[FIX] sale_coupon: fix some use cases

Some use cases were wrong, this commit attempt to fix those.
Here is the most important ones:

1. Discount was offered on free product 'value' aswell

Cart: 4 iPad Mini + one free offered + 10% discount

                      |    qty | unit value |   line total |
	----------------------------------------------------
	iPad Mini     |      4 |        320 |         1280 |
	- 10% discount|      1 |        128 |          128 |
	= 1152
	- free product|      1 |        320 |          320 |
	= 832

Should be

	              |    qty | unit value |   line total |
	----------------------------------------------------
	iPad Mini     |      4 |        320 |         1280 |
	- free product|      1 |        320 |          320 |
	= 960
	- 10% discount|      1 |         96 |           96 |
	= 864

The error result is $32 which is the 10% discount applied on the free iPad.

2. Decreasing product quantity below the minimum threshold to be elligible for
the promotion doesn't remove the product

  - (With a promotion offering a free iPad when you buy 3 (fourth is free))
  - Create a quotation with 3 iPads Mini, save and update promotions, you don't
    have a free one, which is 'correct'
  - Edit, change the quantity to 4 iPads, save, update promotions, you have a
    free iPad (reduced from total), still correct
  - Edit, change the quantity back to 3 ipad, update ptomotions, you still have
    a free iPad even if you only bought 3 of them (the way it is designed, the
    free iPad should only appears when you order your fourth).

The error result in a 'loss' of $320 since at the end we are offering a free
iPad and the user only pays 2 instead of 3.

3. Free product will be considered as regular product when updating quantity
of regular product afterward

This error is kind of exponential: the more you play with the flow explained
bellow, the more incorrect it becomes.

Buy 100 iPads, get 25 free iPads.
Then set quantity (on regular iPad) to 50, it will recalculate the amount of
free iPad thinking the 25 previous free iPads are regular iPad.
(50 + 25) = 75 regular iPads = 18 free iPads (25 previous free iPads were
wrongly used for the calculation but they are simply gone at this point).
Cart is now 50 regular iPads and 18 free one, total: $10240 (50×320 - 18×320).
It should be 12 free iPads, not 18, so $12160 (50×320 − 12×320)

The error result in a loss of $1920: ~ 20% of the total amount of the order.

This error will also appear the other way around if you add quantity instead of
removing some.
Playing with this error multiple times, you can arrive to a negative total
(more free than paid products), 0 total or very low total ($320 for 100 iPads).

4. Free product are wrongly calculated, user get too many of them

  - Create a quotation with 10 iPads, you get 3 free iPads instead of 2
  - Indeed, your first 4 iPads should give you a free one
  - Your next 4 iPads should give you a second one (you got 8)
  - The last 2 (to reach 10) are not enough to give you a third free iPad

The error result in a loss of $320 out of a total of 2560$ which is ~ 15%

5. Paid/regular products related to a promotion won't be taken into account
 when checking if you have the minimum amount threshold to apply the promotion

Promotion: 3 Computer Case(25$) = 1 Free Little Server (40.000$), auto applied
  -Have a cart with 3 'Computer Case' and 2 'Little Server'
  -One little server of the 2 is free (because you have 3 computer cases)
  -You so pay 3x25 + 1x40000 which is 40075$
  -Create a promo code that will give you 10% discount if you bought over $2000
  -You won't get the reduction even if you bought over $40.000 because the
   little server you pay is considered as the product of the reward product
   even if you dont have it free. It doesn't check how many regular product
   should be substracted according to the number of free product you have

6. Wrong product is checked for the required quantity to apply the promotion

Promotion: 3 iPads Mini ($320) = 1 free Bose Mini Bluetooth Speaker ($247)

  - Add 8 iPads Mini and a Bose Mini Bluetooth Speaker to your cart
  - The system should give you a free Bose Mini Bluetooth Speaker since you
    only have one regular Bose
  - But the system is giving you 2 free Bose Mini Bluetooth Speaker

Cart is: 8 iPad ($2560), 1 Bose ($247), 2 free Bose (-$496)
The system think that it should give you 2 free Bose because you are eligible
to, since you have 8 iPad, but it doesn't check that you have enough regular
Bose.

The error result in a loss of $247 out of a total of $2311

7. Auto applying promotion are not applied if there is already a promotion code
Promotion:
  - Free iPad Mini if you buy 3 (so the fourth become free), auto applied
  - 10% discount with code '10pc'

  - Add 4 iPads Mini, you got a free one
  - Set quantity back to 1 iPad, free one is gone
  - Add code 10pc, you got a 10% reduction line
  - Set quantity to 4 iPads again, you dont have the free iPad since there is
    already a promo code

This could make sense but it is not coherent since the 2 promotions would be
applied if they were both on auto apply mode.
Note:
  - If both promotions are on auto apply, you will get both
  - If 10% discount becomes auto applied and iPad promotion now has a code
    (reverse situation) it will work

8. Discount is only applied on untaxed amount, not on tax

Discount will ONLY be calculated on the untaxed amount and then reduced from
the sale order/cart total.
The taxes would be unchanged and charged like the product was full price.

