/*
 * 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.socket.sockjs.transport.session;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Date;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ScheduledFuture;

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

import org.springframework.core.NestedExceptionUtils;
import org.springframework.util.Assert;
import org.springframework.web.socket.CloseStatus;
import org.springframework.web.socket.TextMessage;
import org.springframework.web.socket.WebSocketHandler;
import org.springframework.web.socket.WebSocketMessage;
import org.springframework.web.socket.sockjs.SockJsMessageDeliveryException;
import org.springframework.web.socket.sockjs.SockJsTransportFailureException;
import org.springframework.web.socket.sockjs.frame.SockJsFrame;
import org.springframework.web.socket.sockjs.frame.SockJsMessageCodec;
import org.springframework.web.socket.sockjs.transport.SockJsServiceConfig;
import org.springframework.web.socket.sockjs.transport.SockJsSession;

/**
 * An abstract base class for SockJS sessions implementing {@link SockJsSession}.
 *
 * @author Rossen Stoyanchev
 * @author Sam Brannen
 * @since 4.0
 */
public abstract class AbstractSockJsSession implements SockJsSession {

        private enum State {NEW, OPEN, CLOSED}


        /**
         * Log category to use on network IO exceptions after a client has gone away.
         * <p>The Servlet API does not provide notifications when a client disconnects;
         * see <a href="https://java.net/jira/browse/SERVLET_SPEC-44">SERVLET_SPEC-44</a>.
         * Therefore network IO failures may occur simply because a client has gone away,
         * and that can fill the logs with unnecessary stack traces.
         * <p>We make a best effort to identify such network failures, on a per-server
         * basis, and log them under a separate log category. A simple one-line message
         * is logged at DEBUG level, while a full stack trace is shown at TRACE level.
         * @see #disconnectedClientLogger
         */
        public static final String DISCONNECTED_CLIENT_LOG_CATEGORY =
                        "org.springframework.web.socket.sockjs.DisconnectedClient";

        /**
         * Tomcat: ClientAbortException or EOFException
         * Jetty: EofException
         * WildFly, GlassFish: java.io.IOException "Broken pipe" (already covered)
         * @see #indicatesDisconnectedClient(Throwable)
         */
        private static final Set<String> DISCONNECTED_CLIENT_EXCEPTIONS =
                        new HashSet<String>(Arrays.asList("ClientAbortException", "EOFException", "EofException"));


        /**
         * Separate logger to use on network IO failure after a client has gone away.
         * @see #DISCONNECTED_CLIENT_LOG_CATEGORY
         */
        protected static final Log disconnectedClientLogger = LogFactory.getLog(DISCONNECTED_CLIENT_LOG_CATEGORY);

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

        protected final Object responseLock = new Object();

        private final String id;

        private final SockJsServiceConfig config;

        private final WebSocketHandler handler;

        private final Map<String, Object> attributes = new ConcurrentHashMap<String, Object>();

        private volatile State state = State.NEW;

        private final long timeCreated = System.currentTimeMillis();

        private volatile long timeLastActive = this.timeCreated;

        private ScheduledFuture<?> heartbeatFuture;

        private HeartbeatTask heartbeatTask;

        private volatile boolean heartbeatDisabled;


        /**
         * Create a new instance.
         * @param id the session ID
         * @param config SockJS service configuration options
         * @param handler the recipient of SockJS messages
         * @param attributes attributes from the HTTP handshake to associate with the WebSocket
         * session; the provided attributes are copied, the original map is not used.
         */
        public AbstractSockJsSession(String id, SockJsServiceConfig config, WebSocketHandler handler,
                        Map<String, Object> attributes) {

                Assert.notNull(id, "Session id must not be null");
                Assert.notNull(config, "SockJsServiceConfig must not be null");
                Assert.notNull(handler, "WebSocketHandler must not be null");

                this.id = id;
                this.config = config;
                this.handler = handler;

                if (attributes != null) {
                        this.attributes.putAll(attributes);
                }
        }


        @Override
        public String getId() {
                return this.id;
        }

        protected SockJsMessageCodec getMessageCodec() {
                return this.config.getMessageCodec();
        }

        public SockJsServiceConfig getSockJsServiceConfig() {
                return this.config;
        }

        @Override
        public Map<String, Object> getAttributes() {
                return this.attributes;
        }


