using Microsoft.Extensions.Localization;

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.Json;

namespace PrivaPub.Services
{
	public sealed record EmailVerificationPayload(string VerificationId);

	// Sends the code that proves a login owns the address it asked for. The code exists only in the email; the row keeps its
	// hash. An address another login has verified meanwhile gets nothing, so the answer to the request never told whether
	// the address was taken, and no stranger's inbox receives a code it didn't ask for twice.
	public class EmailVerificationJob : IJobHandler
	{
		public const string Host = "email";

		readonly IMailer _mailer;
		readonly IStringLocalizer<GenericRes> _localizer;
		readonly ILogger<EmailVerificationJob> _logger;

		public EmailVerificationJob(IMailer mailer, IStringLocalizer<GenericRes> localizer, ILogger<EmailVerificationJob> logger)
		{
			_mailer = mailer;
			_localizer = localizer;
			_logger = logger;
		}

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

		public static string NewCode() => RandomNumberGenerator.GetInt32(0, 1_000_000).ToString("D6");

		public async Task<JobOutcome> Handle(Job job, CancellationToken token)
		{
			var payload = JsonSerializer.Deserialize<EmailVerificationPayload>(job.Payload);
			var now = DateTime.UtcNow;
			var pending = string.IsNullOrEmpty(payload?.VerificationId) ? default
				: await DB.Default.Find<EmailVerification>().Match(v => v.ID == payload.VerificationId && v.ExpiresAt > now).ExecuteFirstAsync(token);
			if (pending == default)
				return JobOutcome.Done;
			var user = await DB.Default.Find<RootUser>().MatchID(pending.RootUserId).ExecuteFirstAsync(token);
			if (user is not { DeletedAt: null, IsBanned: false })
				return JobOutcome.Done;
			if (await DB.Default.Find<RootUser>().Match(u => u.Email == pending.Email && u.IsEmailValidated && u.ID != user.ID && u.DeletedAt == null).ExecuteAnyAsync(token))
				return JobOutcome.Done;

			var code = NewCode();
			await DB.Default.Update<EmailVerification>().MatchID(pending.ID).Modify(v => v.CodeHash, RecoveryJob.Hash(code)).ExecuteAsync(token);
			try
			{
				await _mailer.Send(pending.Email, _localizer["PrivaPub - Confirm your email address"],
					string.Format(_localizer[
						"Hello,\n\nThe PrivaPub login {0} asked to use this address. If it was you, enter this code within an hour:\n\n{1}\n\nIf it was not you, ignore this email: the address is not used."],
						user.UserName, code), token);
				return JobOutcome.Done;
			}
			catch (Exception ex) when (ex is not OperationCanceledException || !token.IsCancellationRequested)
			{
				_logger.LogWarning(ex, "The verification email could not be sent");
				return JobOutcome.Retry("smtp");
			}
		}
	}
}