Playa/hosts/Volcanic.AgenticCore.Telegram/Groups/GroupMessage.cs

using System.Globalization;
using Telegram.Bot.Types;
using Telegram.Bot.Types.Enums;

namespace Volcanic.AgenticCore.Telegram.Groups;

/// <summary>The message a group message replies to.</summary>
public sealed record GroupReply(string Sender, string? Text);

/// <summary>A group message as triggers see it: who, where, when, the text (or caption) and what it replies to.</summary>
public sealed record GroupMessage(
    long GroupId,
    string GroupTitle,
    string? GroupUsername,
    bool IsSupergroup,
    int MessageId,
    DateTimeOffset Time,
    string Sender,
    string? Text,
    GroupReply? ReplyTo = null)
{
    /// <summary>
    /// A link to the message: <c>t.me/&lt;username&gt;/&lt;id&gt;</c> for public groups, <c>t.me/c/&lt;id without -100&gt;/&lt;id&gt;</c>
    /// for private supergroups (members only), none for basic groups.
    /// </summary>
    public string? Link
    {
        get
        {
            var mid = MessageId.ToString(CultureInfo.InvariantCulture);
            if (!string.IsNullOrEmpty(GroupUsername)) return $"https://t.me/{GroupUsername}/{mid}";
            if (!IsSupergroup) return null;
            var id = (-GroupId).ToString(CultureInfo.InvariantCulture);
            return id.StartsWith("100", StringComparison.Ordinal) && id.Length > 3 ? $"https://t.me/c/{id[3..]}/{mid}" : null;
        }
    }

    public static GroupMessage From(Message message)
    {
        ArgumentNullException.ThrowIfNull(message);
        var reply = message.ReplyToMessage is { } replied
            ? new GroupReply(SenderOf(replied), replied.Text ?? replied.Caption)
            : null;
        return new GroupMessage(
            message.Chat.Id,
            TitleOf(message.Chat),
            message.Chat.Username,
            message.Chat.Type == ChatType.Supergroup,
            message.Id,
            new DateTimeOffset(DateTime.SpecifyKind(message.Date, DateTimeKind.Utc)),
            SenderOf(message),
            message.Text ?? message.Caption,
            reply);
    }

    public static string TitleOf(Chat chat)
    {
        ArgumentNullException.ThrowIfNull(chat);
        return string.IsNullOrWhiteSpace(chat.Title) ? chat.Id.ToString(CultureInfo.InvariantCulture) : chat.Title;
    }

    /// <summary>"First Last (@username)", or the chat an anonymous admin / channel posted as.</summary>
    public static string SenderOf(Message message)
    {
        ArgumentNullException.ThrowIfNull(message);
        if (message.SenderChat is { } chat) return TitleOf(chat);
        if (message.From is not { } user) return "unknown";
        var name = string.IsNullOrWhiteSpace(user.LastName) ? user.FirstName : $"{user.FirstName} {user.LastName}";
        return string.IsNullOrWhiteSpace(user.Username) ? name : $"{name} (@{user.Username})";
    }
}