Let's illustrate with a $100 product, a 15% tax and a 20% discount:

1. Tax included:
$100   : Product with 15% included taxes
$86.96 : Untaxed product
$13.04 : Taxes

After aplying 20% discount, result should be:
$80    : Product with 15% included taxes
$69.57 : Untaxed product
$10.43 : Taxes

Instead we have:
$82.61 : Product with 15% included taxes
$69.57 : Untaxed product
$13.04 : Taxes

There is a difference of $2.61 which is the result of the taxes not being
discounted: 13.04-10.43 = 2.61

2. Tax excluded:
$115 : Product with 15% excluded taxes
$100 : Untaxed product
$15  : Taxes

After aplying 20% discount, result should be:
$92  : Product with 15% included taxes
$80  : Untaxed product
$12  : Taxes

Instead we have:
$95  : Product with 15% included taxes
$80  : Untaxed product
$15  : Taxes

There is a difference of $3 which is the result of the taxes not being
discounted: 15-12 = 3

9. Taxes of the free shipping reward would be considered as paid value when
checking if required threshold is met.

------------------------------------------

Not really a bug, more an improvement:

1. The way it was designed, the rule_minimum_amount would check if your order
amount was over the required threshold to be eligible for the reward.
'Problem' is that it your order has already a discount (eg: 10%), it would
check if the price without discount is above the required amount.
I don't think it is coherent, let's illustrate:
  - First pomotion (auto applied): 1 iPad Mini for free if you buy over $2000
  - Second promotion (auto applied): 50% on order

If an user is buying for $2000, he is actually paying $1000 thanks to the 50%
discount.
Should we give him the free iPad?
The current implementation is giving it, which is not convenient IMHO.
Now, we use the amount the user really pay to check if he is elligible.

2. Since new promotions have the same sequence by default, they will be sorted
and applied by their creation order. This will result in inconsistent behavior:
  - Promotion 1 : 10% discount
  - Promotion 2 : free shipping
  - Both promotion are auto applied and need a minimum of $872.73 tax excluded

Let's illustrate with a $873 order:
If the promotions were created in the order above, you won't get both rewards
since the 10% discount will be applied first and will lower the SO total.
The order will then fall below the $872.73 required amount and won't be
eligible for the free shipping.
But if you created the free shipping promotion before the discount one, you
will be eligible for both since the free shipping will be applied first and
won't change the SO total.

To keep the same behavior independently of the promotion creation order, we now
sort by reward_type ('discount' > 'free_shipping' > 'product' to apply
discounts first.
This is better IMHO, since you want to give promotions with a minimum threshold
ONLY if the user really pays that amount. It wouldn't be the case if the total
is checked before the discount is applied.

models/sale_coupon.py

@@ -52,15 +52,12 @@ class SaleCoupon(models.Model):
     def _check_coupon_code(self, order):
         message = {}
         applicable_programs = order._get_applicable_programs()
-        amount_total = order.amount_untaxed + order.reward_amount
-        if self.program_id.rule_minimum_amount_tax_inclusion == 'tax_included':
-            amount_total += order.amount_tax
         if self.state in ('used', 'expired') or \
            (self.expiration_date and self.expiration_date < order.date_order):
             message = {'error': _('This coupon %s has been used or is expired.') % (self.code)}
         elif self.state == 'reserved':
             message = {'error': _('This coupon %s exists but the origin sales order is not validated yet.') % (self.code)}
-        elif self.program_id._compute_program_amount('rule_minimum_amount', order.currency_id) > amount_total:
+        elif not self.program_id._filter_on_mimimum_amount(order):
             message = {'error': _('A minimum of %s %s should be purchased to get the reward') % (self.program_id.rule_minimum_amount, self.program_id.currency_id.name)}
         elif not self.program_id.active:
             message = {'error': _('The coupon program for %s is in draft or closed state') % (self.code)}

models/sale_coupon_program.py

@@ -10,7 +10,10 @@ class SaleCouponProgram(models.Model):
     _name = 'sale.coupon.program'
     _description = "Sales Coupon Program"
     _inherits = {'sale.coupon.rule': 'rule_id', 'sale.coupon.reward': 'reward_id'}
-    _order = "sequence"
+    # We should apply 'discount' promotion first to avoid offering free product when we should not.
+    # Eg: If the discount lower the SO total below the required threshold
+    # Note: This is only revelant when programs have the same sequence (which they have by default)
+    _order = "sequence, reward_type"
 
