IdGenerator.cs

using System;
using System.Threading;

namespace Common
{

    /// <summary>
    /// Inspired by <see href="https://github.com/aspnet/AspNetCore/blob/master/src/Servers/Kestrel/shared/CorrelationIdGenerator.cs"/>,
    /// this class generates an efficient 20-bytes ID which is the concatenation of a <c>base36</c> encoded
    /// machine name and <c>base32</c> encoded <see cref="long"/> using the alphabet <c>0-9</c> and <c>A-V</c>.
    /// </summary>
    public static class IdGenerator
    {
        // Base32 encoding - in ascii sort order for easy text based sorting
        private static readonly char[] s_encode32Chars = "0123456789ABCDEFGHIJKLMNOPQRSTUV".ToCharArray();
        private static readonly char[] _prefix = new char[6];


        private static void PopulatePrefix()
        {
            var machineHash = Math.Abs(Environment.MachineName.GetHashCode());
            var machineEncoded = Base36.Encode(machineHash);
            var i = _prefix.Length - 1;
            var j = 0;
            while (i >= 0)
            {
                if (j < machineEncoded.Length)
                {
                    _prefix[i] = machineEncoded[j];			
                    j++;
                } else {
                    _prefix[i] = '0';
                }
                i--;
            }
        }

        static IdGenerator()
        {
            PopulatePrefix();
        }        
        
        private static long _lastId = DateTime.UtcNow.Ticks;

        public static string Next() => GenerateId(Interlocked.Increment(ref _lastId));

        private static string GenerateId(long id)
        {
            char[] encode32Chars = s_encode32Chars;
            char[] prefixChars = _prefix;
            var buffer = new char[20];
            buffer[19] = prefixChars[5];
            buffer[18] = prefixChars[4];
            buffer[17] = prefixChars[3];
            buffer[16] = prefixChars[2];
            buffer[15] = prefixChars[1];
            buffer[14] = prefixChars[0];
            buffer[13] = '-';
            buffer[12] = encode32Chars[id & 31];
            buffer[11] = encode32Chars[(id >> 5) & 31];
            buffer[10] = encode32Chars[(id >> 10) & 31];
            buffer[9] = encode32Chars[(id >> 15) & 31];
            buffer[8] = encode32Chars[(id >> 20) & 31];
            buffer[7] = encode32Chars[(id >> 25) & 31];
            buffer[6] = encode32Chars[(id >> 30) & 31];
            buffer[5] = encode32Chars[(id >> 35) & 31];
            buffer[4] = encode32Chars[(id >> 40) & 31];
            buffer[3] = encode32Chars[(id >> 45) & 31];
            buffer[2] = encode32Chars[(id >> 50) & 31];
            buffer[1] = encode32Chars[(id >> 55) & 31];
            buffer[0] = encode32Chars[(id >> 60) & 31];
            
            return new string(buffer, 0, buffer.Length);
        }
    }
}