Show users currently watching device page

[elinol]

Adds Phoenix Presence, to application in general and device page specifically.

Tracks user on mount, subscribes to events for device's presence and populates user list on presence diff.

Todo:

• Better styling on user circles

[elinol]

[joshk]

This is looking very cool!

I was reading up on Phoenix.Presence myself, to better understand all the bits that were going on, and came across https://hexdocs.pm/phoenix/presence.html#usage-with-liveview

Your approach appears a bit more in line with the channels implementation recommendations. The thing that might be of interested is:

One thing to keep in mind when dealing with LiveView, is that each LiveView is a stateful process, so if we keep the presence state in the LiveView, each LiveView process will contain the full list of online users in memory. Instead, we can keep track of the online users within the Presence process, and pass separate events to the LiveView, which can use a stream to update the online list.

[elinol]

I read that too and that was my first approach but I didn't got it working alright. Might be worth giving it another try though!