feat(transactions): let new recurring transactions and installment plans adopt an existing transaction

app/apps/transactions/forms.py

@@ -887,11 +887,17 @@ class InstallmentPlanForm(forms.ModelForm):
                 ),
             )
 
-    def save(self, **kwargs):
+    def save(self, source_transaction=None, **kwargs):
         is_new = not self.instance.id
 
         instance = super().save(**kwargs)
-        if is_new:
+        if is_new and source_transaction:
+            # The converted transaction becomes the first installment
+            source_transaction.installment_plan = instance
+            source_transaction.installment_id = instance.installment_start
+            source_transaction.save()
+            instance.update_transactions()
+        elif is_new:
             instance.create_transactions()
         else:
             instance.update_transactions()
@@ -1145,12 +1151,12 @@ class RecurringTransactionForm(forms.ModelForm):
 
         return cleaned_data
 
-    def save(self, **kwargs):
+    def save(self, source_transaction=None, **kwargs):
         is_new = not self.instance.id
 
         instance = super().save(**kwargs)
         if is_new:
-            instance.create_upcoming_transactions()
+            instance.create_upcoming_transactions(first_transaction=source_transaction)
         else:
             instance.update_unpaid_transactions()
             instance.generate_upcoming_transactions()

app/apps/transactions/models.py

@@ -915,7 +915,7 @@ class RecurringTransaction(models.Model):
         instance = super().save(*args, **kwargs)
         return instance
 
-    def create_upcoming_transactions(self):
+    def create_upcoming_transactions(self, first_transaction=None):
         current_date = self.start_date
         reference_date = self.reference_date
         end_date = min(
@@ -925,6 +925,12 @@ class RecurringTransaction(models.Model):
             timezone.now().date() + (self.get_recurrence_delta() * self.keep_at_most),
         )
 
+        # When converting an existing transaction, it becomes the first occurrence
+        if first_transaction:
+            self.adopt_transaction(first_transaction, current_date, reference_date)
+            current_date = self.get_next_date(current_date)
+            reference_date = self.get_next_date(reference_date)
+
         while current_date <= end_date:
             self.create_transaction(current_date, reference_date)
             current_date = self.get_next_date(current_date)
@@ -959,6 +965,25 @@ class RecurringTransaction(models.Model):
         created_transaction.tags.set(self.tags(manager="all_objects").all())
         created_transaction.entities.set(self.entities(manager="all_objects").all())
 
+    def adopt_transaction(self, existing_transaction, date, reference_date):
+        existing_transaction.account = self.account
+        existing_transaction.type = self.type
+        existing_transaction.date = date
+        existing_transaction.reference_date = reference_date.replace(day=1)
+        existing_transaction.description = (
+            self.description if self.add_description_to_transaction else ""
+        )
+        existing_transaction.category = self.category
+        existing_transaction.notes = self.notes if self.add_notes_to_transaction else ""
+        existing_transaction.recurring_transaction = self
+
+        if not existing_transaction.is_paid:  # Don't update value for paid transactions
+            existing_transaction.amount = self.amount
+
+        existing_transaction.save()
+        existing_transaction.tags.set(self.tags(manager="all_objects").all())
+        existing_transaction.entities.set(self.entities(manager="all_objects").all())
+
     def get_recurrence_delta(self):
         if self.recurrence_type == self.RecurrenceType.DAY:
             return relativedelta(days=self.recurrence_interval)