/*
 * 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.messaging.handler.invocation;

import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;

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

import org.springframework.beans.factory.InitializingBean;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.core.MethodIntrospector;
import org.springframework.core.MethodParameter;
import org.springframework.messaging.Message;
import org.springframework.messaging.MessageHandler;
import org.springframework.messaging.MessageHandlingException;
import org.springframework.messaging.MessagingException;
import org.springframework.messaging.handler.DestinationPatternsMessageCondition;
import org.springframework.messaging.handler.HandlerMethod;
import org.springframework.messaging.handler.MessagingAdviceBean;
import org.springframework.messaging.support.MessageBuilder;
import org.springframework.messaging.support.MessageHeaderAccessor;
import org.springframework.util.Assert;
import org.springframework.util.ClassUtils;
import org.springframework.util.CollectionUtils;
import org.springframework.util.LinkedMultiValueMap;
import org.springframework.util.MultiValueMap;
import org.springframework.util.concurrent.ListenableFuture;
import org.springframework.util.concurrent.ListenableFutureCallback;

/**
 * Abstract base class for HandlerMethod-based message handling. Provides most of
 * the logic required to discover handler methods at startup, find a matching handler
 * method at runtime for a given message and invoke it.
 *
 * <p>Also supports discovering and invoking exception handling methods to process
 * exceptions raised during message handling.
 *
 * @author Rossen Stoyanchev
 * @author Juergen Hoeller
 * @since 4.0
 * @param <T> the type of the Object that contains information mapping a
 * {@link org.springframework.messaging.handler.HandlerMethod} to incoming messages
 */
public abstract class AbstractMethodMessageHandler<T>
                implements MessageHandler, ApplicationContextAware, InitializingBean {

        /**
         * Bean name prefix for target beans behind scoped proxies. Used to exclude those
         * targets from handler method detection, in favor of the corresponding proxies.
         * <p>We're not checking the autowire-candidate status here, which is how the
         * proxy target filtering problem is being handled at the autowiring level,
         * since autowire-candidate may have been turned to {@code false} for other
         * reasons, while still expecting the bean to be eligible for handler methods.
         * <p>Originally defined in {@link org.springframework.aop.scope.ScopedProxyUtils}
         * but duplicated here to avoid a hard dependency on the spring-aop module.
         */
        private static final String SCOPED_TARGET_NAME_PREFIX = "scopedTarget.";


        protected final Log logger = LogFactory.getLog(getClass());

        private final List<String> destinationPrefixes = new ArrayList<String>();

        private final List<HandlerMethodArgumentResolver> customArgumentResolvers =
                        new ArrayList<HandlerMethodArgumentResolver>(4);

        private final List<HandlerMethodReturnValueHandler> customReturnValueHandlers =
                        new ArrayList<HandlerMethodReturnValueHandler>(4);

        private final HandlerMethodArgumentResolverComposite argumentResolvers =
                        new HandlerMethodArgumentResolverComposite();

        private final HandlerMethodReturnValueHandlerComposite returnValueHandlers =
                        new HandlerMethodReturnValueHandlerComposite();

        private ApplicationContext applicationContext;

        private final Map<T, HandlerMethod> handlerMethods = new LinkedHashMap<T, HandlerMethod>(64);

        private final MultiValueMap<String, T> destinationLookup = new LinkedMultiValueMap<String, T>(64);

        private final Map<Class<?>, AbstractExceptionHandlerMethodResolver> exceptionHandlerCache =
                        new ConcurrentHashMap<Class<?>, AbstractExceptionHandlerMethodResolver>(64);

        private final Map<MessagingAdviceBean, AbstractExceptionHandlerMethodResolver> exceptionHandlerAdviceCache =
                        new LinkedHashMap<MessagingAdviceBean, AbstractExceptionHandlerMethodResolver>(64);


