using System.Net.Sockets;

namespace MSCO.Server;

/// <summary>Muss mit MsgType in der Mod (NetSession.cs) übereinstimmen.</summary>
public enum MsgType : byte
{
    Hello = 1,
    Welcome = 2,
    Reject = 3,
    Player = 4,
    SaveBegin = 5,
    SaveFile = 6,
    StartGame = 7,
    ObjStates = 8,
    ObjOwn = 9,
    ObjRelease = 10,
    FsmEvent = 11,
    PlayerJoined = 12,
    PlayerLeft = 13,
    VehicleFx = 14,
    Ping = 15,
    Ready = 16,        // Client -> Server: Spiel geladen, Objekte erfasst
    WorldSnapshot = 17,// Server -> Client: aktueller Weltzustand
    Info = 18,         // Server-Browser fragt Infos ab (ohne Hello)
    InfoReply = 19,
    WorldTime = 20,    // Uhrzeit + Wetter vom "Weltuhr"-Spieler
    MoneyDelta = 21,   // Geld hat sich geändert (+/- Betrag, gemeinsame Kasse)
    DoorState = 22,    // Tür/Tor/Haube hat den Zustand gewechselt
    AdminStatus = 23,  // Server -> Client: bool, ist Admin
    AdminListRequest = 24, // Client -> Server: Spielerliste fürs Admin-Menü
    AdminList = 25,    // Server -> Client: int Anzahl, je [int id, string name, string steamId, bool admin]
    AdminAction = 26,  // Client -> Server: byte (1 = kick, 2 = ban), int Spieler-ID, string Grund
    AdminResult = 27,  // Server -> Client: string Meldung
    Chat = 28,         // Chatnachricht (string)
    VarSync = 29,      // Fahrzeugzustand: int n, je [int key, byte typ, wert]
    Teleport = 30,     // Admin holt einen Spieler zu sich: 3 float Position
    Pong = 31          // Antwort auf Ping mit demselben Zeitstempel (Laufzeit messen)
}

public readonly record struct Message(MsgType Type, byte[] Payload)
{
    public BinaryReader Reader() => new(new MemoryStream(Payload));
}

public static class Wire
{
    public static byte[] Build(Action<BinaryWriter> write)
    {
        using var ms = new MemoryStream();
        using var w = new BinaryWriter(ms);
        write(w);
        w.Flush();
        return ms.ToArray();
    }

    public static byte[] WithSender(int senderId, byte[] payload)
    {
        var result = new byte[4 + payload.Length];
        BitConverter.GetBytes(senderId).CopyTo(result, 0);
        Buffer.BlockCopy(payload, 0, result, 4, payload.Length);
        return result;
    }

    public static byte[] Frame(MsgType type, byte[] payload)
    {
        payload ??= Array.Empty<byte>();
        var frame = new byte[5 + payload.Length];
        BitConverter.GetBytes(payload.Length + 1).CopyTo(frame, 0);
        frame[4] = (byte)type;
        Buffer.BlockCopy(payload, 0, frame, 5, payload.Length);
        return frame;
    }
}

/// <summary>TCP-Verbindung zu einem Spieler, gleiches Format wie in der Mod: [int Länge][byte Typ][Payload].</summary>
public sealed class Connection
{
    // Spieler schicken nur kleine Pakete (Positionen, Aktionen); der Spielstand geht nur vom Server zum Spieler
    const int MaxFrame = 1024 * 1024;

    public bool IsClosed { get; private set; }
    public string CloseReason { get; private set; }
    public string RemoteAddress { get; }
    /// <summary>Wann zuletzt etwas ankam (Clients schicken alle 2 s einen Ping).</summary>
    public DateTime LastReceiveUtc { get; private set; } = DateTime.UtcNow;

    readonly TcpClient client;
    readonly NetworkStream stream;
    readonly byte[] readBuffer = new byte[64 * 1024];
    byte[] buffer = new byte[64 * 1024];
    int count;

    public Connection(TcpClient client)
    {
        this.client = client;
        client.NoDelay = true;
        client.SendBufferSize = 4 * 1024 * 1024;
        stream = client.GetStream();
        RemoteAddress = client.Client.RemoteEndPoint?.ToString() ?? "?";
    }

    public List<Message> Poll()
    {
        var messages = new List<Message>();
        if (IsClosed) return messages;
        try
        {
            if (client.Client.Poll(0, SelectMode.SelectRead) && client.Available == 0)
            {
                Close("Connection closed");
                return messages;
            }
            while (stream.DataAvailable)
            {
                int read = stream.Read(readBuffer, 0, readBuffer.Length);
                if (read <= 0) break;
                Append(readBuffer, read);
                LastReceiveUtc = DateTime.UtcNow;
            }
            Parse(messages);
        }
        catch (Exception e)
        {
            Close("Network error: " + e.Message);
        }
        return messages;
    }

    public void Send(MsgType type, byte[] payload = null)
    {
        if (IsClosed) return;
        try
        {
            byte[] frame = Wire.Frame(type, payload);
            stream.Write(frame, 0, frame.Length);
        }
        catch (Exception e)
        {
            Close("Network error: " + e.Message);
        }
    }

    public void Close(string reason)
    {
        if (IsClosed) return;
        IsClosed = true;
        CloseReason = reason;
        try { client.Close(); } catch { }
    }

    void Append(byte[] data, int length)
    {
        if (count + length > buffer.Length) Array.Resize(ref buffer, Math.Max(count + length, buffer.Length * 2));
        Buffer.BlockCopy(data, 0, buffer, count, length);
        count += length;
    }

    void Parse(List<Message> messages)
    {
        int offset = 0;
        while (count - offset >= 5)
        {
            int length = BitConverter.ToInt32(buffer, offset);
            if (length < 1 || length > MaxFrame) throw new IOException("Invalid packet");
            if (count - offset - 4 < length) break;
            var payload = new byte[length - 1];
            Buffer.BlockCopy(buffer, offset + 5, payload, 0, payload.Length);
            messages.Add(new Message((MsgType)buffer[offset + 4], payload));
            offset += 4 + length;
        }
        if (offset > 0)
        {
            Buffer.BlockCopy(buffer, offset, buffer, 0, count - offset);
            count -= offset;
        }
    }
}