C# Correct chunk messages for telegram bot (limit 4096 per message) with emoji and unicode support.

Chunk.cs

// Telegram has 4096 limit per message. So use chunkSize = 4096.
public static IEnumerable<string> ChunkUnicode(this string self, int chunkSize)
{
    if (string.IsNullOrEmpty(self))
        return Enumerable.Empty<string>();

    if (chunkSize < 4)
        throw new ArgumentException("Minimum chunk size is 4.", nameof(chunkSize));

    var results = new List<string>();
    var msg = new StringBuilder();
    int messageLength = 0;
    var bytes = Encoding.UTF32.GetBytes(self);

    for (int i = 0; i < bytes.Length; i += 4)
    { 
        uint codepoint = BitConverter.ToUInt32(bytes, i);

        int charSize;
        if (codepoint < 128)
            charSize = 1;
        else if (codepoint < 32768)
            charSize = 2;
        else
            charSize = 4;

        // Append
        if (messageLength + charSize > chunkSize)
        {
            results.Add(msg.ToString());
            msg.Clear();
            messageLength = 0;
        }

        if (charSize < 4)
            msg.Append(Convert.ToChar(codepoint));
        else
            msg.Append(char.ConvertFromUtf32((int) codepoint));

        messageLength += charSize;
    }

    if (msg.Length > 0)
        results.Add(msg.ToString());

    return results;
}