[ADD] sale_async_emails: allow sending order status emails asynchronously

This commit adds a new module to allow delaying the sending of sales
order confirmation emails, thus removing a performance bottleneck in the
order confirmation flow.

This is particularly useful for "flash" sales in which a large number of
event tickets are sold in a very short time span. When the emails are
scheduled to be sent right away, the email rendering that is part of the
payment post-processing keeps the worker busy. When the system parameter
`sale.async_emails` is set to `True`, the email rendering is delegated
to a cron, allowing the payment post-processing to execute much faster.

task-3782827

closes odoo/odoo#157612

Signed-off-by: Antoine Vandevenne (anv) <anv@odoo.com>

addons/sale_async_emails/__init__.py

@@ -0,0 +1,3 @@
+# Part of Odoo. See LICENSE file for full copyright and licensing details.
+
+from . import models

addons/sale_async_emails/__manifest__.py

@@ -0,0 +1,14 @@
+# Part of Odoo. See LICENSE file for full copyright and licensing details.
+
+{
+    'name': "Sales - Async Emails",
+    'category': 'Sales/Sales',
+    'summary': "Send order status emails asynchronously",
+    'depends': ['sale'],
+    'data': [
+        'data/ir_config_parameter.xml',
+        'data/ir_cron.xml',
+    ],
+    'auto_install': True,
+    'license': 'LGPL-3',
+}

addons/sale_async_emails/data/ir_config_parameter.xml

@@ -0,0 +1,9 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<odoo noupdate="1">
+
+    <record id="async_emails" model="ir.config_parameter">
+        <field name="key">sale.async_emails</field>
+        <field name="value">False</field>
+    </record>
+
+</odoo>

addons/sale_async_emails/data/ir_cron.xml

@@ -0,0 +1,16 @@
+<?xml version="1.0" encoding="utf-8"?>
+<odoo noupdate="1">
+
+    <record id="sale_async_emails.cron" model="ir.cron">
+        <field name="name">Sales: Send pending emails</field>
+        <field name="model_id" ref="model_sale_order"/>
+        <field name="state">code</field>
+        <field name="code">model._cron_send_pending_emails()</field>
+        <field name="user_id" ref="base.user_root"/>
+        <field name="interval_number">1</field>
+        <field name="interval_type">days</field>
+        <field name="numbercall">-1</field>
+        <field name="active">True</field>
+    </record>
+
+</odoo>

addons/sale_async_emails/models/__init__.py

@@ -0,0 +1,3 @@
+# Part of Odoo. See LICENSE file for full copyright and licensing details.
+
+from . import sale_order

addons/sale_async_emails/models/sale_order.py

@@ -0,0 +1,45 @@
+# Part of Odoo. See LICENSE file for full copyright and licensing details.
+
+from odoo import api, fields, models
+from odoo.tools.misc import str2bool
+
+
+class SaleOrder(models.Model):
+    _inherit = 'sale.order'
+
+    pending_email_template_id = fields.Many2one(
+        string="Pending Email Template",
+        help="The template of the pending email that must be sent asynchronously.",
+        comodel_name='mail.template',
+        ondelete='set null',
+        readonly=True,
+    )
+
+    def _send_order_notification_mail(self, mail_template):
+        """ Override of `sale` to reschedule order status emails to be sent asynchronously. """
+        async_send = str2bool(self.env['ir.config_parameter'].sudo().get_param('sale.async_emails'))
+        cron = async_send and self.env.ref('sale_async_emails.cron', raise_if_not_found=False)
+        if async_send and cron and not self.env.context.get('is_async_email', False):
+            # Schedule the email to be sent asynchronously.
+            self.pending_email_template_id = mail_template
+            cron._trigger()
+        else:  # We are in the cron job, or the user has disabled async emails.
+            super()._send_order_notification_mail(mail_template)  # Send the email synchronously.
+
+    @api.model
+    def _cron_send_pending_emails(self, auto_commit=True):
+        """ Find and send pending order status emails asynchronously.
+
+        :param bool auto_commit: Whether the database cursor should be committed as soon as an email
+                                 is sent. Set to False in unit tests.
+        :return: None
+        """
+        pending_email_orders = self.search([('pending_email_template_id', '!=', False)])
+        for order in pending_email_orders:
+            order = order[0]  # Avoid pre-fetching after each cache invalidation due to committing.
+            order.with_context(is_async_email=True)._send_order_notification_mail(
+                order.pending_email_template_id
+            )  # Asynchronously resume the email sending.
+            order.pending_email_template_id = None
+            if auto_commit:
+                self.env.cr.commit()  # Save progress in case the cron is killed.

