Refs #131 -- Basic implementation of invoicing

src/pretix/base/models/invoices.py

@@ -0,0 +1,62 @@
+import random
+import string
+from datetime import date
+from decimal import Decimal
+
+from django.db import DatabaseError, models
+from django.db.models import Max
+
+
+def invoice_filename(instance, filename: str) -> str:
+    secret = ''.join(random.choice(string.ascii_letters + string.digits) for _ in range(14))
+    return 'invoices/{org}/{ev}/{ev}-{no}-{code}-{secret}.pdf'.format(
+        org=instance.event.organizer.slug, ev=instance.event.slug,
+        no=instance.invoice_no, code=instance.order.code,
+        secret=secret
+    )
+
+
+class Invoice(models.Model):
+    order = models.ForeignKey('Order', related_name='invoices', db_index=True)
+    event = models.ForeignKey('Event', related_name='invoices', db_index=True)
+    invoice_no = models.PositiveIntegerField(db_index=True)
+    is_cancellation = models.BooleanField(default=False)
+    refers = models.ForeignKey('Invoice', related_name='refered', null=True, blank=True)
+    invoice_from = models.TextField()
+    invoice_to = models.TextField()
+    date = models.DateField(default=date.today)
+    locale = models.CharField(max_length=50, default='en')
+    additional_text = models.TextField(blank=True)
+    file = models.FileField(null=True, blank=True, upload_to=invoice_filename)
+
+    def save(self, *args, **kwargs):
+        if not self.order:
+            raise ValueError('Any invoice needs to be connected to an order')
+        if not self.event:
+            self.event = self.order.event
+        if not self.invoice_no:
+            for i in range(10):
+                self.invoice_no = (Invoice.objects.filter(
+                    event=self.event).aggregate(m=Max('invoice_no'))['m'] or 0) + 1
+                try:
+                    return super().save(*args, **kwargs)
+                except DatabaseError:
+                    # Suppress duplicate key errors and try again
+                    if i == 9:
+                        raise
+        return super().save(*args, **kwargs)
+
+    @property
+    def number(self):
+        return '%s-%05d' % (self.event.slug.upper(), self.invoice_no)
+
+    class Meta:
+        unique_together = ('event', 'invoice_no')
+
+
+class InvoiceLine(models.Model):
+    invoice = models.ForeignKey('Invoice', related_name='lines')
+    description = models.TextField()
+    gross_value = models.DecimalField(max_digits=10, decimal_places=2)
+    tax_value = models.DecimalField(max_digits=10, decimal_places=2, default=Decimal('0.00'))
+    tax_rate = models.DecimalField(max_digits=7, decimal_places=2, default=Decimal('0.00'))