Let next_lesson/prev_lesson base on common method _adjacent_lesson

Also improve documentation and naming

aleksis/apps/chronos/model_extensions.py

@@ -81,35 +81,44 @@ def lesson_periods_as_teacher(self):
 
 
 @Person.method
-def daily_lessons(self, day: date):
-    """Get all lessons of this person on the given day."""
-    return LessonPeriod.objects.on_day(day).filter_from_person(self)
+def lessons_on_day(self, day: date):
+    """Get all lessons of this person (either as participant or teacher) on the given day."""
+    return (
+        LessonPeriod.objects.on_day(day)
+        .filter_from_person(self)
+        .order_by("period__period")
+    )
 
 
 @Person.method
-def next_lesson(self, lesson_period: "LessonPeriod", day: date) -> Union["LessonPeriod", None]:
-    """Get next lesson of the person on the same day."""
-    daily_lessons = self.daily_lessons(day)
+def _adjacent_lesson(
+    self, lesson_period: "LessonPeriod", day: date, offset: int = 1
+) -> Union["LessonPeriod", None]:
+    """Get next/previous lesson of the person (either as participant or teacher) on the same day."""
+    daily_lessons = self.lessons_on_day(day)
     ids = list(daily_lessons.values_list("id", flat=True))
     index = ids.index(lesson_period.pk)
 
-    if index + 1 < len(ids):
-        return daily_lessons[index + 1]
+    if (offset > 0 and index + offset < len(ids)) or (offset < 0 and index >= -offset):
+        return daily_lessons[index + offset]
     else:
         return None
 
 
 @Person.method
-def previous_lesson(self, lesson_period: "LessonPeriod", day: date) -> Union["LessonPeriod", None]:
-    """Get previous lesson of the person on the same day."""
-    daily_lessons = self.daily_lessons(day)
-    ids = list(daily_lessons.values_list("id", flat=True))
-    index = ids.index(lesson_period.pk)
+def next_lesson(
+    self, lesson_period: "LessonPeriod", day: date
+) -> Union["LessonPeriod", None]:
+    """Get next lesson of the person (either as participant or teacher) on the same day."""
+    return self._adjacent_lesson(lesson_period, day)
 
-    if index > 0:
-        return daily_lessons[index - 1]
-    else:
-        return None
+
+@Person.method
+def previous_lesson(
+    self, lesson_period: "LessonPeriod", day: date
+) -> Union["LessonPeriod", None]:
+    """Get previous lesson of the person (either as participant or teacher) on the same day."""
+    return self._adjacent_lesson(lesson_period, day, offset=-1)
 
 
 def for_timetables(cls):