/* CodeQ: an online programming tutor.
   Copyright (C) 2015 UL FRI

This program is free software: you can redistribute it and/or modify it under
the terms of the GNU Affero General Public License as published by the Free
Software Foundation, either version 3 of the License, or (at your option) any
later version.

This program is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
details.

You should have received a copy of the GNU Affero General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */

(function () {
    "use strict";
    // ================================================================================
    // Errors generated in this module
    // ================================================================================

    var BinaryMessageError = function (message) {
        var e = new Error(message);
        this.message = message;
        if (e.stack) {
            this.stack = e.stack;
        }
    };
    BinaryMessageError.prototype = new Error();
    BinaryMessageError.prototype.name = 'BinaryMessageError';

    var MessageParseError = function (message) {
        var e;
        if (message instanceof Error) {
            e = message;
            this.message = 'Message parse error: ' + e.toString();
        } else {
            e = new Error(message);
            this.message = message;
        }
        if (e.stack) {
            this.stack = e.stack;
        }
    };
    MessageParseError.prototype = new Error();
    MessageParseError.prototype.name = 'MessageParseError';

    // ================================================================================
    // engine.io communication support functions (long polling / websocket communication)
    // ================================================================================

    var currentTID = 0, // transaction ID of the next message
        sid = null, // session ID, changes after each successful initial login
        socket = null,
        reconnectTimer = null,
        login_username = null,
        login_password = null,
        waiters = {}, // keyed by TID: {packet, created, promise}
        connected = false,
        connectPromise = null,
        requestHandlers = {}, // handlers for requests (events) from the server, keyed by event ID, value is an array of handlers
        handleIncomingMessageError = function (error, data) {
            if (error instanceof BinaryMessageError) {
                codeq.log.error('Incoming message is not a string, attempting reconnect');
                connected = false;
                socket.close(); // connection will be reestablished in the close event handler
            }
            else if (error instanceof MessageParseError) {
                codeq.log.error('Incoming message is not a JSON message, ignoring: ' + data);
            }
            else {
                codeq.log.error('Unknown error, attempting reconnect: ' + error);
                connected = false;
                socket.close(); // connection will be reestablished in the close event handler
            }
        },
        parseData = function (data) {
            if (typeof data !== 'string') {
                throw new BinaryMessageError('Message is not a string');
            }

            try {
                return JSON.parse(data);
            }
            catch (e) {
                codeq.log.error('Incoming message is not a JSON message, ignoring: ' + data);
                throw new MessageParseError(e);
            }
        },
        onMessage = function (data) {
            var m, waiter, event, handlers, i, N,
                tid, sortedWaiters = [], s;

            try {
                m = parseData(data);
            }
            catch (e) {
                handleIncomingMessageError(e, data);
                return;
            }

            if ('type' in m) {
                // system (meta) protocol
                switch (m.type) {
                    case 'sid':
                        // the peer created or changed our session ID
                        sid = m.sid;
                        break;

                    case 'reset':
                        // the server forced us to reset to the login page
                        // * could not re-register the connection with an existing session ID, username, and password
                        // * the user logged in elsewhere
                        s = 'The server forced us to disconnect';
                        if (typeof m.message === 'string') s += ': ' + m.message;
                        sid = null;
                        codeq.reset(s);
                        return;

                    default:
                        codeq.log.warn('Unknown system message type: ' + m.type);
                }
                if (!connected) {
                    if (sid !== null) {
                        // our connection registration was successful
                        connected = true;
                        if (connectPromise) {
                            // manual connect
                            connectPromise.resolve();
                            connectPromise = null;
                        }
                        else {
                            // auto re-connect
                        }
                        // resend anything not already sent
                        for (tid in waiters) {
                            if (waiters.hasOwnProperty(tid)) {
                                sortedWaiters.push(waiters[tid]);
                            }
                        }
                        // sort by ascending transaction ID before sending
                        sortedWaiters.sort(function (a, b) {return a.tid - b.tid;});
                        for (i = 0; i < sortedWaiters.length; i++) {
                            (function (waiter) {
                                if (!waiter.sent) {
                                    socket.send(JSON.stringify(waiter.packet), function () {
                                        waiter.sent = true;
                                    });
                                }
                            })(sortedWaiters[i]);
                        }
                    }
                    else {
                        codeq.log.error('Operating outside a session!');
                        codeq.reset('Protocol error: server sent a bogus message instead of acknowledging our connection');
                    }
                }
                return;
            }

