/*
 * 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
 *
 *      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.servlet.mvc.method.annotation;

import java.io.IOException;
import java.io.OutputStream;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import javax.servlet.ServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.core.MethodParameter;
import org.springframework.core.ResolvableType;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpStatus;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.http.server.ServerHttpResponse;
import org.springframework.http.server.ServletServerHttpResponse;
import org.springframework.util.Assert;
import org.springframework.web.context.request.NativeWebRequest;
import org.springframework.web.context.request.async.DeferredResult;
import org.springframework.web.context.request.async.WebAsyncUtils;
import org.springframework.web.filter.ShallowEtagHeaderFilter;
import org.springframework.web.method.support.AsyncHandlerMethodReturnValueHandler;
import org.springframework.web.method.support.ModelAndViewContainer;

/**
 * Handler for return values of type {@link ResponseBodyEmitter} (and the
 * {@code ResponseEntity<ResponseBodyEmitter>} sub-class) as well as any other
 * async type with a {@link #getAdapterMap() registered adapter}.
 *
 * @author Rossen Stoyanchev
 * @since 4.2
 */
@SuppressWarnings("deprecation")
public class ResponseBodyEmitterReturnValueHandler implements AsyncHandlerMethodReturnValueHandler {

        private static final Log logger = LogFactory.getLog(ResponseBodyEmitterReturnValueHandler.class);


        private final List<HttpMessageConverter<?>> messageConverters;

        private final Map<Class<?>, ResponseBodyEmitterAdapter> adapterMap;


        public ResponseBodyEmitterReturnValueHandler(List<HttpMessageConverter<?>> messageConverters) {
                Assert.notEmpty(messageConverters, "HttpMessageConverter List must not be empty");
                this.messageConverters = messageConverters;
                this.adapterMap = new HashMap<Class<?>, ResponseBodyEmitterAdapter>(4);
                this.adapterMap.put(ResponseBodyEmitter.class, new SimpleResponseBodyEmitterAdapter());
        }


        /**
         * Return the map with {@code ResponseBodyEmitter} adapters.
         * By default the map contains a single adapter {@code ResponseBodyEmitter}
         * that simply downcasts the return value.
         * @return the map of adapters
         * @deprecated in 4.3.8, see comments on {@link ResponseBodyEmitterAdapter}
         */
        @Deprecated
        public Map<Class<?>, ResponseBodyEmitterAdapter> getAdapterMap() {
                return this.adapterMap;
        }

        private ResponseBodyEmitterAdapter getAdapterFor(Class<?> type) {
                if (type != null) {
                        for (Class<?> adapteeType : getAdapterMap().keySet()) {
                                if (adapteeType.isAssignableFrom(type)) {
                                        return getAdapterMap().get(adapteeType);
                                }
                        }
                }
                return null;
        }


        @Override
        public boolean supportsReturnType(MethodParameter returnType) {
                Class<?> bodyType;
                if (ResponseEntity.class.isAssignableFrom(returnType.getParameterType())) {
                        bodyType = ResolvableType.forMethodParameter(returnType).getGeneric(0).resolve();
                }
                else {
                        bodyType = returnType.getParameterType();
                }
                return (getAdapterFor(bodyType) != null);
        }

        @Override
        public boolean isAsyncReturnValue(Object returnValue, MethodParameter returnType) {
                if (returnValue != null) {
                        Object adaptFrom = returnValue;
                        if (returnValue instanceof ResponseEntity) {
                                adaptFrom = ((ResponseEntity) returnValue).getBody();
                        }
                        if (adaptFrom != null) {
                                return (getAdapterFor(adaptFrom.getClass()) != null);
                        }
                }
                return false;
        }

        @Override
        public void handleReturnValue(Object returnValue, MethodParameter returnType,
                        ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {

                if (returnValue == null) {
                        mavContainer.setRequestHandled(true);
                        return;
                }

                HttpServletResponse response = webRequest.getNativeResponse(HttpServletResponse.class);
                ServerHttpResponse outputMessage = new ServletServerHttpResponse(response);

                if (returnValue instanceof ResponseEntity) {
                        ResponseEntity<?> responseEntity = (ResponseEntity<?>) returnValue;
                        response.setStatus(responseEntity.getStatusCodeValue());
                        outputMessage.getHeaders().putAll(responseEntity.getHeaders());
                        returnValue = responseEntity.getBody();
                        if (returnValue == null) {
                                mavContainer.setRequestHandled(true);
                                outputMessage.flush();
                                return;
                        }
                }

