Calendar.cs

using iCal.PCL.DataModel;
using iCal.PCL.Serialization;
using RestSharp;
using System;
using System.Collections.Generic;
using System.Linq;

namespace GordonWare {

    public enum GroupId {
        Promotion,
        Group1,
        Group2,
        Group3
    }

    public static class Calendar {

        private static bool IsCurrentEvent(DateTime now, iCalVEvent ev) {
            return ev.DTStart.Date == now.Date && ev.DTEnd.Date == now.Date &&
                   ev.DTStart.TimeOfDay <= now.TimeOfDay && ev.DTEnd.TimeOfDay >= now.TimeOfDay;
        }

        private static bool ForGroup(iCalVEvent ev, GroupId groupId) {
            return ev.Description.Contains($"INFO3 {Groups[(int) groupId]}");
        }

        private const string URL =
            "http://edt-v2.univ-nantes.fr/calendar/ics?timetables[0]=20739&timetables[1]=20740&timetables[2]=20741&timetables[3]=20742";

        private static readonly string[] Groups = {"PROMOTION", "G1", "G2", "G3"};

        /// <summary>
        /// Gets current class name of the given <see cref="groupId"/> from the public calendar.
        /// </summary>
        /// <returns>Returns current class name if there is only one. Otherwise, returns null.</returns>
        public static string GetCurrentClass(GroupId groupId) {
            //make and execute a HTTP GET request to get the calendar
            var client = new RestClient(URL);
            var request = new RestRequest(Method.GET);
            var response = client.Execute(request);

            if (!response.IsSuccessful) {
                return null;
            }

            //cut the raw iCal content into lines
            var stringSeparators = new[] {"\r\n"};
            var lines = response.Content.Split(stringSeparators, StringSplitOptions.None);

            IEnumerable<iCalVEvent> vEvents;

            try {
                //deserialize the iCal file
                var iCal = iCalSerializer.Deserialize(lines);
                vEvents = iCal.Cast<iCalVEvent>();
            } catch (InvalidOperationException e) {
                Console.WriteLine(e);
                return null;
            }

            var now = DateTime.Now;

            //add 2 hours to get french time and find current class
            var currentClass = vEvents.Select(ev => {
                ev.DTStart = ev.DTStart.AddHours(2);
                ev.DTEnd = ev.DTEnd.AddHours(2);
                return ev;
            }).Where(ev =>
                IsCurrentEvent(now, ev) && ForGroup(ev, groupId)
            ).ToList();

            //return class name only if there is exactly one current class
            return currentClass.Count == 1 ? currentClass[0].Summary : null;
        }
    }
}