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 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 60 days ahead of the `created_at` tag value;
- `.content` as stringified author kind 0 event JSON for fast lookup.

The event should be replaced by clients from time to time
(lower than 10 min window - see ["Basic Status" section](#custom-status)),
for example every 7 minutes the user is browsing a group.

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:

| Age                                    | Status                         |
| -------------------------------------- | ------------------------------ |
| (now - created_at) < 0                 | *invalid status, not a member* |
| 0 <= (now - created_at) < 10min        | 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*                 |

An user is invisible if it deletes the status event or had never published it.
Invisible should be the default status when joining (browsing) a group.

## 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.

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