addons/sale_async_emails/tests/__init__.py

@@ -0,0 +1,3 @@
+# Part of Odoo. See LICENSE file for full copyright and licensing details.
+
+from . import test_sale_order

addons/sale_async_emails/tests/test_sale_order.py

@@ -0,0 +1,74 @@
+# Part of Odoo. See LICENSE file for full copyright and licensing details.
+
+from unittest.mock import patch
+
+from odoo.tests import tagged
+
+from odoo.addons.sale.tests.common import SaleCommon
+
+
+@tagged('post_install', '-at_install')
+class TestSaleOrder(SaleCommon):
+
+    @classmethod
+    def setUpClass(cls):
+        super().setUpClass()
+        cls.async_emails_cron = cls.env.ref('sale_async_emails.cron')
+        cls.confirmation_email_template = cls.sale_order._get_confirmation_template()
+
+    def test_order_status_email_is_sent_asynchronously(self):
+        """ Test that the order status email is sent asynchronously when configured. """
+        self.env['ir.config_parameter'].set_param('sale.async_emails', 'True')
+
+        with patch(
+            'odoo.addons.sale.models.sale_order.SaleOrder._send_order_notification_mail'
+        ) as sync_email_send_mock:
+            self.sale_order._send_order_notification_mail(self.confirmation_email_template)
+            self.assertTrue(
+                self.sale_order.pending_email_template_id,
+                msg="The email template should be saved on the sales order.",
+            )
+            self.assertTrue(
+                self.env['ir.cron.trigger'].search_count(
+                    [('cron_id', '=', self.async_emails_cron.id)]
+                ),
+                msg="The asynchronous email sending cron should be triggered.",
+            )
+            self.assertEqual(
+                sync_email_send_mock.call_count,
+                0,
+                msg="The email should not also be sent synchronously.",
+            )
+
+    def test_order_status_email_is_sent_synchronously_if_not_configured(self):
+        """ Test that the order status email is sent synchronously when nothing is configured. """
+        self.env['ir.config_parameter'].set_param('sale.async_emails', 'False')
+
+        with patch(
+            'odoo.addons.sale.models.sale_order.SaleOrder._send_order_notification_mail'
+        ) as sync_email_send_mock:
+            self.sale_order._send_order_notification_mail(self.confirmation_email_template)
+            self.assertEqual(
+                sync_email_send_mock.call_count,
+                1,
+                msg="The email should be sent synchronously when the system parameter is not set.",
+            )
+
+    def test_async_emails_cron_does_not_trigger_itself(self):
+        """ Test that the asynchronous email sending cron does not enter an infinite loop. """
+        self.env['ir.config_parameter'].set_param('sale.async_emails', 'True')
+        self.sale_order.pending_email_template_id = self.confirmation_email_template
+
+        with patch(
+            'odoo.addons.sale.models.sale_order.SaleOrder._send_order_notification_mail'
+        ) as sync_email_send_mock:
+            self.env['sale.order']._cron_send_pending_emails(auto_commit=False)
+            self.assertFalse(
+                self.sale_order.pending_email_template_id,
+                msg="The email template should be removed from the sales order.",
+            )
+            self.assertEqual(
+                sync_email_send_mock.call_count,
+                1,
+                msg="The email should be sent synchronously when requested by the cron.",
+            )