     name = fields.Char(required=True, translate=True)
     active = fields.Boolean('Active', default=True, help="A program is available for the customers when active")
@@ -129,12 +132,9 @@ class SaleCouponProgram(models.Model):
     def _check_promo_code(self, order, coupon_code):
         message = {}
         applicable_programs = order._get_applicable_programs()
-        amount_total = order.amount_untaxed + order.reward_amount
-        if self.rule_minimum_amount_tax_inclusion == 'tax_included':
-            amount_total += order.amount_tax
         if self.maximum_use_number != 0 and self.order_count >= self.maximum_use_number:
             message = {'error': _('Promo code %s has been expired.') % (coupon_code)}
-        elif self._compute_program_amount('rule_minimum_amount', order.currency_id) > amount_total:
+        elif not self._filter_on_mimimum_amount(order):
             message = {'error': _('A minimum of %s %s should be purchased to get the reward') % (self.rule_minimum_amount, self.currency_id.name)}
         elif self.promo_code and self.promo_code == order.promo_code:
             message = {'error': _('The promo code is already applied on this order')}
@@ -144,7 +144,7 @@ class SaleCouponProgram(models.Model):
             message = {'error': _('Promo code is invalid')}
         elif self.rule_date_from and self.rule_date_from > order.date_order or self.rule_date_to and order.date_order > self.rule_date_to:
             message = {'error': _('Promo code is expired')}
-        elif order.promo_code:
+        elif order.promo_code and self.promo_code_usage == 'code_needed':
             message = {'error': _('Promotionals codes are not cumulable.')}
         elif self._is_global_discount_program() and order.applied_coupon_ids.mapped('program_id').filtered(lambda program: program._is_global_discount_program()):
             message = {'error': _('Global discounts are not cumulable.')}
@@ -165,12 +165,16 @@ class SaleCouponProgram(models.Model):
 
     @api.model
     def _filter_on_mimimum_amount(self, order):
-        # To get actual total amount of SO without any reward or discount
-        discounted_amount = sum(order.order_line.filtered(lambda line: line.is_reward_line).mapped('price_total'))
-        untaxed_amount = order.amount_untaxed - discounted_amount
+        untaxed_amount = order.amount_untaxed
+        tax_amount = order.amount_tax
+
+        # Some lines should not be considered when checking if threshold is met like delivery
+        untaxed_amount -= sum([line.price_subtotal for line in order._get_no_effect_on_threshold_lines()])
+        tax_amount -= sum([line.price_tax for line in order._get_no_effect_on_threshold_lines()])
+
         return self.filtered(lambda program:
             program.rule_minimum_amount_tax_inclusion == 'tax_included' and
-            program._compute_program_amount('rule_minimum_amount', order.currency_id) <= untaxed_amount + order.amount_tax or
+            program._compute_program_amount('rule_minimum_amount', order.currency_id) <= untaxed_amount + tax_amount or
             program.rule_minimum_amount_tax_inclusion == 'tax_excluded' and
             program._compute_program_amount('rule_minimum_amount', order.currency_id) <= untaxed_amount)
 

models/sale_order.py

@@ -1,7 +1,7 @@
 # -*- coding: utf-8 -*-
 # Part of Odoo. See LICENSE file for full copyright and licensing details.
 
-from odoo import api, fields, models
+from odoo import api, fields, models, _
 
 
 class SaleOrder(models.Model):
@@ -19,7 +19,15 @@ class SaleOrder(models.Model):
     @api.depends('order_line')
     def _compute_reward_total(self):
         for order in self:
-            order.reward_amount = sum([line.price_subtotal for line in order.order_line.filtered(lambda line: line.is_reward_line)])
+            order.reward_amount = sum([line.price_subtotal for line in order._get_reward_lines()])
+
+    def _get_no_effect_on_threshold_lines(self):
+        self.ensure_one()
+        lines = self.env['sale.order.line']
+        # Do not count already applied promo_code discount; Do not substract itself
+        if self.code_promo_program_id and self.code_promo_program_id.reward_type == 'discount':
+            lines = self.order_line.filtered(lambda l: l.product_id == self.code_promo_program_id.discount_line_product_id)
+        return lines
 
