/*
 * Copyright 2002-2019 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.web.method.annotation;

import java.beans.PropertyEditor;
import java.util.Collection;
import java.util.List;
import java.util.Map;
import java.util.Optional;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.Part;

import org.springframework.beans.BeanUtils;
import org.springframework.beans.factory.config.ConfigurableBeanFactory;
import org.springframework.core.MethodParameter;
import org.springframework.core.convert.ConversionService;
import org.springframework.core.convert.TypeDescriptor;
import org.springframework.core.convert.converter.Converter;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.StringUtils;
import org.springframework.web.bind.MissingServletRequestParameterException;
import org.springframework.web.bind.WebDataBinder;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RequestPart;
import org.springframework.web.bind.annotation.ValueConstants;
import org.springframework.web.context.request.NativeWebRequest;
import org.springframework.web.method.support.UriComponentsContributor;
import org.springframework.web.multipart.MultipartException;
import org.springframework.web.multipart.MultipartFile;
import org.springframework.web.multipart.MultipartRequest;
import org.springframework.web.multipart.MultipartResolver;
import org.springframework.web.multipart.support.MissingServletRequestPartException;
import org.springframework.web.multipart.support.MultipartResolutionDelegate;
import org.springframework.web.util.UriComponentsBuilder;

Resolves method arguments annotated with @RequestParam, arguments of type MultipartFile in conjunction with Spring's MultipartResolver abstraction, and arguments of type javax.servlet.http.Part in conjunction with Servlet 3.0 multipart requests. This resolver can also be created in default resolution mode in which simple types (int, long, etc.) not annotated with @RequestParam are also treated as request parameters with the parameter name derived from the argument name. 
If the method parameter type is Map, the name specified in the annotation is used to resolve the request parameter String value. The value is then converted to a Map via type conversion assuming a suitable Converter or PropertyEditor has been registered. Or if a request parameter name is not specified the RequestParamMapMethodArgumentResolver is used instead to provide access to all request parameters in the form of a map. 
A WebDataBinder is invoked to apply type conversion to resolved request header values that don't yet match the method parameter type. 
Author:
Arjen Poutsma, Rossen Stoyanchev, Brian Clozel
See Also:
RequestParamMapMethodArgumentResolver
Since:
3.1/**
 * Resolves method arguments annotated with @{@link RequestParam}, arguments of
 * type {@link MultipartFile} in conjunction with Spring's {@link MultipartResolver}
 * abstraction, and arguments of type {@code javax.servlet.http.Part} in conjunction
 * with Servlet 3.0 multipart requests. This resolver can also be created in default
 * resolution mode in which simple types (int, long, etc.) not annotated with
 * {@link RequestParam @RequestParam} are also treated as request parameters with
 * the parameter name derived from the argument name.
 *
 * <p>If the method parameter type is {@link Map}, the name specified in the
 * annotation is used to resolve the request parameter String value. The value is
 * then converted to a {@link Map} via type conversion assuming a suitable
 * {@link Converter} or {@link PropertyEditor} has been registered.
 * Or if a request parameter name is not specified the
 * {@link RequestParamMapMethodArgumentResolver} is used instead to provide
 * access to all request parameters in the form of a map.
 *
 * <p>A {@link WebDataBinder} is invoked to apply type conversion to resolved request
 * header values that don't yet match the method parameter type.
 *
 * @author Arjen Poutsma
 * @author Rossen Stoyanchev
 * @author Brian Clozel
 * @since 3.1
 * @see RequestParamMapMethodArgumentResolver
 */
public class RequestParamMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolver
		implements UriComponentsContributor {

	private static final TypeDescriptor STRING_TYPE_DESCRIPTOR = TypeDescriptor.valueOf(String.class);

	private final boolean useDefaultResolution;


