Implement date range handling for vacation and unavailable events

- Added helper functions to generate ISO 8601 formatted start and end times for calendar days.
- Introduced logic to merge consecutive vacation dates into a single record for improved data representation.
- Updated the duty schedule import process to utilize the new date handling functions for unavailable and vacation events.
- Enhanced integration tests to validate the correct handling of vacation periods and unavailable dates.
- Modified the web application to display formatted date ranges for vacation and unavailable events.

handlers/import_duty_schedule.py

@@ -60,6 +60,33 @@ def _duty_to_iso(d: date, hour_utc: int, minute_utc: int) -> str:
     return dt.strftime("%Y-%m-%dT%H:%M:%SZ")
 
 
+def _day_start_iso(d: date) -> str:
+    """ISO 8601 start of calendar day UTC: YYYY-MM-DDT00:00:00Z."""
+    return d.isoformat() + "T00:00:00Z"
+
+
+def _day_end_iso(d: date) -> str:
+    """ISO 8601 end of calendar day UTC: YYYY-MM-DDT23:59:59Z."""
+    return d.isoformat() + "T23:59:59Z"
+
+
+def _consecutive_date_ranges(dates: list[date]) -> list[tuple[date, date]]:
+    """Sort dates and merge consecutive ones into (first, last) ranges. Empty list -> []."""
+    if not dates:
+        return []
+    sorted_dates = sorted(set(dates))
+    ranges: list[tuple[date, date]] = []
+    start_d = end_d = sorted_dates[0]
+    for d in sorted_dates[1:]:
+        if (d - end_d).days == 1:
+            end_d = d
+        else:
+            ranges.append((start_d, end_d))
+            start_d = end_d = d
+    ranges.append((start_d, end_d))
+    return ranges
+
+
 async def import_duty_schedule_cmd(update: Update, context: ContextTypes.DEFAULT_TYPE) -> None:
     if not update.message or not update.effective_user:
         return
@@ -118,18 +145,22 @@ def _run_import(
                 insert_duty(session, user.id, start_at, end_at, event_type="duty")
                 num_duty += 1
             for d in entry.unavailable_dates:
-                start_at = _duty_to_iso(d, hour_utc, minute_utc)
-                d_next = d + timedelta(days=1)
-                end_at = _duty_to_iso(d_next, hour_utc, minute_utc)
                 insert_duty(
-                    session, user.id, start_at, end_at, event_type="unavailable"
+                    session,
+                    user.id,
+                    _day_start_iso(d),
+                    _day_end_iso(d),
+                    event_type="unavailable",
                 )
                 num_unavailable += 1
-            for d in entry.vacation_dates:
-                start_at = _duty_to_iso(d, hour_utc, minute_utc)
-                d_next = d + timedelta(days=1)
-                end_at = _duty_to_iso(d_next, hour_utc, minute_utc)
-                insert_duty(session, user.id, start_at, end_at, event_type="vacation")
+            for start_d, end_d in _consecutive_date_ranges(entry.vacation_dates):
+                insert_duty(
+                    session,
+                    user.id,
+                    _day_start_iso(start_d),
+                    _day_end_iso(end_d),
+                    event_type="vacation",
+                )
                 num_vacation += 1
         return (len(result.entries), num_duty, num_unavailable, num_vacation)
     finally: