Luna/Luna.Channels/Telegram/TelegramChannel.cs

using System.Text;
using Luna.Channels.Abstractions;
using Luna.Configuration;
using Luna.Shared;
using Microsoft.Extensions.Logging;
using Telegram.Bot;
using Telegram.Bot.Types.Enums;

namespace Luna.Channels.Telegram;

public class TelegramChannel(
    string chatId,
    ITelegramBotClient botClient,
    ILogger<TelegramChannel> logger,
    TelegramOptions options) : IChannel
{
    private const int TelegramMessageCharLimit = 4096;

    public string ChannelId { get; } = chatId;
    public string ChannelType => Abstractions.ChannelType.Telegram;
    public string DisplayName { get; } = $"Telegram Chat {chatId}";
    public bool IsConnected { get; private set; } = true;

    public event ChannelMessageReceivedEventHandler? MessageReceived;
    public event ChannelConnectionChangedEventHandler? ConnectionStateChanged;

    public async Task SendMessageAsync(ChannelMessage message, CancellationToken cancellationToken = default)
    {
        try
        {
            var targetChatId = long.Parse(ChannelId);
            await botClient.SendMessage(targetChatId, message.Content, cancellationToken: cancellationToken);
        }
        catch (Exception ex)
        {
            logger.LogError(ex, "Failed to send message to Telegram chat {ChatId}", ChannelId);
        }
    }

    public async Task SendStreamingMessageAsync(
        IAsyncEnumerable<ChatStreamUpdate> messageStream,
        CancellationToken cancellationToken = default)
    {
        var targetChatId = long.Parse(ChannelId);

        var typingCts = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
        var _ = KeepTypingAsync(targetChatId, typingCts.Token);

        var messageBuilder = new StringBuilder();
        await foreach (var update in messageStream.WithCancellation(cancellationToken))
        {
            if (update.Content is not null)
                messageBuilder.Append(update.Content);

            if (messageBuilder.Length <= TelegramMessageCharLimit) 
                continue;
            
            try
            {
                var currentMessageContent = messageBuilder.ToString();
                var splitByParagraph = currentMessageContent.Split('\n');

                var i = 0;
                var builder = new StringBuilder();
                foreach (var paragraph in splitByParagraph)
                {
                    if (builder.Length + paragraph.Length < TelegramMessageCharLimit)
                    {
                        builder.AppendLine(paragraph);
                        i++;
                        continue;
                    }

                    await botClient.SendMessage(
                        targetChatId,
                        builder.ToString(),
                        cancellationToken: cancellationToken);

                    messageBuilder.Clear();
                    messageBuilder.Append(string.Join('\n', splitByParagraph[i..]));
                    break;
                }
            }
            catch (Exception ex)
            {
                await typingCts.CancelAsync();
                logger.LogError(ex, "Failed to send streaming update to Telegram chat {ChatId}", ChannelId);
            }
        }
        
        try
        {
            if (messageBuilder.Length > 0)
            {
                await botClient.SendMessage(
                    targetChatId,
                    messageBuilder.ToString(),
                    cancellationToken: cancellationToken);
            }
        }
        catch (Exception ex)
        {
            await typingCts.CancelAsync();
            logger.LogError(ex, "Failed to send streaming update to Telegram chat {ChatId}", ChannelId);
        }
        
        await typingCts.CancelAsync();
    }

    /// <summary>
    /// Called by TelegramAdapter when an incoming message is received for this chat.
    /// Applies AllowedUserIds filtering and null/empty text filtering before raising the event.
    /// </summary>
    public void RaiseMessageReceived(ChannelMessage message)
    {
        if (string.IsNullOrEmpty(message.Content))
            return;

        if (options.AllowedUserIds.Length > 0 &&
            !options.AllowedUserIds.Contains(message.SenderId))
            return;

        MessageReceived?.Invoke(this, new ChannelMessageReceivedEventArgs
        {
            Channel = this,
            Message = message,
            IsHandled = false
        });
    }

    public void Dispose()
    {
        IsConnected = false;
        ConnectionStateChanged?.Invoke(this, new ChannelConnectionEventArgs
        {
            Channel = this,
            IsConnected = false
        });
    }

    private async Task KeepTypingAsync(long chatId, CancellationToken ct)
    {
        while (!ct.IsCancellationRequested)
        {
            try
            {
                await botClient.SendChatAction(chatId, ChatAction.Typing, null, null, ct);
                await Task.Delay(4000, ct);
            }
            catch (OperationCanceledException)
            {
                break;
            }
            catch (Exception ex)
            {
                logger.LogError(ex, "Failed to send typing action to Telegram chat {ChatId}", chatId);
            }
        }
    }
}