using System;
using System.Linq;
using System.Threading.Tasks;
using GB5Shared.DTO.Framework.Login;
using Microsoft.AspNetCore.SignalR;
using Microsoft.Extensions.Logging;

namespace FrameworkSL.Hubs.GOP
{
    // ============================================================
    // GopExecutionHub — server-push hub for real-time GOP execution
    // status updates.
    //
    // Architecture:
    //   • Server-push only: no client-initiated methods.
    //   • GopExecutionPipeline (BackgroundService) injects
    //     IHubContext<GopExecutionHub, IGopExecutionClient> and
    //     calls Clients.Group(...).ReceiveExecutionUpdate(...) after
    //     each pipeline step completes.
    //
    // Group convention:
    //   "gop:client:{clientId}" — all connected clients for a tenant
    //   receive all execution updates for that tenant.
    //
    // LoginDTO:
    //   ALWAYS reconstructed from Context.GetHttpContext() HTTP headers.
    //   NEVER accepted from client payload.
    //
    // Registration (Program.cs):
    //   app.MapHub<GopExecutionHub>("/hubs/gop-execution");
    // ============================================================
    public class GopExecutionHub : Hub<IGopExecutionClient>
    {
        private readonly ILogger<GopExecutionHub> _Logger;

        public GopExecutionHub(ILogger<GopExecutionHub> logger)
        {
            _Logger = logger;
        }

        // ── Group naming convention ───────────────────────────────────────────────

        /// <summary>Tenant-scoped group: all connected clients for a given tenant.</summary>
        public static string TenantGroup(int clientId) => $"gop:client:{clientId}";

        // ── Connection lifecycle ──────────────────────────────────────────────────

        public override async Task OnConnectedAsync()
        {
            var login = GetLoginDTO();
            var group = TenantGroup(login.ClientId);

            await Groups.AddToGroupAsync(Context.ConnectionId, group);

            _Logger.LogInformation(
                "GopExecutionHub connected: {ConnectionId} tenant {ClientId} user {UserId}",
                Context.ConnectionId, login.ClientId, login.UserId);

            await base.OnConnectedAsync();
        }

        public override async Task OnDisconnectedAsync(Exception? exception)
        {
            var login = GetLoginDTO();
            var group = TenantGroup(login.ClientId);

            await Groups.RemoveFromGroupAsync(Context.ConnectionId, group);

            if (exception is not null)
                _Logger.LogWarning(exception,
                    "GopExecutionHub disconnected with error: {ConnectionId}",
                    Context.ConnectionId);

            await base.OnDisconnectedAsync(exception);
        }

        // ── Helper ────────────────────────────────────────────────────────────────

        // ALWAYS reconstruct LoginDTO from verified HTTP context — never from client payload.
        private LoginDTO GetLoginDTO()
        {
            var http = Context.GetHttpContext()
                ?? throw new InvalidOperationException("Hub invoked outside HTTP context.");

            var raw = http.Request.Headers["Login"].FirstOrDefault()
                ?? throw new InvalidOperationException("Login header is missing.");

            return System.Text.Json.JsonSerializer.Deserialize<LoginDTO>(raw)
                ?? throw new InvalidOperationException("Login header contains invalid JSON.");
        }
    }
}