///////////////////////////////////////////////////////////////////////////////
//
//  Microsoft Research Singularity
//
//  Copyright (c) Microsoft Corporation.  All rights reserved.
//
//  File:   DnsClient.cs
//

using System;
using System.Collections;
using System.Diagnostics;
using System.Text;

using System.Net.IP;
using Drivers.Net;

using NetStack.Protocols;

using Dns = NetStack.Protocols.Dns;

using Microsoft.Singularity.Io;


namespace NetStack.Runtime
{
    /// <summary>
    /// Dns Client for UDP lookups.
    /// </summary>
    public class BasicDnsClient
    {
        private IPv4      dnsServer;
        private TimeSpan  timeout;
        private Dns.Flags flags;

        public const int DefaultTimeoutMillis = 500;

        public enum StatusCode : int
        {
            Success         = 0,
                NoNameServer    = 1,
                TransportError  = 2,
                RequestFailed   = 3,
                Timeout         = 4,
                OverSizeMessage = 5
                }

        public BasicDnsClient()
            : this(IPv4.Any)
        {
        }

        public BasicDnsClient(IPv4 dnsServer)
        {
            this.dnsServer  = dnsServer;
            this.timeout    = TimeSpan.FromMilliseconds(DefaultTimeoutMillis);
            this.flags      = Dns.Flags.RD;
        }

        public IPv4 DnsServer
        {
            get {
                if (dnsServer != IPv4.Any)
                    return dnsServer;
                IPModule ip = (IPModule!) Core.Instance().GetProtocolByName("IP");
                return ip.HostConfiguration.GetCurrentNameServer();
            }
        }

        public TimeSpan Timeout
        {
            get { return timeout; }
            set { timeout = value; }
        }

        public Dns.Flags Flags
        {
            get { return flags; }
            set { flags = value; }
        }

        [ System.Diagnostics.Conditional("DEBUG_DNS_CLIENT") ]
        private void DebugPrint(string format, params object [] arguments)
        {
            Core.Log("DnsClient: ");
            Core.Log(format, arguments);
        }

        [ System.Diagnostics.Conditional("DEBUG_DNS_CLIENT") ]
        private static void Dump(byte []! data, int offset)
        {
            for (int i = offset; i < data.Length; i += 16)
            {
                Core.Log("{0:x4}  ", i);
                int n = Math.Min(16, data.Length - i) + i;
                for (int j = i; j < n; j++)
                    Core.Log("{0:x2} ", data[j]);
                for (int j = n; j != i + 16; j++)
                    Core.Log("   ");
                Core.Log("  ");
                for (int j = i; j < n; j++)
                {
                    char c = '.';
                    if (data[j] > 31 && data[j] < 128)
                        c = (char)data[j];
                    Core.Log("{0}", c);
                }
                Core.Log("\n");
            }
        }

        /// <summary>
        /// Gets the DNS information for the specified DNS host name.
        /// </summary>
        public StatusCode GetHostByName(string            name,
                                        out IPv4HostEntry hostEntry)
        {
            hostEntry = null;

            IPv4 dnsServer = DnsServer;
            if (dnsServer == IPv4.Zero)
                return StatusCode.NoNameServer;

            Dns.Query q = new Dns.Query(name, Dns.Type.A, Dns.Class.Internet);
            Dns.Format answer;

            StatusCode askResponse = Ask(dnsServer, q, out answer);
            if (askResponse != StatusCode.Success)
                return askResponse;
            assert answer != null;

            if (answer.GetRCode() != Dns.RCode.NoError)
            {
                DebugPrint("Dns query failed: RCode = {0}\n", answer.GetRCode());
                return StatusCode.RequestFailed;
            }

            hostEntry = new IPv4HostEntry( new string [] { name }, new IPv4[] {} );
            ArrayList addressList = new ArrayList();

            foreach (Dns.ResourceRecord! rr in answer.AnswerRRs)
            {
                if (rr.Type != Dns.Type.A || rr.Class != Dns.Class.Internet)
                    continue;

                byte [] rdata = rr.RData;
                if (rdata == null)
                    continue;

                if ((rdata.Length % IPv4.Length) != 0)
                    continue;

                int offset = 0;
                while (offset != rdata.Length)
                {
                    addressList.Add(IPv4.ParseBytes(rdata, offset));
                    offset += 4;
                }
            }

            IPv4[] al = hostEntry.AddressList = new IPv4 [addressList.Count];
            for (int i = 0; i < addressList.Count; i++)
                al[i] = (IPv4) (!) addressList[i];

            return StatusCode.Success;
        }

        /// <summary>
        /// Gets DNS host information for an IP address.
        /// </summary>
        public StatusCode GetHostByAddress(IPv4              address,
                                           out IPv4HostEntry hostEntry)
        {
            hostEntry = null;