        /**
         * When this property is configured only messages to destinations matching
         * one of the configured prefixes are eligible for handling. When there is a
         * match the prefix is removed and only the remaining part of the destination
         * is used for method-mapping purposes.
         * <p>By default, no prefixes are configured in which case all messages are
         * eligible for handling.
         */
        public void setDestinationPrefixes(Collection<String> prefixes) {
                this.destinationPrefixes.clear();
                if (prefixes != null) {
                        for (String prefix : prefixes) {
                                prefix = prefix.trim();
                                this.destinationPrefixes.add(prefix);
                        }
                }
        }

        /**
         * Return the configured destination prefixes, if any.
         */
        public Collection<String> getDestinationPrefixes() {
                return this.destinationPrefixes;
        }

        /**
         * Sets the list of custom {@code HandlerMethodArgumentResolver}s that will be used
         * after resolvers for supported argument type.
         */
        public void setCustomArgumentResolvers(List<HandlerMethodArgumentResolver> customArgumentResolvers) {
                this.customArgumentResolvers.clear();
                if (customArgumentResolvers != null) {
                        this.customArgumentResolvers.addAll(customArgumentResolvers);
                }
        }

        /**
         * Return the configured custom argument resolvers, if any.
         */
        public List<HandlerMethodArgumentResolver> getCustomArgumentResolvers() {
                return this.customArgumentResolvers;
        }

        /**
         * Set the list of custom {@code HandlerMethodReturnValueHandler}s that will be used
         * after return value handlers for known types.
         */
        public void setCustomReturnValueHandlers(List<HandlerMethodReturnValueHandler> customReturnValueHandlers) {
                this.customReturnValueHandlers.clear();
                if (customReturnValueHandlers != null) {
                        this.customReturnValueHandlers.addAll(customReturnValueHandlers);
                }
        }

        /**
         * Return the configured custom return value handlers, if any.
         */
        public List<HandlerMethodReturnValueHandler> getCustomReturnValueHandlers() {
                return this.customReturnValueHandlers;
        }

        /**
         * Configure the complete list of supported argument types, effectively overriding
         * the ones configured by default. This is an advanced option; for most use cases
         * it should be sufficient to use {@link #setCustomArgumentResolvers}.
         */
        public void setArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers) {
                if (argumentResolvers == null) {
                        this.argumentResolvers.clear();
                        return;
                }
                this.argumentResolvers.addResolvers(argumentResolvers);
        }

        /**
         * Return the complete list of argument resolvers.
         */
        public List<HandlerMethodArgumentResolver> getArgumentResolvers() {
                return this.argumentResolvers.getResolvers();
        }

        /**
         * Configure the complete list of supported return value types, effectively overriding
         * the ones configured by default. This is an advanced option; for most use cases
         * it should be sufficient to use {@link #setCustomReturnValueHandlers}.
         */
        public void setReturnValueHandlers(List<HandlerMethodReturnValueHandler> returnValueHandlers) {
                if (returnValueHandlers == null) {
                        this.returnValueHandlers.clear();
                        return;
                }
                this.returnValueHandlers.addHandlers(returnValueHandlers);
        }

        /**
         * Return the complete list of return value handlers.
         */
        public List<HandlerMethodReturnValueHandler> getReturnValueHandlers() {
                return this.returnValueHandlers.getReturnValueHandlers();
        }

        @Override
        public void setApplicationContext(ApplicationContext applicationContext) {
                this.applicationContext = applicationContext;
        }

        public ApplicationContext getApplicationContext() {
                return this.applicationContext;
        }


        @Override
        public void afterPropertiesSet() {
                if (this.argumentResolvers.getResolvers().isEmpty()) {
                        this.argumentResolvers.addResolvers(initArgumentResolvers());
                }

                if (this.returnValueHandlers.getReturnValueHandlers().isEmpty()) {
                        this.returnValueHandlers.addHandlers(initReturnValueHandlers());
                }

                for (String beanName : this.applicationContext.getBeanNamesForType(Object.class)) {
                        if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX)) {
                                Class<?> beanType = null;
                                try {
                                        beanType = getApplicationContext().getType(beanName);
                                }
                                catch (Throwable ex) {
                                        // An unresolvable bean type, probably from a lazy bean - let's ignore it.
                                        if (logger.isDebugEnabled()) {
                                                logger.debug("Could not resolve target class for bean with name '" + beanName + "'", ex);
                                        }
                                }
                                if (beanType != null && isHandler(beanType)) {
                                        detectHandlerMethods(beanName);
                                }
                        }
                }
        }

