add checks on ProductForm

counter/forms.py

@@ -5,7 +5,7 @@ from datetime import date, datetime, timezone
 
 from dateutil.relativedelta import relativedelta
 from django import forms
-from django.core.exceptions import ValidationError
+from django.core.validators import MaxValueValidator
 from django.db.models import Exists, OuterRef, Q
 from django.forms import BaseModelFormSet
 from django.utils.timezone import now
@@ -318,7 +318,6 @@ class ProductForm(forms.ModelForm):
         }
 
     counters = forms.ModelMultipleChoiceField(
-        help_text=None,
         label=_("Counters"),
         required=False,
         widget=AutoCompleteSelectMultipleCounter,
@@ -329,10 +328,31 @@ class ProductForm(forms.ModelForm):
         super().__init__(*args, instance=instance, **kwargs)
         if self.instance.id:
             self.fields["counters"].initial = self.instance.counters.all()
+            if hasattr(self.instance, "formula"):
+                self.formula_init(self.instance.formula)
         self.action_formset = ScheduledProductActionFormSet(
             *args, product=self.instance, **kwargs
         )
 
+    def formula_init(self, formula: ProductFormula):
+        """Part of the form initialisation specific to formula products."""
+        self.fields["selling_price"].help_text = _(
+            "This product is a formula. "
+            "Its price cannot be greater than the price "
+            "of the products constituting it, which is %(price)s €"
+        ) % {"price": formula.max_selling_price}
+        self.fields["special_selling_price"].help_text = _(
+            "This product is a formula. "
+            "Its special price cannot be greater than the price "
+            "of the products constituting it, which is %(price)s €"
+        ) % {"price": formula.max_special_selling_price}
+        for key, price in (
+            ("selling_price", formula.max_selling_price),
+            ("special_selling_price", formula.max_special_selling_price),
+        ):
+            self.fields[key].widget.attrs["max"] = price
+            self.fields[key].validators.append(MaxValueValidator(price))
+
     def is_valid(self):
         return super().is_valid() and self.action_formset.is_valid()
 
@@ -362,11 +382,25 @@ class ProductFormulaForm(forms.ModelForm):
 
     def clean(self):
         cleaned_data = super().clean()
+        if cleaned_data["result"] in cleaned_data["products"]:
+            self.add_error(
+                None,
+                _(
+                    "The same product cannot be at the same time "
+                    "the result and a part of the formula."
+                ),
+            )
         prices = [p.selling_price for p in cleaned_data["products"]]
+        special_prices = [p.special_selling_price for p in cleaned_data["products"]]
         selling_price = cleaned_data["result"].selling_price
-        if selling_price > sum(prices):
-            raise ValidationError(
-                _("This formula is more expensive than its constituant products.")
+        special_selling_price = cleaned_data["result"].special_selling_price
+        if selling_price > sum(prices) or special_selling_price > sum(special_prices):
+            self.add_error(
+                "result",
+                _(
+                    "The result cannot be more expensive "
+                    "than the total of the other products."
+                ),
             )
         return cleaned_data
 

counter/models.py

@@ -464,6 +464,7 @@ class ProductFormula(models.Model):
     )
     result = models.OneToOneField(
         Product,
+        related_name="formula",
         on_delete=models.CASCADE,
         verbose_name=_("result product"),
         help_text=_("The product got with the formula."),
@@ -472,6 +473,18 @@ class ProductFormula(models.Model):
     def __str__(self):
         return self.result.name
 
+    @cached_property
+    def max_selling_price(self) -> float:
+        # iterating over all products is less efficient than doing
+        # a simple aggregation, but this method is likely to be used in
+        # coordination with `max_special_selling_price`,
+        # and Django caches the result of the `all` queryset.
+        return sum(p.selling_price for p in self.products.all())
+
+    @cached_property
+    def max_special_selling_price(self) -> float:
+        return sum(p.special_selling_price for p in self.products.all())
+
 
 class CounterQuerySet(models.QuerySet):
     def annotate_has_barman(self, user: User) -> Self: