using System.Text.RegularExpressions;

namespace decePubClient.Services
{
	/// <summary>One request HttpService sent, for the nerd stats.</summary>
	public sealed record RequestStat(DateTime At, string Method, string Route, int Status, double DurationMs, long? Bytes,
		int? RateLimitRemaining, DateTime? RateLimitReset);

	/// <summary>
	/// The last requests HttpService sent (a ring of Capacity entries), with route templates instead of ids. It holds no
	/// bodies and no tokens: method, route, status, duration, size and PrivaPub's rate limit headers only.
	/// </summary>
	public partial class RequestStats
	{
		public const int Capacity = 200;

		readonly RequestStat[] ring = new RequestStat[Capacity];
		int next;
		int count;

		public event Action Recorded;

		public int Count => count;

		public void Record(RequestStat stat)
		{
			lock (ring)
			{
				ring[next] = stat;
				next = (next + 1) % Capacity;
				count = Math.Min(count + 1, Capacity);
			}
			Recorded?.Invoke();
		}

		/// <summary>The recorded requests, newest first.</summary>
		public List<RequestStat> Latest(int take = Capacity)
		{
			lock (ring)
			{
				var latest = new List<RequestStat>(Math.Min(take, count));
				for (var i = 1; i <= Math.Min(take, count); i++)
					latest.Add(ring[(next - i + Capacity) % Capacity]);
				return latest;
			}
		}

		/// <summary>The newest request to a route template, or null.</summary>
		public RequestStat LastOf(string route) => Latest().FirstOrDefault(stat => stat.Route == route);

		/// <summary>The mean duration of the successful requests recorded, in milliseconds.</summary>
		public double? AverageMs()
		{
			var answered = Latest().Where(stat => stat.Status is >= 200 and < 400).ToList();
			return answered.Count == 0 ? null : answered.Average(stat => stat.DurationMs);
		}

		/// <summary>The route without its query, with ids replaced by :id, so requests to the same endpoint group.</summary>
		public static string Template(string uri)
		{
			var path = uri?.Split('?', 2)[0] ?? string.Empty;
			if (Uri.TryCreate(path, UriKind.Absolute, out var absolute))
				path = absolute.AbsolutePath.TrimStart('/');
			return Id().Replace(path, "/:id$1");
		}

		[GeneratedRegex(@"/(?:[0-9a-f]{24}|[0-9a-f]{32}|\d{6,}|[0-9A-Za-z_-]{20,})(/|$)")]
		private static partial Regex Id();
	}
}