Postgresql – Identify groups of sequential records

I have very simple table:

create table tmp(
    id int,
    source_id int,
    event_user varchar,
    event_date timestamp
);
 

and here is the data:

insert into tmp(id, source_id, event_user, event_date)
values (1, 1,  'A', now()),
       (2, 1,  'A', now()+interval '1 day'),
       (3, 1,  'B', now()+interval '2 day'),
       (4, 1,  'B', now()+interval '3 day'),
       (5, 1,  'A', now()+interval '4 day'),
       (6, 1,  'A', now()+interval '5 day'),
       (7, 1,  'A', now()+interval '6 day'),
       (8, 2,  'A', now()+interval '7 day'),
       (9, 2,  'B', now()+interval '8 day'),
       (10, 2,  'A', now()+interval '9 day'),
       (11, 2,  'B', now()+interval '10 day'),
       (12, 2,  'B', now()+interval '11 day') ;

(Here for the sake of simplicity I just added 1 day to ‘now’ timestamp in column event_date to show time sequence. In real case no any assumption about distribution of event_date could be made. Also columns ‘id’ and ‘source_id’ in real case are of type uuid.)

When I query this table:

select * from tmp
order by event_date;

I get:
initial data

Now, and here is the question, I need additional column (series_id) which identifies the groups of sequential (in order of event_date) records belonging to the same source_id and event_user.

so when I’ll query I would like to get the following result:

expected result

I’ve tried window functions (rank(), dense_rank()), but didn’t succeed, sure because records in expected groups do not have no common features except they’re ‘consequent’ in time. May be it’s a kind of ‘gaps and islands’ problem, but unfortunately I cant catch how to solve it.