using MailKit.Net.Smtp;

using Microsoft.Extensions.Localization;

using MimeKit;

using MongoDB.Entities;

using PrivaPub.Infrastructure.Jobs;
using PrivaPub.Models.Jobs;
using PrivaPub.Models.User;
using PrivaPub.Resources;

using System.Security.Cryptography;
using System.Text;
using System.Text.Json;

namespace PrivaPub.Services
{
	public sealed record RecoveryPayload(string RootUserId, string Host);

	// Sends a password recovery link. Every request queues one of these, for an account that exists or not, so the answer
	// to the request and its timing say nothing; SMTP's slowness and failures happen here, where nobody waits on them.
	// The code exists only in the email: the database keeps its hash, for an hour.
	public class RecoveryJob : IJobHandler
	{
		public const string Host = "recovery";
		public static readonly TimeSpan CodeLifetime = TimeSpan.FromHours(1);

		readonly AppConfigurationService _app;
		readonly IStringLocalizer<GenericRes> _localizer;
		readonly ILogger<RecoveryJob> _logger;

		public RecoveryJob(AppConfigurationService app, IStringLocalizer<GenericRes> localizer, ILogger<RecoveryJob> logger)
		{
			_app = app;
			_localizer = localizer;
			_logger = logger;
		}

		public JobKind Kind => JobKind.SendRecovery;
		public int Concurrency => 1;
		public int MaxAttempts => 3;
		public int PerHostLimit => 1;

		public static string Hash(string code) => Convert.ToHexStringLower(SHA256.HashData(Encoding.UTF8.GetBytes(code ?? string.Empty)));

		public async Task<JobOutcome> Handle(Job job, CancellationToken token)
		{
			var payload = JsonSerializer.Deserialize<RecoveryPayload>(job.Payload);
			if (string.IsNullOrEmpty(payload?.RootUserId))
				return JobOutcome.Done;//asked for an account that does not exist: there is nobody to write to
			var user = await DB.Default.Find<RootUser>().MatchID(payload.RootUserId).ExecuteFirstAsync(token);
			if (user is not { DeletedAt: null, IsBanned: false } || string.IsNullOrEmpty(user.Email))
				return JobOutcome.Done;

			var code = Convert.ToHexStringLower(RandomNumberGenerator.GetBytes(32));
			await DB.Default.DeleteAsync<EmailRecovery>(r => r.RootUserId == user.ID);
			await DB.Default.SaveAsync(new EmailRecovery { RootUserId = user.ID, CodeHash = Hash(code), ExpiresAt = DateTime.UtcNow + CodeLifetime }, token);

			var email = _app.AppConfiguration.EmailConfiguration;
			var message = new MimeMessage();
			message.From.Add(new MailboxAddress("PrivaPub", email.SmtpUsername));
			message.To.Add(MailboxAddress.Parse(user.Email));
			message.Subject = _localizer["PrivaPub - Password recovery link"];
			message.Body = new TextPart("plain")
			{
				Text = string.Format(_localizer[
					"Hello,\n\nSomeone asked to reset the password of the PrivaPub login {0}. If it was you, open this link within an hour:\n{1}\n\nIf it was not you, ignore this email: nothing changes."],
					user.UserName, $"{payload.Host}/password-recovery?rc={code}")
			};
			try
			{
				using var smtp = new SmtpClient();
				await smtp.ConnectAsync(email.SmtpServer, email.SmtpPort, email.UseSSL, token);
				await smtp.AuthenticateAsync(email.SmtpUsername, email.SmtpPassword, token);
				await smtp.SendAsync(message, token);
				await smtp.DisconnectAsync(quit: true, token);
				return JobOutcome.Done;
			}
			catch (Exception ex) when (ex is not OperationCanceledException || !token.IsCancellationRequested)
			{
				_logger.LogWarning(ex, "The recovery email could not be sent");
				return JobOutcome.Retry("smtp");
			}
		}
	}
}