Playa/hosts/Volcanic.AgenticCore.Telegram/Chats/UpdateRouter.cs

using Microsoft.Extensions.Logging;
using Telegram.Bot.Types;
using Telegram.Bot.Types.Enums;
using Volcanic.AgenticCore.Telegram.Inbound;
using Volcanic.AgenticCore.Telegram.Polling;
using Volcanic.AgenticCore.Telegram.Rendering;

namespace Volcanic.AgenticCore.Telegram.Chats;

/// <summary>
/// Routes an update to its chat: only allow-listed users in private chats get through; button presses and answers go to
/// the chat's pending dialog, bot commands run directly, everything else goes through the chat's <see cref="ChatInbox"/>:
/// the router takes a lease in update order, composes the message in the background, and the inbox turns the batch into
/// a prompt that runs in the background. The admin's <c>/impersonate</c> is handled first; while it is on, the admin's
/// updates are routed as the impersonated user's (see <see cref="Impersonation"/>).
/// </summary>
public sealed class UpdateRouter(
    TelegramOptions options,
    ChatRegistry chats,
    ChatCommands commands,
    TelegramSender sender,
    InboundComposer composer,
    ILogger<UpdateRouter> logger,
    Impersonation? impersonation = null) : IUpdateRouter
{
    /// <summary>The id the bot acts for: the impersonated user's for the admin while impersonating, else <paramref name="id"/>.</summary>
    private long Effective(long id) => impersonation?.EffectiveId(id) ?? id;

    public async Task RouteAsync(Update update, CancellationToken cancellationToken)
    {
        switch (update)
        {
            case { CallbackQuery: { } query }:
                await OnCallbackAsync(query, cancellationToken).ConfigureAwait(false);
                break;
            case { Message: { } message }:
                await OnMessageAsync(message, cancellationToken).ConfigureAwait(false);
                break;
        }
    }

    private async Task OnCallbackAsync(CallbackQuery query, CancellationToken cancellationToken)
    {
        var userId = Effective(query.From.Id);
        if (!options.IsAllowed(userId))
        {
            logger.LogWarning("Ignored a button press from user {UserId} (not allowed)", userId);
            return;
        }
        if (impersonation?.IsBlocked(query.From.Id) == true)
        {
            await sender.AnswerCallbackAsync(query.Id, Impersonation.BlockedNotice, cancellationToken).ConfigureAwait(false);
            return;
        }
        // The impersonated chat's question first, then the admin's own (asked before impersonation started).
        var resolved = query.Message is { } message && query.Data is { } data
                       && ((chats.Find(Effective(message.Chat.Id)) is { } chat && chat.Ui.TryResolveCallback(data))
                           || (Effective(message.Chat.Id) != message.Chat.Id && chats.Find(message.Chat.Id) is { } own && own.Ui.TryResolveCallback(data)));
        await sender.AnswerCallbackAsync(query.Id, resolved ? null : "This question has expired.", cancellationToken).ConfigureAwait(false);
    }

    private async Task OnMessageAsync(Message message, CancellationToken cancellationToken)
    {
        if (await TryImpersonateAsync(message, cancellationToken).ConfigureAwait(false)) return;
        var userId = message.From?.Id is { } from ? Effective(from) : (long?)null;
        if (!options.IsAllowed(userId))
        {
            logger.LogWarning("Ignored a message from user {UserId} ({Username}) in chat {ChatId}: not in the allow-list",
                userId, message.From?.Username, message.Chat.Id);
            return;
        }
        if (message.Chat.Type != ChatType.Private)
        {
            logger.LogInformation("Ignored a message in non-private chat {ChatId}", message.Chat.Id);
            return;
        }
        if (impersonation?.IsBlocked(message.From?.Id) == true)
        {
            // Straight to the user's own chat: its output goes to the admin meanwhile.
            await sender.SendTextAsync(message.Chat.Id, Impersonation.BlockedNotice, cancellationToken: cancellationToken).ConfigureAwait(false);
            return;
        }

        if (!InboundComposer.IsSupported(message))
        {
            await sender.SendTextAsync(message.Chat.Id, InboundComposer.UnsupportedReply, cancellationToken: cancellationToken).ConfigureAwait(false);
            return;
        }

        var chat = await chats.GetAsync(Effective(message.Chat.Id), cancellationToken).ConfigureAwait(false);
        var text = message.Text ?? message.Caption ?? "";
        // Commands and pending answers are checked before the inbox, and only for messages without an attachment that
        // weren't forwarded: a forwarded message is content, never a command or an answer.
        if (!InboundComposer.HasAttachment(message) && message.ForwardOrigin is null)
        {
            if (ChatCommands.Parse(text) is not null)
            {
                if (await commands.TryHandleAsync(chat, text, cancellationToken).ConfigureAwait(false)) return;
                // Not one of ours: straight to the session, without headers or the window, so extension commands still parse.
                _ = chat.PromptInBackground(text);
                return;
            }
            if (chat.Ui.IsWaitingForInput && chat.Ui.TryResolveInput(text)) return;
        }

        // Take the lease now, in update order; compose (downloads) in the background so polling isn't blocked.
        var lease = chat.Inbox.Begin(message.Id);
        _ = Task.Run(async () =>
        {
            using (lease)
            {
                try
                {
                    lease.Complete(await composer.ComposeAsync(chat, message, cancellationToken).ConfigureAwait(false));
                }
                catch (OperationCanceledException) when (cancellationToken.IsCancellationRequested)
                {
                    // shutting down: the lease completes empty
                }
                catch (Exception ex)
                {
                    logger.LogWarning(ex, "Reading message {MessageId} in chat {ChatId} failed", message.Id, chat.ChatId);
                    chat.Report("I could not read that message.");
                }
            }
        }, CancellationToken.None);
    }

    /// <summary>The admin's <c>/impersonate &lt;user_id&gt;</c> in a private chat, checked before the allow-list. False otherwise.</summary>
    private async Task<bool> TryImpersonateAsync(Message message, CancellationToken cancellationToken)
    {
        if (impersonation is null || !impersonation.IsAdmin(message.From?.Id) || message.Chat.Type != ChatType.Private
            || InboundComposer.HasAttachment(message) || message.ForwardOrigin is not null
            || ChatCommands.Parse(message.Text ?? "") is not { Name: "impersonate" } command)
            return false;
        var reply = impersonation.Apply(command.Args);
        logger.LogInformation("Admin {AdminId}: impersonating {Target}", message.From!.Id, impersonation.Target?.ToString(System.Globalization.CultureInfo.InvariantCulture) ?? "nobody");
        await sender.SendTextAsync(message.Chat.Id, reply, cancellationToken: cancellationToken).ConfigureAwait(false);
        return true;
    }
}