SVSimServer/SVSim.BattleNode/Hosting/BattleNodeWebSocketHandler.cs

using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Logging;
using SVSim.BattleNode.Sessions;
using SVSim.BattleNode.Sessions.Participants;
using SVSim.BattleNode.Wire;

namespace SVSim.BattleNode.Hosting;

/// <summary>
/// Validates an incoming WebSocket upgrade request, accepts it, and hands off to a fresh
/// <see cref="BattleSession"/>. Singleton; no per-request state.
/// </summary>
/// <remarks>
/// <para>The validation chain — cheapest checks first, crypto only after both params are
/// present, WS accept only after the store lookup confirms the credentials match an outstanding
/// pending battle:</para>
/// <list type="number">
///   <item>Reject non-WS requests with 400 (someone hit <c>/socket.io/</c> via plain HTTP).</item>
///   <item>Read <c>BattleId</c> and encrypted <c>viewerId</c> from request headers, falling back
///         to query string. The real client puts them on headers despite BestHTTP's
///         <c>AdditionalQueryParams</c> API name — see project README §Wire-format gotchas.</item>
///   <item>Decrypt the viewerId with <see cref="NodeCrypto.DecryptForNode"/>; reject on
///         parse/decrypt failure.</item>
///   <item>Look up the <see cref="PendingBattle"/> in the store and verify the decrypted viewer
///         matches the one the <see cref="Bridge.IMatchingBridge"/> registered.</item>
///   <item>AcceptWebSocketAsync, remove the pending entry (it's now an active session), construct
///         <see cref="BattleSession"/>, await <see cref="BattleSession.RunAsync"/> until the WS
///         closes.</item>
/// </list>
/// </remarks>
public sealed class BattleNodeWebSocketHandler
{
    private readonly IBattleSessionStore _store;
    private readonly ILogger<BattleNodeWebSocketHandler> _log;
    private readonly ILoggerFactory _loggerFactory;

    public BattleNodeWebSocketHandler(IBattleSessionStore store, ILoggerFactory loggerFactory)
    {
        _store = store;
        _loggerFactory = loggerFactory;
        _log = loggerFactory.CreateLogger<BattleNodeWebSocketHandler>();
    }

    /// <summary>
    /// Endpoint entry point. Sets <see cref="HttpContext.Response"/> to 400 on any validation
    /// failure; otherwise upgrades to a WebSocket and awaits
    /// <see cref="BattleSession.RunAsync"/> until the connection closes.
    /// </summary>
    public async Task HandleAsync(HttpContext ctx)
    {
        // Status code mapping: 400 protocol violations (not WS, missing creds);
        // 401 credential validation failures (decrypt, viewer mismatch); 404 unknown
        // BattleId. Log messages carry the diagnostic detail; the wire code gives the
        // client class of failure.
        if (!ctx.WebSockets.IsWebSocketRequest)
        {
            ctx.Response.StatusCode = StatusCodes.Status400BadRequest;
            return;
        }

        // BestHTTP's SocketOptions.AdditionalQueryParams puts these on HTTP request HEADERS
        // for the WebSocket-only transport (not on the URL query string). Real clients
        // therefore send BattleId/viewerId as headers; the integration test sends them as
        // query params for convenience. Check headers first, fall back to query.
        var battleId = ReadCredential(ctx, "BattleId");
        var encryptedViewerId = ReadCredential(ctx, "viewerId");
        if (string.IsNullOrEmpty(battleId) || string.IsNullOrEmpty(encryptedViewerId))
        {
            _log.LogWarning("WS upgrade missing BattleId or viewerId (header or query).");
            ctx.Response.StatusCode = StatusCodes.Status400BadRequest;
            return;
        }

        long viewerId;
        try
        {
            var plain = NodeCrypto.DecryptForNode(encryptedViewerId);
            viewerId = long.Parse(plain);
        }
        catch (Exception ex)
        {
            _log.LogWarning(ex, "viewerId failed to decrypt (encryptedLen={Len})", encryptedViewerId.Length);
            ctx.Response.StatusCode = StatusCodes.Status401Unauthorized;
            return;
        }

        var pending = _store.TryGetPending(battleId);
        if (pending is null)
        {
            _log.LogWarning(
                "WS upgrade for unknown BattleId={Bid} (decrypted viewerId={Vid}). " +
                "Bridge may not have minted this battle, or it was already consumed/expired.",
                battleId, viewerId);
            ctx.Response.StatusCode = StatusCodes.Status404NotFound;
            return;
        }
        if (pending.P1.ViewerId != viewerId)
        {
            _log.LogWarning(
                "WS upgrade viewer-id mismatch on BattleId={Bid}: bridge expected={Expected}, decrypted={Got}.",
                battleId, pending.P1.ViewerId, viewerId);
            ctx.Response.StatusCode = StatusCodes.Status401Unauthorized;
            return;
        }

        var ws = await ctx.WebSockets.AcceptWebSocketAsync();
        _store.RemovePending(battleId);

        // Phase 1: only Scripted is wired; Pvp + Bot land in subsequent phases.
        if (pending.Type != BattleType.Scripted)
        {
            _log.LogWarning(
                "WS upgrade for BattleId={Bid} with unsupported type={Type} (Phase 1 only handles Scripted).",
                battleId, pending.Type);
            return;
        }

        var realParticipant = new RealParticipant(ws, viewerId, pending.P1.Context,
            _loggerFactory.CreateLogger<RealParticipant>());
        var scriptedBot = new ScriptedBotParticipant();
        var session = new BattleSession(battleId, pending.Type, realParticipant, scriptedBot,
            _loggerFactory.CreateLogger<BattleSession>());
        await session.RunAsync(ctx.RequestAborted);
    }

    private static string ReadCredential(HttpContext ctx, string name)
    {
        var header = ctx.Request.Headers[name].ToString();
        if (!string.IsNullOrEmpty(header)) return header;
        return ctx.Request.Query[name].ToString();
    }
}