using System.Collections.Concurrent;
using System.Net;
using System.Security.Cryptography;

using MeWeb.Shared;

namespace MeWeb.Server;

public class SpeedService
{
  const int PerHour = 12;
  const int AtOnce = 4;
  int active;
  static readonly byte[] Noise = RandomNumberGenerator.GetBytes(1024 * 1024);
  readonly ConcurrentDictionary<string, List<DateTimeOffset>> uses = new();

  public bool Allow(IPAddress caller)
  {
    var now = DateTimeOffset.UtcNow;
    var times = uses.GetOrAdd(ProbeService.NetworkOf(caller), _ => []);
    lock (times)
    {
      times.RemoveAll(t => now - t > TimeSpan.FromHours(1));
      if (times.Count >= PerHour) return false;
      times.Add(now);
      return true;
    }
  }

  public bool Enter()
  {
    if (Interlocked.Increment(ref active) <= AtOnce) return true;
    Interlocked.Decrement(ref active);
    return false;
  }

  public void Leave() => Interlocked.Decrement(ref active);

  public static async Task Stream(HttpResponse response, int bytes, CancellationToken ct)
  {
    response.ContentType = "application/octet-stream";
    response.ContentLength = bytes;
    response.Headers.CacheControl = "no-store";
    var left = bytes;
    while (left > 0)
    {
      var chunk = Math.Min(left, Noise.Length);
      await response.Body.WriteAsync(Noise.AsMemory(0, chunk), ct);
      left -= chunk;
    }
  }

  public static async Task<long> Drain(Stream body, CancellationToken ct)
  {
    var buffer = new byte[64 * 1024];
    long total = 0;
    var read = default(int);
    while ((read = await body.ReadAsync(buffer, ct)) > 0)
    {
      total += read;
      if (total > Endpoints.Speed.MaxUpBytes) return -1;
    }
    return total;
  }
}