[FIX] website_sale_coupon: merge 'sibling' discount lines in cart

A discount on products with different taxes will result in as many discount
lines as there is different taxes.

This commit will merge all these lines in a single one on the front-end (cart)
to not change the behavior/display for the end user. This will be purely visual
as it does not affect SO lines.

task-1866977
Related to #2224

models/sale_order.py

@@ -6,6 +6,44 @@ from odoo.http import request
 class SaleOrder(models.Model):
     _inherit = "sale.order"
 
+    @api.one
+    def _compute_website_order_line(self):
+        """ This method will merge multiple discount lines generated by a same program
+            into a single one (temporary line with `new()`).
+            This case will only occur when the program is a discount applied on multiple
+            products with different taxes.
+            In this case, each taxes will have their own discount line. This is required
+            to have correct amount of taxes according to the discount.
+            But we wan't these lines to be `visually` merged into a single one in the
+            e-commerce since the end user should only see one discount line.
+            This is only possible since we don't show taxes in cart.
+            eg:
+                line 1: 10% discount on product with tax `A` - $15
+                line 2: 10% discount on product with tax `B` - $11.5
+                line 3: 10% discount on product with tax `C` - $10
+            would be `hidden` and `replaced` by
+                line 1: 10% discount - $36.5
+
+            Note: The line will be created without tax(es) and the amount will be computed
+                  depending if B2B or B2C is enabled.
+        """
+        super(SaleOrder, self)._compute_website_order_line()
+        for program in self._get_applied_programs_with_rewards_on_current_order():
+            program_lines = self.order_line.filtered(lambda line: line.product_id == program.discount_line_product_id)
+            if len(program_lines) > 1:
+                price_unit = sum(l.price_subtotal if self.env.user.has_group('sale.group_show_price_subtotal') else l.price_total for l in program_lines)
+                self.website_order_line += self.env['sale.order.line'].new({
+                    'product_id': program_lines[0].product_id.id,
+                    'price_unit': price_unit,
+                    'name': program_lines[0].name,
+                    'product_uom_qty': 1,
+                    'product_uom': program_lines[0].product_uom.id,
+                    'order_id': self.id,
+                    'is_reward_line': True,
+                })
+                self.website_order_line -= program_lines
+
+
     def _compute_cart_info(self):
         super(SaleOrder, self)._compute_cart_info()
         for order in self:

static/src/js/website_sale_coupon.test.js

@@ -36,9 +36,9 @@ tour.register('shop_sale_coupon', {
             trigger: '.oe_product_cart a:contains("iPad Mini")',
         },
         {
-            content: "add 3 iPad Mini into cart",
+            content: "add 2 iPad Mini into cart",
             trigger: '#product_details input[name="add_qty"]',
-            run: "text 3",
+            run: "text 2",
         },
         {
             content: "click on 'Add to Cart' button",
@@ -68,31 +68,79 @@ tour.register('shop_sale_coupon', {
             trigger: '.reward_product:contains("10.0 % discount on total amount")',
             run: function () {}, // it's a check
         },
-        /* 2. Add some iPad to get a free one, play with quantity */
+        /* 2. Add an Ice Cream in the cart (which has different tax than iPad) and ensure only one discount line is shown */
+        {
+            content: "go to shop",
+            trigger: '.reward_product:contains("10.0 % discount on total amount")',
+            run: function () {
+                location.href = '/shop'
+            },
+        },
+        {
+            content: "type Ice Cream in search",
+            trigger: 'form input[name="search"]',
+            run: "text Ice Cream",
+        },
+        {
+            content: "start search",
+            trigger: 'form:has(input[name="search"]) .oe_search_button',
+        },
+        {
+            content: "select Ice Cream",
+            extra_trigger: '.oe_search_found', // Wait to be on search results or it sometimes throws concurent error (sent search form + click on product on /shop)
+            trigger: '.oe_product_cart a:containsExact("Ice Cream")',
+        },
+        {
+            content: "click on 'Add to Cart' button",
+            trigger: "a:contains(Add to Cart)",
+        },
+        {
+            content: "check reduction amount got recomputed and merged both discount lines into one only",
+            extra_trigger: '.oe_currency_value:contains("‑74.00")',
+            trigger: '.oe_website_sale .oe_cart',
+            run: function () {}, // it's a check
+        },
+        /* 3. Add some iPad to get a free one, play with quantity */
+        {
+            content: "add one iPad",
+            trigger: '#cart_products input.js_quantity',
+            run: "text 3",
+        },
+        {
+            content: "check reduction amount got recomputed when changing qty",
+            trigger: '.oe_currency_value:contains("‑106.00")',
+            run: function () {}, // it's a check
+        },
         {
             content: "add more iPad Mini into cart",
             trigger: '#cart_products input.js_quantity',
             run: "text 4",
         },
         {
-            content: "check reduction amount got recomputed",
-            extra_trigger: '.oe_currency_value:contains("96.00")', // For some reason, "-96.00" won't work
-            trigger: '.reward_product:contains("Free Product - iPad Mini")',
+            content: "check free product is added",
+            trigger: '#wrap:has(.reward_product:contains("Free Product - iPad Mini"))',
             run: function () {}, // it's a check
         },
         {
             content: "remove one iPad from cart",
-            trigger: '#cart_products a.js_add_cart_json:first',
+            trigger: '#cart_products input.js_quantity[value="4"]',
+            run: "text 3",
         },
         {
             content: "check free product is removed",
             trigger: '#wrap:not(:has(.reward_product:contains("Free Product - iPad Mini")))',
             run: function () {}, // it's a check
         },
-        /* 3. Empty cart and disable coupon */
+        /* 4. Empty cart and disable coupon */
         {
             content: "remove iPad Mini from cart",
-            trigger: '#cart_products input.js_quantity:first',
+            trigger: '#cart_products input.js_quantity[value="3"]',
+            run: "text 0",
+        },
+        {
+            content: "remove Ice Cream from cart",
+            extra_trigger: '#wrap:not(:has(.td-product_name:contains("iPad Mini")))', // wait iPad got removed
+            trigger: '#cart_products input.js_quantity[value="1"]',
             run: "text 0",
         },
         {
@@ -100,7 +148,7 @@ tour.register('shop_sale_coupon', {
             trigger: '#wrap:not(:has(#cart_products))',
             run: function () {}, // it's a check
         },
-        /* 4. Disabled customize options coupon box & 'Show # found'*/
+        /* 5. Disabled customize options coupon box & 'Show # found'*/
         {
             content: "open customize menu",
             extra_trigger: '.oe_website_sale .oe_cart',
@@ -135,7 +183,6 @@ if ('website_sale_options.website_sale' in odoo.__DEBUG__.services) {
               content: "click in modal on 'Proceed to checkout' button",
               trigger: 'a:contains("Proceed to checkout")',
           });
-          break;
       }
   }
 }