Add billables to invoice model

Calculate next invoicing date for billables

core/models/billable.py

@@ -1,9 +1,14 @@
 from django.db.models import IntegerChoices, Model, ForeignKey, CASCADE, TextField, PositiveIntegerField, BooleanField, DateField
+from django.utils import timezone
 
 from core.models.profiles import ClientProfile
 from core.models.brands import Brand
 from core.fields.base import LongCharField
 from core.fields.numbers import CostField
+from core.models.invoices import InvoiceItem, Invoice
+
+from dateutil.relativedelta import relativedelta
+
 
 class ActionChoices(IntegerChoices):
     WAIT = 0, "Do not invoice for now"
@@ -11,12 +16,14 @@ class ActionChoices(IntegerChoices):
     CRON = 2, "Invoice at next cron run"
     DATE = 3, "Invoice at date"
 
+
 class CycleChoices(IntegerChoices):
     DAYS = 0, "Days"
     WEEKS = 1, "Weeks"
     MONTHS = 2, "Months"
     YEARS = 3, "Years"
 
+
 class Billable(Model):
     client = ForeignKey(ClientProfile, on_delete=CASCADE)
     brand = ForeignKey(Brand, on_delete=CASCADE)
@@ -29,3 +36,21 @@ class Billable(Model):
     date = DateField(null=True)
     recur_cycle = PositiveIntegerField(choices=CycleChoices.choices, null=True)
     recur_count = PositiveIntegerField(null=True)
+
+    def next_invoicing(self):
+        try:
+            invoiceitems = InvoiceItem.objects.filter(billable=self)
+
+            if not recur_cycle:
+                return False
+
+            invoice = Invoice.objects.filter(invoiceitem_set__contains=invoiceitems).latest("created")
+            delta = relativedelta(days=self.recur_count if self.recur_cycle == CycleChoices.DAYS else 0, 
+                                  weeks=self.recur_count if self.recur_cycle == CycleChoices.WEEKS else 0,
+                                  months=self.recur_count if self.recur_cycle == CycleChoices.MONTHS else 0, 
+                                  years=self.recur_count if self.recur_cycle == CycleChoices.YEARS else 0)
+
+            return invoice.created + delta
+
+        except:
+            return self.date

core/models/invoices.py

@@ -5,6 +5,7 @@ from core.fields.numbers import CostField
 from core.models.services import Service
 from core.models.profiles import ClientProfile
 from core.models.local import Currency
+from core.models.billable import Billable
 
 class Invoice(Model):
     client = ForeignKey(ClientProfile, on_delete=CASCADE)
@@ -23,3 +24,4 @@ class InvoiceItem(Model):
     discount = CostField()
     taxable = BooleanField()
     service = ForeignKey(Service, on_delete=SET_NULL, null=True)
+    billable = ForeignKey(Billable, on_delete=SET_NULL, null=True)