[tasks] Refactor tasks to not store a time index state

It's better to recompute it every time rather than suffer from
maintaining the extra state.

discord/ext/tasks/__init__.py

@@ -148,13 +148,17 @@ class Loop(Generic[LF]):
         self._handle = SleepHandle(dt=dt, loop=asyncio.get_running_loop())
         return self._handle.wait()
 
+    def _is_relative_time(self) -> bool:
+        return self._time is MISSING
+
+    def _is_explicit_time(self) -> bool:
+        return self._time is not MISSING
+
     async def _loop(self, *args: Any, **kwargs: Any) -> None:
         backoff = ExponentialBackoff()
         await self._call_loop_function('before_loop')
         self._last_iteration_failed = False
-        if self._time is not MISSING:
-            # the time index should be prepared every time the internal loop is started
-            self._prepare_time_index()
+        if self._is_explicit_time():
             self._next_iteration = self._get_next_sleep_time()
         else:
             self._next_iteration = datetime.datetime.now(datetime.timezone.utc)
@@ -164,7 +168,7 @@ class Loop(Generic[LF]):
                 return
             while True:
                 # sleep before the body of the task for explicit time intervals
-                if self._time is not MISSING:
+                if self._is_explicit_time():
                     await self._try_sleep_until(self._next_iteration)
                 if not self._last_iteration_failed:
                     self._last_iteration = self._next_iteration
@@ -182,7 +186,7 @@ class Loop(Generic[LF]):
                         return
 
                     # sleep after the body of the task for relative time intervals
-                    if self._time is MISSING:
+                    if self._is_relative_time():
                         await self._try_sleep_until(self._next_iteration)
 
                     self._current_loop += 1
@@ -553,47 +557,36 @@ class Loop(Generic[LF]):
         self._error = coro  # type: ignore
         return coro
 
-    def _get_next_sleep_time(self) -> datetime.datetime:
+    def _get_next_sleep_time(self, now: datetime.datetime = MISSING) -> datetime.datetime:
         if self._sleep is not MISSING:
             return self._last_iteration + datetime.timedelta(seconds=self._sleep)
 
-        if self._time_index >= len(self._time):
-            self._time_index = 0
-            if self._current_loop == 0:
-                # if we're at the last index on the first iteration, we need to sleep until tomorrow
-                return datetime.datetime.combine(
-                    datetime.datetime.now(datetime.timezone.utc) + datetime.timedelta(days=1), self._time[0]
-                )
-
-        next_time = self._time[self._time_index]
+        if now is MISSING:
+            now = datetime.datetime.now(datetime.timezone.utc)
 
-        if self._current_loop == 0:
-            self._time_index += 1
-            return datetime.datetime.combine(datetime.datetime.now(datetime.timezone.utc), next_time)
+        index = self._start_time_relative_to(now)
 
-        next_date = self._last_iteration
-        if self._time_index == 0:
-            # we can assume that the earliest time should be scheduled for "tomorrow"
-            next_date += datetime.timedelta(days=1)
+        if index is None:
+            time = self._time[0]
+            tomorrow = now + datetime.timedelta(days=1)
+            date = tomorrow.date()
+        else:
+            date = now.date()
+            time = self._time[index]
 
-        self._time_index += 1
-        return datetime.datetime.combine(next_date, next_time)
+        return datetime.datetime.combine(date, time, tzinfo=time.tzinfo or datetime.timezone.utc)
 
-    def _prepare_time_index(self, now: datetime.datetime = MISSING) -> None:
+    def _start_time_relative_to(self, now: datetime.datetime) -> Optional[int]:
         # now kwarg should be a datetime.datetime representing the time "now"
         # to calculate the next time index from
 
         # pre-condition: self._time is set
-        time_now = (
-            now if now is not MISSING else datetime.datetime.now(datetime.timezone.utc).replace(microsecond=0)
-        ).timetz()
-        idx = -1
+        time_now = now.timetz()
         for idx, time in enumerate(self._time):
             if time >= time_now:
-                self._time_index = idx
-                break
+                return idx
         else:
-            self._time_index = idx + 1
+            return None
 
     def _get_time_parameter(
         self,
@@ -683,10 +676,6 @@ class Loop(Generic[LF]):
             self._sleep = self._seconds = self._minutes = self._hours = MISSING
 
         if self.is_running():
-            if self._time is not MISSING:
-                # prepare the next time index starting from after the last iteration
-                self._prepare_time_index(now=self._last_iteration)
-
             self._next_iteration = self._get_next_sleep_time()
             if self._handle and not self._handle.done():
                 # the loop is sleeping, recalculate based on new interval
@@ -701,7 +690,6 @@ def loop(
     time: Union[datetime.time, Sequence[datetime.time]] = MISSING,
     count: Optional[int] = None,
     reconnect: bool = True,
-    loop: asyncio.AbstractEventLoop = MISSING,
 ) -> Callable[[LF], Loop[LF]]:
     """A decorator that schedules a task in the background for you with
     optional reconnect logic. The decorator returns a :class:`Loop`.
@@ -745,6 +733,14 @@ def loop(
     """
 
     def decorator(func: LF) -> Loop[LF]:
-        return Loop[LF](func, seconds=seconds, minutes=minutes, hours=hours, count=count, time=time, reconnect=reconnect)
+        return Loop[LF](
+            func,
+            seconds=seconds,
+            minutes=minutes,
+            hours=hours,
+            count=count,
+            time=time,
+            reconnect=reconnect,
+        )
 
     return decorator

tests/test_ext_tasks.py

@@ -75,3 +75,23 @@ async def test_explicit_initial_runs_tomorrow_multi():
         assert not has_run
     finally:
         loop.cancel()
+
+
+def test_task_regression_issue7659():
+    jst = datetime.timezone(datetime.timedelta(hours=9))
+
+    # 00:00, 03:00, 06:00, 09:00, 12:00, 15:00, 18:00, 21:00
+    times = [datetime.time(hour=h, tzinfo=jst) for h in range(0, 24, 3)]
+
+    @tasks.loop(time=times)
+    async def loop():
+        pass
+
+    before_midnight = datetime.datetime(2022, 3, 12, 23, 50, 59, tzinfo=jst)
+    after_midnight = before_midnight + datetime.timedelta(minutes=9, seconds=2)
+
+    expected_before_midnight = datetime.datetime(2022, 3, 13, 0, 0, 0, tzinfo=jst)
+    expected_after_midnight = datetime.datetime(2022, 3, 13, 3, 0, 0, tzinfo=jst)
+
+    assert loop._get_next_sleep_time(before_midnight) == expected_before_midnight
+    assert loop._get_next_sleep_time(after_midnight) == expected_after_midnight