/*
 * 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
 *
 *      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.Method;
import java.lang.reflect.Modifier;

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.MethodExecutor;
import org.springframework.expression.TypedValue;
import org.springframework.lang.Nullable;
import org.springframework.util.ClassUtils;
import org.springframework.util.ReflectionUtils;

MethodExecutor that works via reflection. 
Author:
Andy Clement, Juergen Hoeller
Since:
3.0/**
 * {@link MethodExecutor} that works via reflection.
 *
 * @author Andy Clement
 * @author Juergen Hoeller
 * @since 3.0
 */
public class ReflectiveMethodExecutor implements MethodExecutor {

	private final Method originalMethod;

	private final Method methodToInvoke;

	@Nullable
	private final Integer varargsPosition;

	private boolean computedPublicDeclaringClass = false;

	@Nullable
	private Class<?> publicDeclaringClass;

	private boolean argumentConversionOccurred = false;


	
Create a new executor for the given method.
Params:
method – the method to invoke/**
	 * Create a new executor for the given method.
	 * @param method the method to invoke
	 */
	public ReflectiveMethodExecutor(Method method) {
		this.originalMethod = method;
		this.methodToInvoke = ClassUtils.getInterfaceMethodIfPossible(method);
		if (method.isVarArgs()) {
			this.varargsPosition = method.getParameterCount() - 1;
		}
		else {
			this.varargsPosition = null;
		}
	}


	
Return the original method that this executor has been configured for.
/**
	 * Return the original method that this executor has been configured for.
	 */
	public final Method getMethod() {
		return this.originalMethod;
	}

	
Find the first public class in the methods declaring class hierarchy that declares this method.
Sometimes the reflective method discovery logic finds a suitable method that can easily be
called via reflection but cannot be called from generated code when compiling the expression
because of visibility restrictions. For example if a non-public class overrides toString(),
this helper method will walk up the type hierarchy to find the first public type that declares
the method (if there is one!). For toString() it may walk as far as Object.
/**
	 * Find the first public class in the methods declaring class hierarchy that declares this method.
	 * Sometimes the reflective method discovery logic finds a suitable method that can easily be
	 * called via reflection but cannot be called from generated code when compiling the expression
	 * because of visibility restrictions. For example if a non-public class overrides toString(),
	 * this helper method will walk up the type hierarchy to find the first public type that declares
	 * the method (if there is one!). For toString() it may walk as far as Object.
	 */
	@Nullable
	public Class<?> getPublicDeclaringClass() {
		if (!this.computedPublicDeclaringClass) {
			this.publicDeclaringClass =
					discoverPublicDeclaringClass(this.originalMethod, this.originalMethod.getDeclaringClass());
			this.computedPublicDeclaringClass = true;
		}
		return this.publicDeclaringClass;
	}

	@Nullable
	private Class<?> discoverPublicDeclaringClass(Method method, Class<?> clazz) {
		if (Modifier.isPublic(clazz.getModifiers())) {
			try {
				clazz.getDeclaredMethod(method.getName(), method.getParameterTypes());
				return clazz;
			}
			catch (NoSuchMethodException ex) {
				// Continue below...
			}
		}
		if (clazz.getSuperclass() != null) {
			return discoverPublicDeclaringClass(method, clazz.getSuperclass());
		}
		return null;
	}

	public boolean didArgumentConversionOccur() {
		return this.argumentConversionOccurred;
	}


	@Override
	public TypedValue execute(EvaluationContext context, Object target, Object... arguments) throws AccessException {
		try {
			this.argumentConversionOccurred = ReflectionHelper.convertArguments(
					context.getTypeConverter(), arguments, this.originalMethod, this.varargsPosition);
			if (this.originalMethod.isVarArgs()) {
				arguments = ReflectionHelper.setupArgumentsForVarargsInvocation(
						this.originalMethod.getParameterTypes(), arguments);
			}
			ReflectionUtils.makeAccessible(this.methodToInvoke);
			Object value = this.methodToInvoke.invoke(target, arguments);
			return new TypedValue(value, new TypeDescriptor(new MethodParameter(this.originalMethod, -1)).narrow(value));
		}
		catch (Exception ex) {
			throw new AccessException("Problem invoking method: " + this.methodToInvoke, ex);
		}
	}

}