namespace PrivaPub.Infrastructure.Backup
{
	// What Program asks before migrations: whether a restore waits, and what this process does about it. The service carries
	// it out; a command waits for it (exit 75, EX_TEMPFAIL), except asking how it went.
	public static class MaintenanceGate
	{
		/// <summary>The exit code that stops systemd restarting the service (RestartPreventExitStatus=75): a restore gave up.</summary>
		public const int TryLater = 75;

		/// <summary>Null to go on booting; else the code to exit with.</summary>
		public static async Task<int?> Enter(IServiceProvider services, string[] command, CancellationToken token)
		{
			var backups = services.GetRequiredService<Backups>();
			var logger = services.GetRequiredService<ILoggerFactory>().CreateLogger(nameof(MaintenanceGate));
			if (command != default)
			{
				var waiting = RestoreMarker.Read(backups.Root);
				if (waiting == default || command is ["restore", ..])
					return default;
				Console.Error.WriteLine($"the restore of {waiting.Backup} is {waiting.State}{(waiting.Error == default ? string.Empty : $" ({waiting.Error})")}: try again once the service has carried it out (PrivaPub admin restore --status)");
				return TryLater;
			}
			return await ServerRestore.ApplyPending(backups.Context(), logger, token) switch
			{
				RestoreOutcome.Failed => 1,//systemd starts it again, and the next attempt redoes everything
				RestoreOutcome.GaveUp => TryLater,
				_ => (int?)null
			};
		}
	}

	// A restore asked for while the service runs (from the administrator's page or the CLI): the service stops within
	// seconds, systemd starts it again, and the restore runs before anything else.
	public class RestoreWatcher(Backups backups, IHostApplicationLifetime lifetime, ILogger<RestoreWatcher> logger) : BackgroundService
	{
		static readonly TimeSpan Interval = TimeSpan.FromSeconds(3);

		protected override async Task ExecuteAsync(CancellationToken stoppingToken)
		{
			while (!stoppingToken.IsCancellationRequested)
			{
				try
				{
					await Task.Delay(Interval, stoppingToken);
				}
				catch (OperationCanceledException)
				{
					return;
				}
				if (RestoreMarker.Read(backups.Root) is { State: "pending" } marker)
				{
					logger.LogWarning("A restore of {Backup} was asked for by {RequestedBy}: stopping, to restore it at the next start", marker.Backup, marker.RequestedBy);
					lifetime.StopApplication();
					return;
				}
			}
		}
	}
}