namespace Supercell.Laser.Server.SCID
{
    using System.Collections.Concurrent;
    using System.Net;
    using Microsoft.AspNetCore.Http;

    internal static class SCIDRateLimiter
    {
        private static readonly ConcurrentDictionary<string, Queue<DateTime>> Requests = new();
        private static readonly object Sync = new();

        public static bool AllowCodeRequest(HttpRequest request, string identity)
        {
            string address = GetAddress(request);
            bool allowed = Allow($"identity:{identity}", 1, TimeSpan.FromMinutes(1)) &&
                   Allow($"identity-hour:{identity}", 5, TimeSpan.FromHours(1)) &&
                   Allow($"address-hour:{address}", 20, TimeSpan.FromHours(1));
            SCIDStart.Log($"rate limit check address={address} allowed={allowed}");
            return allowed;
        }

        // A failed delivery must not lock the user out for a minute.  Otherwise
        // every retry is rejected before the mail provider is called and the
        // client only shows its generic "temporarily unavailable" message.
        public static void ResetIdentity(string identity)
        {
            lock (Sync)
            {
                Requests.TryRemove($"identity:{identity}", out _);
            }
        }

        private static bool Allow(string key, int limit, TimeSpan period)
        {
            lock (Sync)
            {
                DateTime now = DateTime.UtcNow;
                Queue<DateTime> requests = Requests.GetOrAdd(key, _ => new Queue<DateTime>());
                while (requests.Count > 0 && now - requests.Peek() >= period)
                    requests.Dequeue();

                if (requests.Count >= limit)
                    return false;

                requests.Enqueue(now);
                return true;
            }
        }

        private static string GetAddress(HttpRequest request)
        {
            if (request == null)
                return "unknown";
            string forwardedAddress = request.Headers["X-Forwarded-For"].FirstOrDefault()?.Split(',')[0].Trim();
            string value = forwardedAddress ?? request.HttpContext.Connection.RemoteIpAddress?.ToString();
            return IPAddress.TryParse(value, out IPAddress address) ? address.ToString() : value ?? "unknown";
        }
    }
}