/*
 * 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.messaging.core;

import java.util.Map;

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

import org.springframework.messaging.Message;
import org.springframework.messaging.MessageHeaders;
import org.springframework.messaging.MessagingException;
import org.springframework.messaging.converter.MessageConversionException;
import org.springframework.messaging.converter.MessageConverter;
import org.springframework.messaging.converter.SimpleMessageConverter;
import org.springframework.messaging.converter.SmartMessageConverter;
import org.springframework.util.Assert;

/**
 * Abstract base class for implementations of {@link MessageSendingOperations}.
 *
 * @author Mark Fisher
 * @author Rossen Stoyanchev
 * @author Stephane Nicoll
 * @since 4.0
 */
public abstract class AbstractMessageSendingTemplate<D> implements MessageSendingOperations<D> {

        /**
         * Name of the header that can be set to provide further information
         * (e.g. a {@code MethodParameter} instance) about the origin of the
         * payload, to be taken into account as a conversion hint.
         * @since 4.2
         */
        public static final String CONVERSION_HINT_HEADER = "conversionHint";


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

        private volatile D defaultDestination;

        private volatile MessageConverter converter = new SimpleMessageConverter();


        /**
         * Configure the default destination to use in send methods that don't have
         * a destination argument. If a default destination is not configured, send methods
         * without a destination argument will raise an exception if invoked.
         */
        public void setDefaultDestination(D defaultDestination) {
                this.defaultDestination = defaultDestination;
        }

        /**
         * Return the configured default destination.
         */
        public D getDefaultDestination() {
                return this.defaultDestination;
        }

        /**
         * Set the {@link MessageConverter} to use in {@code convertAndSend} methods.
         * <p>By default, {@link SimpleMessageConverter} is used.
         * @param messageConverter the message converter to use
         */
        public void setMessageConverter(MessageConverter messageConverter) {
                Assert.notNull(messageConverter, "MessageConverter must not be null");
                this.converter = messageConverter;
        }

        /**
         * Return the configured {@link MessageConverter}.
         */
        public MessageConverter getMessageConverter() {
                return this.converter;
        }


        @Override
        public void send(Message<?> message) {
                send(getRequiredDefaultDestination(), message);
        }

        protected final D getRequiredDefaultDestination() {
                Assert.state(this.defaultDestination != null, "No 'defaultDestination' configured");
                return this.defaultDestination;
        }

        @Override
        public void send(D destination, Message<?> message) {
                doSend(destination, message);
        }

        protected abstract void doSend(D destination, Message<?> message);


        @Override
        public void convertAndSend(Object payload) throws MessagingException {
                convertAndSend(payload, null);
        }

        @Override
        public void convertAndSend(D destination, Object payload) throws MessagingException {
                convertAndSend(destination, payload, (Map<String, Object>) null);
        }

        @Override
        public void convertAndSend(D destination, Object payload, Map<String, Object> headers) throws MessagingException {
                convertAndSend(destination, payload, headers, null);
        }

        @Override
        public void convertAndSend(Object payload, MessagePostProcessor postProcessor) throws MessagingException {
                convertAndSend(getRequiredDefaultDestination(), payload, postProcessor);
        }

        @Override
        public void convertAndSend(D destination, Object payload, MessagePostProcessor postProcessor)
                        throws MessagingException {

                convertAndSend(destination, payload, null, postProcessor);
        }

        @Override
        public void convertAndSend(D destination, Object payload, Map<String, Object> headers,
                        MessagePostProcessor postProcessor) throws MessagingException {

                Message<?> message = doConvert(payload, headers, postProcessor);
                send(destination, message);
        }

        /**
         * Convert the given Object to serialized form, possibly using a
         * {@link MessageConverter}, wrap it as a message with the given
         * headers and apply the given post processor.
         * @param payload the Object to use as payload
         * @param headers headers for the message to send
         * @param postProcessor the post processor to apply to the message
         * @return the converted message
         */
        protected Message<?> doConvert(Object payload, Map<String, Object> headers, MessagePostProcessor postProcessor) {
                MessageHeaders messageHeaders = null;
                Object conversionHint = (headers != null ? headers.get(CONVERSION_HINT_HEADER) : null);

                Map<String, Object> headersToUse = processHeadersToSend(headers);
                if (headersToUse != null) {
                        if (headersToUse instanceof MessageHeaders) {
                                messageHeaders = (MessageHeaders) headersToUse;
                        }
                        else {
                                messageHeaders = new MessageHeaders(headersToUse);
                        }
                }

                MessageConverter converter = getMessageConverter();
                Message<?> message = (converter instanceof SmartMessageConverter ?
                                ((SmartMessageConverter) converter).toMessage(payload, messageHeaders, conversionHint) :
                                converter.toMessage(payload, messageHeaders));
                if (message == null) {
                        String payloadType = (payload != null ? payload.getClass().getName() : null);
                        Object contentType = (messageHeaders != null ? messageHeaders.get(MessageHeaders.CONTENT_TYPE) : null);
                        throw new MessageConversionException("Unable to convert payload with type='" + payloadType +
                                        "', contentType='" + contentType + "', converter=[" + getMessageConverter() + "]");
                }
                if (postProcessor != null) {
                        message = postProcessor.postProcessMessage(message);
                }
                return message;
        }

        /**
         * Provides access to the map of input headers before a send operation.
         * Subclasses can modify the headers and then return the same or a different map.
         * <p>This default implementation in this class returns the input map.
         * @param headers the headers to send (or {@code null} if none)
         * @return the actual headers to send (or {@code null} if none)
         */
        protected Map<String, Object> processHeadersToSend(Map<String, Object> headers) {
                return headers;
        }

}