time series data

Hi everyone,

I have a data stream of a call center application coming in to postgres in
this format :

user_name, user_status, event_time

'user1', 'ready', '2017-01-01 10:00:00'
'user1', 'talking', '2017-01-01 10:02:00'
'user1', 'after_call', '2017-01-01 10:07:00'
'user1', 'ready', '2017-01-01 10:08:00'
'user1', 'talking', '2017-01-01 10:10:00'
'user1', 'after_call', '2017-01-01 10:15:00'
'user1', 'paused', '2017-01-01 10:20:00'
...
...

so as you see each new insert of an "event" is in fact the start_time of
that event and also the end_time of the previous one so should be used to
calculate the duration of this previous one.

What is the best way to get user_status statistics like total duration,
frequency, avg ...etc , does any body have an experience with this sort of
data streams ?

Thanks in advance.