using System.Net;
using System.Net.Sockets;
using System.Text;
using Inspectron.Epson;

// POS895 discovery probe.
//
// The POS895 does not answer Epson's ENPC broadcast, but it does answer the
// vendor's own SPRT discovery, which the EasySet tool uses. Protocol, taken from
// a packet capture of EasySet on the printer's segment:
//
//   query  UDP broadcast 255.255.255.255:3289, sent FROM source port 9100
//          53 50 52 54 2D 49 6E 66 6F 72 00 00 0D   "SPRT-Infor\0\0\r"
//
//   reply  from <printer>:3289 back to <querier>:9100, 39 bytes of ASCII
//          "28-0e-8b-3d-ca-f1            2608120478"
//           |<-- MAC, 17 -->||<- 12 sp ->||<- serial, 10 ->|
//
// The printer's address is the reply's source IP; the payload carries only MAC
// and serial, no model name. Note 3289 is the same UDP port Epson ENPC uses, so
// a composite IDiscoveryService can reuse the socket it already has.
//
// All settings are the constants below. Edit them here; there are no arguments.

const string ProbeMagic = "SPRT-Infor";
const int DiscoveryPort = 3289;
const int ReplyPort = 9100;
const int ListenSeconds = 3;

// EasySet sends from source port 9100 and the reply comes back to 9100. Whether
// the firmware honours the sender's port or hard-codes 9100 is unknown from a
// single capture. Set this false to bind an ephemeral port instead: if replies
// still arrive, the firmware replies to the sender; if they stop, 9100 is
// hard-coded and any implementation must bind it.
bool bindSourcePort9100 = true;

byte[] probe = BuildProbe(ProbeMagic);

Console.WriteLine("POS895 / SPRT discovery probe");
Console.WriteLine($"  probe -> 255.255.255.255:{DiscoveryPort}  ({probe.Length} bytes)");
Console.WriteLine(Describe(probe));
Console.WriteLine();

using var udp = new UdpClient(AddressFamily.InterNetwork);
udp.EnableBroadcast = true;

try
{
    udp.Client.Bind(new IPEndPoint(IPAddress.Any, bindSourcePort9100 ? ReplyPort : 0));
}
catch (SocketException ex)
{
    Console.Error.WriteLine($"[FAIL] Could not bind UDP {ReplyPort}: {ex.Message}");
    Console.Error.WriteLine("       Something else holds it, or this needs elevation.");
    Console.Error.WriteLine("       Set bindSourcePort9100 = false to try an ephemeral port.");
    return 1;
}

int localPort = ((IPEndPoint)udp.Client.LocalEndPoint!).Port;
Console.WriteLine($"  listening on UDP {localPort} for {ListenSeconds}s");
Console.WriteLine();

await udp.SendAsync(probe, probe.Length, new IPEndPoint(IPAddress.Broadcast, DiscoveryPort));

var found = new Dictionary<string, string>();
DateTime deadline = DateTime.UtcNow.AddSeconds(ListenSeconds);

while (DateTime.UtcNow < deadline)
{
    using var cts = new CancellationTokenSource(deadline - DateTime.UtcNow);
    UdpReceiveResult res;
    try
    {
        res = await udp.ReceiveAsync(cts.Token);
    }
    catch (OperationCanceledException)
    {
        break;
    }

    string ip = res.RemoteEndPoint.Address.ToString();
    var parsed = ParseReply(res.Buffer);

    if (parsed is null)
    {
        Console.WriteLine($"  {ip}:{res.RemoteEndPoint.Port}  unrecognised, {res.Buffer.Length} bytes");
        Console.WriteLine(Describe(res.Buffer));
        continue;
    }

    (string mac, string serial) = parsed.Value;
    found[ip] = mac;
    Console.WriteLine($"  FOUND  {ip,-15}  mac {mac}  serial {serial}");
}

Console.WriteLine();
if (found.Count == 0)
{
    Console.WriteLine("[--] No replies.");
    Console.WriteLine("     - is this machine on the printer's broadcast domain?");
    Console.WriteLine("     - does the firewall allow inbound UDP on this port?");
    Console.WriteLine($"     - try flipping bindSourcePort9100 (currently {bindSourcePort9100}).");
    return 1;
}

Console.WriteLine($"[OK] {found.Count} printer(s) answered SPRT discovery.");
return 0;

