Add the circular next methods for Task.

tasks/models.py

@@ -25,3 +25,23 @@ class Task(models.Model):
     def __str__(self):
         return self.name
 
+    @staticmethod
+    def get_statuses():
+        return list(map(lambda _: _[1], Task.STATUSES))
+
+    def _get_status_index(self):
+        return Task.get_statuses().index(self.status)
+
+    def circular_next_status_index(self):
+        current_index = self._get_status_index()
+        next_index = (current_index + 1) % len(Task.STATUSES)
+        return next_index
+
+    def circular_next_status(self):
+        next_index = self.circular_next_status_index()
+        return Task.get_statuses()[next_index]
+
+    def set_circular_next_status(self):
+        self.status = self.circular_next_status()
+        self.save()
+