telegram-bot/Core/Service/EntityFormatter.cs

#nullable enable

using System;
using System.Collections.Generic;
using System.Linq;
using Telegram.Bot.Types;
using Telegram.Bot.Types.Enums;

namespace Kruzya.TelegramBot.Core.Service;

internal class EntityFormatter
{
    private static readonly Dictionary<MessageEntityType, string> HtmlMap = new()
    {
        { MessageEntityType.Bold, "<b>{0}</b>" },
        { MessageEntityType.Code, "<code>{0}</code>" },
        { MessageEntityType.Italic, "<i>{0}</i>" },
        { MessageEntityType.TextMention, "<a href=\"tg://user?id={1}\">{0}</a>" },
        { MessageEntityType.Pre, "<pre>{0}</pre>" },
        { MessageEntityType.Underline, "<u>{0}</u>" },
        { MessageEntityType.TextLink, "<a href=\"{1}\">{0}</a>" }
    };

    private static readonly Dictionary<MessageEntityType, string> MarkdownMap = new()
    {
        { MessageEntityType.Bold, "*{0}*" },
        { MessageEntityType.Code, "```{0}```" },
        { MessageEntityType.Italic, "_{0}_" },
        { MessageEntityType.TextMention, "[{0}](tg://user?id={1})" },
        { MessageEntityType.Pre, "```{0}```" },
        { MessageEntityType.Underline, "__{0}__" },
        { MessageEntityType.TextLink, "[{0}]({1})" }
    };

    /// <summary>
    /// Performs the formatting a text representation of message from <see cref="Message"/> entity with 
    /// </summary>
    /// <param name="msg"></param>
    /// <param name="parseMode"></param>
    /// <returns></returns>
    public string? FormatMessage(Message msg, ParseMode parseMode = ParseMode.Html)
    {
        var text = "";
        var entities = msg.Entities;

        if (entities != null)
        {
            // Suppress the warning about possibility using empty ref (CS8602).
            text = msg.Text!;

            // TODO: Currently, this algo don't support inherited entities. This need thinking.
            foreach (var entity in entities.Reverse())
            {
                var entityText = text.Substring(entity.Offset, entity.Length);

                text = text.Replace(entityText, FormatEntity(entity, entityText, parseMode));
            }            
        }

        return text;
    }

    public string FormatEntity(MessageEntity entity, string text, ParseMode parseMode)
    {
        var dict = parseMode switch
        {
            ParseMode.Html => HtmlMap,
            ParseMode.Markdown => MarkdownMap,
            ParseMode.MarkdownV2 => MarkdownMap,
            _ => throw new Exception("Unsupported parse mode")
        };

        var arg = entity.Type switch
        {
            MessageEntityType.TextMention => entity.User!.Id.ToString(),
            MessageEntityType.TextLink => entity.Url!,
            _ => ""
        };

        return dict[entity.Type].Replace("{0}", text)
            .Replace("{1}", arg);
    }
}