/*
 * Copyright 2002-2021 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.reactive.result.method.annotation;

import java.util.Collection;
import java.util.Collections;
import java.util.List;

import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

import org.springframework.core.MethodParameter;
import org.springframework.core.ReactiveAdapter;
import org.springframework.core.ReactiveAdapterRegistry;
import org.springframework.core.io.buffer.DataBuffer;
import org.springframework.http.HttpHeaders;
import org.springframework.http.codec.HttpMessageReader;
import org.springframework.http.codec.multipart.Part;
import org.springframework.http.server.reactive.ServerHttpRequest;
import org.springframework.http.server.reactive.ServerHttpRequestDecorator;
import org.springframework.lang.Nullable;
import org.springframework.util.CollectionUtils;
import org.springframework.util.StringUtils;
import org.springframework.web.bind.annotation.RequestPart;
import org.springframework.web.reactive.BindingContext;
import org.springframework.web.server.MissingRequestValueException;
import org.springframework.web.server.ServerWebExchange;

/**
 * Resolver for {@code @RequestPart} arguments where the named part is decoded
 * much like an {@code @RequestBody} argument but based on the content of an
 * individual part instead. The arguments may be wrapped with a reactive type
 * for a single value (e.g. Reactor {@code Mono}, RxJava {@code Single}).
 *
 * <p>This resolver also supports arguments of type {@link Part} which may be
 * wrapped with a reactive type for a single value or multiple values.
 *
 * @author Rossen Stoyanchev
 * @since 5.0
 */
public class RequestPartMethodArgumentResolver extends AbstractMessageReaderArgumentResolver {

	public RequestPartMethodArgumentResolver(List<HttpMessageReader<?>> readers, ReactiveAdapterRegistry registry) {
		super(readers, registry);
	}


	@Override
	public boolean supportsParameter(MethodParameter parameter) {
		return (parameter.hasParameterAnnotation(RequestPart.class) ||
				checkParameterType(parameter, Part.class::isAssignableFrom));
	}

	@Override
	public Mono<Object> resolveArgument(
			MethodParameter parameter, BindingContext bindingContext, ServerWebExchange exchange) {

		RequestPart requestPart = parameter.getParameterAnnotation(RequestPart.class);
		boolean isRequired = (requestPart == null || requestPart.required());
		Class<?> paramType = parameter.getParameterType();
		Flux<Part> partValues = getPartValues(parameter, requestPart, isRequired, exchange);

		if (Part.class.isAssignableFrom(paramType)) {
			return partValues.next().cast(Object.class);
		}

		if (Collection.class.isAssignableFrom(paramType) || List.class.isAssignableFrom(paramType)) {
			MethodParameter elementType = parameter.nested();
			if (Part.class.isAssignableFrom(elementType.getNestedParameterType())) {
				return partValues.collectList().cast(Object.class);
			}
			else {
				return partValues.next()
						.flatMap(part -> decode(part, parameter, bindingContext, exchange, isRequired))
						.defaultIfEmpty(Collections.emptyList());
			}
		}

		ReactiveAdapter adapter = getAdapterRegistry().getAdapter(paramType);
		if (adapter == null) {
			return partValues.next().flatMap(part ->
					decode(part, parameter, bindingContext, exchange, isRequired));
		}

		MethodParameter elementType = parameter.nested();
		if (Part.class.isAssignableFrom(elementType.getNestedParameterType())) {
			return Mono.just(adapter.fromPublisher(partValues));
		}

		Flux<?> flux = partValues.flatMap(part -> decode(part, elementType, bindingContext, exchange, isRequired));
		return Mono.just(adapter.fromPublisher(flux));
	}

	public Flux<Part> getPartValues(
			MethodParameter parameter, @Nullable RequestPart requestPart, boolean isRequired,
			ServerWebExchange exchange) {

		String name = getPartName(parameter, requestPart);
		return exchange.getMultipartData()
				.flatMapIterable(map -> {
					List<Part> list = map.get(name);
					if (CollectionUtils.isEmpty(list)) {
						if (isRequired) {
							throw new MissingRequestValueException(
									name, parameter.getParameterType(), "request part", parameter);
						}
						return Collections.emptyList();
					}
					return list;
				});
	}

	private String getPartName(MethodParameter methodParam, @Nullable RequestPart requestPart) {
		String name = null;
		if (requestPart != null) {
			name = requestPart.name();
		}
		if (!StringUtils.hasLength(name)) {
			name = methodParam.getParameterName();
		}
		if (!StringUtils.hasLength(name)) {
			throw new IllegalArgumentException("Request part name for argument type [" +
					methodParam.getNestedParameterType().getName() +
					"] not specified, and parameter name information not found in class file either.");
		}
		return name;
	}

	@SuppressWarnings("unchecked")
	private <T> Mono<T> decode(
			Part part, MethodParameter elementType, BindingContext bindingContext,
			ServerWebExchange exchange, boolean isRequired) {

		ServerHttpRequest partRequest = new PartServerHttpRequest(exchange.getRequest(), part);
		ServerWebExchange partExchange = exchange.mutate().request(partRequest).build();
		if (logger.isDebugEnabled()) {
			logger.debug(exchange.getLogPrefix() + "Decoding part '" + part.name() + "'");
		}
		return (Mono<T>) readBody(elementType, isRequired, bindingContext, partExchange);
	}


	private static class PartServerHttpRequest extends ServerHttpRequestDecorator {

		private final Part part;

		public PartServerHttpRequest(ServerHttpRequest delegate, Part part) {
			super(delegate);
			this.part = part;
		}

		@Override
		public HttpHeaders getHeaders() {
			return this.part.headers();
		}

		@Override
		public Flux<DataBuffer> getBody() {
			return this.part.content();
		}
	}

}
