/*
 * 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.servlet.function.support;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Map;

import javax.servlet.http.HttpServletRequest;

import org.springframework.beans.factory.BeanFactoryUtils;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.context.ApplicationContext;
import org.springframework.http.converter.ByteArrayHttpMessageConverter;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.http.converter.StringHttpMessageConverter;
import org.springframework.http.converter.support.AllEncompassingFormHttpMessageConverter;
import org.springframework.http.converter.xml.SourceHttpMessageConverter;
import org.springframework.lang.Nullable;
import org.springframework.util.CollectionUtils;
import org.springframework.web.servlet.function.RouterFunction;
import org.springframework.web.servlet.function.RouterFunctions;
import org.springframework.web.servlet.function.ServerRequest;
import org.springframework.web.servlet.handler.AbstractHandlerMapping;

/**
 * {@code HandlerMapping} implementation that supports {@link RouterFunction RouterFunctions}.
 *
 * <p>If no {@link RouterFunction} is provided at
 * {@linkplain #RouterFunctionMapping(RouterFunction) construction time}, this mapping
 * will detect all router functions in the application context, and consult them in
 * {@linkplain org.springframework.core.annotation.Order order}.
 *
 * @author Arjen Poutsma
 * @since 5.2
 */
public class RouterFunctionMapping extends AbstractHandlerMapping implements InitializingBean {

        @Nullable
        private RouterFunction<?> routerFunction;

        private List<HttpMessageConverter<?>> messageConverters = Collections.emptyList();

        private boolean detectHandlerFunctionsInAncestorContexts = false;



        /**
         * Create an empty {@code RouterFunctionMapping}.
         * <p>If this constructor is used, this mapping will detect all
         * {@link RouterFunction} instances available in the application context.
         */
        public RouterFunctionMapping() {
        }

        /**
         * Create a {@code RouterFunctionMapping} with the given {@link RouterFunction}.
         * <p>If this constructor is used, no application context detection will occur.
         * @param routerFunction the router function to use for mapping
         */
        public RouterFunctionMapping(RouterFunction<?> routerFunction) {
                this.routerFunction = routerFunction;
        }

        /**
         * Set the router function to map to.
         * <p>If this property is used, no application context detection will occur.
         */
        public void setRouterFunction(@Nullable RouterFunction<?> routerFunction) {
                this.routerFunction = routerFunction;
        }

        /**
         * Return the configured {@link RouterFunction}.
         * <p><strong>Note:</strong> When router functions are detected from the
         * ApplicationContext, this method may return {@code null} if invoked
         * prior to {@link #afterPropertiesSet()}.
         * @return the router function or {@code null}
         */
        @Nullable
        public RouterFunction<?> getRouterFunction() {
                return this.routerFunction;
        }

        public void setMessageConverters(List<HttpMessageConverter<?>> messageConverters) {
                this.messageConverters = messageConverters;
        }

        /**
         * Set whether to detect handler functions in ancestor ApplicationContexts.
         * <p>Default is "false": Only handler functions in the current ApplicationContext
         * will be detected, i.e. only in the context that this HandlerMapping itself
         * is defined in (typically the current DispatcherServlet's context).
         * <p>Switch this flag on to detect handler beans in ancestor contexts
         * (typically the Spring root WebApplicationContext) as well.
         */
        public void setDetectHandlerFunctionsInAncestorContexts(boolean detectHandlerFunctionsInAncestorContexts) {
                this.detectHandlerFunctionsInAncestorContexts = detectHandlerFunctionsInAncestorContexts;
        }

        @Override
        public void afterPropertiesSet() throws Exception {
                if (this.routerFunction == null) {
                        initRouterFunction();
                }
                if (CollectionUtils.isEmpty(this.messageConverters)) {
                        initMessageConverters();
                }
        }

        /**
         * Detect a all {@linkplain RouterFunction router functions} in the
         * current application context.
         */
        @SuppressWarnings({"rawtypes", "unchecked"})
        private void initRouterFunction() {
                ApplicationContext applicationContext = obtainApplicationContext();
                Map<String, RouterFunction> beans =
                                (this.detectHandlerFunctionsInAncestorContexts ?
                                                BeanFactoryUtils.beansOfTypeIncludingAncestors(applicationContext, RouterFunction.class) :
                                                applicationContext.getBeansOfType(RouterFunction.class));

                List<RouterFunction> routerFunctions = new ArrayList<>(beans.values());
                if (!CollectionUtils.isEmpty(routerFunctions) && logger.isInfoEnabled()) {
                        routerFunctions.forEach(routerFunction -> logger.info("Mapped " + routerFunction));
                }
                this.routerFunction = routerFunctions.stream()
                                .reduce(RouterFunction::andOther)
                                .orElse(null);
        }

        /**
         * Initializes a default set of {@linkplain HttpMessageConverter message converters}.
         */
        private void initMessageConverters() {
                List<HttpMessageConverter<?>> messageConverters = new ArrayList<>(4);
                messageConverters.add(new ByteArrayHttpMessageConverter());
                messageConverters.add(new StringHttpMessageConverter());

                try {
                        messageConverters.add(new SourceHttpMessageConverter<>());
                }
                catch (Error err) {
                        // Ignore when no TransformerFactory implementation is available
                }
                messageConverters.add(new AllEncompassingFormHttpMessageConverter());

                this.messageConverters = messageConverters;
        }

        @Nullable
        @Override
        protected Object getHandlerInternal(HttpServletRequest servletRequest) throws Exception {
                String lookupPath = getUrlPathHelper().getLookupPathForRequest(servletRequest);
                servletRequest.setAttribute(LOOKUP_PATH, lookupPath);
                if (this.routerFunction != null) {
                        ServerRequest request = ServerRequest.create(servletRequest, this.messageConverters);
                        servletRequest.setAttribute(RouterFunctions.REQUEST_ATTRIBUTE, request);
                        return this.routerFunction.route(request).orElse(null);
                }
                else {
                        return null;
                }
        }

}