        /**
         * Return the list of argument resolvers to use. Invoked only if the resolvers
         * have not already been set via {@link #setArgumentResolvers}.
         * <p>Subclasses should also take into account custom argument types configured via
         * {@link #setCustomArgumentResolvers}.
         */
        protected abstract List<? extends HandlerMethodArgumentResolver> initArgumentResolvers();

        /**
         * Return the list of return value handlers to use. Invoked only if the return
         * value handlers have not already been set via {@link #setReturnValueHandlers}.
         * <p>Subclasses should also take into account custom return value types configured
         * via {@link #setCustomReturnValueHandlers}.
         */
        protected abstract List<? extends HandlerMethodReturnValueHandler> initReturnValueHandlers();


        /**
         * Whether the given bean type should be introspected for messaging handling methods.
         */
        protected abstract boolean isHandler(Class<?> beanType);

        /**
         * Detect if the given handler has any methods that can handle messages and if
         * so register it with the extracted mapping information.
         * @param handler the handler to check, either an instance of a Spring bean name
         */
        protected final void detectHandlerMethods(final Object handler) {
                Class<?> handlerType = (handler instanceof String ?
                                this.applicationContext.getType((String) handler) : handler.getClass());
                final Class<?> userType = ClassUtils.getUserClass(handlerType);

                Map<Method, T> methods = MethodIntrospector.selectMethods(userType,
                                new MethodIntrospector.MetadataLookup<T>() {
                                        @Override
                                        public T inspect(Method method) {
                                                return getMappingForMethod(method, userType);
                                        }
                                });

                if (logger.isDebugEnabled()) {
                        logger.debug(methods.size() + " message handler methods found on " + userType + ": " + methods);
                }
                for (Map.Entry<Method, T> entry : methods.entrySet()) {
                        registerHandlerMethod(handler, entry.getKey(), entry.getValue());
                }
        }

        /**
         * Provide the mapping for a handler method.
         * @param method the method to provide a mapping for
         * @param handlerType the handler type, possibly a sub-type of the method's declaring class
         * @return the mapping, or {@code null} if the method is not mapped
         */
        protected abstract T getMappingForMethod(Method method, Class<?> handlerType);

        /**
         * Register a handler method and its unique mapping.
         * @param handler the bean name of the handler or the handler instance
         * @param method the method to register
         * @param mapping the mapping conditions associated with the handler method
         * @throws IllegalStateException if another method was already registered
         * under the same mapping
         */
        protected void registerHandlerMethod(Object handler, Method method, T mapping) {
                Assert.notNull(mapping, "Mapping must not be null");
                HandlerMethod newHandlerMethod = createHandlerMethod(handler, method);
                HandlerMethod oldHandlerMethod = this.handlerMethods.get(mapping);

                if (oldHandlerMethod != null && !oldHandlerMethod.equals(newHandlerMethod)) {
                        throw new IllegalStateException("Ambiguous mapping found. Cannot map '" + newHandlerMethod.getBean() +
                                        "' bean method \n" + newHandlerMethod + "\nto " + mapping + ": There is already '" +
                                        oldHandlerMethod.getBean() + "' bean method\n" + oldHandlerMethod + " mapped.");
                }

                this.handlerMethods.put(mapping, newHandlerMethod);
                if (logger.isInfoEnabled()) {
                        logger.info("Mapped \"" + mapping + "\" onto " + newHandlerMethod);
                }

                for (String pattern : getDirectLookupDestinations(mapping)) {
                        this.destinationLookup.add(pattern, mapping);
                }
        }

