added chats & business page.

src/2/README.md

@@ -9,5 +9,6 @@
   - [Document & Animation](send-msg/document-animation-msg.md)
   - [Native Polls](send-msg/native-polls-msg.md)
   - [Other Messages](send-msg/other-msg.md)
+- [Dealing with chats](chats.md)
 - [Reply Markup](reply-markup.md)
 - [Forward, Copy or Delete](forward-copy-delete.md)

src/2/chats.md

@@ -0,0 +1,95 @@
+# 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 <u>public</u> 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 `"@username"` string
+
+## Receiving chat messages
+
+See chapter [Getting Updates](../3/updates/README.md) 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](../4/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.
+
+> [!IMPORTANT]  
+> By default, for privacy reasons, bots in groups receive only messages that are targeted at them (reply to their messages, inline messages, or targeted `/commands@botname` with the bot username suffix)  
+> If you want your bot to receive ALL messages in the group, you can either make it admin, or <u>disable</u> the **Bot Settings** : [**Group Privacy** mode](https://core.telegram.org/bots/features#privacy-mode) in @BotFather
+
+## 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:
+```csharp
+var chatFullInfo = await bot.GetChatAsync(chatId); // you should call this only once
+Console.WriteLine(chatFullInfo.InviteLink);
+```
+- create new invite links on demand
+```csharp
+var link = await bot.CreateChatInviteLinkAsync(chatId, "name/reason", ...);
+Console.WriteLine(link.InviteLink);
+```
+
+See also [some other methods for managing invite links](https://core.telegram.org/bots/api#exportchatinvitelink).
+
+### Detecting new group members and changed member status
+
+Note: Bots can't detect new <u>channel</u> 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 `GetUpdatesAsync`, `SetWebhookAsync` 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`)

src/4/README.md

@@ -2,6 +2,7 @@
 
 - [Proxy](proxy.md)
 - [Mini Apps](webapps.md)
+- [Business Features](business.md)
 - [Passport](passport/)
   - [Quickstart](passport/quickstart.md)
   - [Files & Documents](passport/files-docs.md)

src/4/business.md

@@ -0,0 +1,6 @@
+# Business Features
+
+> This chapter is not yet written.
+
+See https://telegram.org/blog/telegram-business  
+and https://core.telegram.org/bots/features#bots-for-business

src/SUMMARY.md

@@ -14,6 +14,7 @@
     - [Document & Animation](2/send-msg/document-animation-msg.md)
     - [Native Polls](2/send-msg/native-polls-msg.md)
     - [Other Messages](2/send-msg/other-msg.md)
+  - [Dealing with chats](2/chats.md)
   - [Reply Markup](2/reply-markup.md)
   - [Forward, Copy or Delete](2/forward-copy-delete.md)
 - [Intermediate](3/README.md)
@@ -28,6 +29,7 @@
 - [Advanced](4/README.md)
   - [Proxy](4/proxy.md)
   - [Mini Apps](4/webapps.md)
+  - [Business Features](4/business.md)
   - [Passport](4/passport/README.md)
     - [Quickstart](4/passport/quickstart.md)
     - [Files & Documents](4/passport/files-docs.md)