/*
 * #%L
 * HAPI FHIR Subscription Server
 * %%
 * Copyright (C) 2014 - 2023 Smile CDR, Inc.
 * %%
 * 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
 *
 *      http://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.
 * #L%
 */
package ca.uhn.fhir.jpa.subscription.match.deliver.websocket;

import ca.uhn.fhir.i18n.Msg;
import ca.uhn.fhir.jpa.subscription.channel.subscription.SubscriptionChannelRegistry;
import ca.uhn.fhir.jpa.subscription.channel.subscription.SubscriptionChannelWithHandlers;
import ca.uhn.fhir.jpa.subscription.match.registry.ActiveSubscription;
import ca.uhn.fhir.jpa.subscription.model.ResourceDeliveryMessage;
import org.hl7.fhir.instance.model.api.IIdType;
import org.hl7.fhir.r4.model.IdType;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.messaging.Message;
import org.springframework.messaging.MessageHandler;
import org.springframework.messaging.MessagingException;
import org.springframework.web.socket.CloseStatus;
import org.springframework.web.socket.TextMessage;
import org.springframework.web.socket.WebSocketHandler;
import org.springframework.web.socket.WebSocketSession;
import org.springframework.web.socket.handler.TextWebSocketHandler;

import java.io.IOException;
import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;

public class SubscriptionWebsocketHandler extends TextWebSocketHandler implements WebSocketHandler {
        private static Logger ourLog = LoggerFactory.getLogger(SubscriptionWebsocketHandler.class);

        @Autowired
        protected WebsocketConnectionValidator myWebsocketConnectionValidator;

        @Autowired
        SubscriptionChannelRegistry mySubscriptionChannelRegistry;

        /**
         * Constructor
         */
        public SubscriptionWebsocketHandler() {
                super();
        }

        private IState myState = new InitialState();

        @Override
        public void afterConnectionClosed(WebSocketSession theSession, CloseStatus theStatus) throws Exception {
                super.afterConnectionClosed(theSession, theStatus);
                ourLog.info("Closing WebSocket connection from {}", theSession.getRemoteAddress());
        }

        @Override
        public void afterConnectionEstablished(WebSocketSession theSession) throws Exception {
                super.afterConnectionEstablished(theSession);
                ourLog.info("Incoming WebSocket connection from {}", theSession.getRemoteAddress());
        }

        protected void handleFailure(Exception theE) {
                ourLog.error("Failure during communication", theE);
        }

        @Override
        protected void handleTextMessage(WebSocketSession theSession, TextMessage theMessage) throws Exception {
                ourLog.info("Textmessage: " + theMessage.getPayload());
                myState.handleTextMessage(theSession, theMessage);
        }

        @Override
        public void handleTransportError(WebSocketSession theSession, Throwable theException) throws Exception {
                super.handleTransportError(theSession, theException);
                ourLog.error("Transport error", theException);
        }

        @PostConstruct
        public synchronized void postConstruct() {
                ourLog.info("Websocket connection has been created");
        }

        @PreDestroy
        public synchronized void preDescroy() {
                ourLog.info("Websocket connection is closing");
                IState state = myState;
                if (state != null) {
                        state.closing();
                }
        }

        private interface IState {

                void closing();

                void handleTextMessage(WebSocketSession theSession, TextMessage theMessage);
        }

        private class BoundStaticSubscriptionState implements IState, MessageHandler {

                private final WebSocketSession mySession;
                private final ActiveSubscription myActiveSubscription;

                public BoundStaticSubscriptionState(WebSocketSession theSession, ActiveSubscription theActiveSubscription) {
                        mySession = theSession;
                        myActiveSubscription = theActiveSubscription;

                        SubscriptionChannelWithHandlers subscriptionChannelWithHandlers =
                                        mySubscriptionChannelRegistry.getDeliveryReceiverChannel(theActiveSubscription.getChannelName());
                        subscriptionChannelWithHandlers.addHandler(this);
                }

                @Override
                public void closing() {
                        SubscriptionChannelWithHandlers subscriptionChannelWithHandlers =
                                        mySubscriptionChannelRegistry.getDeliveryReceiverChannel(myActiveSubscription.getChannelName());
                        subscriptionChannelWithHandlers.removeHandler(this);
                }

                private void deliver() {
                        try {
                                String payload = "ping " + myActiveSubscription.getId();
                                ourLog.info("Sending WebSocket message: {}", payload);
                                mySession.sendMessage(new TextMessage(payload));
                        } catch (IOException e) {
                                handleFailure(e);
                        }
                }

                @Override
                public void handleMessage(Message<?> theMessage) {
                        if (!(theMessage.getPayload() instanceof ResourceDeliveryMessage)) {
                                return;
                        }
                        try {
                                ResourceDeliveryMessage msg = (ResourceDeliveryMessage) theMessage.getPayload();
                                if (myActiveSubscription.getSubscription().equals(msg.getSubscription())) {
                                        deliver();
                                }
                        } catch (Exception e) {
                                ourLog.error("Failure handling subscription payload", e);
                                throw new MessagingException(theMessage, Msg.code(6) + "Failure handling subscription payload", e);
                        }
                }

                @Override
                public void handleTextMessage(WebSocketSession theSession, TextMessage theMessage) {
                        try {
                                theSession.sendMessage(new TextMessage("Unexpected client message: " + theMessage.getPayload()));
                        } catch (IOException e) {
                                handleFailure(e);
                        }
                }
        }

        private class InitialState implements IState {

                private IIdType bindSimple(WebSocketSession theSession, String theBindString) {
                        IdType id = new IdType(theBindString);

                        WebsocketValidationResponse response = myWebsocketConnectionValidator.validate(id);
                        if (!response.isValid()) {
                                try {
                                        ourLog.warn(response.getMessage());
                                        theSession.close(new CloseStatus(CloseStatus.PROTOCOL_ERROR.getCode(), response.getMessage()));
                                } catch (IOException e) {
                                        handleFailure(e);
                                }
                                return null;
                        }

                        myState = new BoundStaticSubscriptionState(theSession, response.getActiveSubscription());

                        return id;
                }

                @Override
                public void closing() {
                        // nothing
                }

                @Override
                public void handleTextMessage(WebSocketSession theSession, TextMessage theMessage) {
                        String message = theMessage.getPayload();
                        if (message.startsWith("bind ")) {
                                String remaining = message.substring("bind ".length());

                                IIdType subscriptionId;
                                subscriptionId = bindSimple(theSession, remaining);
                                if (subscriptionId == null) {
                                        return;
                                }

                                try {
                                        theSession.sendMessage(new TextMessage("bound " + subscriptionId.getIdPart()));
                                } catch (IOException e) {
                                        handleFailure(e);
                                }
                        }
                }
        }
}