[REF] sale_margin_tax: refactor for correct accounting

When accounting for margin tax sales, the purchase price
and margin (that form the base for the tax lines) need to be split.
This is because a different tax grid should be applied on both line.
However, Odoo does not provide a way to split the base as it does to
split the tax. Furthermore, adding a 'margin' line type does not work
because the functions that apply the repartition lines etc are basically
impossible to override (they do not provide any hook,
and the arbitrary compute order would make any tentative very brittle).
To avoid these difficulty, another line is created on a "margin" product
(a service), so that both the purchase and the margin can be accounted
as base lines.

This provide the advantage that no further override of basic accounting
functions are needed, and that the tax rate of the margin tax is always
either the initial rate (say 21) or 0.

The downside is that it makes so statistics harder.
Since the margin line and the product lines are linked by a many2one,
it is still possible to extract the relevant info, just a bit harder.

This refactoring also merges the margin behaviour from invoice and sale
into a mixin to avoid desync of the essentially duplicated code
(if only both line/tax fields had the same name...).
This solved a bug where an invoice would think to be margin-based but
without finding a witness margin tax.

Last, this now handles the case where the margin is negative,
in which case no tax is due.

sale_margin_tax/README.rst

@@ -7,7 +7,7 @@ Sale Margin Tax
    !! This file is generated by oca-gen-addon-readme !!
    !! changes will be overwritten.                   !!
    !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
-   !! source digest: sha256:416d0b79eaaa0c0f1e1a0e5a318854e8c96763da78689885a682a6dab2556725
+   !! source digest: sha256:c643555de95864a024f53fe400bc41b671c13907fe80729c92c7365c5de15f28
    !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 
 .. |badge1| image:: https://img.shields.io/badge/maturity-Beta-yellow.png

sale_margin_tax/__manifest__.py

@@ -14,6 +14,7 @@
     "data": [
         "views/tax.xml",
         "data/account_tax.xml",
+        "data/product.xml",
         "reports/report_invoice_document.xml",
     ],
 }

sale_margin_tax/data/account_tax.xml

@@ -2,6 +2,14 @@
 <odoo noupdate="1">
     <record id="tax_group_margin" model="account.tax.group">
         <field name="name">[Margin Tax]</field>
+    </record>
+        <record id="tax_margin_null" model="account.tax">
+        <field name="name">Margin 0%</field>
+        <field name="amount_type">margin</field>
+        <field name="margin_description_template">Margin Tax</field>
+        <field name="amount">0</field>
+        <field name="price_include" eval="True" />
+        <field name="tax_group_id" ref="tax_group_margin" />
     </record>
     <record id="tax_margin" model="account.tax">
         <field name="name">Margin 21%</field>
@@ -10,5 +18,6 @@
         <field name="amount">21</field>
         <field name="price_include" eval="True" />
         <field name="tax_group_id" ref="tax_group_margin" />
+        <field name="margin_base_tax_id" ref="tax_margin_null" />
     </record>
 </odoo>

sale_margin_tax/data/product.xml

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<odoo noupdate="1">
+    <record id="product_margin" model="product.product">
+        <field name="name">Margin on secondhand sales</field>
+        <field name="type">service</field>
+    </record>
+</odoo>

