tetri5/backend/Program.cs

using System.Net.WebSockets;
using System.Text;
using System.Text.Json;
using System.Collections.Concurrent;

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

var games = new ConcurrentDictionary<string, Game>();

app.UseWebSockets();

app.Map("/", async context =>
{
    if (!context.WebSockets.IsWebSocketRequest)
    {
        context.Response.StatusCode = 400;
        return;
    }

    var ws = await context.WebSockets.AcceptWebSocketAsync();
    var remoteAddress = context.Connection.RemoteIpAddress?.ToString();

    var player = new Player(ws, remoteAddress);

    try
    {
        var buffer = new byte[4096];
        var messageBuffer = new ArraySegment<byte>(buffer);
        while (ws.State == WebSocketState.Open)
        {
            var message = new MemoryStream();
            WebSocketReceiveResult result;

            do
            {
                result = await ws.ReceiveAsync(messageBuffer, CancellationToken.None);
                message.Write(buffer, 0, result.Count);
            }
            while (!result.EndOfMessage);

            if (result.MessageType == WebSocketMessageType.Close)
                break;

            var msgText = Encoding.UTF8.GetString(message.ToArray());

            if (msgText == "ping")
            {
                await player.SendTextAsync("pong");
                continue;
            }

            var json = JsonDocument.Parse(msgText).RootElement;
            var action = json.GetProperty("action").GetString();
            var gameId = json.GetProperty("gameId").GetString();
            var clientId = json.GetProperty("clientId").GetString();

            switch (action)
            {
                case "enter_game":
                    await GameHandlers.EnterGame(gameId, clientId, player, games);
                    break;
                case "send_piece":
                    await GameHandlers.SendToOpponent(gameId, player, "receive_piece", json.GetProperty("piece"), games);
                    break;
                case "send_stack":
                    await GameHandlers.SendToOpponent(gameId, player, "receive_stack", json.GetProperty("stack"), games);
                    break;
                case "send_stats":
                    await GameHandlers.SendToOpponent(gameId, player, "receive_stats", json.GetProperty("stats"), games);
                    break;
                default:
                    Console.WriteLine("Unsupported action.");
                    break;
            }
        }
    }
    catch (Exception ex)
    {
        Console.WriteLine($"Error: {ex.Message}");
    }
    finally
    {
        Console.WriteLine("Disconnecting player...");
        await GameHandlers.ExitGame(player, games);
        Console.WriteLine("Connection closed.");
    }
});

app.Run();

// -------------------------
// Models
// -------------------------

record Player(WebSocket Socket, string? RemoteAddress)
{
    public async Task SendTextAsync(string message)
    {
        var bytes = Encoding.UTF8.GetBytes(message);
        await Socket.SendAsync(new ArraySegment<byte>(bytes), WebSocketMessageType.Text, true, CancellationToken.None);
    }

    public async Task SendJsonAsync(object obj)
    {
        var json = JsonSerializer.Serialize(obj);
        await SendTextAsync(json);
    }
}

class Game
{
    public string GameId { get; }
    public List<Player> Players { get; } = new();
    public List<string> Clients { get; } = new();

    public Game(string gameId)
    {
        GameId = gameId;
    }

    public Player? GetOpponent(Player player) => Players.FirstOrDefault(p => p != player);
}

// -------------------------
// Handlers
// -------------------------

static class GameHandlers
{
    public static async Task EnterGame(string gameId, string clientId, Player player, ConcurrentDictionary<string, Game> games)
    {
        var game = games.GetOrAdd(gameId, _ => new Game(gameId));

        if (!game.Clients.Contains(clientId))
        {
            game.Clients.Add(clientId);
            game.Players.Add(player);

            if (game.Players.Count == 1)
            {
                await player.SendJsonAsync(new { type = "wait_for_opponent" });
            }
            else if (game.Players.Count == 2)
            {
                foreach (var p in game.Players)
                    await p.SendJsonAsync(new { type = "start_game" });
            }
        }
        else
        {
            Console.WriteLine("Already in game...");
        }
    }

    public static async Task SendToOpponent(string gameId, Player sender, string type, JsonElement content, ConcurrentDictionary<string, Game> games)
    {
        if (!games.TryGetValue(gameId, out var game))
            return;

        var opponent = game.GetOpponent(sender);
        if (opponent != null)
        {
            switch (type)
            {
                case "receive_piece":
                    await opponent.SendJsonAsync(new { type, piece = content });
                    break;
                case "receive_stack":
                    await opponent.SendJsonAsync(new { type, stack = content });
                    break;
                case "receive_stats":
                    await opponent.SendJsonAsync(new { type, stats = content });
                    break;
            }
        }
    }

    public static async Task ExitGame(Player disconnectingPlayer, ConcurrentDictionary<string, Game> games)
    {
        var game = games.Values.FirstOrDefault(g => g.Players.Contains(disconnectingPlayer));
        if (game != null)
        {
            games.TryRemove(game.GameId, out _);

            var opponent = game.GetOpponent(disconnectingPlayer);
            if (opponent != null)
            {
                await opponent.SendJsonAsync(new { type = "exit_game" });
            }
        }
    }
}