using System.Numerics;
using System.Security.Cryptography;

namespace KronaStaffTerminal.Models;

internal static class UlidGenerator
{
    private const string Alphabet = "0123456789ABCDEFGHJKMNPQRSTVWXYZ";

    public static string New()
    {
        Span<byte> value = stackalloc byte[16];
        var timestamp = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds();
        for (var index = 5; index >= 0; index--)
        {
            value[index] = (byte)(timestamp & 0xff);
            timestamp >>= 8;
        }

        RandomNumberGenerator.Fill(value[6..]);
        var number = new BigInteger(value, isUnsigned: true, isBigEndian: true);
        Span<char> result = stackalloc char[26];
        for (var index = 25; index >= 0; index--)
        {
            result[index] = Alphabet[(int)(number & 31)];
            number >>= 5;
        }

        return new string(result);
    }
}