Align release date calculation with documentation

To improve the predictability of release dates, it was agreed to start
the stabilization phase on the last Monday of the first Month in the
quarter. Consequently, the release is expected two weeks after the
stabilization period is started.

Signed-off-by: Marcus Burghardt <[email protected]>

utils/release_helper.py

@@ -332,15 +332,42 @@ def get_monday_that_follows(date) -> datetime:
     return date + timedelta((0 - date.weekday()) % 7)
 
 
+def get_next_quarter_first_month(latest_release_date: datetime) -> int:
+    last_release_quarter = (latest_release_date.month - 1) // 3 + 1
+    if last_release_quarter == 4:
+        next_release_quarter = 1
+    else:
+        next_release_quarter = last_release_quarter + 1
+    return (next_release_quarter - 1) * 3 + 1
+
+
+def get_last_monday_of_month(year: int, month: int) -> datetime:
+    if month == 12:
+        last_month_day = datetime(year, month, 31)
+    else:
+        last_month_day = datetime(year, month + 1, 1) - timedelta(days=1)
+
+    days_since_monday = (last_month_day.weekday() - 0) % 7
+    return last_month_day - timedelta(days=days_since_monday)
+
+
 def get_next_stabilization_date(release_date) -> datetime:
     two_weeks_before = release_date - timedelta(weeks=2)
     stabilization_monday = get_monday_that_follows(two_weeks_before)
     return stabilization_monday.date()
 
 
-def get_next_release_date(latest_release_date) -> datetime:
-    three_months_ahead = latest_release_date + timedelta(days=90)
-    return get_friday_that_follows(three_months_ahead)
+def get_next_release_date(latest_release_date: datetime) -> datetime:
+    month = get_next_quarter_first_month(latest_release_date)
+    now = datetime.now()
+
+    if month > 9 and latest_release_date <= now:
+        year = latest_release_date.year + 1
+    else:
+        year = latest_release_date.year
+
+    last_monday = get_last_monday_of_month(year, month)
+    return get_friday_that_follows(last_monday + timedelta(weeks=1))
 
 
 def is_next_release_in_progress(repo) -> bool: