Voucher: Add min_usages parameter (#2853)

src/pretix/base/services/cart.py

@@ -110,6 +110,11 @@ error_messages = {
                              'positions have been removed from your cart.'),
     'price_too_high': _('The entered price is to high.'),
     'voucher_invalid': _('This voucher code is not known in our database.'),
+    'voucher_min_usages': _('The voucher code "%(voucher)s" can only be used if you select at least %(number)s '
+                            'matching products.'),
+    'voucher_min_usages_removed': _('The voucher code "%(voucher)s" can only be used if you select at least '
+                                    '%(number)s matching products. We have therefore removed some positions from '
+                                    'your cart that can no longer be purchased like this.'),
     'voucher_redeemed': _('This voucher code has already been used the maximum number of times allowed.'),
     'voucher_redeemed_cart': _('This voucher code is currently locked since it is already contained in a cart. This '
                                'might mean that someone else is redeeming this voucher right now, or that you tried '
@@ -524,6 +529,15 @@ class CartManager:
             voucher_use_diff[voucher] += 1
             ops.append((listed_price - price_after_voucher, self.VoucherOperation(p, voucher, price_after_voucher)))
 
+        for voucher, cnt in list(voucher_use_diff.items()):
+            if 0 < cnt < (voucher.min_usages - voucher.redeemed):
+                raise CartError(
+                    _(error_messages['voucher_min_usages']) % {
+                        'voucher': voucher.code,
+                        'number': (voucher.min_usages - voucher.redeemed),
+                    }
+                )
+
         # If there are not enough voucher usages left for the full cart, let's apply them in the order that benefits
         # the user the most.
         ops.sort(key=lambda k: k[0], reverse=True)
@@ -915,6 +929,41 @@ class CartManager:
                     )
         return err
 
+    def _check_min_per_voucher(self):
+        vouchers = Counter()
+        for p in self.positions:
+            vouchers[p.voucher] += 1
+        for op in self._operations:
+            if isinstance(op, self.AddOperation):
+                vouchers[op.voucher] += op.count
+            elif isinstance(op, self.RemoveOperation):
+                vouchers[op.position.voucher] -= 1
+
+        err = None
+        for voucher, count in vouchers.items():
+            if not voucher or count == 0:
+                continue
+            if count < (voucher.min_usages - voucher.redeemed):
+                self._operations = [o for o in self._operations if not (
+                    isinstance(o, self.AddOperation) and o.voucher.pk == voucher.pk
+                )]
+                removals = [o.position.pk for o in self._operations if isinstance(o, self.RemoveOperation)]
+                for p in self.positions:
+                    if p.voucher_id == voucher.pk and p.pk not in removals:
+                        self._operations.append(self.RemoveOperation(position=p))
+                        err = _(error_messages['voucher_min_usages_removed']) % {
+                            'voucher': voucher.code,
+                            'number': (voucher.min_usages - voucher.redeemed),
+                        }
+                if not err:
+                    raise CartError(
+                        _(error_messages['voucher_min_usages']) % {
+                            'voucher': voucher.code,
+                            'number': (voucher.min_usages - voucher.redeemed),
+                        }
+                    )
+        return err
+
     def _perform_operations(self):
         vouchers_ok = self._get_voucher_availability()
         quotas_ok = _get_quota_availability(self._quota_diff, self.now_dt)
@@ -1171,6 +1220,7 @@ class CartManager:
 
         err = self._delete_out_of_timeframe()
         err = self.extend_expired_positions() or err
+        err = err or self._check_min_per_voucher()
 
         lockfn = NoLockManager
         if self._require_locking():

src/pretix/base/services/orders.py

@@ -115,6 +115,8 @@ error_messages = {
               'server was too busy. Please try again.'),
     'not_started': _('The booking period for this event has not yet started.'),
     'ended': _('The booking period has ended.'),
+    'voucher_min_usages': _('The voucher code "%(voucher)s" can only be used if you select at least %(number)s '
+                            'matching products.'),
     'voucher_invalid': _('The voucher code used for one of the items in your cart is not known in our database.'),
     'voucher_redeemed': _('The voucher code used for one of the items in your cart has already been used the maximum '
                           'number of times allowed. We removed this item from your cart.'),
@@ -569,6 +571,7 @@ def _check_positions(event: Event, now_dt: datetime, positions: List[CartPositio
     products_seen = Counter()
     q_avail = Counter()
     v_avail = Counter()
+    v_usages = Counter()
     v_budget = {}
     deleted_positions = set()
     seats_seen = set()
@@ -606,6 +609,7 @@ def _check_positions(event: Event, now_dt: datetime, positions: List[CartPositio
             break
 
         if cp.voucher:
+            v_usages[cp.voucher] += 1
             if cp.voucher not in v_avail:
                 redeemed_in_carts = CartPosition.objects.filter(
                     Q(voucher=cp.voucher) & Q(event=event) & Q(expires__gte=now_dt)
@@ -717,6 +721,13 @@ def _check_positions(event: Event, now_dt: datetime, positions: List[CartPositio
             # Sorry, can't let you keep that!
             delete(cp)
 
+    for voucher, cnt in v_usages.items():
+        if 0 < cnt < voucher.min_usages - voucher.redeemed:
+            raise OrderError(error_messages['voucher_min_usages'], {
+                'voucher': voucher.code,
+                'number': (voucher.min_usages - voucher.redeemed),
+            })
+
     # Check prices
     sorted_positions = [cp for cp in sorted_positions if cp.pk and cp.pk not in deleted_positions]
     old_total = sum(cp.price for cp in sorted_positions)