            if (!connected) {
                codeq.log.warn('Not in the connected state, but receiving a user message anyway');
            }

            if ('tid' in m) {
                waiter = waiters[m.tid];
                if (waiter) {
                    delete waiters[m.tid];
                    waiter.promise.resolve(m);
                    codeq.log.debug('Delivered an incoming message, TID=' + m.tid);
                    return;
                }
                else {
                    codeq.log.debug('There is noone waiting for the incoming message, TID=' + m.tid);
                }
            }

            event = m.event;
            if (typeof event !== 'string') {
                codeq.log.info('Incoming message without a TID and with no event name, dropping it on the floor: ' + data);
                return;
            }

            handlers = requestHandlers[event];
            if (!handlers) {
                codeq.log.info('Incoming event message cannot be handled: no handler registered for ' + event);
                return;
            }

            N = handlers.length;
            for (i = 0; i < N; i++) {
                setTimeout((function (handler) {return function () {
                    handler(m);
                }})(handlers[i]), 0);
            }
        },
        onConnect = function () {
            // register our connection
            if (sid === null) socket.send(JSON.stringify({'type': 'create_session'}));
            else socket.send(JSON.stringify({'type': 'connect_session', 'sid': sid, 'username': login_username, 'password': login_password}));
        },
        onClose = function () {
            connected = false;
            if (connectPromise) {
                // resulted from manual connect, don't attempt reconnect
                connectPromise.reject(new Error('Connection failed'));
                connectPromise = null;
                socket.off('open', onConnect);
                socket.off('close', onClose);
                socket.off('message', onMessage);
                socket = null;
            }
            else {
                // spurious disconnect, attempt reconnect
                reconnectTimer = setTimeout(function () {
                    reconnectTimer = null;
                    socket.open();
                }, 250); // reconnect in quarter of a second
            }
        };

    // ================================================================================
    // AJAX communication support functions (loading of static web resources)
    // ================================================================================

    var languageCache = {}, // language defs, keyed by language identifier
        ajaxGet = function (url) {
            return Q.Promise(function (resolve, reject, notify) {
                $.ajax({
                    dataType: 'json',
                    type: 'GET',
                    url: url,
                    error: function (jqXHR, textStatus, errorThrown) {
                        codeq.log.error('AJAX to ' + url + ' failed with status ' + textStatus, errorThrown);
                        reject(errorThrown || new Error(textStatus));
                    },
                    success: function (data, textStatus, jqXHR) {
                        var s;
                        if ((typeof data === 'object') && (data !== null)) {
                            // got a JSON
                            resolve(data);
                        }
                        else {
                            s = 'AJAX to ' + url + ' did not result in a JSON object';
                            if (typeof data === 'string') {
                                s += ', the response was:\n' + data;
                            }
                            else if (typeof textStatus === 'string') {
                                s += ', status was: ' + textStatus;
                            }
                            codeq.log.error(s);
                            reject(new Error(s));
                        }
                    }
                });
            });
        },
        ajaxPrefix, ajaxDataPrefix, ajaxResPrefix;

    ajaxPrefix = codeq.ajaxPrefix;
    if (!ajaxPrefix) ajaxPrefix = '/';
    else if (ajaxPrefix[ajaxPrefix.length - 1] !== '/') {
        ajaxPrefix = ajaxPrefix.split('/');
        ajaxPrefix[ajaxPrefix.length - 1] = '';
        ajaxPrefix = ajaxPrefix.join('/');
    }
    ajaxDataPrefix = ajaxPrefix + 'data/';
    ajaxResPrefix = ajaxPrefix + 'res/';

    // ================================================================================
    // Try to be polite and logout on page close/reload
    // ================================================================================

    window.onbeforeunload = function () {
        if (sid) {
            // we need to perform an action inside the current iteration of the event loop
            // so no fancy promises etc., just the raw AJAX request
            $.ajax({
                type: 'GET',
                url: '/ws/logout?sid=' + sid + '&t=' + Date.now()
            });
        }
    };

