Berufsschule_HAM/src/Helpers/UsersHelper.cs

using System.Globalization;
using System.Text;
using System.Text.RegularExpressions;
namespace Berufsschule_HAM.Helpers;

public static partial class UsersHelper
{
    public static string CreateUsername(string givenName, string surname)
    {
        if (string.IsNullOrWhiteSpace(givenName) || string.IsNullOrWhiteSpace(surname))
            throw new ArgumentException("Given name and surname must not be empty.");

        string combined = (surname + givenName).ToLowerInvariant();
        combined = combined.Replace("ä", "ae").Replace("ö", "oe").Replace("ü", "ue");
        // Normalize to decompose accents (e.g., é -> e +  ́)
        string normalized = combined.Normalize(NormalizationForm.FormD);

        // Remove diacritics
        var sb = new StringBuilder();
        foreach (var c in normalized)
        {
            var category = CharUnicodeInfo.GetUnicodeCategory(c);
            if (category != UnicodeCategory.NonSpacingMark)
                sb.Append(c);
        }

        string cleaned = sb.ToString();

        // Replace German ligatures etc.
        cleaned = cleaned
            .Replace("ß", "ss")
            .Replace("æ", "ae")
            .Replace("œ", "oe")
            .Replace("ø", "o");

        // Remove everything not a-z
        cleaned = AtoZ().Replace(cleaned, "");

        return cleaned;
    }

    [GeneratedRegex("[^a-z]")]
    private static partial Regex AtoZ();
}