// "SPRT-Infor" followed by 00 00 0D. The trailing 0x0D is also the total length
// of the datagram, which may or may not be a coincidence.
static byte[] BuildProbe(string magic)
{
    var p = new List<byte>(Encoding.ASCII.GetBytes(magic));
    p.AddRange(new byte[] { 0x00, 0x00, 0x0D });
    return p.ToArray();
}

// 17 ASCII bytes of dashed lowercase MAC, space padding, then the serial.
static (string Mac, string Serial)? ParseReply(byte[] payload)
{
    if (payload.Length < 17)
    {
        return null;
    }

    string text = Encoding.ASCII.GetString(payload);
    string mac = text[..17];

    bool looksLikeMac = mac.Split('-') is { Length: 6 } parts
        && parts.All(p => p.Length == 2 && p.All(Uri.IsHexDigit));

    return looksLikeMac ? (mac, text[17..].Trim()) : null;
}

// Hex plus a printable-ASCII gutter.
static string Describe(byte[] bytes)
{
    var sb = new StringBuilder();
    for (int offset = 0; offset < bytes.Length; offset += 16)
    {
        int count = Math.Min(16, bytes.Length - offset);
        sb.Append($"  {offset:X4}  ");

        for (int i = 0; i < 16; i++)
        {
            sb.Append(i < count ? $"{bytes[offset + i]:X2} " : "   ");
        }

        sb.Append(' ');
        for (int i = 0; i < count; i++)
        {
            byte b = bytes[offset + i];
            sb.Append(b >= 0x20 && b < 0x7F ? (char)b : '.');
        }

        sb.AppendLine();
    }

    return sb.ToString().TrimEnd();
}

/* =====================================================================
   PRINT TEST -- disabled.

   Confirmed working against the printer through the AnyDesk tunnel on
   127.0.0.1:8888. Font A is 48 columns on the 576-dot line, and GS !
   magnification works at width 1x/2x/3x with height 2x. ESC d n appears
   to be ignored, hence the literal LF bytes before the cut.

   To re-enable, move this code above the discovery section.

const string PrinterIp = "127.0.0.1";
const int PrinterPort = 8888;
const int ConnectTimeoutSeconds = 5;

const int FontAColumns = 48;
const int HeightMagnification = 2;
int[] widths = { 1, 2, 3 };
const int BlankLinesAfterText = 10;
bool useRawAscii = false;

byte[] job = BuildJob(FontAColumns, widths, HeightMagnification, BlankLinesAfterText, useRawAscii);

Console.WriteLine("Byte sequence:");
Console.WriteLine(Describe(job));

await using var printer = new EpsonPrinter();
await printer.ConnectAsync(PrinterIp, PrinterPort, ConnectTimeoutSeconds);
await printer.SendRawCommandAsync(job);

static byte[] BuildJob(int fontACols, int[] widths, int heightMag, int blankLines, bool rawAscii)
{
    var job = new List<byte> { 0x1B, 0x40 };            // ESC @   initialize

    if (!rawAscii)
    {
        job.AddRange(new byte[] { 0x1B, 0x74, 0x12 });  // ESC t 18  code page 852
    }

    job.AddRange(new byte[] { 0x1B, 0x21, 0x00 });      // ESC ! 0   Font A

    foreach (int w in widths)
    {
        job.AddRange(new byte[] { 0x1D, 0x21, SizeByte(w, heightMag) });
        job.AddRange(Encoding.ASCII.GetBytes(Ruler(fontACols / w)));
        job.Add(0x0A);
    }

    job.AddRange(new byte[] { 0x1D, 0x21, 0x00 });      // GS ! 0    back to 1x1

    for (int i = 0; i < blankLines; i++)
    {
        job.Add(0x0A);
    }

    job.AddRange(new byte[] { 0x1D, 0x56, 0x00 });      // GS V 0  full cut
    return job.ToArray();
}

// GS ! n: bits 4-6 width magnification - 1, bits 0-2 height - 1.
static byte SizeByte(int width, int height) =>
    (byte)(((height - 1) & 0x07) | (((width - 1) & 0x07) << 4));

static string Ruler(int columns)
{
    var sb = new StringBuilder();
    while (sb.Length < columns)
    {
        sb.Append("|---");
    }

    return sb.ToString(0, columns);
}

   ===================================================================== */