sale_margin_tax/i18n/sale_margin_tax.pot

@@ -0,0 +1,140 @@
+# Translation of Odoo Server.
+# This file contains the translation of the following modules:
+# 	* sale_margin_tax
+#
+msgid ""
+msgstr ""
+"Project-Id-Version: Odoo Server 16.0+e\n"
+"Report-Msgid-Bugs-To: \n"
+"Last-Translator: \n"
+"Language-Team: \n"
+"MIME-Version: 1.0\n"
+"Content-Type: text/plain; charset=UTF-8\n"
+"Content-Transfer-Encoding: \n"
+"Plural-Forms: \n"
+
+#. module: sale_margin_tax
+#: model:ir.model.fields,help:sale_margin_tax.field_account_tax__amount_type
+msgid ""
+"\n"
+"    - Group of Taxes: The tax is a set of sub taxes.\n"
+"    - Fixed: The tax amount stays the same whatever the price.\n"
+"    - Percentage of Price: The tax amount is a % of the price:\n"
+"        e.g 100 * (1 + 10%) = 110 (not price included)\n"
+"        e.g 110 / (1 + 10%) = 100 (price included)\n"
+"    - Percentage of Price Tax Included: The tax amount is a division of the price:\n"
+"        e.g 180 / (1 - 10%) = 200 (not price included)\n"
+"        e.g 200 * (1 - 10%) = 180 (price included)\n"
+"        "
+msgstr ""
+
+#. module: sale_margin_tax
+#: model:ir.model.fields,field_description:sale_margin_tax.field_account_bank_statement_line__has_margin_taxes
+#: model:ir.model.fields,field_description:sale_margin_tax.field_account_move__has_margin_taxes
+#: model:ir.model.fields,field_description:sale_margin_tax.field_account_move_line__has_margin_taxes
+#: model:ir.model.fields,field_description:sale_margin_tax.field_account_payment__has_margin_taxes
+#: model:ir.model.fields,field_description:sale_margin_tax.field_sale_order__has_margin_taxes
+msgid "Has Margin Taxes"
+msgstr ""
+
+#. module: sale_margin_tax
+#: model:ir.model,name:sale_margin_tax.model_account_move
+msgid "Journal Entry"
+msgstr ""
+
+#. module: sale_margin_tax
+#: model:ir.model,name:sale_margin_tax.model_account_move_line
+msgid "Journal Item"
+msgstr ""
+
+#. module: sale_margin_tax
+#: model:account.tax,name:sale_margin_tax.tax_margin
+msgid "Margin 21%"
+msgstr ""
+
+#. module: sale_margin_tax
+#: model:account.tax,margin_mention:sale_margin_tax.tax_margin
+msgid "Margin EN mention"
+msgstr ""
+
+#. module: sale_margin_tax
+#: model:account.tax,margin_description_template:sale_margin_tax.tax_margin
+msgid "Margin Tax"
+msgstr ""
+
+#. module: sale_margin_tax
+#: model:account.tax,margin_name_template:sale_margin_tax.tax_margin
+msgid "Margin: {}%"
+msgstr ""
+
+#. module: sale_margin_tax
+#: model:ir.model.fields,field_description:sale_margin_tax.field_account_tax__margin_mention
+msgid "Mention on invoice"
+msgstr ""
+
+#. module: sale_margin_tax
+#: model:ir.model,name:sale_margin_tax.model_sale_order
+msgid "Sales Order"
+msgstr ""
+
+#. module: sale_margin_tax
+#: model:ir.model,name:sale_margin_tax.model_sale_order_line
+msgid "Sales Order Line"
+msgstr ""
+
+#. module: sale_margin_tax
+#: model:ir.model.fields,field_description:sale_margin_tax.field_account_move_line__price_subtotal_report
+msgid "Subtotal (Report)"
+msgstr ""
+
+#. module: sale_margin_tax
+#: model:ir.model,name:sale_margin_tax.model_account_tax
+msgid "Tax"
+msgstr ""
+
+#. module: sale_margin_tax
+#: model:ir.model.fields,field_description:sale_margin_tax.field_account_tax__amount_type
+msgid "Tax Computation"
+msgstr ""
+
+#. module: sale_margin_tax
+#: model:ir.model.fields.selection,name:sale_margin_tax.selection__account_tax__amount_type__margin
+msgid "Tax on margin"
+msgstr ""
+
+#. module: sale_margin_tax
+#: model:ir.model.fields,field_description:sale_margin_tax.field_account_tax__margin_description_template
+msgid "Template used for the generated tax description"
+msgstr ""
+
+#. module: sale_margin_tax
+#: model:ir.model.fields,field_description:sale_margin_tax.field_account_tax__margin_name_template
+msgid "Template used for the generated tax names"
+msgstr ""
+
+#. module: sale_margin_tax
+#: model:ir.model.fields,help:sale_margin_tax.field_account_tax__margin_mention
+msgid "This mention will be automatically added to the invoice."
+msgstr ""
+
+#. module: sale_margin_tax
+#: model:ir.model.fields,help:sale_margin_tax.field_account_tax__margin_description_template
+msgid "This name can accept the rate as parameter, e.g. use 'Margin: {:.2f}%'"
+msgstr ""
+
+#. module: sale_margin_tax
+#: model:ir.model.fields,help:sale_margin_tax.field_account_tax__margin_name_template
+msgid "This name must accept the rate as parameter, e.g. use 'Margin: {}%'"
+msgstr ""
+
+#. module: sale_margin_tax
+#. odoo-python
+#: code:addons/sale_margin_tax/models/account_tax.py:0
+#, python-format
+msgid "Untaxed Amount"
+msgstr ""
+
+#. module: sale_margin_tax
+#: model:account.tax.group,name:sale_margin_tax.tax_group_margin
+msgid "[Margin Tax]"
+msgstr ""