            IPv4 dnsServer = DnsServer;
            if (dnsServer == IPv4.Zero)
                return StatusCode.NoNameServer;

            // Formulate request a.b.c.d -> d.b.c.a
            IPv4 reversed = new IPv4(ByteOrder.Swap((uint)address));
            string name = String.Format("{0}.IN-ADDR.ARPA", reversed);

            DebugPrint("Looking up {0}\n", name);

            Dns.Query q = new Dns.Query(name, Dns.Type.PTR, Dns.Class.Internet);
            Dns.Format answer;

            StatusCode askResponse = Ask(dnsServer, q, out answer);
            if (askResponse != StatusCode.Success)
                return askResponse;
            assert answer != null;

            if (answer.GetRCode() != Dns.RCode.NoError)
            {
                DebugPrint("Dns query failed: RCode = {0}\n", answer.GetRCode());
                return StatusCode.RequestFailed;
            }

            hostEntry = new IPv4HostEntry(new string[]{}, new IPv4 [] { address });

            ArrayList aliases = new ArrayList();
            foreach (Dns.ResourceRecord! rr in answer.AnswerRRs)
            {
                DebugPrint("Answer: Type = {0} Class = {1} TTL = {2}\n",
                           rr.Type, rr.Class, rr.TtlSeconds);
                if ((rr.Type != Dns.Type.PTR && rr.Type != Dns.Type.CNAME) ||
                    rr.Class != Dns.Class.Internet)
                    continue;

                byte [] rdata = rr.RData;
                if (rdata == null)
                    continue;

                int offset = 0;
                while (offset != rdata.Length)
                {
                    string alias;
                    offset += Dns.LabelEncoding.GetString(rdata, offset,
                                                          out alias);
                    aliases.Add(alias);
                }
            }
            hostEntry.Aliases = (string []!) aliases.ToArray(typeof(string));

            return StatusCode.Success;
        }

        /// <summary>
        /// Resolves a DNS host name or IP address to an IPv4HostEntry instance.
        /// </summary>
        public StatusCode Resolve(string            hostName,
                                  out IPv4HostEntry hostEntry)
        {
            IPv4 hostAddress;

            if (IPv4.Parse(hostName, out hostAddress) == true)
            {
                StatusCode status = GetHostByAddress(hostAddress, out hostEntry);

                if (status != StatusCode.Success)
                {
                    // As a convenience to the caller, instead of failing
                    // outright, at least give back the parsed version of
                    // the net address.
                    hostEntry = new IPv4HostEntry(new string [] { hostName },
                                                  new IPv4 [] { hostAddress });

                    return StatusCode.Success;
                }
            }

            return GetHostByName(hostName, out hostEntry);
        }

        private StatusCode Ask(IPv4           dnsServer,
                               Dns.Query []!  queries,
                               out Dns.Format answer)
        {
            answer = null;

            Dns.Format outFrame = new Dns.Format();
            outFrame.SetFlags(flags);
            outFrame.Queries.AddRange(queries);

            byte[] outData = new byte [outFrame.Size];
            if (outData.Length > Dns.Format.MaxUdpMessageLength)
            {
                return StatusCode.OverSizeMessage;
            }

            int offset = 0;
            outFrame.Write(outData, ref offset);

            byte[] rcvData;
            StatusCode askResponse = AskDnsServer(dnsServer, outData, out rcvData);
            if (askResponse != StatusCode.Success)
            {
                return askResponse;
            }
            assert rcvData != null;

            try
            {
                offset = 0;
                Dump(rcvData, offset);
                answer = Dns.Format.Parse(rcvData, ref offset);
            }
            catch (Exception e)
            {
                DebugPrint("Parser threw {0}", e);
                return StatusCode.TransportError;
            }

            return StatusCode.Success;
        }

        public StatusCode Ask(IPv4           dnsServer,
                              Dns.Query      query,
                              out Dns.Format answer)
        {
            return Ask(dnsServer, new Dns.Query [] { query }, out answer);
        }

        private StatusCode AskDnsServer(IPv4       dnsServer,
                                        byte[]!    outData,
                                        out byte[] rcvData)
        {
            Core      core      = Core.Instance();
            UdpModule udpModule = core.GetProtocolByName("UDP") as UdpModule;
            if (udpModule == null)
            {
                rcvData = null;
                return StatusCode.TransportError;
            }

            UdpSession udpSession =
                udpModule.CreateBoundSession(IPv4.Any, 0,
                                             dnsServer, Dns.Format.ServerPort);
            udpSession.WriteData(outData);
            rcvData = udpSession.PollCopyData((int) (timeout.Ticks /
                                                     TimeSpan.TicksPerMillisecond));
            if (rcvData == null)
                return StatusCode.Timeout;

            return StatusCode.Success;
        }
    }
}