                ServletRequest request = webRequest.getNativeRequest(ServletRequest.class);
                ShallowEtagHeaderFilter.disableContentCaching(request);

                ResponseBodyEmitterAdapter adapter = getAdapterFor(returnValue.getClass());
                if (adapter == null) {
                        throw new IllegalStateException(
                                        "Could not find ResponseBodyEmitterAdapter for return value type: " + returnValue.getClass());
                }
                ResponseBodyEmitter emitter = adapter.adaptToEmitter(returnValue, outputMessage);
                emitter.extendResponse(outputMessage);

                // Commit the response and wrap to ignore further header changes
                outputMessage.getBody();
                outputMessage.flush();
                outputMessage = new StreamingServletServerHttpResponse(outputMessage);

                DeferredResult<?> deferredResult = new DeferredResult<Object>(emitter.getTimeout());
                WebAsyncUtils.getAsyncManager(webRequest).startDeferredResultProcessing(deferredResult, mavContainer);

                HttpMessageConvertingHandler handler = new HttpMessageConvertingHandler(outputMessage, deferredResult);
                emitter.initialize(handler);
        }


        /**
         * Adapter for {@code ResponseBodyEmitter} return values.
         */
        private static class SimpleResponseBodyEmitterAdapter implements ResponseBodyEmitterAdapter {

                @Override
                public ResponseBodyEmitter adaptToEmitter(Object returnValue, ServerHttpResponse response) {
                        Assert.isInstanceOf(ResponseBodyEmitter.class, returnValue, "ResponseBodyEmitter expected");
                        return (ResponseBodyEmitter) returnValue;
                }
        }

        /**
         * ResponseBodyEmitter.Handler that writes with HttpMessageConverter's.
         */
        private class HttpMessageConvertingHandler implements ResponseBodyEmitter.Handler {

                private final ServerHttpResponse outputMessage;

                private final DeferredResult<?> deferredResult;

                public HttpMessageConvertingHandler(ServerHttpResponse outputMessage, DeferredResult<?> deferredResult) {
                        this.outputMessage = outputMessage;
                        this.deferredResult = deferredResult;
                }

                @Override
                public void send(Object data, MediaType mediaType) throws IOException {
                        sendInternal(data, mediaType);
                }

                @SuppressWarnings("unchecked")
                private <T> void sendInternal(T data, MediaType mediaType) throws IOException {
                        for (HttpMessageConverter<?> converter : ResponseBodyEmitterReturnValueHandler.this.messageConverters) {
                                if (converter.canWrite(data.getClass(), mediaType)) {
                                        ((HttpMessageConverter<T>) converter).write(data, mediaType, this.outputMessage);
                                        this.outputMessage.flush();
                                        if (logger.isDebugEnabled()) {
                                                logger.debug("Written [" + data + "] using [" + converter + "]");
                                        }
                                        return;
                                }
                        }
                        throw new IllegalArgumentException("No suitable converter for " + data.getClass());
                }

                @Override
                public void complete() {
                        this.deferredResult.setResult(null);
                }

                @Override
                public void completeWithError(Throwable failure) {
                        this.deferredResult.setErrorResult(failure);
                }

                @Override
                public void onTimeout(Runnable callback) {
                        this.deferredResult.onTimeout(callback);
                }

                @Override
                public void onCompletion(Runnable callback) {
                        this.deferredResult.onCompletion(callback);
                }
        }


        /**
         * Wrap to silently ignore header changes HttpMessageConverter's that would
         * otherwise cause HttpHeaders to raise exceptions.
         */
        private static class StreamingServletServerHttpResponse implements ServerHttpResponse {

                private final ServerHttpResponse delegate;

                private final HttpHeaders mutableHeaders = new HttpHeaders();

                public StreamingServletServerHttpResponse(ServerHttpResponse delegate) {
                        this.delegate = delegate;
                        this.mutableHeaders.putAll(delegate.getHeaders());
                }

                @Override
                public void setStatusCode(HttpStatus status) {
                        this.delegate.setStatusCode(status);
                }

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

                @Override
                public OutputStream getBody() throws IOException {
                        return this.delegate.getBody();
                }

                @Override
                public void flush() throws IOException {
                        this.delegate.flush();
                }

                @Override
                public void close() {
                        this.delegate.close();
                }
        }

}