perf: 优化定时任务cron表达式处理，支持使用标准cron表达式写法

Author: insistence

dash-fastapi-backend/config/get_scheduler.py

@@ -20,11 +20,49 @@ class MyCronTrigger(CronTrigger):
     @classmethod
     def from_crontab(cls, expr, timezone=None):
         values = expr.split()
-        if len(values) != 7:
-            raise ValueError('Wrong number of fields; got {}, expected 7'.format(len(values)))
+        if len(values) != 6 and len(values) != 7:
+            raise ValueError('Wrong number of fields; got {}, expected 6 or 7'.format(len(values)))
 
-        return cls(second=values[0], minute=values[1], hour=values[2], day=values[3], month=values[4],
-                   day_of_week=values[5], year=values[6], timezone=timezone)
+        second = values[0]
+        minute = values[1]
+        hour = values[2]
+        if '?' in values[3]:
+            day = None
+        elif 'L' in values[5]:
+            day = f"last {values[5].replace('L', '')}"
+        elif 'W' in values[3]:
+            day = cls.__find_recent_workday(int(values[3].split('W')[0]))
+        else:
+            day = values[3].replace('L', 'last')
+        month = values[4]
+        if '?' in values[5] or 'L' in values[5]:
+            week = None
+        elif '#' in values[5]:
+            week = int(values[5].split('#')[1])
+        else:
+            week = values[5]
+        if '#' in values[5]:
+            day_of_week = int(values[5].split('#')[0]) - 1
+        else:
+            day_of_week = None
+        year = values[6] if len(values) == 7 else None
+        return cls(second=second, minute=minute, hour=hour, day=day, month=month, week=week,
+                   day_of_week=day_of_week, year=year, timezone=timezone)
+
+    @classmethod
+    def __find_recent_workday(cls, day):
+        now = datetime.now()
+        date = datetime(now.year, now.month, day)
+        if date.weekday() < 5:
+            return date.day
+        else:
+            diff = 1
+            while True:
+                previous_day = date - timedelta(days=diff)
+                if previous_day.weekday() < 5:
+                    return previous_day.day
+                else:
+                    diff += 1
 
 
 job_stores = {