        /**
         * Create a HandlerMethod instance from an Object handler that is either a handler
         * instance or a String-based bean name.
         */
        protected HandlerMethod createHandlerMethod(Object handler, Method method) {
                HandlerMethod handlerMethod;
                if (handler instanceof String) {
                        String beanName = (String) handler;
                        handlerMethod = new HandlerMethod(beanName,
                                        this.applicationContext.getAutowireCapableBeanFactory(), method);
                }
                else {
                        handlerMethod = new HandlerMethod(handler, method);
                }
                return handlerMethod;
        }

        /**
         * Return destinations contained in the mapping that are not patterns and are
         * therefore suitable for direct lookups.
         */
        protected abstract Set<String> getDirectLookupDestinations(T mapping);

        /**
         * Subclasses can invoke this method to populate the MessagingAdviceBean cache
         * (e.g. to support "global" {@code @MessageExceptionHandler}).
         * @since 4.2
         */
        protected void registerExceptionHandlerAdvice(
                        MessagingAdviceBean bean, AbstractExceptionHandlerMethodResolver resolver) {

                this.exceptionHandlerAdviceCache.put(bean, resolver);
        }

        /**
         * Return a map with all handler methods and their mappings.
         */
        public Map<T, HandlerMethod> getHandlerMethods() {
                return Collections.unmodifiableMap(this.handlerMethods);
        }


        @Override
        public void handleMessage(Message<?> message) throws MessagingException {
                String destination = getDestination(message);
                if (destination == null) {
                        return;
                }
                String lookupDestination = getLookupDestination(destination);
                if (lookupDestination == null) {
                        return;
                }
                MessageHeaderAccessor headerAccessor = MessageHeaderAccessor.getMutableAccessor(message);
                headerAccessor.setHeader(DestinationPatternsMessageCondition.LOOKUP_DESTINATION_HEADER, lookupDestination);
                headerAccessor.setLeaveMutable(true);
                message = MessageBuilder.createMessage(message.getPayload(), headerAccessor.getMessageHeaders());

                if (logger.isDebugEnabled()) {
                        logger.debug("Searching methods to handle " +
                                        headerAccessor.getShortLogMessage(message.getPayload()) +
                                        ", lookupDestination='" + lookupDestination + "'");
                }

                handleMessageInternal(message, lookupDestination);
                headerAccessor.setImmutable();
        }

        protected abstract String getDestination(Message<?> message);

        /**
         * Check whether the given destination (of an incoming message) matches to
         * one of the configured destination prefixes and if so return the remaining
         * portion of the destination after the matched prefix.
         * <p>If there are no matching prefixes, return {@code null}.
         * <p>If there are no destination prefixes, return the destination as is.
         */
        protected String getLookupDestination(String destination) {
                if (destination == null) {
                        return null;
                }
                if (CollectionUtils.isEmpty(this.destinationPrefixes)) {
                        return destination;
                }
                for (String prefix : this.destinationPrefixes) {
                        if (destination.startsWith(prefix)) {
                                return destination.substring(prefix.length());
                        }
                }
                return null;
        }

        protected void handleMessageInternal(Message<?> message, String lookupDestination) {
                List<Match> matches = new ArrayList<Match>();

                List<T> mappingsByUrl = this.destinationLookup.get(lookupDestination);
                if (mappingsByUrl != null) {
                        addMatchesToCollection(mappingsByUrl, message, matches);
                }
                if (matches.isEmpty()) {
                        // No direct hits, go through all mappings
                        Set<T> allMappings = this.handlerMethods.keySet();
                        addMatchesToCollection(allMappings, message, matches);
                }
                if (matches.isEmpty()) {
                        handleNoMatch(this.handlerMethods.keySet(), lookupDestination, message);
                        return;
                }

                Comparator<Match> comparator = new MatchComparator(getMappingComparator(message));
                Collections.sort(matches, comparator);
                if (logger.isTraceEnabled()) {
                        logger.trace("Found " + matches.size() + " handler methods: " + matches);
                }

