Dealing with chats

All messages in Telegram are sent/received on a specific chat.
The chat.Type can be one of 4 types:

• ChatType.Private:
  A private discussion with a user. The chat.Id is the same as the user.Id (positive number)
• ChatType.Group:
  A private chat group with less than 200 users
• ChatType.Supergroup:
  An advanced chat group, capable of being public, supporting more than 200 users, with specific user/admin rights
• ChatType.Channel:
  A broadcast type of publishing feed (only admins can write to it)

Additional notes:

• For groups/channels, the chat.Id is a negative number, and the chat.Title will be filled.
• For public groups/channels, the chat.Username will be filled.
• For private chat with a user, the chat.FirstName will be filled, and optionally, the chat.LastName and chat.Username if the user has one.

Calling chat methods

All methods for dealing with chats (like sending messages, etc..) take a ChatId parameter.

For this parameter, you can pass directly a long (the chat or user ID), or when sending to a public group/channel, you can pass a "@chatname" string

Getting full info about a chat (GetChat)

Once a bot has joined a group/channel or has started receiving messages from a user, it can use method GetChat to get detailed info about that chat/user.

There are lots of information returned depending on the type of chat, and most are optional and may be unavailable.
Here are a few interesting ones:

• For private chat with a User:
  • Birthdate
  • Personal channel
  • Business information
  • Bio
• For groups/channels:
  • Description
  • default Permissions (non-administrator access rights)
  • Linked ChatId (the associated channel/discussion group for this chat)
  • IsForum (This chat group has topics)
• Common information for all chats:
  • Photo (use GetInfoAndDownloadFile and the photo.BigFileId to download it)
  • Active Usernames (premium user & public chats can have multiple usernames)
  • Available reactions in this chat
  • Pinned Message (the most recent one)

Receiving chat messages

See chapter Getting Updates for how to receive updates & messages.

For groups or private chats, you would receive an update of type UpdateType.Message (which means only the field update.Message will be set)

For channel messages, you would receive an update with field update.ChannelPost.

For business messages, you would receive an update with field update.BusinessMessage.

If someone modifies an existing message, you would receive an update with one of the fields update.Edited*

Note: if you use the bot.OnMessage event, this is simplified and you can just check the UpdateType argument.

Migration to Supergroup

When you create a private chat group in Telegram, it is usually a ChatType.Group.

If you change settings (like admin rights or making it public), or if members reach 200, the Group may be migrated into a Supergroup.

In such case, the Supergroup is like a separate chat with a different ID. The old Group will have a service message MigrateToChatId with the new supergroup ID. The new Supergroup will have a service message MigrateFromChatId with the old group ID.

Managing new members in a group

Bots can't directly add members into a group/channel.
To invite users to join a group/channel, you can send to the users the public link https://t.me/chatusername (if chat has a username), or invite links:

Invite links

Invite links are typically of the form https://t.me/+1234567890aAbBcCdDeEfF and allow users clicking on them to join the chat.

You can send those links as a text message or as an InlineKeyboardButton.WithUrl(...).

If your bot is administrator on a private (or public) group/channel, it can:

• read the (fixed) primary link of the chat:

var chatFullInfo = await bot.GetChat(chatId); // you should call this only once
Console.WriteLine(chatFullInfo.InviteLink);

• create new invite links on demand

var link = await bot.CreateChatInviteLink(chatId, "name/reason", ...);
Console.WriteLine(link.InviteLink);

See also some other methods for managing invite links.

Detecting new group members and changed member status

Note: Bots can't detect new channel members

The simpler approach to detecting new members joining a group is to handle service messages of type MessageType.NewChatMembers: the field message.NewChatMembers will contain an array of the new User details.
Same for a user leaving the chat, with the message.LeftChatMember service message.

However, under various circumstances (bigger groups, hidden member lists, etc..), these service messages may not be sent out.

The more complex (and more reliable) approach is instead to handle updates of type UpdateType.ChatMember:

• First you need to enable this specific update type among the allowedUpdates parameter when calling GetUpdates, SetWebhook or StartReceiving+ReceiverOptions.
• Typically, you would pass Update.AllTypes as the allowedUpdates parameter.
• After that, you will receive an update.ChatMember structure for each user changing status with their old & their new status
• The OldChatMember/NewChatMember status fields can be one of the derived ChatMember* class: Owner/Creator, Administrator, Member, Restricted, Left, Banned/Kicked)

Forum & Topics

Group owners can enable the Forum feature on their chat, which allows them to create topics for specialized discussions.

Messages in topics are indicated with the MessageThreadId property. This property is equal to 1 for the General topic, or to the Message ID of the first message in topic.

Bots can create/edit/close/reopen/delete specific topics or the General topic.

Important: Bots can't fetch the current list of all topics in the chat.
However, your bot can keep track of active topics by listening to these service messages (with MessageThreadId set):

• MessageType.ForumTopicCreated and the message.ForumTopicCreated structure
• MessageType.ForumTopicEdited and the message.ForumTopicEdited structure
• MessageType.ForumTopicClosed
• MessageType.ForumTopicReopened
• ...