# Chat

The *chat* is a built-in platform mechanism for exchanging text messages between system users and for broadcasting system notifications. The chat supports group rooms and one-to-one dialogs, file attachments, replies, editing and deletion within a bounded time window, read-status tracking, and push notifications.

### Chats, dialogs and participants[​](#chats-dialogs-and-participants "Direct link to Chats, dialogs and participants")

A *chat* is an entity with a set of participants. A user becomes a participant when added to the chat. For each participant a per-user *read-only* flag is stored independently, forbidding that participant from sending messages.

A *dialog* is the special case of a chat with exactly two participants. The dialog between two users is unique: an attempt to open a dialog with an interlocutor with whom one already exists uses the existing dialog rather than creating a new one.

### Messages[​](#messages "Direct link to Messages")

A *message* has an author, formatted text, a send moment, and a last-edit moment. A message may be a *reply* to another message in the same chat — in that case it references the source message and is shown with a quote. A message may carry exactly one attached file with a specified name.

The author can *edit* or *delete* their own message within a bounded time window — one hour from the send moment. An edited message is annotated with an edit marker carrying the last-edit moment. After the editing window closes, the message becomes immutable.

### Statuses and unread messages[​](#statuses-and-unread-messages "Direct link to Statuses and unread messages")

For each *(message, recipient)* pair a delivery status of one of three levels is stored:

| Status    | Meaning                                                                                         |
| --------- | ----------------------------------------------------------------------------------------------- |
| Sent      | The message has been recorded on the server                                                     |
| Delivered | The message has been received by the recipient's client                                         |
| Read      | The recipient has marked the message as read — typically by opening the corresponding chat form |

In the list of their own messages the author sees an aggregated status — the highest level reached by any recipient: *read* once at least one recipient has read the message, otherwise *delivered* once at least one has received it, otherwise *sent*.

For each user and each chat an *unread* message count is maintained — the number of messages with status *delivered* or *sent* not yet marked read. This count appears in the chat list and serves as an indicator of dialogs requiring attention.

### System messages[​](#system-messages "Direct link to System messages")

The platform uses the chat for its own notifications — for example, about the start and restart of the application server. System messages are broadcast to all users into a dedicated system chat. A separate retention period of 30 days applies to them, so the service event log does not accumulate indefinitely.

### Push notifications[​](#push-notifications "Direct link to Push notifications")

When a new message appears, push notifications are sent to the participants' currently connected clients. Delivery runs on a separate thread, so as not to delay the send action. Having received a notification, the client redraws the chat list and updates the unread counter. If the form of the corresponding chat is open, the message appears in the feed without a reload.

### Forms[​](#forms "Direct link to Forms")

The platform provides two chat forms:

| Form         | Purpose                                                                                                                                                              |
| ------------ | -------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Full form    | The chat list, the message feed of the selected chat, an input field with attachment — the main interface                                                            |
| Compact form | A notification popup surfacing the most recent unread messages across all the user's chats — for a quick reply or for opening the full interface on the related chat |

Chat is available in both the web and desktop clients and works on top of the same data. In the message feed, text formatting and links are rendered automatically.