/* ------------------------------------------------------------------------
 * JSUpdater - periodically polls for new data from server
 * ------------------------------------------------------------------------
 * Exposes the following method on the global STUDIP.JSUpdater object:
 *
 * - start()
 * - stop()
 * - register(index, callback, data)
 * - unregister(index)
 *
 * Refer to the according function definitions for further info.
 * ------------------------------------------------------------------------ */
import { $gettext } from './gettext.js';

let active = false;
let lastAjaxDuration = 200; //ms of the duration of an ajax-call
let currentDelayFactor = 0;
let lastJsonResult = null;
let dateOfLastCall = +new Date(); // Get milliseconds of date object
let serverTimestamp = STUDIP.server_timestamp;
let ajaxRequest = null;
let timeout = null;
let registeredHandlers = {};

// Reset json memory, used to delay polling if consecutive requests always
// return the same result
function resetJSONMemory(json) {
    if (json.hasOwnProperty('server_timestamp')) {
        delete json.server_timestamp;
    }
    json = JSON.stringify(json);
    if (json !== lastJsonResult) {
        currentDelayFactor = 0;
    }
    lastJsonResult = json;
}

// Process returned json object by calling registered handlers
function process(json) {
    for (const [index, value] of Object.entries(json)) {
        // Set timestamp
        if (index === 'server_timestamp') {
            serverTimestamp = value;
        } else {
            // Call registered handler callback by index
            if (index in registeredHandlers) {
                registeredHandlers[index].callback(value);
            }
        }
    }

    // Reset json memory
    resetJSONMemory(json);
}

// Registers next poll
function registerNextPoll() {
    // Calculate smallest registered polling interval (but no more than 60 seconds)
    let interval = 60000;
    for (const [index, handler] of Object.entries(registeredHandlers)) {
        if (handler.interval < interval) {
            interval = handler.interval;
        }
    }

    // Define delay by last poll request (respond to load on server) and
    // current delay factor (respond to user activity)
    var delay = (interval || lastAjaxDuration * 15) * Math.pow(1.33, currentDelayFactor);

    // Clear any previously scheduled polling
    window.clearTimeout(timeout);
    timeout = window.setTimeout(poll, delay);

    // Increase current delay factor
    currentDelayFactor += 1;
}

// Collect data for polling
function collectData() {
    var data = {};
    // Pull data from all registered handlers, either by collecting the data
    // itself or by calling the appropriate function
    for (const [index, handler] of Object.entries(registeredHandlers)) {
        if (handler.data) {
            const thisData = $.isFunction(handler.data) ? handler.data() : handler.data;
            if (thisData !== null && !$.isEmptyObject(thisData)) {
                data[index] = thisData;
            }
        }
    }

    return data;
}

// User activity handler
function userActivityHandler() {
    currentDelayFactor = 0;
    if (+new Date() - dateOfLastCall > 5000) {
        poll(true);
    }
}

// Window activity handler
function windowActivityHandler(event) {
    if (event.type === 'blur') {
        // Increase delay factor and reschedule next polling
        currentDelayFactor += 10;
        registerNextPoll();
    } else if (event.type === 'focus') {
        // Reset delay factor and start polling if neccessary
        userActivityHandler();
    }
}

// Actually poll data
function poll(forced) {
    // Skip polling if an ajax request is already running, unless forced
    if (!forced && ajaxRequest) {
        registerNextPoll();
        return false;
    }

    // If forced, abort potential current ajax request
    if (ajaxRequest) {
        ajaxRequest.abort();
        ajaxRequest = null;
    }
    // Abort potentially scheduled polling
    window.clearTimeout(timeout);

    // Store current timestamp
    dateOfLastCall = +new Date();

    // Prepare variables
    var url = STUDIP.ABSOLUTE_URI_STUDIP + 'dispatch.php/jsupdater/get',
        page = window.location.href.replace(STUDIP.ABSOLUTE_URI_STUDIP, '');

    // Actual poll request, uses promises
    ajaxRequest = $.ajax(url, {
        data: {
            page: page,
            page_info: collectData(),
            server_timestamp: serverTimestamp
        },
        type: 'POST',
        dataType: 'json',
        timeout: 5000
    })
        .done(function(json) {
            process(json);
        })
        .fail(function(jqXHR, textStatus, errorThrown) {
            resetJSONMemory({
                text: textStatus,
                error: errorThrown
            });
        })
        .always(function() {
            ajaxRequest = null;
            lastAjaxDuration = +new Date() - dateOfLastCall;

            // If logged out
            if (arguments.length === 3 && arguments[1] === 'error' && arguments[0].status === 403) {
                // Stop updater
                JSUpdater.stop();

                // Present appropriate message in dialog
                var message = $gettext('Bitte laden Sie die Seite neu, um fortzufahren'),
                    buttons = {};
                buttons[$gettext('Neu laden')] = function() {
                    location.reload();
                };
                buttons[$gettext('Schließen')] = function() {
                    $(this).dialog('close');
                };

                $('<div>')
                    .html(message)
                    .css({
                        textAlign: 'center',
                        padding: '2em 0'
                    })
                    .dialog({
                        width: '50%',
                        modal: true,
                        buttons: buttons,
                        title: $gettext('Sie sind nicht mehr im System angemeldet.')
                    });
            } else {
                registerNextPoll();
            }
        });
}

// Register global object
const JSUpdater = {
    // Starts the updater, also registers the activity handlers
    start() {
        if (!active) {
            $(document).on('mousemove', userActivityHandler);
            $(window).on('blur focus', windowActivityHandler);
            registerNextPoll();
        }
        active = true;
    },

    // Stops the updater, also unregisters the activity handlers
    stop() {
        if (active) {
            $(document).off('mousemove', userActivityHandler);
            $(window).off('blur focus', windowActivityHandler);
            if (ajaxRequest) {
                ajaxRequest.abort();
                ajaxRequest = null;
            }
            window.clearTimeout(timeout);
        }
        active = false;
    },

    // Registers a new handler by an index, a callback and an optional data
    // object or function
    register(index, callback, data = null, interval = 0) {
        registeredHandlers[index] = { callback, data, interval };
    },

    // Unregisters/removes a previously registered handler
    unregister(index) {
        delete registeredHandlers[index];
    }
}

export default JSUpdater;