                Match bestMatch = matches.get(0);
                if (matches.size() > 1) {
                        Match secondBestMatch = matches.get(1);
                        if (comparator.compare(bestMatch, secondBestMatch) == 0) {
                                Method m1 = bestMatch.handlerMethod.getMethod();
                                Method m2 = secondBestMatch.handlerMethod.getMethod();
                                throw new IllegalStateException("Ambiguous handler methods mapped for destination '" +
                                                lookupDestination + "': {" + m1 + ", " + m2 + "}");
                        }
                }

                handleMatch(bestMatch.mapping, bestMatch.handlerMethod, lookupDestination, message);
        }

        private void addMatchesToCollection(Collection<T> mappingsToCheck, Message<?> message, List<Match> matches) {
                for (T mapping : mappingsToCheck) {
                        T match = getMatchingMapping(mapping, message);
                        if (match != null) {
                                matches.add(new Match(match, this.handlerMethods.get(mapping)));
                        }
                }
        }

        /**
         * Check if a mapping matches the current message and return a possibly
         * new mapping with conditions relevant to the current request.
         * @param mapping the mapping to get a match for
         * @param message the message being handled
         * @return the match or {@code null} if there is no match
         */
        protected abstract T getMatchingMapping(T mapping, Message<?> message);

        protected void handleNoMatch(Set<T> ts, String lookupDestination, Message<?> message) {
                logger.debug("No matching message handler methods.");
        }

        /**
         * Return a comparator for sorting matching mappings.
         * The returned comparator should sort 'better' matches higher.
         * @param message the current Message
         * @return the comparator, never {@code null}
         */
        protected abstract Comparator<T> getMappingComparator(Message<?> message);

        protected void handleMatch(T mapping, HandlerMethod handlerMethod, String lookupDestination, Message<?> message) {
                if (logger.isDebugEnabled()) {
                        logger.debug("Invoking " + handlerMethod.getShortLogMessage());
                }
                handlerMethod = handlerMethod.createWithResolvedBean();
                InvocableHandlerMethod invocable = new InvocableHandlerMethod(handlerMethod);
                invocable.setMessageMethodArgumentResolvers(this.argumentResolvers);
                try {
                        Object returnValue = invocable.invoke(message);
                        MethodParameter returnType = handlerMethod.getReturnType();
                        if (void.class == returnType.getParameterType()) {
                                return;
                        }
                        if (this.returnValueHandlers.isAsyncReturnValue(returnValue, returnType)) {
                                ListenableFuture<?> future = this.returnValueHandlers.toListenableFuture(returnValue, returnType);
                                if (future != null) {
                                        future.addCallback(new ReturnValueListenableFutureCallback(invocable, message));
                                }
                        }
                        else {
                                this.returnValueHandlers.handleReturnValue(returnValue, returnType, message);
                        }
                }
                catch (Exception ex) {
                        processHandlerMethodException(handlerMethod, ex, message);
                }
                catch (Throwable ex) {
                        Exception handlingException =
                                        new MessageHandlingException(message, "Unexpected handler method invocation error", ex);
                        processHandlerMethodException(handlerMethod, handlingException, message);
                }
        }

        protected void processHandlerMethodException(HandlerMethod handlerMethod, Exception exception, Message<?> message) {
                InvocableHandlerMethod invocable = getExceptionHandlerMethod(handlerMethod, exception);
                if (invocable == null) {
                        logger.error("Unhandled exception from message handler method", exception);
                        return;
                }
                invocable.setMessageMethodArgumentResolvers(this.argumentResolvers);
                if (logger.isDebugEnabled()) {
                        logger.debug("Invoking " + invocable.getShortLogMessage());
                }
                try {
                        Throwable cause = exception.getCause();
                        Object returnValue = (cause != null ?
                                        invocable.invoke(message, exception, cause, handlerMethod) :
                                        invocable.invoke(message, exception, handlerMethod));
                        MethodParameter returnType = invocable.getReturnType();
                        if (void.class == returnType.getParameterType()) {
                                return;
                        }
                        this.returnValueHandlers.handleReturnValue(returnValue, returnType, message);
                }
                catch (Throwable ex2) {
                        logger.error("Error while processing handler method exception", ex2);
                }
        }

