Add daily sessions pending view and accompanying snapshot table (#3217)

* feat: add a new daily billing view

* update views and table based on early feedback

* address review comments

* update CTE to be an accurate result of what we expect

* remove 'with time zone' from daily range

* remove timezone

* Update internal/db/schema/migrations/oss/postgres/70/01_hcp_billing_daily.up.sql

Co-authored-by: Michael Gaffney <mgaffney@users.noreply.github.com>

* Apply suggestions from code review

Co-authored-by: Timothy Messier <tim.messier@gmail.com>

* go mod updates

* fix tests

---------

Co-authored-by: Michael Gaffney <mgaffney@users.noreply.github.com>
Co-authored-by: Timothy Messier <tim.messier@gmail.com>

internal/db/schema/migrations/oss/postgres/70/01_hcp_billing_daily.up.sql

@@ -0,0 +1,64 @@
+-- Copyright (c) HashiCorp, Inc.
+-- SPDX-License-Identifier: MPL-2.0
+
+begin;
+  create table sessions_pending_daily_snapshot (
+    snapshot_date date primary key,
+    sessions_pending_count bigint not null
+  );
+
+  create view hcp_billing_daily_sessions_yesterday as
+  with
+  daily_counts (day, sessions_pending_count) as (
+      select date_trunc('day', session_pending_time), count(*)
+        from wh_session_accumulating_fact
+       where session_pending_time >= date_trunc('day', timestamp 'yesterday')
+         and session_pending_time < date_trunc('day', timestamp 'today')
+    group by date_trunc('day', session_pending_time)
+  ),
+  daily_range (day) as (
+      select date_trunc('day', timestamp 'yesterday')
+  ),
+  final (day, sessions_pending_count) as (
+      select daily_range.day, coalesce(daily_counts.sessions_pending_count, 0)
+        from daily_range
+   left join daily_counts on daily_range.day = daily_counts.day
+  )
+    select day, sessions_pending_count
+      from final
+  order by day desc;
+  comment on view hcp_billing_daily_sessions_yesterday is
+    'hcp_billing_daily_sessions_yesterday is a view that contains '
+      'the sum of pending sessions '
+      'from the beginning of the previous day '
+      'until the start of the current day (exclusive).';
+
+  create view hcp_billing_daily_sessions_all as
+  with
+  daily_counts (day, sessions_pending_count) as (
+      select date_trunc('day', session_pending_time), count(*)
+        from wh_session_accumulating_fact
+       where session_pending_time < date_trunc('day', timestamp 'today')
+    group by date_trunc('day', session_pending_time)
+  ),
+  daily_range (day) as (
+      select bucket
+        from generate_series(
+                   date_trunc('day', (select min(session_pending_time) from wh_session_accumulating_fact)),
+                   timestamp 'yesterday',
+                   '1 day'::interval
+               ) as bucket
+  ),
+  final (day, sessions_pending_count) as (
+         select daily_range.day::timestamp,
+                coalesce(daily_counts.sessions_pending_count, 0)
+           from daily_range
+      left join daily_counts on daily_range.day = daily_counts.day
+  )
+    select day, sessions_pending_count
+      from final
+  order by day desc;
+  comment on view hcp_billing_daily_sessions_all is
+    'hcp_billing_daily_sessions_all is a view that contains '
+      'the sum of pending sessions for yesterday and all previous days.';
+commit;