     @api.multi
     def recompute_coupon_lines(self):
@@ -30,7 +38,7 @@ class SaleOrder(models.Model):
 
     def copy(self, default=None):
         order = super(SaleOrder, self).copy(dict(default or {}, order_line=False))
-        for line in self.order_line.filtered(lambda line: not line.is_reward_line):
+        for line in self._get_reward_lines():
             line.copy({'order_id': order.id})
         order.with_context(sale_coupon_no_loop=False)._create_new_no_code_promo_reward_lines()
         return order
@@ -72,7 +80,7 @@ class SaleOrder(models.Model):
         if program._is_valid_product(program.reward_product_id):
             reward_product_qty = max_product_qty // (program.rule_min_quantity + program.reward_product_quantity)
         else:
-            reward_product_qty = max_product_qty
+            reward_product_qty = min(max_product_qty, self.order_line.filtered(lambda x: x.product_id == program.reward_product_id).product_uom_qty)
 
         reward_qty = min(int(int(max_product_qty / program.rule_min_quantity) * program.reward_product_quantity), reward_product_qty)
         # Take the default taxes on the reward product, mapped with the fiscal position
@@ -84,14 +92,16 @@ class SaleOrder(models.Model):
             'price_unit': - price_unit,
             'product_uom_qty': reward_qty,
             'is_reward_line': True,
-            'name': "Free Product - " + program.reward_product_id.name,
+            'name': _("Free Product") + " - " + program.reward_product_id.name,
             'product_uom': program.reward_product_id.uom_id.id,
             'tax_id': [(4, tax.id, False) for tax in taxes],
         }
 
-    def _get_order_lines_untaxed_amount(self):
-        """ Returns the untaxed sale order total amount without the rewards amount"""
-        return sum([x.price_subtotal for x in self.order_line.filtered(lambda x: not x.is_reward_line)])
+    def _get_order_lines_tax_included_amount(self):
+        """ Returns the taxes included sale order total amount without the rewards amount"""
+        free_reward_product = self.env['sale.coupon.program'].search([('reward_type', '=', 'product')]).mapped('discount_line_product_id')
+        return sum([x.price_total for x in self.order_line.filtered(lambda x: not x.is_reward_line or x.product_id in free_reward_product)])
+
 
     def _get_reward_values_discount_fixed_amount(self, program):
         total_amount = sum(self.order_line.filtered(lambda line: not line.is_reward_line).mapped('price_total'))
@@ -106,15 +116,15 @@ class SaleOrder(models.Model):
 
     def _get_reward_values_discount_percentage(self, program):
         discount_amount = 0
-        amount_untaxed = self._get_order_lines_untaxed_amount()
+        amount_total = self._get_order_lines_tax_included_amount()
         max_amount = program._compute_program_amount('discount_max_amount', self.currency_id)
         if program.discount_apply_on == 'on_order':
-            discount_amount = amount_untaxed * (program.discount_percentage / 100)
+            discount_amount = amount_total * (program.discount_percentage / 100)
         if program.discount_apply_on == 'cheapest_product':
             unit_prices = self._get_lines_unit_prices()
             discount_amount = (min(unit_prices) * (program.discount_percentage) / 100)
         if program.discount_apply_on == 'specific_product':
-            discount_amount = sum([(x.price_unit * x.product_uom_qty) * (program.discount_percentage / 100) for x in self.order_line.filtered(
+            discount_amount = sum([(x.price_total * x.product_uom_qty) * (program.discount_percentage / 100) for x in self.order_line.filtered(
                 lambda x: x.product_id == program.discount_specific_product_id)])
         if program.discount_max_amount and discount_amount > max_amount:
             discount_amount = max_amount
@@ -126,7 +136,7 @@ class SaleOrder(models.Model):
         elif program.discount_type == 'fixed_amount':
             discount_amount = self._get_reward_values_discount_fixed_amount(program)
         return {
-            'name': "Discount: %s" % (program.name),
+            'name': _("Discount: ") + program.name,
             'product_id': program.discount_line_product_id.id,
             'price_unit': - discount_amount,
             'product_uom_qty': 1.0,
@@ -155,7 +165,10 @@ class SaleOrder(models.Model):
             'discount_line_product_id': program.discount_line_product_id.id
         })
         self.generated_coupon_ids |= coupon
-        subject = '%s, a coupon has been generated from your order %s' % (self.partner_id.name, self.name)
+        subject = _('%(partner_name)s, a coupon has been generated from your order %(order_name)s') % {
+            'partner_name': self.partner_id.name,
+            'order_name': self.name,
+        }
         body = self.env.ref('sale_coupon.sale_coupon_created_coupon_email_template').render({
             'code': coupon.code,
             'reward_description': coupon.program_id.discount_line_product_id.name
@@ -183,7 +196,7 @@ class SaleOrder(models.Model):
             ('promo_code_usage', '=', 'no_code_needed'),
             # ('promo_applicability', '=', 'on_current_order')
         ])._filter_programs_from_common_rules(self)
-        return programs.sorted('sequence')
+        return programs
 
     def _create_new_no_code_promo_reward_lines(self):
         '''Apply new programs that are applicable'''