blazor-calendar/BlazorApp/Data/Event.cs

using System;
using System.Collections.Generic;
using System.Text;

namespace BlazorApp.Data
{
    public class Event
    {
        public string Uid { get; set; }
        public string Summary { get; set; }
        public DateTime? DtStart { get; set; }
        public DateTime? DtEnd { get; set; }
        public string Description { get; set; }
        public TimeSpan? Duration { get; set; }

        public List<(string, string, string)> RawProperties { get; } = new();
        public string ETag { get; set; }
        public string Href { get; set; }

        public DateTime? CalculatedEnd => DtEnd ?? DtStart + Duration;

        private static string _escape(string s)
        {
            return s
                .Replace(@"\", @"\\")
                .Replace(",", @"\,")
                .Replace(";", @"\;")
                .Replace("\n", @"\n");
        }

        public string ToICal()
        {
            var sb = new StringBuilder();
            sb.Append("BEGIN:VCALENDAR\r\n");
            sb.Append("VERSION:2.0\r\n");
            sb.Append("PRODID:-//Sijmen//blazor-calendar//EN\r\n");
            sb.Append("BEGIN:VEVENT\r\n");

            foreach (var (name, parameters, oldValue) in RawProperties)
            {
                sb.Append(name);
                if (parameters != null)
                    sb.Append($";{parameters}");

                var value = name switch
                {
                    "SUMMARY" => _escape(Summary),
                    _ => oldValue
                };

                sb.Append($":{value}\r\n");
            }

            sb.Append("END:VEVENT\r\n");
            sb.Append("END:VCALENDAR\r\n");
            return sb.ToString();
        }
    }
}