using MongoDB.Entities;

using PrivaPub.Models.Statistics;

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

namespace PrivaPub.Infrastructure.Statistics
{
	public class InteractionSalts
	{
		readonly ConcurrentDictionary<DateTime, byte[]> _known = new();

		public async Task<byte[]> For(DateTime day, CancellationToken token)
		{
			day = day.Date;
			if (_known.TryGetValue(day, out var cached))
				return cached;
			InteractionSalt salt;
			if (day == DateTime.UtcNow.Date)
				salt = await DB.Default.UpdateAndGet<InteractionSalt>()
					.Match(s => s.Day == day)
					.Modify(b => b.SetOnInsert(s => s.Key, Convert.ToBase64String(RandomNumberGenerator.GetBytes(32))))
					.Modify(b => b.SetOnInsert(s => s.ExpiresAt, day.AddHours(30)))
					.Option(o => o.IsUpsert = true)
					.ExecuteAsync(token);
			else
				salt = await DB.Default.Find<InteractionSalt>().Match(s => s.Day == day).ExecuteFirstAsync(token);
			if (salt?.Key == default)
				return default;
			var key = Convert.FromBase64String(salt.Key);
			foreach (var old in _known.Keys.Where(k => k < day.AddDays(-1)))
				_known.TryRemove(old, out _);
			_known[day] = key;
			return key;
		}

		public static string Hash(byte[] salt, string actorUri) =>
			salt == default || string.IsNullOrEmpty(actorUri)
				? default
				: Convert.ToBase64String(HMACSHA256.HashData(salt, Encoding.UTF8.GetBytes(actorUri))[..12]).TrimEnd('=').Replace('+', '-').Replace('/', '_');
	}
}