[IMP] pos: better default start date

1;2802;0c
now() was bad as it excluded the orders of the latest session
midnight is not good either because
- midnight server != midnight user (timezone)
- some restaurant, bars start in the evening and finish after midgnight

With this default, with 4 sessions:
- POS A, start 2016-12-21 08:05:36
- POS B, start 2016-12-21 08:08:11
- POS A, start 2016-12-22 08:17:51
- POS B, start 2016-12-21 08:19:23

The default start date will be 2016-12-22 08:17:51 to include all orders of
both sessions.

addons/point_of_sale/wizard/pos_details.py

@@ -9,7 +9,25 @@ class PosDetails(models.TransientModel):
     _name = 'pos.details.wizard'
     _description = 'Open Sale Details Report'
 
-    start_date = fields.Datetime(required=True, default=fields.Datetime.now)
+    def _default_start_date(self):
+        """ Find the earliest start_date of the latests sessions """
+        # restrict to configs available to the user
+        config_ids = self.env['pos.config'].search([]).ids
+        # exclude configs has not been opened for 2 days
+        self.env.cr.execute("""
+            SELECT
+            max(start_at) as start,
+            config_id
+            FROM pos_session
+            WHERE config_id = ANY(%s)
+            AND start_at > (NOW() - INTERVAL '2 DAYS')
+            GROUP BY config_id
+        """, (config_ids,))
+        latest_start_dates = [res['start'] for res in self.env.cr.dictfetchall()]
+        # earliest of the latest sessions
+        return latest_start_dates and min(latest_start_dates) or fields.Datetime.now()
+
+    start_date = fields.Datetime(required=True, default=_default_start_date)
     end_date = fields.Datetime(required=True, default=fields.Datetime.now)
     pos_config_ids = fields.Many2many('pos.config', 'pos_detail_configs',
         default=lambda s: s.env['pos.config'].search([]))