TweetDecoder.cs

public enum TweetSectionType { NormalText, Url, AtName, HashCode }

public class TweetSection
{
    public TweetSectionType SectionType;
    public string Text;
}

public class TweetDecoder
{
    #region regex patterns
        
    public const string atRegexPattern = @"@([A-Za-z0-9_]+)";
    public const string hashRegexPattern = @"#([A-Za-z0-9_]+)";

    // here be dragons
    public const string urlRegexDragonPattern = @"^(?#Protocol)(?:(?:ht|f)tp(?:s?)\:\/\/|~\/|\/)?(?#Username:Password)(?:\w+:\w+@)?((?#Subdomains)(?:(?:[-\w\d{1-3}]+\.)+(?#TopLevel Domains)(?:com|org|net|gov|mil|biz|info|mobi|name|aero|jobs|edu|co\.uk|ac\.uk|it|fr|tv|museum|asia|local|travel|[a-z]{2})?)|(?#IP)((\b25[0-5]\b|\b[2][0-4][0-9]\b|\b[0-1]?[0-9]?[0-9]\b)(\.(\b25[0-5]\b|\b[2][0-4][0-9]\b|\b[0-1]?[0-9]?[0-9]\b)){3}))(?#Port)(?::[\d]{1,5})?(?#Directories)(?:(?:(?:\/(?:[-\w~!$+|.,=]|%[a-f\d]{2})+)+|\/)+|\?|#)?(?#Query)(?:(?:\?(?:[-\w~!$+|.,*:]|%[a-f\d{2}])+=?(?:[-\w~!$+|.,*:=]|%[a-f\d]{2})*)(?:&(?:[-\w~!$+|.,*:]|%[a-f\d{2}])+=?(?:[-\w~!$+|.,*:=]|%[a-f\d]{2})*)*)*(?#Anchor)(?:#(?:[-\w~!$ |/.,*:;=]|%[a-f\d]{2})*)?$";

    #endregion

    #region regexes

    // always the same so declare once as compiled for faster execution
    private static Regex atRegex = new Regex(atRegexPattern, RegexOptions.Compiled);
    private static Regex hashRegex = new Regex(hashRegexPattern, RegexOptions.Compiled);
    private static Regex urlRegex = new Regex(urlRegexDragonPattern, RegexOptions.Compiled);

    #endregion

    // Here be magic.
    public static List<TweetSection> DecodeSections(string originalTweet)
    {
        // declare return variable
        var sectionz = new List<TweetSection>();

        // split in words
        var wordz = new List<string>(originalTweet.Split(' '));

        // loop through words and figure out what kind of section.
        foreach(var word in wordz)
        {
            // section defaults to normal text
            var sectionType = TweetSectionType.NormalText;

            if (atRegex.IsMatch(word))
            {
                sectionType = TweetSectionType.AtName;
            }
            else if (hashRegex.IsMatch(word))
            {              
                sectionType = TweetSectionType.HashCode;
            }
            else if (urlRegex.IsMatch(word))
            {    
                sectionType = TweetSectionType.Url;
            }

            // add word to section list
            sectionz.Add(new TweetSection { SectionType = sectionType, Text = word });
        }

        return sectionz;
    }
}