using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using Telegram.Bot;
using Telegram.Bot.Types;
using Volcanic.AgenticCore.Extensions.GoogleCalendar;
using Volcanic.AgenticCore.Telegram.Chats;
using Volcanic.AgenticCore.Telegram.Rendering;

namespace Volcanic.AgenticCore.Telegram;

/// <summary>
/// Best-effort start-up calls: log who the bot is and publish the command menu, retried in the background until the
/// first success so a host started without network still comes up. Then, once per process, tell the owner
/// (<c>AllowedUserIds[0]</c>) the bot is back. That message is never retried: a 403 (the owner never started the bot)
/// is logged by <see cref="TelegramSender"/> and that's all.
/// </summary>
public sealed class BotSetupService(ITelegramBotClient bot, TelegramOptions options, TelegramSender sender, ILogger<BotSetupService> logger,
    GoogleCalendarOptions? calendar = null) : BackgroundService
{
    public const string OnlineText = "🟢 Online.";

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        if (!await SetUpAsync(stoppingToken).ConfigureAwait(false) || options.AllowedUserIds.Count == 0) return;
        try
        {
            await sender.SendTextAsync(options.AllowedUserIds[0], OnlineText, cancellationToken: stoppingToken).ConfigureAwait(false);
        }
        catch (OperationCanceledException)
        {
        }
    }

    /// <summary>
    /// The admin's chat also lists <c>/impersonate</c>. Best-effort and not retried: it fails while the admin has never
    /// started the bot, and the command works without the menu entry.
    /// </summary>
    private async Task SetAdminMenuAsync(IEnumerable<BotCommand> menu, CancellationToken stoppingToken)
    {
        if (options.AdminUserId is not { } admin) return;
        try
        {
            await bot.SetMyCommands([.. menu, ChatCommands.ImpersonateCommand], BotCommandScope.Chat(admin), cancellationToken: stoppingToken).ConfigureAwait(false);
        }
        catch (Exception ex) when (ex is not OperationCanceledException)
        {
            logger.LogWarning(ex, "Setting the admin's command menu failed");
        }
    }

    /// <summary>True once <c>getMe</c> and <c>setMyCommands</c> succeeded; false when stopped first.</summary>
    private async Task<bool> SetUpAsync(CancellationToken stoppingToken)
    {
        var delay = options.ReconnectInitialDelay;
        while (!stoppingToken.IsCancellationRequested)
        {
            try
            {
                var me = await bot.GetMe(stoppingToken).ConfigureAwait(false);
                var menu = GoogleCalendarSetup.MenuFor(ChatCommands.Menu, calendar);
                await bot.SetMyCommands(menu, cancellationToken: stoppingToken).ConfigureAwait(false);
                logger.LogInformation("Bot @{Username} ({Id}) is ready", me.Username, me.Id);
                if (options.Triggers.IsEnabled && !me.CanReadAllGroupMessages)
                    logger.LogWarning("Privacy mode is on: in groups the bot only sees commands, mentions and replies, so group triggers miss most messages. " +
                                      "Turn it off with @BotFather (/setprivacy → Disable), then remove and re-add the bot to each group, or make it a group admin.");
                await SetAdminMenuAsync(menu, stoppingToken).ConfigureAwait(false);
                return true;
            }
            catch (OperationCanceledException) when (stoppingToken.IsCancellationRequested)
            {
                return false;
            }
            catch (Exception ex)
            {
                logger.LogDebug(ex, "Bot setup failed; retrying in {Delay}", delay);
            }
            try
            {
                await Task.Delay(delay, stoppingToken).ConfigureAwait(false);
            }
            catch (OperationCanceledException)
            {
                return false;
            }
            delay = TimeSpan.FromTicks(Math.Min(delay.Ticks * 2, options.ReconnectMaxDelay.Ticks));
        }
        return false;
    }
}