[IMP] point of sale : Show discount when option enabled on pricelist

Many users are confused when using pricelists on the PoS :
When they tick the box "Show discount" on the pricelist, it has no impact when the pricelist is applied on the PoS.
They often report a ticket thinking it's a bug.

It can be useful to show the discount on the PoS when applying a pricelist, when users benefit from a preferred price,
the vendor often wants to show it to the customer.

addons/point_of_sale/static/src/js/models.js

@@ -294,7 +294,7 @@ exports.PosModel = Backbone.Model.extend({
         loaded: function(self, locations){ self.shop = locations[0]; },
     },{
         model:  'product.pricelist',
-        fields: ['name', 'display_name'],
+        fields: ['name', 'display_name', 'discount_policy'],
         domain: function(self) { return [['id', 'in', self.config.available_pricelist_ids]]; },
         loaded: function(self, pricelists){
             _.map(pricelists, function (pricelist) { pricelist.items = []; });
@@ -1306,6 +1306,9 @@ exports.Product = Backbone.Model.extend({
         // because it would cause inconsistencies with the backend for
         // pricelist that have base == 'pricelist'.
         return price;
+    }, 
+    get_discount_policy: function(pricelist){
+        return pricelist.discount_policy;
     },
 });
 
@@ -1780,6 +1783,12 @@ exports.Orderline = Backbone.Model.extend({
             "taxDetails": taxdetail,
         };
     },
+    display_discount_policy: function(){
+        return this.product.get_discount_policy(this.order.pricelist);
+    },
+    get_list_price: function(){
+        return this.product.list_price;
+    },
 });
 
 var OrderlineCollection = Backbone.Collection.extend({
@@ -2450,7 +2459,9 @@ exports.Order = Backbone.Model.extend({
     },
     get_total_discount: function() {
         return round_pr(this.orderlines.reduce((function(sum, orderLine) {
-            return sum + (orderLine.get_unit_price() * (orderLine.get_discount()/100) * orderLine.get_quantity());
+            sum += (orderLine.get_unit_price() * (orderLine.get_discount()/100) * orderLine.get_quantity());
+            sum += ((orderLine.get_list_price() - orderLine.get_unit_price()) * orderLine.get_quantity());
+            return sum
         }), 0), this.pos.currency.rounding);
     },
     get_total_tax: function() {

addons/point_of_sale/static/src/xml/pos.xml

@@ -1284,7 +1284,16 @@
                         </em>
                         <t t-esc="line.get_unit().name" />
                         at
-                        <t t-esc="widget.format_currency(line.get_unit_display_price(),'Product Price')" />
+                        <t t-if="line.display_discount_policy() == 'without_discount' &amp;&amp; 
+                            line.get_unit_display_price() != line.get_list_price()">
+                            <strike>
+                                <t t-esc="widget.format_currency(line.get_list_price(),'Product List Price')" />
+                            </strike> 
+                            <t t-esc="widget.format_currency(line.get_unit_display_price(),'Product Price')" />
+                        </t>
+                        <t t-else="">
+                            <t t-esc="widget.format_currency(line.get_unit_display_price(),'Product Price')" />
+                        </t>
                         /
                         <t t-esc="line.get_unit().name" />
                     </li>
@@ -1472,6 +1481,16 @@
                 <tr t-foreach="orderlines" t-as="orderline">
                     <td>
                         <t t-esc="orderline.get_product().display_name"/>
+                        <t t-if="orderline.display_discount_policy() == 'without_discount' &amp;&amp; 
+                            orderline.get_unit_display_price() != orderline.get_list_price()">
+                            <div class="pos-disc-font">
+                                <strike>
+                                    <t t-esc="widget.format_currency(orderline.get_list_price(),'Product List Price')"/>
+                                </strike>
+                                   -> 
+                                <t t-esc="widget.format_currency(orderline.get_unit_display_price(),'Product Price')"/>
+                            </div>
+                        </t>
                          <t t-if="orderline.get_discount() > 0">
                             <div class="pos-disc-font">
                                 With a <t t-esc="orderline.get_discount()"/>% discount

addons/product/models/product_pricelist.py

@@ -37,6 +37,11 @@ class Pricelist(models.Model):
     country_group_ids = fields.Many2many('res.country.group', 'res_country_group_pricelist_rel',
                                          'pricelist_id', 'res_country_group_id', string='Country Groups')
 
+    discount_policy = fields.Selection([
+        ('with_discount', 'Discount included in the price'),
+        ('without_discount', 'Show public price & discount to the customer')],
+        default='with_discount')
+
     @api.multi
     def name_get(self):
         return [(pricelist.id, '%s (%s)' % (pricelist.name, pricelist.currency_id.name)) for pricelist in self]

addons/sale/models/__init__.py

@@ -3,7 +3,6 @@
 
 from . import analytic
 from . import account_invoice
-from . import product_pricelist
 from . import product_product
 from . import product_template
 from . import res_company

addons/sale/models/product_pricelist.py

@@ -1,13 +0,0 @@
-# -*- coding: utf-8 -*-
-# Part of Odoo. See LICENSE file for full copyright and licensing details.
-
-from odoo import fields, models
-
-
-class ProductPricelist(models.Model):
-    _inherit = 'product.pricelist'
-
-    discount_policy = fields.Selection([
-        ('with_discount', 'Discount included in the price'),
-        ('without_discount', 'Show public price & discount to the customer')],
-        default='with_discount')