Minor enhancements

* refactors eco account rest surface calculation into designated method get_available_rest()
* refactors placeholder setter for BaseForm
* adds automatic eco account identifier generating on saving
* fixes ServerMessageImportance template tag

compensation/models.py

@@ -12,7 +12,8 @@ from django.db.models import Sum
 from django.utils.timezone import now
 from django.utils.translation import gettext_lazy as _
 
-from compensation.settings import COMPENSATION_IDENTIFIER_LENGTH, COMPENSATION_IDENTIFIER_TEMPLATE
+from compensation.settings import COMPENSATION_IDENTIFIER_LENGTH, COMPENSATION_IDENTIFIER_TEMPLATE, \
+    ECO_ACCOUNT_IDENTIFIER_LENGTH, ECO_ACCOUNT_IDENTIFIER_TEMPLATE
 from intervention.models import Intervention, ResponsibilityData
 from konova.models import BaseObject, BaseResource, Geometry, UuidModel
 from konova.settings import DEFAULT_SRID_RLP, LANIS_LINK_TEMPLATE
@@ -218,13 +219,44 @@ class EcoAccount(AbstractCompensation):
     def __str__(self):
         return "{}".format(self.identifier)
 
+    def save(self, *args, **kwargs):
+        if self.identifier is None or len(self.identifier) == 0:
+            # Create new identifier
+            new_id = self._generate_new_identifier()
+            while EcoAccount.objects.filter(identifier=new_id).exists():
+                new_id = self._generate_new_identifier()
+            self.identifier = new_id
+        super().save(*args, **kwargs)
+
     def get_surface_withdraws(self) -> float:
         """ Calculates the compensation's/account's surface
 
         Returns:
             sum_surface (float)
         """
-        return self.withdraws.all().aggregate(Sum("surface"))["surface__sum"]
+        return self.withdraws.all().aggregate(Sum("surface"))["surface__sum"] or 0
+
+    def get_available_rest(self, as_percentage: bool = False):
+        """ Calculates available rest surface of the eco account
+
+        Args:
+            as_percentage (bool): Whether to return the result as m² or %
+
+        Returns:
+
+        """
+        ret_val = 0
+        withdraws = self.withdraws.all()
+        withdraw_surfaces = withdraws.aggregate(Sum("surface"))["surface__sum"] or 0
+        after_states_surfaces = self.after_states.all().aggregate(Sum("surface"))["surface__sum"] or withdraw_surfaces ## no division by zero
+        ret_val = after_states_surfaces - withdraw_surfaces
+
+        if as_percentage:
+            if after_states_surfaces > 0:
+                ret_val = int((ret_val / after_states_surfaces) * 100)
+            else:
+                ret_val = 0
+        return ret_val
 
     def get_LANIS_link(self) -> str:
         """ Generates a link for LANIS depending on the geometry
@@ -252,6 +284,22 @@ class EcoAccount(AbstractCompensation):
         # ToDo
         pass
 
+    @staticmethod
+    def _generate_new_identifier() -> str:
+        """ Generates a new identifier for the intervention object
+
+        Returns:
+            str
+        """
+        curr_month = str(now().month)
+        curr_year = str(now().year)
+        rand_str = generate_random_string(
+            length=ECO_ACCOUNT_IDENTIFIER_LENGTH,
+            only_numbers=True,
+        )
+        _str = "{}{}{}".format(curr_month, curr_year, rand_str)
+        return ECO_ACCOUNT_IDENTIFIER_TEMPLATE.format(_str)
+
 
 class EcoAccountWithdraw(BaseResource):
     """