        // Message sending

        public final void sendMessage(WebSocketMessage<?> message) throws IOException {
                Assert.state(!isClosed(), "Cannot send a message when session is closed");
                Assert.isInstanceOf(TextMessage.class, message, "SockJS supports text messages only");
                sendMessageInternal(((TextMessage) message).getPayload());
        }

        protected abstract void sendMessageInternal(String message) throws IOException;


        // Lifecycle related methods

        public boolean isNew() {
                return State.NEW.equals(this.state);
        }

        @Override
        public boolean isOpen() {
                return State.OPEN.equals(this.state);
        }

        public boolean isClosed() {
                return State.CLOSED.equals(this.state);
        }

        /**
         * Performs cleanup and notify the {@link WebSocketHandler}.
         */
        @Override
        public final void close() throws IOException {
                close(new CloseStatus(3000, "Go away!"));
        }

        /**
         * Performs cleanup and notify the {@link WebSocketHandler}.
         */
        @Override
        public final void close(CloseStatus status) throws IOException {
                if (isOpen()) {
                        if (logger.isDebugEnabled()) {
                                logger.debug("Closing SockJS session " + getId() + " with " + status);
                        }
                        this.state = State.CLOSED;
                        try {
                                if (isActive() && !CloseStatus.SESSION_NOT_RELIABLE.equals(status)) {
                                        try {
                                                writeFrameInternal(SockJsFrame.closeFrame(status.getCode(), status.getReason()));
                                        }
                                        catch (Throwable ex) {
                                                logger.debug("Failure while sending SockJS close frame", ex);
                                        }
                                }
                                updateLastActiveTime();
                                cancelHeartbeat();
                                disconnect(status);
                        }
                        finally {
                                try {
                                        this.handler.afterConnectionClosed(this, status);
                                }
                                catch (Throwable ex) {
                                        logger.debug("Error from WebSocketHandler.afterConnectionClosed in " + this, ex);
                                }
                        }
                }
        }

        @Override
        public long getTimeSinceLastActive() {
                if (isNew()) {
                        return (System.currentTimeMillis() - this.timeCreated);
                }
                else {
                        return (isActive() ? 0 : System.currentTimeMillis() - this.timeLastActive);
                }
        }

        /**
         * Should be invoked whenever the session becomes inactive.
         */
        protected void updateLastActiveTime() {
                this.timeLastActive = System.currentTimeMillis();
        }

        @Override
        public void disableHeartbeat() {
                this.heartbeatDisabled = true;
                cancelHeartbeat();
        }

        public void sendHeartbeat() throws SockJsTransportFailureException {
                synchronized (this.responseLock) {
                        if (isActive() && !this.heartbeatDisabled) {
                                writeFrame(SockJsFrame.heartbeatFrame());
                                scheduleHeartbeat();
                        }
                }
        }

        protected void scheduleHeartbeat() {
                if (this.heartbeatDisabled) {
                        return;
                }
                synchronized (this.responseLock) {
                        cancelHeartbeat();
                        if (!isActive()) {
                                return;
                        }
                        Date time = new Date(System.currentTimeMillis() + this.config.getHeartbeatTime());
                        this.heartbeatTask = new HeartbeatTask();
                        this.heartbeatFuture = this.config.getTaskScheduler().schedule(this.heartbeatTask, time);
                        if (logger.isTraceEnabled()) {
                                logger.trace("Scheduled heartbeat in session " + getId());
                        }
                }
        }

        protected void cancelHeartbeat() {
                synchronized (this.responseLock) {
                        if (this.heartbeatFuture != null) {
                                if (logger.isTraceEnabled()) {
                                        logger.trace("Cancelling heartbeat in session " + getId());
                                }
                                this.heartbeatFuture.cancel(false);
                                this.heartbeatFuture = null;
                        }
                        if (this.heartbeatTask != null) {
                                this.heartbeatTask.cancel();
                                this.heartbeatTask = null;
                        }
                }
        }

        /**
         * Polling and Streaming sessions periodically close the current HTTP request and
         * wait for the next request to come through. During this "downtime" the session is
         * still open but inactive and unable to send messages and therefore has to buffer
         * them temporarily. A WebSocket session by contrast is stateful and remain active
         * until closed.
         */
        public abstract boolean isActive();

        /**
         * Actually close the underlying WebSocket session or in the case of HTTP
         * transports complete the underlying request.
         */
        protected abstract void disconnect(CloseStatus status) throws IOException;


