Playa/hosts/Volcanic.AgenticCore.Telegram/Inbound/InboundComposer.cs

using Microsoft.Extensions.Logging;
using Telegram.Bot;
using Telegram.Bot.Types;
using Volcanic.AgenticCore.Telegram.Chats;
using Volcanic.AgenticCore.Telegram.Rendering;
using ImageContent = Volcanic.AgenticCore.Abstractions.Messages.ImageContent;

namespace Volcanic.AgenticCore.Telegram.Inbound;

/// <summary>What the content steps have gathered for one message so far.</summary>
internal sealed class InboundDraft
{
    public List<string> Body { get; } = [];
    public List<ImageContent> Images { get; } = [];
    /// <summary>A step refused the message (and sent its own notice): nothing is prompted.</summary>
    public bool Refused { get; set; }
    /// <summary>Where step 2 saved the message's file, for step 3 (audio).</summary>
    public string? SavedPath { get; set; }
}

/// <summary>
/// Turns one Telegram message into an <see cref="InboundPart"/>: reply and forward headers, then the content steps in a
/// fixed order: step 1 text and photo, step 2 files saved to the inbox (<see cref="InboundMedia"/>), step 3 voice and
/// audio transcription. Any slow work for a message happens here, while the router holds that message's
/// <see cref="InboundLease"/>. A step never talks to the <see cref="ChatInbox"/> itself.
/// </summary>
public sealed class InboundComposer(TelegramSender sender, InboundMedia media, ILogger<InboundComposer> logger)
{
    /// <summary>The reply to a message kind the bot can't read (stickers, video notes, polls…; no lease is taken).</summary>
    public const string UnsupportedReply = "I can read text, photos, files and voice messages.";

    /// <summary>Kinds the content steps can read. Checked by the router before it takes a lease.</summary>
    public static bool IsSupported(Message message)
    {
        ArgumentNullException.ThrowIfNull(message);
        return message.Photo is { Length: > 0 } || message.Document is not null || message.Video is not null
               || message.Audio is not null || message.Voice is not null || (message.Text ?? message.Caption) is { Length: > 0 };
    }

    /// <summary>A message with an attachment is never a command or a pending answer; its caption is prompt text.</summary>
    public static bool HasAttachment(Message message)
    {
        ArgumentNullException.ThrowIfNull(message);
        return message.Photo is { Length: > 0 } || message.Document is not null || message.Video is not null
               || message.Audio is not null || message.Voice is not null || message.VideoNote is not null
               || message.Animation is not null || message.Sticker is not null;
    }

    /// <summary>The message's part, or null when it has nothing usable or a step refused it.</summary>
    public async Task<InboundPart?> ComposeAsync(ChatContext chat, Message message, CancellationToken cancellationToken)
    {
        ArgumentNullException.ThrowIfNull(chat);
        ArgumentNullException.ThrowIfNull(message);
        var draft = new InboundDraft();

        // Content steps, in order. Each may add body lines and images, send a notice, or refuse the message.
        await AddTextAndPhotoAsync(chat, message, draft, cancellationToken).ConfigureAwait(false); // step 1
        if (!draft.Refused) await media.AddFilesAsync(chat, message, draft, cancellationToken).ConfigureAwait(false); // step 2
        // Step 3 (voice and audio transcription) goes here.

        if (draft.Refused || (draft.Body.Count == 0 && draft.Images.Count == 0)) return null;
        return new InboundPart(
            message.Id,
            new DateTimeOffset(DateTime.SpecifyKind(message.Date, DateTimeKind.Utc)),
            message.MediaGroupId,
            MessageContext.ReplyHeader(message, sender.Bot.BotId),
            message.ForwardOrigin is { } origin ? MessageContext.ForwardLabel(origin) : null,
            draft.Body,
            draft.Images);
    }

    /// <summary>Step 1: the text or caption, and the largest photo size.</summary>
    private async Task AddTextAndPhotoAsync(ChatContext chat, Message message, InboundDraft draft, CancellationToken cancellationToken)
    {
        if ((message.Text ?? message.Caption) is { Length: > 0 } text) draft.Body.Add(text);
        if (message.Photo is not { Length: > 0 } sizes) return;
        try
        {
            var largest = sizes.MaxBy(p => p.FileSize ?? (long)p.Width * p.Height)!;
            using var stream = new MemoryStream();
            await media.DownloadAsync(largest.FileId, stream, cancellationToken).ConfigureAwait(false);
            draft.Images.Add(new ImageContent(Convert.ToBase64String(stream.ToArray()), "image/jpeg"));
        }
        catch (Exception ex) when (ex is not OperationCanceledException)
        {
            logger.LogWarning(ex, "Downloading a photo in chat {ChatId} failed", chat.ChatId);
            chat.Report("I could not download that photo.");
        }
    }
}