src/SilkroadBot.Core/Networking/Packet.cs

namespace SilkroadBot.Core.Networking;

/// <summary>
/// Represents a Silkroad packet with opcode and payload.
/// </summary>
public class Packet
{
    public ushort Opcode { get; }
    public byte[] Payload { get; }
    public bool IsEncrypted { get; }
    public DateTime Timestamp { get; }
    public PacketDirection Direction { get; }

    public Packet(ushort opcode, byte[] payload, PacketDirection direction, bool isEncrypted = false)
    {
        Opcode = opcode;
        Payload = payload ?? Array.Empty<byte>();
        IsEncrypted = isEncrypted;
        Timestamp = DateTime.UtcNow;
        Direction = direction;
    }

    /// <summary>Create a client-to-server packet.</summary>
    public static Packet ToServer(ushort opcode, byte[] payload, bool encrypted = false)
        => new(opcode, payload, PacketDirection.ClientToServer, encrypted);

    /// <summary>Create a server-to-client packet.</summary>
    public static Packet FromServer(ushort opcode, byte[] payload, bool encrypted = false)
        => new(opcode, payload, PacketDirection.ServerToClient, encrypted);

    public override string ToString() => $"[{Direction}] 0x{Opcode:X4} ({Payload.Length} bytes)";
}

public enum PacketDirection
{
    ClientToServer,
    ServerToClient
}

/// <summary>
/// Packet reader utility for extracting data from packet payloads.
/// </summary>
public class PacketReader
{
    private readonly byte[] _data;
    private int _position;

    public PacketReader(byte[] data)
    {
        _data = data;
        _position = 0;
    }

    public int Remaining => _data.Length - _position;
    public int Position => _position;

    public byte ReadByte() => _data[_position++];
    
    public ushort ReadUInt16()
    {
        var value = BitConverter.ToUInt16(_data, _position);
        _position += 2;
        return value;
    }
    
    public uint ReadUInt32()
    {
        var value = BitConverter.ToUInt32(_data, _position);
        _position += 4;
        return value;
    }
    
    public ulong ReadUInt64()
    {
        var value = BitConverter.ToUInt64(_data, _position);
        _position += 8;
        return value;
    }
    
    public float ReadSingle()
    {
        var value = BitConverter.ToSingle(_data, _position);
        _position += 4;
        return value;
    }
    
    public string ReadAscii()
    {
        ushort length = ReadUInt16();
        var text = System.Text.Encoding.ASCII.GetString(_data, _position, length);
        _position += length;
        return text;
    }
    
    public string ReadUnicode()
    {
        ushort length = ReadUInt16();
        var text = System.Text.Encoding.Unicode.GetString(_data, _position, length * 2);
        _position += length * 2;
        return text;
    }
    
    public byte[] ReadBytes(int count)
    {
        var bytes = new byte[count];
        Array.Copy(_data, _position, bytes, 0, count);
        _position += count;
        return bytes;
    }
    
    public void Skip(int count) => _position += count;
}

/// <summary>
/// Packet writer utility for constructing packet payloads.
/// </summary>
public class PacketWriter
{
    private readonly MemoryStream _stream;

    public PacketWriter(int initialCapacity = 64)
    {
        _stream = new MemoryStream(initialCapacity);
    }

    public PacketWriter WriteByte(byte value) { _stream.WriteByte(value); return this; }
    
    public PacketWriter WriteUInt16(ushort value) 
    { 
        _stream.Write(BitConverter.GetBytes(value)); 
        return this; 
    }
    
    public PacketWriter WriteUInt32(uint value) 
    { 
        _stream.Write(BitConverter.GetBytes(value)); 
        return this; 
    }
    
    public PacketWriter WriteUInt64(ulong value) 
    { 
        _stream.Write(BitConverter.GetBytes(value)); 
        return this; 
    }
    
    public PacketWriter WriteSingle(float value) 
    { 
        _stream.Write(BitConverter.GetBytes(value)); 
        return this; 
    }
    
    public PacketWriter WriteAscii(string text)
    {
        var bytes = System.Text.Encoding.ASCII.GetBytes(text);
        WriteUInt16((ushort)bytes.Length);
        _stream.Write(bytes);
        return this;
    }
    
    public PacketWriter WriteUnicode(string text)
    {
        var bytes = System.Text.Encoding.Unicode.GetBytes(text);
        WriteUInt16((ushort)(bytes.Length / 2));
        _stream.Write(bytes);
        return this;
    }
    
    public PacketWriter WriteBytes(byte[] data) { _stream.Write(data); return this; }
    
    public byte[] ToArray() => _stream.ToArray();
}