        /**
         * Find an {@code @MessageExceptionHandler} method for the given exception.
         * The default implementation searches methods in the class hierarchy of the
         * HandlerMethod first and if not found, it continues searching for additional
         * {@code @MessageExceptionHandler} methods among the configured
         * {@linkplain org.springframework.messaging.handler.MessagingAdviceBean
         * MessagingAdviceBean}, if any.
         * @param handlerMethod the method where the exception was raised
         * @param exception the raised exception
         * @return a method to handle the exception, or {@code null}
         * @since 4.2
         */
        protected InvocableHandlerMethod getExceptionHandlerMethod(HandlerMethod handlerMethod, Exception exception) {
                if (logger.isDebugEnabled()) {
                        logger.debug("Searching methods to handle " + exception.getClass().getSimpleName());
                }
                Class<?> beanType = handlerMethod.getBeanType();
                AbstractExceptionHandlerMethodResolver resolver = this.exceptionHandlerCache.get(beanType);
                if (resolver == null) {
                        resolver = createExceptionHandlerMethodResolverFor(beanType);
                        this.exceptionHandlerCache.put(beanType, resolver);
                }
                Method method = resolver.resolveMethod(exception);
                if (method != null) {
                        return new InvocableHandlerMethod(handlerMethod.getBean(), method);
                }
                for (MessagingAdviceBean advice : this.exceptionHandlerAdviceCache.keySet()) {
                        if (advice.isApplicableToBeanType(beanType)) {
                                resolver = this.exceptionHandlerAdviceCache.get(advice);
                                method = resolver.resolveMethod(exception);
                                if (method != null) {
                                        return new InvocableHandlerMethod(advice.resolveBean(), method);
                                }
                        }
                }
                return null;
        }

        protected abstract AbstractExceptionHandlerMethodResolver createExceptionHandlerMethodResolverFor(
                        Class<?> beanType);


        @Override
        public String toString() {
                return getClass().getSimpleName() + "[prefixes=" + getDestinationPrefixes() + "]";
        }


        /**
         * A thin wrapper around a matched HandlerMethod and its matched mapping for
         * the purpose of comparing the best match with a comparator in the context
         * of a message.
         */
        private class Match {

                private final T mapping;

                private final HandlerMethod handlerMethod;

                public Match(T mapping, HandlerMethod handlerMethod) {
                        this.mapping = mapping;
                        this.handlerMethod = handlerMethod;
                }

                @Override
                public String toString() {
                        return this.mapping.toString();
                }
        }


        private class MatchComparator implements Comparator<Match> {

                private final Comparator<T> comparator;

                public MatchComparator(Comparator<T> comparator) {
                        this.comparator = comparator;
                }

                @Override
                public int compare(Match match1, Match match2) {
                        return this.comparator.compare(match1.mapping, match2.mapping);
                }
        }


        private class ReturnValueListenableFutureCallback implements ListenableFutureCallback<Object> {

                private final InvocableHandlerMethod handlerMethod;

                private final Message<?> message;

                public ReturnValueListenableFutureCallback(InvocableHandlerMethod handlerMethod, Message<?> message) {
                        this.handlerMethod = handlerMethod;
                        this.message = message;
                }

                @Override
                public void onSuccess(Object result) {
                        try {
                                MethodParameter returnType = this.handlerMethod.getAsyncReturnValueType(result);
                                returnValueHandlers.handleReturnValue(result, returnType, this.message);
                        }
                        catch (Throwable ex) {
                                handleFailure(ex);
                        }
                }

                @Override
                public void onFailure(Throwable ex) {
                        handleFailure(ex);
                }

                private void handleFailure(Throwable ex) {
                        Exception cause = (ex instanceof Exception ? (Exception) ex : new IllegalStateException(ex));
                        processHandlerMethodException(this.handlerMethod, cause, this.message);
                }
        }

}