using System.Security.Claims;
using Microsoft.Extensions.Caching.Memory;
using PowderCoating.Web.Services;

namespace PowderCoating.Web.Middleware;

/// <summary>
/// Updates the OnlineUserTracker for every authenticated page request.
/// Throttled to once per 60 seconds per user to avoid excessive work.
/// </summary>
public class OnlineUserMiddleware
{
    private readonly RequestDelegate _next;
    private readonly IMemoryCache _cache;

    /// <summary>
    /// Initialises the middleware with the next request delegate in the pipeline.
    /// </summary>
    /// <param name="next">The next middleware component.</param>
    /// <param name="cache">Shared app cache used for expiring per-user throttle entries.</param>
    public OnlineUserMiddleware(RequestDelegate next, IMemoryCache cache)
    {
        _next = next;
        _cache = cache;
    }

    /// <summary>
    /// Calls the downstream pipeline first, then — after the response is
    /// produced — records the requesting user as online in the tracker if the
    /// 60-second throttle window has elapsed.
    /// <para>
    /// Tracking runs <em>after</em> the response (rather than before) so that
    /// slow downstream operations do not delay the response to the client.
    /// The tracker update is best-effort: if it throws, the exception propagates
    /// but does not affect the already-sent response.
    /// </para>
    /// <para>
    /// API, hub, and static-file requests are excluded because they are too
    /// frequent and do not represent meaningful user navigation activity.
    /// Static files are identified by the presence of a dot in the path
    /// (e.g. <c>.js</c>, <c>.css</c>), which is a pragmatic heuristic that
    /// avoids the overhead of checking extensions individually.
    /// </para>
    /// </summary>
    /// <param name="context">The current HTTP context.</param>
    /// <param name="tracker">
    /// Scoped service that maintains the in-memory registry of online users.
    /// </param>
    public async Task InvokeAsync(HttpContext context, IOnlineUserTracker tracker)
    {
        await _next(context);

        // Skip AJAX/JSON responses — they are not page navigations and would
        // cause the "current page" to show the polling endpoint (e.g. /InAppNotifications/Recent)
        // rather than the actual page the user is on.
        if (context.Response.ContentType?.Contains("application/json", StringComparison.OrdinalIgnoreCase) == true)
            return;

        // Only track authenticated, non-API, non-asset requests
        if (!context.User.Identity?.IsAuthenticated ?? true) return;
        var path = context.Request.Path.Value ?? string.Empty;
        if (path.StartsWith("/hubs") || path.StartsWith("/api") ||
            path.Contains('.'))   // static files have extensions
            return;

        var userId = context.User.FindFirstValue(ClaimTypes.NameIdentifier);
        if (string.IsNullOrEmpty(userId)) return;

        // Throttle: only update the tracker once per 60 seconds per user.
        // IMemoryCache automatically expires old entries so the throttle state
        // does not grow without bound across the lifetime of the process.
        var now = DateTime.UtcNow;
        var throttleKey = $"online-user-touch:{userId}";
        if (_cache.TryGetValue(throttleKey, out _))
            return;

        _cache.Set(throttleKey, true, TimeSpan.FromSeconds(60));

        var email       = context.User.FindFirstValue(ClaimTypes.Email) ?? string.Empty;
        var firstName   = context.User.FindFirstValue(ClaimTypes.GivenName) ?? string.Empty;
        var lastName    = context.User.FindFirstValue(ClaimTypes.Surname) ?? string.Empty;
        var displayName = $"{firstName} {lastName}".Trim();
        if (string.IsNullOrEmpty(displayName)) displayName = email;

        var isSuperAdmin = context.User.IsInRole("SuperAdmin");

        tracker.Touch(new OnlineUserEntry
        {
            UserId      = userId,
            Email       = email,
            DisplayName = displayName,
            IsSuperAdmin = isSuperAdmin,
            CurrentPath = path,
            IpAddress   = context.Connection.RemoteIpAddress?.ToString(),
            LastSeen    = now
        });
    }
}