// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System;
using System.Threading;

namespace Microsoft.AspNetCore.Connections
{
  public static class CorrelationIdGenerator
  {
    // Base32 encoding - in ascii sort order for easy text based sorting
    private static readonly char[] s_encode32Chars = "0123456789ABCDEFGHIJKLMNOPQRSTUV".ToCharArray();

    // Seed the _lastConnectionId for this application instance with
    // the number of 100-nanosecond intervals that have elapsed since 12:00:00 midnight, January 1, 0001
    // for a roughly increasing _lastId over restarts
    private static long _lastId = DateTime.UtcNow.Ticks;

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

    private static string GenerateId(long id)
    {
      return string.Create(13, id, (buffer, value) =>
      {
        char[] encode32Chars = s_encode32Chars;

        buffer[12] = encode32Chars[value & 31];
        buffer[11] = encode32Chars[(value >> 5) & 31];
        buffer[10] = encode32Chars[(value >> 10) & 31];
        buffer[9] = encode32Chars[(value >> 15) & 31];
        buffer[8] = encode32Chars[(value >> 20) & 31];
        buffer[7] = encode32Chars[(value >> 25) & 31];
        buffer[6] = encode32Chars[(value >> 30) & 31];
        buffer[5] = encode32Chars[(value >> 35) & 31];
        buffer[4] = encode32Chars[(value >> 40) & 31];
        buffer[3] = encode32Chars[(value >> 45) & 31];
        buffer[2] = encode32Chars[(value >> 50) & 31];
        buffer[1] = encode32Chars[(value >> 55) & 31];
        buffer[0] = encode32Chars[(value >> 60) & 31];
      });
    }
  }
}