# backend-heartbeat

Beep backend records and makes available the last seen times of users.

## Environment variables

Supply environment variables by either exporting them or editing ```.env```.

| ENV | Description | Default |
| ---- | ----------- | ------- |
| LISTEN | Host and port number to listen on | :8080 |
| REDIS | Host and port of redis | :6379 |

## API

### Subscribe User

```
GET /subscribe/:userid/client/:clientid
```

Subscribe to a user. Every time a user pings this service, the time will be sent to all subscribed users. Upon subscription, if it exists, the last cached time of the target user will be pushed immediately to the stream.

```js
const es = new EventSource(`${host}/subscribe/${user}/client/${device}`);
es.onmessage = (e) => {
  const timestamp = e.data;
  // Do whatever with the timestamp
};
```

#### URL Params

| Name | Type | Description | Required |
| ---- | ---- | ----------- | -------- |
| userid | String | Target user's ID. | ✓ |
| clientid | String | Target user's device's ID. | ✓ |

#### Success Response (200 OK)

An [EventSource](https://developer.mozilla.org/en-US/docs/Web/API/EventSource) stream.

---

### Ping Server

```
POST /ping/:userid/client/:clientid
```

Ping the server.

#### URL Params

| Name | Type | Description | Required |
| ---- | ---- | ----------- | -------- |
| userid | String | User's ID. | ✓ |
| clientid | String | User's device's ID. | ✓ |

#### Success Response (200 OK)

Empty body.