using System;

using System.Globalization;

using System.Text;

​

public static class Program

{

    public static string UnicodeSafeTruncate(this string value, int maxLength)

    {

        if (value.Length <= maxLength)

        {

            return value;

        }

​

        var builder = new StringBuilder();

        var builderForward = new StringBuilder();

        var textElementEnumerator = StringInfo.GetTextElementEnumerator(value);

        while (textElementEnumerator.MoveNext())

        {

            builderForward.Append(textElementEnumerator.Current);

            if (builderForward.ToString().Length > maxLength)

            {

                return builder.ToString();

            }

​

            builder.Append(textElementEnumerator.Current);

        }

​

        return value;

    }

​

    public static void Main()

    {

        // .net fiddle has problems to handle unicode 👩•🚒 - "Woman Firefighter", falling back to base64 for https://emojipedia.org/woman-firefighter

        var base64EncodedBytes = System.Convert.FromBase64String("YfCfkanwn4+94oCN8J+akvCfkanwn4+94oCN8J+akmI=");

        var value = System.Text.Encoding.UTF8.GetString(base64EncodedBytes);

        Console.WriteLine($"Input value: {value} (Length {value.Length})");

        var maxLength = 10;

        var brokenUnicode = value.Substring(0, maxLength);

        Console.WriteLine($"Substring Outcome: {brokenUnicode}");

        var actualTruncatedString = value.UnicodeSafeTruncate(maxLength);

        Console.WriteLine($"UnicodeSafeTruncate Outcome: {actualTruncatedString}");

    }

}