using MongoDB.Entities;

using PrivaPub.Models.Federation;
using PrivaPub.StaticServices;

using System.Net;
using System.Net.Http.Headers;
using System.Text;
using System.Text.Json.Nodes;

namespace PrivaPub.Services.Federation
{
	public interface IDeliveryService
	{
		Task Enqueue(LocalActor signer, IEnumerable<string> inboxes, JsonObject activity, CancellationToken token);
		Task EnqueueToFollowers(LocalActor signer, JsonObject activity, CancellationToken token, IEnumerable<string> extraInboxes = default);
		Task<IReadOnlyList<string>> FollowerInboxes(LocalActor actor, CancellationToken token);
	}

	public class DeliveryService : IDeliveryService
	{
		readonly DbEntities _dbEntities;

		public DeliveryService(DbEntities dbEntities)
		{
			_dbEntities = dbEntities;
		}

		public async Task Enqueue(LocalActor signer, IEnumerable<string> inboxes, JsonObject activity, CancellationToken token)
		{
			var body = activity.ToJsonString();
			var deliveries = inboxes
				.Where(i => !string.IsNullOrEmpty(i) && !i.StartsWith(signer.BaseAddress + "/", StringComparison.OrdinalIgnoreCase))
				.Distinct(StringComparer.Ordinal)
				.Select(inbox => new Delivery
				{
					SignerId = signer.Id,
					SignerKind = signer.Kind,
					InboxURL = inbox,
					Body = body
				})
				.ToList();
			if (deliveries.Count > 0)
				await DB.Default.SaveAsync(deliveries, token);
		}

		public async Task EnqueueToFollowers(LocalActor signer, JsonObject activity, CancellationToken token, IEnumerable<string> extraInboxes = default)
		{
			var inboxes = (await FollowerInboxes(signer, token)).Concat(extraInboxes ?? Enumerable.Empty<string>());
			await Enqueue(signer, inboxes, activity, token);
		}

		public async Task<IReadOnlyList<string>> FollowerInboxes(LocalActor actor, CancellationToken token)
		{
			var followers = await _dbEntities.Followers
				.Match(f => f.LocalActorId == actor.Id && f.LocalActorKind == actor.Kind && f.IsAccepted)
				.ExecuteAsync(token);
			return followers.Select(f => string.IsNullOrEmpty(f.SharedInboxURL) ? f.InboxURL : f.SharedInboxURL)
				.Distinct(StringComparer.Ordinal)
				.ToList();
		}
	}

	public class DeliveryWorker : BackgroundService
	{
		const int MaxAttempts = 8;
		static readonly TimeSpan Poll = TimeSpan.FromSeconds(3);

		readonly IServiceProvider _services;
		readonly IHttpClientFactory _httpClientFactory;
		readonly ILogger<DeliveryWorker> _logger;

		public DeliveryWorker(IServiceProvider services, IHttpClientFactory httpClientFactory, ILogger<DeliveryWorker> logger)
		{
			_services = services;
			_httpClientFactory = httpClientFactory;
			_logger = logger;
		}

		protected override async Task ExecuteAsync(CancellationToken stoppingToken)
		{
			while (!stoppingToken.IsCancellationRequested)
			{
				try
				{
					await DeliverDue(stoppingToken);
				}
				catch (OperationCanceledException) when (stoppingToken.IsCancellationRequested)
				{
					return;
				}
				catch (Exception ex)
				{
					_logger.LogError(ex, "{Worker} pass failed", nameof(DeliveryWorker));
				}
				await Task.Delay(Poll, stoppingToken);
			}
		}

		async Task DeliverDue(CancellationToken token)
		{
			using var scope = _services.CreateScope();
			var dbEntities = scope.ServiceProvider.GetRequiredService<DbEntities>();
			var actors = scope.ServiceProvider.GetRequiredService<ILocalActorService>();
			var now = DateTime.UtcNow;
			var due = await dbEntities.Deliveries
				.Match(d => !d.DeliveredAt.HasValue && !d.AbandonedAt.HasValue && d.NextAttemptAt <= now)
				.Sort(d => d.NextAttemptAt, Order.Ascending)
				.Limit(20)
				.ExecuteAsync(token);

			foreach (var delivery in due)
			{
				var signer = await actors.FindById(delivery.SignerKind, delivery.SignerId, token);
				if (signer == default)
				{
					delivery.AbandonedAt = DateTime.UtcNow;
					delivery.LastError = "the signing actor no longer exists";
					await DB.Default.SaveAsync(delivery, token);
					continue;
				}
				await Deliver(delivery, signer, token);
				await DB.Default.SaveAsync(delivery, token);
			}
		}

		async Task Deliver(Delivery delivery, LocalActor signer, CancellationToken token)
		{
			delivery.Attempts++;
			try
			{
				if (!Uri.TryCreate(delivery.InboxURL, UriKind.Absolute, out var inbox) || !RemoteActorService.IsFetchable(inbox))
				{
					delivery.AbandonedAt = DateTime.UtcNow;
					delivery.LastError = "not a deliverable inbox";
					return;
				}

				var body = Encoding.UTF8.GetBytes(delivery.Body);
				using var request = new HttpRequestMessage(HttpMethod.Post, inbox)
				{
					Content = new ByteArrayContent(body)
				};
				request.Content.Headers.ContentType = MediaTypeHeaderValue.Parse(RemoteActorService.ActivityJson);
				HttpSignatures.Sign(request, signer, body);

				using var response = await _httpClientFactory.CreateClient(RemoteActorService.HttpClientName).SendAsync(request, token);
				if (response.IsSuccessStatusCode)
				{
					delivery.DeliveredAt = DateTime.UtcNow;
					delivery.LastError = default;
					return;
				}

				delivery.LastError = $"{(int)response.StatusCode} {response.ReasonPhrase}";
				if (response.StatusCode is HttpStatusCode.Gone or HttpStatusCode.NotFound or HttpStatusCode.BadRequest or HttpStatusCode.Forbidden)
				{
					delivery.AbandonedAt = DateTime.UtcNow;
					_logger.LogWarning("Delivery {Id} to {Inbox} abandoned: {Status}", delivery.ID, delivery.InboxURL, delivery.LastError);
					return;
				}
			}
			catch (Exception ex) when (ex is HttpRequestException or TaskCanceledException && !token.IsCancellationRequested)
			{
				delivery.LastError = ex.Message;
			}

			if (delivery.Attempts >= MaxAttempts)
			{
				delivery.AbandonedAt = DateTime.UtcNow;
				_logger.LogWarning("Delivery {Id} to {Inbox} abandoned after {Attempts} attempts: {Error}",
					delivery.ID, delivery.InboxURL, delivery.Attempts, delivery.LastError);
				return;
			}
			delivery.NextAttemptAt = DateTime.UtcNow.AddMinutes(Math.Pow(2, delivery.Attempts));
		}
	}
}