Add snapshots

nummi/main/models.py

@@ -72,3 +72,52 @@ class InvoiceForm(ModelForm):
     class Meta:
         model = Invoice
         fields = ["name", "file"]
+
+
+class Snapshot(models.Model):
+    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
+    date = models.DateField(default=date.today, unique=True)
+    value = models.DecimalField(max_digits=12, decimal_places=2, default=0)
+    previous = models.OneToOneField(
+        "self", on_delete=models.SET_NULL, blank=True, null=True, editable=False
+    )
+
+    def __str__(self):
+        if self.previous is None:
+            return f"Snapshot {self.date}: {self.value}€"
+        return f"Snapshot {self.date}: {self.value}€ (Previous: {self.previous.date})"
+
+    def save(self, *args, only_super=False, **kwargs):
+        if not only_super:
+            _prev = (
+                self.__class__.objects.order_by("-date")
+                .filter(date__lt=self.date)
+                .first()
+            )
+
+            try:
+                _next = self.__class__.objects.get(previous=_prev)
+            except self.__class__.DoesNotExist:
+                pass
+            else:
+                _next.previous = self
+                _next.save(only_super=True)
+
+            self.previous = _prev
+        super().save(*args, **kwargs)
+
+    def delete(self, *args, only_super=False, **kwargs):
+        if not only_super:
+            try:
+                _next = self.__class__.objects.get(previous=self)
+            except self.__class__.DoesNotExist:
+                pass
+            else:
+                _next.previous = self.previous
+                super().delete(*args, **kwargs)
+                _next.save(only_super=True)
+        else:
+            super().delete(*args, **kwargs)
+
+    class Meta:
+        ordering = ["-date"]