using System;

namespace DnsClient
{
    /* Reference: https://tools.ietf.org/html/rfc6895#section-2
     * Response header fields
     *
                                            1  1  1  1  1  1
              0  1  2  3  4  5  6  7  8  9  0  1  2  3  4  5
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
             |                      ID                       |
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
       ==>   |QR|   OpCode  |AA|TC|RD|RA| Z|AD|CD|   RCODE   |  <==
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
             |                QDCOUNT/ZOCOUNT                |
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
             |                ANCOUNT/PRCOUNT                |
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
             |                NSCOUNT/UPCOUNT                |
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
             |                    ARCOUNT                    |
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

     * */

    /// <summary>
    /// The flags of the header's second 16bit value
    /// </summary>
    public enum DnsHeaderFlag : ushort
    {
        IsCheckingDisabled      = 0x0010,
        IsAuthenticData         = 0x0020,
        FutureUse               = 0x0040,             // Z bit seems to be ignored now, see https://tools.ietf.org/html/rfc6895#section-2.1
        RecursionAvailable      = 0x0080,
        RecursionDesired        = 0x0100,
        ResultTruncated         = 0x0200,
        HasAuthorityAnswer      = 0x0400,
        HasQuery                 = 0x8000,
    }

    public static class DnsHeader
    {
        public static readonly ushort OPCODE_MASK = 0x7800;
        public static readonly ushort OPCODE_SHIFT = 11;
        public static readonly ushort RCODE_MASK = 0x000F;
    }
}