Add snapshots

nummi/main/admin.py

@@ -1,7 +1,8 @@
 from django.contrib import admin
 
-from .models import Transaction, Invoice, Category
+from .models import Transaction, Invoice, Category, Snapshot
 
 admin.site.register(Transaction)
 admin.site.register(Invoice)
 admin.site.register(Category)
+admin.site.register(Snapshot)

nummi/main/migrations/0009_snapshot.py

@@ -0,0 +1,44 @@
+# Generated by Django 4.0.4 on 2022-05-21 18:40
+
+import datetime
+from django.db import migrations, models
+import django.db.models.deletion
+import uuid
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("main", "0008_alter_category_options_category_icon"),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name="Snapshot",
+            fields=[
+                (
+                    "id",
+                    models.UUIDField(
+                        default=uuid.uuid4,
+                        editable=False,
+                        primary_key=True,
+                        serialize=False,
+                    ),
+                ),
+                ("date", models.DateField(default=datetime.date.today)),
+                (
+                    "value",
+                    models.DecimalField(decimal_places=2, default=0, max_digits=12),
+                ),
+                (
+                    "previous",
+                    models.OneToOneField(
+                        blank=True,
+                        null=True,
+                        on_delete=django.db.models.deletion.SET_NULL,
+                        to="main.snapshot",
+                    ),
+                ),
+            ],
+        ),
+    ]

nummi/main/migrations/0010_alter_snapshot_previous.py

@@ -0,0 +1,25 @@
+# Generated by Django 4.0.4 on 2022-05-21 18:44
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("main", "0009_snapshot"),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name="snapshot",
+            name="previous",
+            field=models.OneToOneField(
+                blank=True,
+                editable=False,
+                null=True,
+                on_delete=django.db.models.deletion.SET_NULL,
+                to="main.snapshot",
+            ),
+        ),
+    ]

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"]