Following on from my last post on stripping HTML from text using C#, once I had removed all signs of HTML from the incoming text, I was also required to show a short preview of the text. I originally went with a truncation method, as follows:

namespace ExtensionMethods
{
    public static class StringExtensionMethods
    {
        public static string Truncate(this string text, int maximumLength)
        {
            if (string.IsNullOrEmpty(text))
            {
                return text;
            }

            return text.Length <= maximumLength ? text : text.Substring(0, maximumLength);
        }
    }
}

This works, but the results look a little odd if the truncate happens half-way through a word.

Instead, I came up this method to truncate at the first word break within the allowed number of characters:

using System.Linq;

namespace ExtensionMethods
{
    public static class StringExtensionMethods
    {
        private static readonly char[] Punctuation = {'.', ',', ';', ':'};

        public static string TruncateAtWordBoundary(this string text, int maximumLength)
        {
            if (string.IsNullOrEmpty(text))
            {
                return text;
            }

            if (text.Length <= maximumLength)
            {
                return text;
            }

            // If the character after the cut off is white space or punctuation 
            // then return what we've got using substring:
            var isCutOffWhiteSpaceOrPunctuation = char.IsWhiteSpace(text[maximumLength]) || Punctuation.Contains(text[maximumLength]);
            text = text.Substring(0, maximumLength);

            if (isCutOffWhiteSpaceOrPunctuation)
            {
                return text;
            }

            // Find the last white-space or punctuation and chop off there:
            var lastWhiteSpaceOrPunctuationPosition = 0;
            for (var i = text.Length - 1; i >= 0; i--)
            {
                if (char.IsWhiteSpace(text[i]) || Punctuation.Contains(text[i]))
                {
                    lastWhiteSpaceOrPunctuationPosition = i;
                    break;
                }
            }

            text = text.Substring(0, lastWhiteSpaceOrPunctuationPosition).Trim();

            return text;
        }
    }
}

While not perfect, this approach works a lot better. Please feel free to suggest improvements.