sale_margin_tax/models/__init__.py

@@ -1,3 +1,4 @@
+from . import margin_mixin
 from . import account_tax
 from . import sale_order_line
 from . import sale_order

sale_margin_tax/models/account_move.py

@@ -2,27 +2,24 @@
 # License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl.html).
 
 
-from odoo import api, fields, models
+from odoo import fields, models
 
 
 class AccountMove(models.Model):
-    _inherit = "account.move"
-
-    has_margin_taxes = fields.Boolean(compute="_compute_has_margin_taxes")
-
-    @api.depends("line_ids.tax_ids")
-    def _compute_has_margin_taxes(self):
-        for move in self:
-            move.has_margin_taxes = any(move.mapped("line_ids.has_margin_taxes"))
-
-    def _get_margin_taxes(self):
-        filter_tax = lambda t: t.amount_type == "margin"  # noqa: E731
-        return self.line_ids.tax_ids.filtered(filter_tax)
-
-    def _get_margin_mention(self):
-        margin_tax = self._get_margin_taxes()[0]
-        margin_tax = margin_tax.with_context(lang=self.partner_id.lang)
-        return margin_tax.margin_mention
+    _name = "account.move"
+    _inherit = ["account.move", "margin.mixin"]
+
+    invoice_report_line_ids = fields.One2many(
+        "account.move.line",
+        "move_id",
+        string="Invoice Report lines",
+        copy=False,
+        readonly=True,
+        domain=[
+            ("display_type", "in", ("product", "line_section", "line_note")),
+            ("is_margin_line", "=", False),
+        ],
+    )
 
     def action_post(self):
         res = super().action_post()

sale_margin_tax/models/account_move_line.py

@@ -6,23 +6,35 @@
 
 
 class AccountMoveLine(models.Model):
-    _inherit = "account.move.line"
+    _name = "account.move.line"
+    _inherit = ["account.move.line", "margin.line.mixin"]
 
-    has_margin_taxes = fields.Boolean(compute="_compute_has_margin_taxes")
     price_subtotal_report = fields.Monetary(
         string="Subtotal (Report)",
         compute="_compute_price_subtotal_report",
         currency_field="currency_id",
     )
-
-    @api.depends("tax_ids")
-    def _compute_has_margin_taxes(self):
-        mg = self.env.ref("sale_margin_tax.tax_group_margin")
-        for line in self:
-            line.has_margin_taxes = mg in line.mapped("tax_ids.tax_group_id")
+    price_unit_report = fields.Monetary(
+        string="Price Unit (Report)",
+        compute="_compute_price_subtotal_report",
+        currency_field="currency_id",
+    )
+    is_margin_line = fields.Boolean(
+        help="True if this line is a margin line.",
+        default=False,
+    )
+    margin_line_id = fields.Many2one(
+        "account.move.line",
+        help="The margin line for this line.",
+    )
 
