[FIX] purchase: compute the average of the delays in report

When consulting the Purchase Analysis, the measure "Days to Confirm" may
not be easily understandable

To reproduce the issue:
1. Create a purchase order PO:
    - Order Deadline: <today + 10 days>
    - Add 2 products
2. Confirm PO
3. Purchase > Reporting:
    - Measures: Days to Confirm
    - Group By: Order

Error: For PO, the value of "Days to Confirm" is -20, it should be -10

The report computes the sum of the delay (i.e., "Days to Confirm") of
each purchase order line. Computing an average seems more relevant

A similar flow could be reproduce with the measure "Days to Receive"
(i.e., the difference between the Order Deadline and the Receipt Date)

OPW-2678673

closes odoo/odoo#81053

X-original-commit: da3fa1f8887e06e7a86e761ef844f79cc0d06e6f
Signed-off-by: Arnold Moyaux <arm@odoo.com>
Signed-off-by: Adrien Widart <awt@odoo.com>

addons/purchase/report/purchase_report.py

@@ -34,8 +34,9 @@ class PurchaseReport(models.Model):
     company_id = fields.Many2one('res.company', 'Company', readonly=True)
     currency_id = fields.Many2one('res.currency', 'Currency', readonly=True)
     user_id = fields.Many2one('res.users', 'Purchase Representative', readonly=True)
-    delay = fields.Float('Days to Confirm', digits=(16, 2), readonly=True, help="Amount of time between purchase approval and order by date.")
-    delay_pass = fields.Float('Days to Receive', digits=(16, 2), readonly=True, help="Amount of time between date planned and order by date for each purchase order line.")
+    delay = fields.Float('Days to Confirm', digits=(16, 2), readonly=True, group_operator='avg', help="Amount of time between purchase approval and order by date.")
+    delay_pass = fields.Float('Days to Receive', digits=(16, 2), readonly=True, group_operator='avg',
+                              help="Amount of time between date planned and order by date for each purchase order line.")
     avg_days_to_purchase = fields.Float(
         'Average Days to Purchase', digits=(16, 2), readonly=True, store=False,  # needs store=False to prevent showing up as a 'measure' option
         help="Amount of time between purchase approval and document creation date. Due to a hack needed to calculate this, \

addons/purchase/tests/test_purchase_order_report.py

@@ -3,7 +3,7 @@
 from odoo.addons.account.tests.common import AccountTestInvoicingCommon
 from odoo.tests import Form, tagged
 
-from datetime import datetime
+from datetime import datetime, timedelta
 
 
 @tagged('post_install', '-at_install')
@@ -66,3 +66,25 @@ class TestPurchaseOrderReport(AccountTestInvoicingCommon):
         self.assertEqual(res_product2.qty_ordered, 1.0, 'No conversion needed since product_b is already a dozen')
         # report should show in company currency (amount/rate) = (200/2)
         self.assertEqual(res_product2.price_total, 100.0, 'Currency conversion is not working')
+
+    def test_01_delay_and_delay_pass(self):
+        po_form = Form(self.env['purchase.order'])
+        po_form.partner_id = self.partner_a
+        po_form.date_order = datetime.now() + timedelta(days=10)
+        with po_form.order_line.new() as line:
+            line.product_id = self.product_a
+        with po_form.order_line.new() as line:
+            line.product_id = self.product_b
+        po_form.date_planned = datetime.now() + timedelta(days=15)
+        po = po_form.save()
+
+        po.button_confirm()
+
+        po.flush()
+        report = self.env['purchase.report'].read_group(
+            [('order_id', '=', po.id)],
+            ['order_id', 'delay', 'delay_pass'],
+            ['order_id'],
+        )
+        self.assertEqual(round(report[0]['delay']), -10, msg="The PO has been confirmed 10 days in advance")
+        self.assertEqual(round(report[0]['delay_pass']), 5, msg="There are 5 days between the order date and the planned date")