[FIX] sale_product_pack: adjust discount formula for detailed packs

The discount formula for detailed packs has been updated to address inconsistencies when pricelists explicitly display discounts.

The new formula ensures accurate representation of the combined discount by correctly factoring in both the parent pack and component discounts.

Example:

Parent pack discount: 5%
Component A discount: 10%
Component B discount: 20%
The issue occurred when pricelists explicitly displayed discounts. For example, when the pricelist showed the discount percentage but did not properly calculate the combined effect of the pack discount and the component discounts, the displayed total was inconsistent.

With the new formula:

Component A effective discount:
100.0 - ((100.0 - 5.0) * (100.0 - 10.0) / 100.0) = 14.5%
Component B effective discount:
100.0 - ((100.0 - 5.0) * (100.0 - 20.0) / 100.0) = 24.0%
This ensures that when pricelists explicitly show discounts, the displayed percentage matches the calculated prices.

Author: lef-adhoc

Diff for: sale_product_pack/models/sale_order_line.py

@@ -153,7 +153,9 @@ def _get_pack_line_discount(self):
         if self.pack_parent_line_id.pack_component_price == "detailed":
             for pack_line in self.pack_parent_line_id.product_id.pack_line_ids:
                 if pack_line.product_id == self.product_id:
-                    discount = pack_line.sale_discount
+                    discount = 100.0 - (
+                        (100.0 - self.discount) * (100.0 - pack_line.sale_discount) / 100.0
+                    )
                     break
         return discount
 

Diff for: sale_product_pack/tests/test_sale_product_pack.py

@@ -335,3 +335,37 @@ def test_create_several_lines_03(self):
         self.assertEqual(sequence_tp, self.sale_order.order_line[2].sequence)
         self.assertEqual(sequence_tp, self.sale_order.order_line[3].sequence)
         self.assertEqual(self.sale_order.order_line[4].product_id, product)
+
+    def test_compute_discount_for_detailed_packs(self):
+        group_discount = self.env.ref("sale.group_discount_per_so_line")
+        self.env.user.write({"groups_id": [(4, group_discount.id)]})
+        product_pack = self.env.ref("product_pack.product_pack_cpu_detailed_components")
+        sale_order = self.env["sale.order"].create(
+            {
+                "partner_id": self.env.ref("base.res_partner_12").id,
+                "pricelist_id": self.discount_pricelist.id,
+                "order_line": [
+                    (
+                        0,
+                        0,
+                        {
+                            "product_id": product_pack.id,
+                            "product_uom_qty": 1,
+                            "pack_component_price": "detailed",
+                        },
+                    )
+                ],
+            }
+        )
+        sale_order.action_update_prices()
+        pack_lines = sale_order.order_line.filtered(
+            lambda line: line.pack_parent_line_id
+        )
+        self.assertEqual(
+            len(pack_lines), 3, "Expected 3 lines for the components of the pack."
+        )
+        self.assertEqual(
+            pack_lines.mapped("discount"),
+            [19, 19, 10],
+            "Discounts for the pack lines are not calculated correctly.",
+        )