    // ================================================================================
    // This module's API methods
    // ================================================================================

    codeq.comms = {
        'getSid':function(){
          return sid;
        },
        'connect': function () {
            var deferred = Q.defer();

            if (connectPromise) {
                // connection already taking place
                connectPromise.then(deferred.resolve, deferred.reject, deferred.notify);
            }
            else if (socket) {
                // already connected
                if (connected) {
                    deferred.resolve();
                }
                else {
                    // auto re-connecting
                    connectPromise = deferred;
                }
            }
            else {
                // create a new connection
                connectPromise = deferred;
                socket = eio(codeq.eioHost, {
                    'upgrade': true,
                    'path': '/ws',
                    'transports': ['polling', 'websocket']
                });
                socket.on('open', onConnect);
                socket.on('close', onClose);
                socket.on('message', onMessage);
            }

            return deferred.promise;
        },
        'disconnect': function (reason) { // reason is optional
            var tid;
            if (socket) {
                socket.off('open', onConnect);
                socket.off('close', onClose);
                socket.off('message', onMessage);
                socket.close();
                socket = null;
            }
            if (reconnectTimer !== null) {
                clearTimeout(reconnectTimer);
                reconnectTimer = null;
            }
            connected = false;
            if (connectPromise) {
                connectPromise.reject(new Error('Forced disconnect'));
                connectPromise = null;
            }
            login_password = null; // manual disconnect will prevent auto-login
            sid = null;
            // reject any outstanding promises
            for (tid in waiters) {
                if (waiters.hasOwnProperty(tid)) {
                    waiters[tid].promise.reject(new Error(reason || 'Forced disconnect'));
                    delete waiters[tid];
                }
            }
        },
        'send': function (packet) {
            return Q.Promise(function (resolve, reject, notify) {
                var waiter = {
                    'packet': packet,
                    'created': Date.now(),
                    'promise': {'resolve': resolve, 'reject': reject, 'notify': notify},
                    'sent': false
                };
                packet.tid = currentTID;
                if (sid !== null) packet.sid = sid;
                waiters[currentTID] = waiter;
                currentTID++;
                if (connected) {
                    socket.send(JSON.stringify(packet), function () { waiter.sent = true; });
                }
            });
        },
        'login': function (username, password) {
            var packet = {'action': 'login', 'username': username, 'password': password},
                myself = this,
                performLogin = function () {
                    return myself.send(packet).then(function (response) {
                        if (response.code === 0) {
                            // login successful, remember the login credentials for auto-reconnects
                            login_username = username;
                            login_password = password;
                            sid = response.new_sid || response.sid;
                        }
                        return response;
                    });
                };
            if (socket) return performLogin();
            // this is the 1st method where we do connect() first, if we're not already connected
            return this.connect().then(performLogin);
        },

        'logout': function () {
            var performLogout = function() {
                var promise = codeq.comms.send({'action': 'logout'});
                sid = null;
                return promise;
            };

            if (socket) return performLogout();
            return this.connect().then(performLogout);
        },

        'signup': function (username, name, email, password) {
            var myself = this,
                performSignUp = function () {
                    return myself.send({'action': 'signup', 'username': username, 'name': name, 'email': email, 'password': password});
                };

            if (socket) return performSignUp();
            // this is the 2nd method where we do connect() first, if we're not already connected
            return this.connect().then(performSignUp);
        },

        'changePassword': function (newpassword) {
            return this.send({'action': 'change_password', 'password': newpassword});
        },

        'getUserStat': function () {
            return this.send({'action': 'user_stat'});
        },

        'updateSettings': function (new_settings){
            return this.send({'action': 'update_settings', 'settings': new_settings});
        },

        sendActivity: function commsSendActivity (trace, solution, problem_id) {
            return this.send({'action': 'activity', 'trace': trace, 'solution': solution, 'problem_id': problem_id});
        },

        sendQuery: function commsSendQuery (query, problem_id) {
            query['action'] = 'query';
            return this.send(query);
        },

        sendPythonExec: function commsSendPythonExec (json) {
            json['action'] = 'python_exec';
            return this.send(json);
        },

        sendPythonPush: function commsSendPythonPush (json) {
            json['action'] = 'python_push';
            return this.send(json);
        },

