NIP-35
======

Member List
-----------

`draft` `optional` `author:arthurfranca`

Groups, channels, communities and the like may use status events
to dynamically build a member list.

## Motivation

An user may never send a message to a group but still want
to be on a group member list for receiving DMs.

Also one may want to discover his friends' groups.

## Status Event

It is a kind `34549` parameterized replaceable event (PRE) with:
- `d` tag which is a reference to the group creation event as `<kind>:<pubkey>:<d-identifier>` if PRE or `<kind>:<pubkey>` if replaceable or `<event id>` if regular event;
- `k` tag as `<group creation event kind>` for discoverability;
- optional `status` tag (see ["Custom Status" section](#custom-status));
- [NIP-40](40.md) `expiration` tag that should be by default 60 days ahead of the `created_at` tag value;
- `.content` as stringified author kind 0 event JSON for fast lookup.

The event by default MUST be replaced by clients from time to time
(usually at a frequency lower than 10 minutes window so that the user
is not considered `away` - see ["Basic Status" section](#basic-status)).

If the `created_at` tag age (`now - created_at`) is higher than 10 minutes,
the client should consider the `.content` stale for important things such as zap address.


```js
{
  "id": "<32-bytes lowercase hex-encoded SHA-256 of the the serialized event data>",
  "pubkey": "<32-bytes lowercase hex-encoded public key of the event creator>",
  "created_at": "<Unix timestamp in seconds>",
  "kind": 34549,
  "tags": [
    ["d", "f39e9b451a73d62abc5016cffdd294b1a904e2f34536a208874fe5e22bbd47cf"],
    ["k", "40"],
    ["status", "Feeling gOoOod"]
    ["expiration", "<Unix timestamp in seconds>"]
  ],
  "content": "{<author kind 0 JSON>}"
  "sig": "<64-bytes hex of the signature of the sha256 hash of the serialized event data>"
}
```

## Basic Status

Basic status don't rely on `status` tags.
Clients find out the user status by the following rules regarding status event's `created_at` age:

| Status Event Age                       | User Status                    |
| -------------------------------------- | ------------------------------ |
| (now - created_at) < 0                 | *invalid status, not a member* |
| 0 <= (now - created_at) < 10 min       | online                         |
| 10 min <= (now - created_at) < 30 min  | away                           |
| 30 min <= (now - created_at) < 5 days  | offline                        |
| 5 days <= (now - created_at) < 60 days | inactive                       |
| 60 days <= (now - created_at)`         | *not a member*                 |

Clients by default MUST update the status event every 7 minutes user is browsing a group.

An user is considered `invisible` if it deletes the status event or had never published it.
The `invisible` status should be the default for most use cases when joining (browsing) a group.

### Special Case

Some group NIPs may define bespoke status event update frequency along with expiration tag value and basic status tables.

| NIP           | Name            | Configuration                        |
| ------------- | --------------- | ------------------------------------ |
| [102](102.md) | Live Activities | [#live-activities](#live-activities) |

## Custom Status

Clients can choose to support extra custom status that may override the basic ones
by using `status` tags; even multiple `status` tags at once.

For example, a client may add a tag `["status", "offline"]` right after user leaves a group view.

The following are the standardized `status` tag values:
- "online"
- "away"
- "offline"
- "inactive"
- "busy"
- "free-for-chat"

## Live Activities

When joining a NIP-102 Live Activity the default status is `online` instead of `invisible`.

| User Role      | Status Event Update Frequency  | Status Event NIP-40 Epiration Tag |
| -------------- | ------------------------------ | --------------------------------- |
| Host / Speaker | 1 min 30 s                     | created_at + 10 min               |
| Participant    | 5 min 15 s                     | created_at + 10 min               |

| Status Event Age                          | User Role      | User Status                         |
| ----------------------------------------- | -------------- | ----------------------------------- |
| (now - created_at) < 0                    | *All*          | *invalid status, not participating* |
| 0 <= (now - created_at) < 2 min 15 s      | Host / Speaker | online                              |
| 2 min 15 s <= (now - created_at) < 10 min | Host / Speaker | offline                             |
| 10 min <= (now - created_at)              | Host / Speaker | *not participating*                 |
| 0 <= (now - created_at) < 6 min           | Participant    | online                              |
| 6 <= (now - created_at) < 10 min          | Participant    | offline                             |
| 10 min <= (now - created_at)              | Participant    | *not participating*                 |