethodExecutor;
import org.springframework.expression.MethodFilter;
import org.springframework.expression.MethodResolver;
import org.springframework.expression.TypeConverter;
import org.springframework.expression.spel.SpelEvaluationException;
import org.springframework.expression.spel.SpelMessage;
import org.springframework.lang.Nullable;

Reflection-based MethodResolver used by default in StandardEvaluationContext unless explicit method resolvers have been specified. 
Author:
Andy Clement, Juergen Hoeller, Chris Beams
See Also:
StandardEvaluationContext.addMethodResolver(MethodResolver)
Since:
3.0/**
 * Reflection-based {@link MethodResolver} used by default in {@link StandardEvaluationContext}
 * unless explicit method resolvers have been specified.
 *
 * @author Andy Clement
 * @author Juergen Hoeller
 * @author Chris Beams
 * @since 3.0
 * @see StandardEvaluationContext#addMethodResolver(MethodResolver)
 */
public class ReflectiveMethodResolver implements MethodResolver {

	// Using distance will ensure a more accurate match is discovered,
	// more closely following the Java rules.
	private final boolean useDistance;

	@Nullable
	private Map<Class<?>, MethodFilter> filters;


	public ReflectiveMethodResolver() {
		this.useDistance = true;
	}

	
This constructor allows the ReflectiveMethodResolver to be configured such that it
will use a distance computation to check which is the better of two close matches
(when there are multiple matches). Using the distance computation is intended to
ensure matches are more closely representative of what a Java compiler would do
when taking into account boxing/unboxing and whether the method candidates are
declared to handle a supertype of the type (of the argument) being passed in.
Params:
useDistance – true if distance computation should be used when calculating matches; false otherwise/**
	 * This constructor allows the ReflectiveMethodResolver to be configured such that it
	 * will use a distance computation to check which is the better of two close matches
	 * (when there are multiple matches). Using the distance computation is intended to
	 * ensure matches are more closely representative of what a Java compiler would do
	 * when taking into account boxing/unboxing and whether the method candidates are
	 * declared to handle a supertype of the type (of the argument) being passed in.
	 * @param useDistance {@code true} if distance computation should be used when
	 * calculating matches; {@code false} otherwise
	 */
	public ReflectiveMethodResolver(boolean useDistance) {
		this.useDistance = useDistance;
	}


	
Register a filter for methods on the given type.
Params:
type – the type to filter on
filter – the corresponding method filter, or null to clear any filter for the given type/**
	 * Register a filter for methods on the given type.
	 * @param type the type to filter on
	 * @param filter the corresponding method filter,
	 * or {@code null} to clear any filter for the given type
	 */
	public void registerMethodFilter(Class<?> type, @Nullable MethodFilter filter) {
		if (this.filters == null) {
			this.filters = new HashMap<>();
		}
		if (filter != null) {
			this.filters.put(type, filter);
		}
		else {
			this.filters.remove(type);
		}
	}

	
Locate a method on a type. There are three kinds of match that might occur:

an exact match where the types of the arguments match the types of the constructor
an in-exact match where the types we are looking for are subtypes of those defined on the constructor
a match where we are able to convert the arguments into those expected by the constructor,
according to the registered type converter

/**
	 * Locate a method on a type. There are three kinds of match that might occur:
	 * <ol>
	 * <li>an exact match where the types of the arguments match the types of the constructor
	 * <li>an in-exact match where the types we are looking for are subtypes of those defined on the constructor
	 * <li>a match where we are able to convert the arguments into those expected by the constructor,
	 * according to the registered type converter
	 * </ol>
	 */
	@Override
	@Nullable
	public MethodExecutor resolve(EvaluationContext context, Object targetObject, String name,
			List<TypeDescriptor> argumentTypes) throws AccessException {

		try {
			TypeConverter typeConverter = context.getTypeConverter();
			Class<?> type = (targetObject instanceof Class ? (Class<?>) targetObject : targetObject.getClass());
			ArrayList<Method> methods = new ArrayList<>(getMethods(type, targetObject));

			// If a filter is registered for this type, call it
			MethodFilter filter = (this.filters != null ? this.filters.get(type) : null);
			if (filter != null) {
				List<Method> filtered = filter.filter(methods);
				methods = (filtered instanceof ArrayList ? (ArrayList<Method>) filtered : new ArrayList<>(filtered));
			}

			// Sort methods into a sensible order
			if (methods.size() > 1) {
				methods.sort((m1, m2) -> {
					int m1pl = m1.getParameterCount();
					int m2pl = m2.getParameterCount();
					// vararg methods go last
					if (m1pl == m2pl) {
						if (!m1.isVarArgs() && m2.isVarArgs()) {
							return -1;
						}
						else if (m1.isVarArgs() && !m2.isVarArgs()) {
							return 1;
						}
						else {
							return 0;
						}
					}
					return Integer.compare(m1pl, m2pl);
				});
			}

			// Resolve any bridge methods
			for (int i = 0; i < methods.size(); i++) {
				methods.set(i, BridgeMethodResolver.findBridgedMethod(methods.get(i)));
			}

			// Remove duplicate methods (possible due to resolved bridge methods)
			Set<Method> methodsToIterate = new LinkedHashSet<>(methods);