     @api.depends("price_subtotal", "price_total", "has_margin_taxes")
     def _compute_price_subtotal_report(self):
         for line in self:
-            price = line.price_total if line.has_margin_taxes else line.price_subtotal
+            price = line.price_subtotal
+            price_unit = line.price_unit
+            if line.has_margin_taxes:
+                price = line.price_total + line.margin_line_id.price_total
+                price_unit = price_unit + line.margin_line_id.price_unit
             line.price_subtotal_report = price
+            line.price_unit_report = price_unit

sale_margin_tax/models/account_tax.py

@@ -33,6 +33,10 @@ class AccountTax(models.Model):
 
     _inherit = "account.tax"
 
+    is_margin_tax = fields.Boolean(
+        compute="_compute_is_margin_tax",
+        help="True if this tax is a margin tax.",
+    )
     amount_type = fields.Selection(
         selection_add=[("margin", "Tax on margin")], ondelete={"margin": "cascade"}
     )
@@ -55,6 +59,16 @@ class AccountTax(models.Model):
         default="Margin: {:.2f}%",
         help="This name can accept the rate as parameter, e.g. use 'Margin: {:.2f}%'",
     )
+    margin_base_tax_id = fields.Many2one(
+        "account.tax",
+        string="Base Tax",
+        help="The tax to be applied on the base amount of the margin tax.",
+    )
+
+    def _compute_is_margin_tax(self):
+        margin_group = self.env.ref("sale_margin_tax.tax_group_margin")
+        for tax in self:
+            tax.is_margin_tax = tax.tax_group_id == margin_group
 
     def _get_or_create_margin_tax(self, base_amount, margin):
         """On non margin tax, simply return the tax;

sale_margin_tax/models/margin_mixin.py

@@ -0,0 +1,68 @@
+# Copyright 2023 len-foss/Financial Way
+# License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl.html).
+
+
+from odoo import api, fields, models
+
+
+class MarginLineMixin(models.AbstractModel):
+    _name = "margin.line.mixin"
+    _description = "Margin Line Mixin"
+
+    has_margin_taxes = fields.Boolean(compute="_compute_has_margin_taxes")
+
+    @api.model
+    def _get_tax_field(self):
+        return "tax_id" if self._name == "sale.order.line" else "tax_ids"
+
+    @api.model
+    def _get_margin_depends(self):
+        tax_field = self._get_tax_field()
+        return [tax_field + ".is_margin_tax"]
+
+    def _get_line_taxes(self):
+        tax_field = self._get_tax_field()
+        return self[tax_field]
+
+    def _get_margin_taxes(self):
+        taxes = self._get_line_taxes()
+        return taxes.filtered("is_margin_tax")
+
+    @api.depends(lambda self: self._get_margin_depends())
+    def _compute_has_margin_taxes(self):
+        for line in self:
+            line.has_margin_taxes = line._get_margin_taxes()
+
+
+class MarginMixin(models.AbstractModel):
+    _name = "margin.mixin"
+    _description = "Margin Mixin"
+
+    has_margin_taxes = fields.Boolean(compute="_compute_has_margin_taxes")
+
+    @api.model
+    def _get_margin_depends(self):
+        line_field = self._get_lines_field()
+        return [line_field + ".has_margin_taxes"]
+
+    def _get_lines_field(self):
+        return "order_line" if self._name == "sale.order" else "line_ids"
+
+    def _get_lines(self):
+        line_field = self._get_lines_field()
+        return self[line_field]
+
+    @api.depends(lambda self: self._get_margin_depends())
+    def _compute_has_margin_taxes(self):
+        for record in self:
+            lines = record._get_lines()
+            record.has_margin_taxes = any(lines.mapped("has_margin_taxes"))
+
+    def _get_margin_taxes(self):
+        lines = self._get_lines()
+        return lines._get_margin_taxes()
+
+    def _get_margin_mention(self):
+        margin_tax = self._get_margin_taxes()[0]
+        margin_tax = margin_tax.with_context(lang=self.partner_id.lang)
+        return margin_tax.margin_mention