using Telegram.Bot;
using Telegram.Bot.Types;
using Telegram.Bot.Types.Enums;

namespace GmRelay.Bot.Infrastructure.Telegram;

/// <summary>
/// Long polling loop for Telegram Bot API.
/// Stateless — all state is in PostgreSQL. Safe to restart at any time.
/// </summary>
public sealed class TelegramBotService(
    ITelegramBotClient bot,
    UpdateRouter router,
    ILogger<TelegramBotService> logger) : BackgroundService
{
    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        logger.LogInformation("Telegram bot polling started");

        // Skip any pending updates from before this startup
        try
        {
            var pending = await bot.GetUpdates(offset: -1, limit: 1, cancellationToken: stoppingToken);
            if (pending.Length > 0)
            {
                logger.LogInformation("Skipped {Count} pending update(s)", pending[^1].Id);
            }
        }
        catch (Exception ex)
        {
            logger.LogWarning(ex, "Failed to clear pending updates, continuing anyway");
        }

        var offset = 0;

        while (!stoppingToken.IsCancellationRequested)
        {
            try
            {
                var updates = await bot.GetUpdates(
                    offset: offset,
                    timeout: 30,
                    allowedUpdates: [UpdateType.Message, UpdateType.CallbackQuery],
                    cancellationToken: stoppingToken);

                foreach (var update in updates)
                {
                    try
                    {
                        await router.RouteAsync(update, stoppingToken);
                    }
                    catch (Exception ex)
                    {
                        logger.LogError(ex, "Error handling update {UpdateId}", update.Id);
                    }

                    offset = update.Id + 1;
                }
            }
            catch (OperationCanceledException) when (stoppingToken.IsCancellationRequested)
            {
                break;
            }
            catch (Exception ex)
            {
                logger.LogError(ex, "Polling error, retrying in 5s");
                await Task.Delay(TimeSpan.FromSeconds(5), stoppingToken);
            }
        }

        logger.LogInformation("Telegram bot polling stopped");
    }
}