using System.Net.WebSockets;
using System.Text;
using Microsoft.Extensions.Logging;
using SVSim.BattleNode.Protocol;
using SVSim.BattleNode.Reliability;
using SVSim.BattleNode.Wire;

namespace SVSim.BattleNode.Sessions;

/// <summary>
/// One per connected client. Owns the WebSocket + reliability ledgers + lifecycle phase.
/// </summary>
public sealed class BattleSession
{
    private readonly WebSocket _ws;
    private readonly ILogger<BattleSession> _log;

    public string BattleId { get; }
    public long ViewerId { get; }
    public BattleSessionPhase Phase { get; internal set; } = BattleSessionPhase.AwaitingInitNetwork;
    public InboundTracker Inbound { get; } = new();
    public OutboundSequencer Outbound { get; } = new();

    public BattleSession(WebSocket ws, string battleId, long viewerId, ILogger<BattleSession> log)
    {
        _ws = ws;
        _log = log;
        BattleId = battleId;
        ViewerId = viewerId;
    }

    /// <summary>
    /// Send the EIO3 open handshake then enter the read loop. Returns when the WS closes.
    /// Dispatch is a no-op in this task; Task 13 fills it in.
    /// </summary>
    public async Task RunAsync(CancellationToken cancellation)
    {
        await SendEioOpenAsync(cancellation);

        var buffer = new byte[8192];
        var pendingAttachments = new List<byte[]>();
        SocketIoFrame? pendingFrame = null;

        while (_ws.State == WebSocketState.Open && !cancellation.IsCancellationRequested)
        {
            var msg = await ReadCompleteMessageAsync(buffer, cancellation);
            if (msg is null) break;

            if (msg.Value.IsText)
            {
                var text = Encoding.UTF8.GetString(msg.Value.Bytes);
                if (text.Length == 0) continue;
                var eio = EngineIoFrame.Parse(text);
                if (eio.Type == EngineIoPacketType.Ping)
                {
                    await SendTextAsync("3", cancellation);  // EIO3 pong
                    continue;
                }
                if (eio.Type != EngineIoPacketType.Message) continue;

                // SIO inside the message payload.
                var sio = SocketIoFrame.Parse(eio.Payload);
                if (sio.AttachmentCount > 0)
                {
                    pendingFrame = sio;
                    pendingAttachments.Clear();
                    continue;
                }
                DispatchSocketIo(sio);
            }
            else
            {
                // Binary frame — an attachment for a pending binary event.
                pendingAttachments.Add(msg.Value.Bytes);
                if (pendingFrame is not null && pendingAttachments.Count == pendingFrame.AttachmentCount)
                {
                    var assembled = pendingFrame.WithAttachments(pendingAttachments.ToArray());
                    pendingFrame = null;
                    DispatchSocketIo(assembled);
                }
            }
        }
    }

    private void DispatchSocketIo(SocketIoFrame frame)
    {
        // v1 task 11 stub: log and drop. Task 13 wires the lifecycle dispatch in.
        _log.LogDebug("BattleSession {Bid}: received SIO {Type} event={Event}",
            BattleId, frame.Type, frame.EventName);
    }

    private async Task SendEioOpenAsync(CancellationToken ct)
    {
        var sid = Guid.NewGuid().ToString("N").Substring(0, 16);
        var handshake = new EngineIoHandshake(sid, Array.Empty<string>(), 25000, 60000).ToJson();
        await SendTextAsync($"0{handshake}", ct);
    }

    private Task SendTextAsync(string text, CancellationToken ct)
    {
        var bytes = Encoding.UTF8.GetBytes(text);
        return _ws.SendAsync(bytes, WebSocketMessageType.Text, endOfMessage: true, ct);
    }

    private async Task<(byte[] Bytes, bool IsText)?> ReadCompleteMessageAsync(byte[] buffer, CancellationToken ct)
    {
        using var ms = new MemoryStream();
        WebSocketReceiveResult result;
        do
        {
            try { result = await _ws.ReceiveAsync(buffer, ct); }
            catch (OperationCanceledException) { return null; }
            catch (WebSocketException) { return null; }
            if (result.MessageType == WebSocketMessageType.Close) return null;
            ms.Write(buffer, 0, result.Count);
        } while (!result.EndOfMessage);
        return (ms.ToArray(), result.MessageType == WebSocketMessageType.Text);
    }
}