	
Create a new RequestParamMethodArgumentResolver instance. 
Params:
useDefaultResolution – in default resolution mode a method argument that is a simple type, as defined in BeanUtils.isSimpleProperty, is treated as a request parameter even if it isn't annotated, the request parameter name is derived from the method parameter name./**
	 * Create a new {@link RequestParamMethodArgumentResolver} instance.
	 * @param useDefaultResolution in default resolution mode a method argument
	 * that is a simple type, as defined in {@link BeanUtils#isSimpleProperty},
	 * is treated as a request parameter even if it isn't annotated, the
	 * request parameter name is derived from the method parameter name.
	 */
	public RequestParamMethodArgumentResolver(boolean useDefaultResolution) {
		this.useDefaultResolution = useDefaultResolution;
	}

	
Create a new RequestParamMethodArgumentResolver instance. 
Params:
beanFactory – a bean factory used for resolving ${...} placeholder and #{...} SpEL expressions in default values, or null if default values are not expected to contain expressions
useDefaultResolution – in default resolution mode a method argument that is a simple type, as defined in BeanUtils.isSimpleProperty, is treated as a request parameter even if it isn't annotated, the request parameter name is derived from the method parameter name./**
	 * Create a new {@link RequestParamMethodArgumentResolver} instance.
	 * @param beanFactory a bean factory used for resolving  ${...} placeholder
	 * and #{...} SpEL expressions in default values, or {@code null} if default
	 * values are not expected to contain expressions
	 * @param useDefaultResolution in default resolution mode a method argument
	 * that is a simple type, as defined in {@link BeanUtils#isSimpleProperty},
	 * is treated as a request parameter even if it isn't annotated, the
	 * request parameter name is derived from the method parameter name.
	 */
	public RequestParamMethodArgumentResolver(@Nullable ConfigurableBeanFactory beanFactory,
			boolean useDefaultResolution) {

		super(beanFactory);
		this.useDefaultResolution = useDefaultResolution;
	}


	
Supports the following:

@RequestParam-annotated method arguments. This excludes Map params where the annotation does not specify a name. See RequestParamMapMethodArgumentResolver instead for such params. 
Arguments of type MultipartFile unless annotated with @RequestPart. 
Arguments of type Part unless annotated with @RequestPart. 
In default resolution mode, simple type arguments even if not with @RequestParam. 
/**
	 * Supports the following:
	 * <ul>
	 * <li>@RequestParam-annotated method arguments.
	 * This excludes {@link Map} params where the annotation does not specify a name.
	 * See {@link RequestParamMapMethodArgumentResolver} instead for such params.
	 * <li>Arguments of type {@link MultipartFile} unless annotated with @{@link RequestPart}.
	 * <li>Arguments of type {@code Part} unless annotated with @{@link RequestPart}.
	 * <li>In default resolution mode, simple type arguments even if not with @{@link RequestParam}.
	 * </ul>
	 */
	@Override
	public boolean supportsParameter(MethodParameter parameter) {
		if (parameter.hasParameterAnnotation(RequestParam.class)) {
			if (Map.class.isAssignableFrom(parameter.nestedIfOptional().getNestedParameterType())) {
				RequestParam requestParam = parameter.getParameterAnnotation(RequestParam.class);
				return (requestParam != null && StringUtils.hasText(requestParam.name()));
			}
			else {
				return true;
			}
		}
		else {
			if (parameter.hasParameterAnnotation(RequestPart.class)) {
				return false;
			}
			parameter = parameter.nestedIfOptional();
			if (MultipartResolutionDelegate.isMultipartArgument(parameter)) {
				return true;
			}
			else if (this.useDefaultResolution) {
				return BeanUtils.isSimpleProperty(parameter.getNestedParameterType());
			}
			else {
				return false;
			}
		}
	}

	@Override
	protected NamedValueInfo createNamedValueInfo(MethodParameter parameter) {
		RequestParam ann = parameter.getParameterAnnotation(RequestParam.class);
		return (ann != null ? new RequestParamNamedValueInfo(ann) : new RequestParamNamedValueInfo());
	}