			Method closeMatch = null;
			int closeMatchDistance = Integer.MAX_VALUE;
			Method matchRequiringConversion = null;
			boolean multipleOptions = false;

			for (Method method : methodsToIterate) {
				if (method.getName().equals(name)) {
					Class<?>[] paramTypes = method.getParameterTypes();
					List<TypeDescriptor> paramDescriptors = new ArrayList<>(paramTypes.length);
					for (int i = 0; i < paramTypes.length; i++) {
						paramDescriptors.add(new TypeDescriptor(new MethodParameter(method, i)));
					}
					ReflectionHelper.ArgumentsMatchInfo matchInfo = null;
					if (method.isVarArgs() && argumentTypes.size() >= (paramTypes.length - 1)) {
						// *sigh* complicated
						matchInfo = ReflectionHelper.compareArgumentsVarargs(paramDescriptors, argumentTypes, typeConverter);
					}
					else if (paramTypes.length == argumentTypes.size()) {
						// Name and parameter number match, check the arguments
						matchInfo = ReflectionHelper.compareArguments(paramDescriptors, argumentTypes, typeConverter);
					}
					if (matchInfo != null) {
						if (matchInfo.isExactMatch()) {
							return new ReflectiveMethodExecutor(method);
						}
						else if (matchInfo.isCloseMatch()) {
							if (this.useDistance) {
								int matchDistance = ReflectionHelper.getTypeDifferenceWeight(paramDescriptors, argumentTypes);
								if (closeMatch == null || matchDistance < closeMatchDistance) {
									// This is a better match...
									closeMatch = method;
									closeMatchDistance = matchDistance;
								}
							}
							else {
								// Take this as a close match if there isn't one already
								if (closeMatch == null) {
									closeMatch = method;
								}
							}
						}
						else if (matchInfo.isMatchRequiringConversion()) {
							if (matchRequiringConversion != null) {
								multipleOptions = true;
							}
							matchRequiringConversion = method;
						}
					}
				}
			}
			if (closeMatch != null) {
				return new ReflectiveMethodExecutor(closeMatch);
			}
			else if (matchRequiringConversion != null) {
				if (multipleOptions) {
					throw new SpelEvaluationException(SpelMessage.MULTIPLE_POSSIBLE_METHODS, name);
				}
				return new ReflectiveMethodExecutor(matchRequiringConversion);
			}
			else {
				return null;
			}
		}
		catch (EvaluationException ex) {
			throw new AccessException("Failed to resolve method", ex);
		}
	}

	private Set<Method> getMethods(Class<?> type, Object targetObject) {
		if (targetObject instanceof Class) {
			Set<Method> result = new LinkedHashSet<>();
			// Add these so that static methods are invocable on the type: e.g. Float.valueOf(..)
			Method[] methods = getMethods(type);
			for (Method method : methods) {
				if (Modifier.isStatic(method.getModifiers())) {
					result.add(method);
				}
			}
			// Also expose methods from java.lang.Class itself
			Collections.addAll(result, getMethods(Class.class));
			return result;
		}
		else if (Proxy.isProxyClass(type)) {
			Set<Method> result = new LinkedHashSet<>();
			// Expose interface methods (not proxy-declared overrides) for proper vararg introspection
			for (Class<?> ifc : type.getInterfaces()) {
				Method[] methods = getMethods(ifc);
				for (Method method : methods) {
					if (isCandidateForInvocation(method, type)) {
						result.add(method);
					}
				}
			}
			return result;
		}
		else {
			Set<Method> result = new LinkedHashSet<>();
			Method[] methods = getMethods(type);
			for (Method method : methods) {
				if (isCandidateForInvocation(method, type)) {
					result.add(method);
				}
			}
			return result;
		}
	}

	
Return the set of methods for this type. The default implementation returns the result of Class.getMethods() for the given type, but subclasses may override in order to alter the results, e.g. specifying static methods declared elsewhere. 
Params:
type – the class for which to return the methods
Since:
3.1.1/**
	 * Return the set of methods for this type. The default implementation returns the
	 * result of {@link Class#getMethods()} for the given {@code type}, but subclasses
	 * may override in order to alter the results, e.g. specifying static methods
	 * declared elsewhere.
	 * @param type the class for which to return the methods
	 * @since 3.1.1
	 */
	protected Method[] getMethods(Class<?> type) {
		return type.getMethods();
	}

	
Determine whether the given Method is a candidate for method resolution on an instance of the given target class. 
The default implementation considers any method as a candidate, even for static methods sand non-user-declared methods on the Object base class. 
Params:
method – the Method to evaluate
targetClass – the concrete target class that is being introspected
Since:
4.3.15/**
	 * Determine whether the given {@code Method} is a candidate for method resolution
	 * on an instance of the given target class.
	 * <p>The default implementation considers any method as a candidate, even for
	 * static methods sand non-user-declared methods on the {@link Object} base class.
	 * @param method the Method to evaluate
	 * @param targetClass the concrete target class that is being introspected
	 * @since 4.3.15
	 */
	protected boolean isCandidateForInvocation(Method method, Class<?> targetClass) {
		return true;
	}

}