vutt.js

var parseTT = function() {
	
	var plusAWeek = function(date, count) {
		let newDate = date.valueOf() + count * 604800000;
		newDate = new Date(newDate);
		return(newDate);
	}
	
	var range = function(begin, end) {
		let numbers = [];
		for (let i = begin; i <= end; i++) {
		    numbers.push(i);
		}
		return(numbers);
	}
	
	var parseRange = function(rangeString) {
		let [begin, end] = rangeString.split("-");
		begin = parseInt(begin);
		end = parseInt(end);
		if (isNaN(end)) {
			return([begin]);
		} else {
			return(range(begin, end));
		}
	}
	
	var parseRanges = function(rangeString) {
		let ranges = rangeString.split(",");
		let thisYear = [];
		let nextYear = [];
		for (let i = 0; i < ranges.length; i++) {
			let numbers = parseRange(ranges[i]);
			if (i == 0 || numbers[0] > thisYear[0])
				thisYear = thisYear.concat(numbers);
			else
				nextYear = nextYear.concat(numbers);
		}
		return([thisYear, nextYear]);
	}
	
	var icsFormatter = function() {
		'use strict';

		var SEP = '\r\n';
		var CALSEP = '\\n';

		var calendarEvents = [];
		var calendarStart = [
			'BEGIN:VCALENDAR',
			'PRODID:-//Mahmood Shafeie Zargar//VU🐓//EN',
			'VERSION:2.0',
			'BEGIN:VTIMEZONE',
			'TZID:Europe/Amsterdam',
			'BEGIN:DAYLIGHT',
			'TZOFFSETFROM:+0100',
			'RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=-1SU',
			'DTSTART:19810329T020000',
			'TZNAME:GMT+2',
			'TZOFFSETTO:+0200',
			'END:DAYLIGHT',
			'BEGIN:STANDARD',
			'TZOFFSETFROM:+0200',
			'RRULE:FREQ=YEARLY;BYMONTH=10;BYDAY=-1SU',
			'DTSTART:19961027T030000',
			'TZNAME:GMT+1',
			'TZOFFSETTO:+0100',
			'END:STANDARD',
			'END:VTIMEZONE'
		].join(SEP);
		var calendarEnd = SEP + 'END:VCALENDAR';

		return {
			'events': function() {
				return calendarEvents;
			},

			'calendar': function() {
				return calendarStart + SEP + calendarEvents.join(SEP) + calendarEnd;
			},

			'addEvent': function(args) {
				let [code, date, weeks, begin, end, title, description, type, locations, staff, comment] = args;

				title = title + " (" + type + ")";

				let [day, month, year] = date.split("/");
				day = ('00' + day).substring(day.length);
				month = ('00' + month).substring(month.length);
				year = '20' + ('00' + year).substring(year.length);
				date = year + month + day;

				let [bhour, bmin] = begin.split(":");
				bhour = ('00' + bhour).substring(bhour.length);
				bmin = ('00' + bmin).substring(bmin.length);
				begin = date + "T" + bhour + bmin + "00";

				let [ehour, emin] = end.split(":");
				ehour = ('00' + ehour).substring(ehour.length);
				emin = ('00' + emin).substring(emin.length);
				end = date + "T" + ehour + emin + "00";
				
				let nextyear = (Number.parseInt(year) + 1).toString();
				let until = nextyear + "01" + "01" + "T" + "00" + "00" + "00";

				description = [
					code == "" ? "" : "Code: " + code,
					staff == "" ? "" : CALSEP + "Staff: " + staff,
					description == "" ? "" : CALSEP + "Description: " + description,
					comment == "" ? "" : CALSEP + "Comment: " + comment
				].join("");
				
				let stamp = new Date();
				stamp = stamp.toISOString().replace(/([-:]|\.\d{3})/g, "");
				
				weeks = weeks.replace(/\s/g, "");
				var weekRanges = parseRanges(weeks);
				
				for (let i = 0 ; i < weekRanges.length; i++) {
					if (weekRanges[i].length > 0) {
						var calendarEvent = [
							'BEGIN:VEVENT',
							'DTSTAMP:' + stamp,
							'DTEND;TZID=Europe/Amsterdam:' + end,
							'LOCATION:' + locations,
							'DESCRIPTION:' + description,
							'SUMMARY:' + title,
							'DTSTART;TZID=Europe/Amsterdam:' + begin,
							(weekRanges[i].length == 1 ? "" : 'RRULE:FREQ=YEARLY;BYWEEKNO=' + weekRanges[i].toString() + ';UNTIL=' + until + SEP) + 'END:VEVENT'
						].join(SEP);

						calendarEvents.push(calendarEvent);
					}
				}

				return calendarEvent;
			},
			'download': function(filename) {
				if (calendarEvents.length < 1) {
					return false;
				}

				var calendar = calendarStart + SEP + calendarEvents.join(SEP) + calendarEnd;
				var blob = new Blob([calendar], {
					type: "text/calendar;charset=utf-8;"
				});
				if (window.navigator.msSaveOrOpenBlob) {
					window.navigator.msSaveBlob(blob, filename);
				} else {
					var elem = window.document.createElement('a');
					elem.href = window.URL.createObjectURL(blob);
					elem.download = filename;
					document.body.appendChild(elem);
					elem.click();
					document.body.removeChild(elem);
					window.URL.revokeObjectURL(elem.href);
				}
			}
		}
	}

	var cal = icsFormatter();
	var rows = document.querySelectorAll("table.spreadsheet tr:not(.columnTitles)");
	rows.forEach(
		function(row) {
			var fields = [];
			row.querySelectorAll("td").forEach(function(cell) {
				fields.push(cell.textContent.replace(/\s+/g, " ").trim());
			});
			cal.addEvent(fields);
		}
	);
	if (cal.events().length == 0) {
		if (window.location.hostname != "rooster.vu.nl") {
			alert("VUTt is unable to find the timetable information on the current page, and you don't seem to be on the Rooster website! Note that VU🐓 only works with VU's Rooster web app.");
		} else {
			alert("Although you seem to be on the Rooster website, VU🐓 can not find any timetable information on the current page! Either there is no timetable on this page, or you have found a bug. Please try once more and if you can't make it work, file a bug report.");
		}
	} else {
		var calname = document.querySelector("span.header-2-0-1");
		calname = (calname != null) ? calname.textContent.replace(/[^A-Za-z0-9]/g, " ").trim().replace(/\s+/g, "_").toLowerCase() : "";
		if (calname.length > 0) {
			cal.download(calname + ".ics");
		} else {
			cal.download("calendar.ics");
		}
	}
};