[FIX] hr_contract: Reset current contract on stage modification

Purpose
=======

Let's say we have 2 contracts A and B:

A --> Running
B --> Cancelled
contract_id : A

B is set to Running
Contract_id : B

B is set to Cancelled
contract_id : B

In this case, the current contract should be reset to A.

X-original-commit: f736264881cbb3086430ea8cd7dba7c4f5a351f4
Part-of: odoo/odoo#92040

addons/hr_contract/models/hr_contract.py

@@ -215,9 +215,23 @@ class Contract(models.Model):
         return 'wage'
 
     def write(self, vals):
+        old_state = {c.id: c.state for c in self}
         res = super(Contract, self).write(vals)
+        new_state = {c.id: c.state for c in self}
         if vals.get('state') == 'open':
             self._assign_open_contract()
+        today = fields.Date.today()
+        for contract in self:
+            if contract == contract.employee_id.contract_id \
+                and old_state[contract.id] == 'open' \
+                and new_state[contract.id] != 'open':
+                running_contract = self.env['hr.contract'].search([
+                    ('employee_id', '=', contract.employee_id.id),
+                    ('company_id', '=', contract.company_id.id),
+                    ('state', '=', 'open'),
+                ]).filtered(lambda c: c.date_start <= today and (not c.date_end or c.date_end >= today))
+                if running_contract:
+                    contract.employee_id.contract_id = running_contract[0]
         if vals.get('state') == 'close':
             for contract in self.filtered(lambda c: not c.date_end):
                 contract.date_end = max(date.today(), contract.date_start)

addons/hr_contract/tests/test_contract.py

@@ -2,10 +2,13 @@
 # Part of Odoo. See LICENSE file for full copyright and licensing details.
 
 from datetime import datetime, date
+from dateutil.relativedelta import relativedelta
+
 from odoo.exceptions import ValidationError
 from odoo.addons.hr_contract.tests.common import TestContractCommon
+from odoo.tests import tagged
 
-
+@tagged('test_contracts')
 class TestHrContracts(TestContractCommon):
 
     @classmethod
@@ -101,3 +104,15 @@ class TestHrContracts(TestContractCommon):
         # New contract, with gap
         self.create_contract('open', 'normal', date(2016, 1, 1), date(2016, 1, 31))
         self.assertEqual(self.employee.first_contract_date, date(2017, 1, 1))
+
+    def test_current_contract_stage_change(self):
+        today = date.today()
+        contract = self.create_contract('open', 'normal', today + relativedelta(day=1), today + relativedelta(day=31))
+        self.assertEqual(self.employee.contract_id, contract)
+
+        draft_contract = self.create_contract('draft', 'normal', today + relativedelta(months=1, day=1), today + relativedelta(months=1, day=31))
+        draft_contract.state = 'open'
+        self.assertEqual(self.employee.contract_id, draft_contract)
+
+        draft_contract.state = 'draft'
+        self.assertEqual(self.employee.contract_id, contract)