	@Override
	@Nullable
	protected Object resolveName(String name, MethodParameter parameter, NativeWebRequest request) throws Exception {
		HttpServletRequest servletRequest = request.getNativeRequest(HttpServletRequest.class);

		if (servletRequest != null) {
			Object mpArg = MultipartResolutionDelegate.resolveMultipartArgument(name, parameter, servletRequest);
			if (mpArg != MultipartResolutionDelegate.UNRESOLVABLE) {
				return mpArg;
			}
		}

		Object arg = null;
		MultipartRequest multipartRequest = request.getNativeRequest(MultipartRequest.class);
		if (multipartRequest != null) {
			List<MultipartFile> files = multipartRequest.getFiles(name);
			if (!files.isEmpty()) {
				arg = (files.size() == 1 ? files.get(0) : files);
			}
		}
		if (arg == null) {
			String[] paramValues = request.getParameterValues(name);
			if (paramValues != null) {
				arg = (paramValues.length == 1 ? paramValues[0] : paramValues);
			}
		}
		return arg;
	}

	@Override
	protected void handleMissingValue(String name, MethodParameter parameter, NativeWebRequest request)
			throws Exception {

		HttpServletRequest servletRequest = request.getNativeRequest(HttpServletRequest.class);
		if (MultipartResolutionDelegate.isMultipartArgument(parameter)) {
			if (servletRequest == null || !MultipartResolutionDelegate.isMultipartRequest(servletRequest)) {
				throw new MultipartException("Current request is not a multipart request");
			}
			else {
				throw new MissingServletRequestPartException(name);
			}
		}
		else {
			throw new MissingServletRequestParameterException(name,
					parameter.getNestedParameterType().getSimpleName());
		}
	}

	@Override
	public void contributeMethodArgument(MethodParameter parameter, @Nullable Object value,
			UriComponentsBuilder builder, Map<String, Object> uriVariables, ConversionService conversionService) {

		Class<?> paramType = parameter.getNestedParameterType();
		if (Map.class.isAssignableFrom(paramType) || MultipartFile.class == paramType || Part.class == paramType) {
			return;
		}

		RequestParam requestParam = parameter.getParameterAnnotation(RequestParam.class);
		String name = (requestParam != null && StringUtils.hasLength(requestParam.name()) ?
				requestParam.name() : parameter.getParameterName());
		Assert.state(name != null, "Unresolvable parameter name");

		parameter = parameter.nestedIfOptional();
		if (value instanceof Optional) {
			value = ((Optional<?>) value).orElse(null);
		}

		if (value == null) {
			if (requestParam != null &&
					(!requestParam.required() || !requestParam.defaultValue().equals(ValueConstants.DEFAULT_NONE))) {
				return;
			}
			builder.queryParam(name);
		}
		else if (value instanceof Collection) {
			for (Object element : (Collection<?>) value) {
				element = formatUriValue(conversionService, TypeDescriptor.nested(parameter, 1), element);
				builder.queryParam(name, element);
			}
		}
		else {
			builder.queryParam(name, formatUriValue(conversionService, new TypeDescriptor(parameter), value));
		}
	}

	@Nullable
	protected String formatUriValue(
			@Nullable ConversionService cs, @Nullable TypeDescriptor sourceType, @Nullable Object value) {

		if (value == null) {
			return null;
		}
		else if (value instanceof String) {
			return (String) value;
		}
		else if (cs != null) {
			return (String) cs.convert(value, sourceType, STRING_TYPE_DESCRIPTOR);
		}
		else {
			return value.toString();
		}
	}


	private static class RequestParamNamedValueInfo extends NamedValueInfo {

		public RequestParamNamedValueInfo() {
			super("", false, ValueConstants.DEFAULT_NONE);
		}

		public RequestParamNamedValueInfo(RequestParam annotation) {
			super(annotation.name(), annotation.required(), annotation.defaultValue());
		}
	}

}