        // Frame writing

        /**
         * For internal use within a TransportHandler and the (TransportHandler-specific)
         * session class.
         */
        protected void writeFrame(SockJsFrame frame) throws SockJsTransportFailureException {
                if (logger.isTraceEnabled()) {
                        logger.trace("Preparing to write " + frame);
                }
                try {
                        writeFrameInternal(frame);
                }
                catch (Throwable ex) {
                        logWriteFrameFailure(ex);
                        try {
                                // Force disconnect (so we won't try to send close frame)
                                disconnect(CloseStatus.SERVER_ERROR);
                        }
                        catch (Throwable disconnectFailure) {
                                // Ignore
                        }
                        try {
                                close(CloseStatus.SERVER_ERROR);
                        }
                        catch (Throwable closeFailure) {
                                // Nothing of consequence, already forced disconnect
                        }
                        throw new SockJsTransportFailureException("Failed to write " + frame, getId(), ex);
                }
        }

        protected abstract void writeFrameInternal(SockJsFrame frame) throws IOException;

        private void logWriteFrameFailure(Throwable ex) {
                if (indicatesDisconnectedClient(ex)) {
                        if (disconnectedClientLogger.isTraceEnabled()) {
                                disconnectedClientLogger.trace("Looks like the client has gone away", ex);
                        }
                        else if (disconnectedClientLogger.isDebugEnabled()) {
                                disconnectedClientLogger.debug("Looks like the client has gone away: " + ex +
                                                " (For a full stack trace, set the log category '" + DISCONNECTED_CLIENT_LOG_CATEGORY +
                                                "' to TRACE level.)");
                        }
                }
                else {
                        logger.debug("Terminating connection after failure to send message to client", ex);
                }
        }

        private boolean indicatesDisconnectedClient(Throwable ex)  {
                String message = NestedExceptionUtils.getMostSpecificCause(ex).getMessage();
                message = (message != null ? message.toLowerCase() : "");
                String className = ex.getClass().getSimpleName();
                return (message.contains("broken pipe") || DISCONNECTED_CLIENT_EXCEPTIONS.contains(className));
        }


        // Delegation methods

        public void delegateConnectionEstablished() throws Exception {
                this.state = State.OPEN;
                this.handler.afterConnectionEstablished(this);
        }

        public void delegateMessages(String... messages) throws SockJsMessageDeliveryException {
                List<String> undelivered = new ArrayList<String>(Arrays.asList(messages));
                for (String message : messages) {
                        try {
                                if (isClosed()) {
                                        throw new SockJsMessageDeliveryException(this.id, undelivered, "Session closed");
                                }
                                else {
                                        this.handler.handleMessage(this, new TextMessage(message));
                                        undelivered.remove(0);
                                }
                        }
                        catch (Throwable ex) {
                                throw new SockJsMessageDeliveryException(this.id, undelivered, ex);
                        }
                }
        }

        /**
         * Invoked when the underlying connection is closed.
         */
        public final void delegateConnectionClosed(CloseStatus status) throws Exception {
                if (!isClosed()) {
                        try {
                                updateLastActiveTime();
                                // Avoid cancelHeartbeat() and responseLock within server "close" callback
                                ScheduledFuture<?> future = this.heartbeatFuture;
                                if (future != null) {
                                        this.heartbeatFuture = null;
                                        future.cancel(false);
                                }
                        }
                        finally {
                                this.state = State.CLOSED;
                                this.handler.afterConnectionClosed(this, status);
                        }
                }
        }

        /**
         * Close due to error arising from SockJS transport handling.
         */
        public void tryCloseWithSockJsTransportError(Throwable error, CloseStatus closeStatus) {
                if (logger.isDebugEnabled()) {
                        logger.debug("Closing due to transport error for " + this);
                }
                try {
                        delegateError(error);
                }
                catch (Throwable delegateException) {
                        // Ignore
                        logger.debug("Exception from error handling delegate", delegateException);
                }
                try {
                        close(closeStatus);
                }
                catch (Throwable closeException) {
                        logger.debug("Failure while closing " + this, closeException);
                }
        }

        public void delegateError(Throwable ex) throws Exception {
                this.handler.handleTransportError(this, ex);
        }


        // Self description

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


        private class HeartbeatTask implements Runnable {

                private boolean expired;

                @Override
                public void run() {
                        synchronized (responseLock) {
                                if (!this.expired && !isClosed()) {
                                        try {
                                                sendHeartbeat();
                                        }
                                        catch (Throwable ex) {
                                                // Ignore: already handled in writeFrame...
                                        }
                                        finally {
                                                this.expired = true;
                                        }
                                }
                        }
                }

                void cancel() {
                        this.expired = true;
                }
        }

}