(function () {

    var send = function (service, json) {
        if (json instanceof Object) json = codeq.jsonize(json);
        return Q.Promise(function (resolve, reject, notify) {
            $.ajax({
                'type': 'POST',
                'url': codeq.urlPrefix + service,
                'accepts': 'application/json',
                'contentType': 'application/json; charset=UTF-8', // type of our request
                'data': json,
                'processData': false, // don't process outgoing data
                'dataType': 'json', // expected type of the response
                'timeout': 60000, // one minute
                'error': function sendErrorHandler(jqXHR, textStatus, errorThrown) {
                    reject(new Error(errorThrown || textStatus));
                },
                'success': function sendSuccessHandler(data, textStatus, jqXHR) {
                    resolve(data);
                }
            });
        });
    };

    var activities = {}, // keyed by problem_id: activity info waiting to be sent to the server
        activityKeys = [], // the keys to activities dictionary
        resolveActivity = function (promiseResolvers) {
            var i;
            // signal everyone that the queue is flushed
            for (i = 0; i < promiseResolvers.length; i++) {
                try {
                    promiseResolvers[i][0]();
                }
                catch (e) {}
            }
            promiseResolvers.length = 0;
        },
        sendActivityInternal = function () {
            var activityKey, activityDescriptor, trace, sendCount;
            // send max. 100 activities, do not be excessive
            if (activityKeys.length == 0) return;
            activityKey = activityKeys[0];
            activityDescriptor = activities[activityKey];
            trace = activityDescriptor.trace;
            if (trace.length > 100) {
                sendCount = 100;
                trace = trace.slice(0, 100);
            }
            else {
                sendCount = trace.length;
            }
            send('activity', {'trace': trace, 'solution': activityDescriptor.solution, 'problem_id': activityDescriptor.problem_id, 'sid': codeq.sid}).then(
                function sendActivitySuccess() {
                    activityDescriptor.trace.splice(0, sendCount);
                    if (activityDescriptor.trace.length > 0) sendActivityInternal();
                    else {
                        delete activities[activityKey];
                        activityKeys.shift();
                        resolveActivity(activityDescriptor.promiseResolvers);
                    }
                },
                function sendActivityFailure() {
                    Q.delay(500).then(sendActivityInternal).done();
                }
            ).done();
        };

    codeq.comms = {
        sendActivity: function commsSendActivity (trace, solution, problem_id) {
            return Q.Promise(function (resolve, reject, notify) {
                var triggerSending = activityKeys.length == 0,
                    activityDescriptor = activities[problem_id],
                    problemTrace, promiseResolvers, i;
                if (!activityDescriptor) {
                    problemTrace = [];
                    promiseResolvers = [];
                    activityDescriptor = {
                        'problem_id': problem_id,
                        'trace': problemTrace,
                        'solution': solution,
                        'promiseResolvers': promiseResolvers
                    };
                    activities[problem_id] = activityDescriptor;
                    activityKeys.push(problem_id);
                }
                else {
                    problemTrace = activityDescriptor.trace;
                    promiseResolvers = activityDescriptor.promiseResolvers;
                    if (solution) activityDescriptor.solution = solution;
                }
                if (trace instanceof Array) {
                    for (i = 0; i < trace.length; i++) {
                        problemTrace.push(trace[i]);
                    }
                }
                else {
                    problemTrace.push(trace);
                }
                promiseResolvers.push([resolve, reject]);
                if (triggerSending) {
                    setTimeout(sendActivityInternal, 0); // async trigger: see if you can collect some more payload
                }
            });
        },

        sendQuery: function commsSendQuery (query, problem_id) {
            var existingActivity = activities[problem_id],
                tmp;
            query['sid'] = codeq.sid;
            if (existingActivity) {
                tmp = query['trace'];
                if (tmp) {
                    // the trace will be sent separately, so it will be in the proper order
                    tmp.splice(0, 0, existingActivity.trace.length, 0); // add two parameters in front, they will form the first two parameters to the following splice() invocation
                    existingActivity.trace.splice.apply(existingActivity.trace, tmp);
                    delete query['trace'];
                }
                tmp = query['program'];
                if (tmp) existingActivity.solution = tmp;
            }
            return send('query', query);
        },

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

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

        getProblem: function commsGetProblem (language, problem_group, problem) {
            return send('get_problem', {
                'sid': codeq.sid,
                'language': language,
                'problem_group': problem_group,
                'problem': problem
            });
        }
    };
})();