        sendPythonStop: function commsSendPythonStop (json) {
            json['action'] = 'python_stop';
            return this.send(json);
        },

        sendHint: function commsSendHint (json) {
            json['action'] = 'hint';
            return this.send(json);
        },

        sendTest: function commsSendTest (json) {
            json['action'] = 'test';
            return this.send(json);
        },

        getCurrentSolution: function commsGetCurrentSolution (problem_id) {
            return this.send({
                'action': 'get_current_solution',
                'problem_id': problem_id
            });
        },

        getAttempts: function commsGetAttempts (language) {
            return this.send({
                'action': 'get_attempts',
                'language': language
            });
        },

        getSolutions: function commsGetSolutions (problem_ids) {
            return this.send({
                'action': 'get_solutions',
                'problem_ids': problem_ids
            });
        },

        loadProblem: function commsLoadProblem (problem_id) {
            return this.send({
                'action': 'load_problem',
                'problem_id': problem_id
            });
        },

        endProblem: function commsLoadProblem (problem_id) {
            return this.send({
                'action': 'end_problem'
            });
        },

        'on': function (event, handler) {
            var handlers = requestHandlers[event],
                N, i;
            if (!handlers) {
                handlers = [handler];
                requestHandlers[event] = handlers;
                return;
            }
            N = handlers.length;
            for (i = 0; i < N; i++) {
                if (handlers[i] === handler) return; // already registered
            }
            handlers.push(handler);
        },

        'off': function (event, handler) {
            var handlers = requestHandlers[event],
                N, i;
            if (!handlers) return; // none registered
            if (arguments.length == 1) {
                // no handler specified -> remove all handlers for this event
                delete requestHandlers[event];
                handlers.length = 0;
            }
            else {
                N = handlers.length;
                for (i = 0; i < N; i++) {
                    if (handlers[i] === handler) {
                        handlers.splice(i, 1);
                        if (handlers.length === 0) {
                            delete requestHandlers[event];
                        }
                        return;
                    }
                }
            }
        },

        'getLanguageDef': function (identifier) {
            var x = languageCache[identifier];
            if ((typeof x === 'object') && (x !== null)) {
                // already defined
                if (typeof x.then === 'function') {
                    // it's a promise, it means it's not resolved yet
                    return x;
                }
                else {
                    // return a resolved promise with the cached value
                    return Q(x);
                }
            }
            x = ajaxGet(ajaxDataPrefix + identifier + '/language.json').then(
                function getLanguageDefSuccess(data) {
                    languageCache[identifier] = data;
                    return data; // proxy further
                },
                function getLanguageDefFail(exception) {
                    delete languageCache[identifier];
                    throw exception || new Error('Could not load language ' + identifier); // proxy further
                }
            );
            languageCache[identifier] = x;
            return x;
        },

        'getProblemDef': function (language, group, problem) {
            return ajaxGet(ajaxDataPrefix + language + '/' + group + '/' + problem + '/problem.json');
        },

        'getGuiTranslation': function (lang) {
            return ajaxGet(ajaxResPrefix + lang + '.json');
        },

        'getResourceTree': function () {
            return ajaxGet(ajaxDataPrefix + 'resources.json');
        },

        'samlLogin': function(upgrade_account, upgrade_password){
            if (upgrade_account === undefined) return this.send({'action':'saml_login','gui_lang':codeq.getLang()});
            else if (upgrade_account) return this.send({'action':'saml_login','gui_lang':codeq.getLang(), 'upgrade_account': true, 'upgrade_password': upgrade_password});
            else return this.send({'action':'saml_login','gui_lang':codeq.getLang(), 'upgrade_account': false});
        },

        'samlLogout': function(){
            return this.send({'action':'saml_logout'});
        },

        'forceReset': function () {
            var p;
            if (sid !== null) {
                p = Q.Promise(function (resolve, reject, notify) {
                    var t = setTimeout(function () {
                        t = null;
                        resolve();
                    }, 3000); // 3 seconds
                    codeq.comms.logout().then(function () {
                        if (t !== null) {
                            clearTimeout(t);
                            t = null;
                            resolve();
                        }
                    });
                });
            }
            else p = Q();
            return p.fin(codeq.comms.disconnect);
        }
    };
})();