[FIX] hw_drivers: Read weight from IoT Scale

We had two issues when reading the weight from a scale connected to
the IoT Box :

When using the '/hw_proxy/scale_read' route, if the same weight was
read twice, the value in PoS was reset to 0.
If the product was placed on the scale before opening the weight
screen, the weight was never read.

closes odoo#46411

Signed-off-by: Quentin Lejeune (qle) <[email protected]>

addons/hw_drivers/drivers/SerialScaleDriver.py

@@ -93,6 +93,7 @@ def scale_read(self):
 
 class ScaleDriver(SerialDriver):
     """Abstract base class for scale drivers."""
+    last_sent_value = None
 
     def __init__(self, device):
         self._device_type = 'scale'
@@ -145,6 +146,7 @@ def _read_once_action(self, data):
         """Reads the scale current weight value and pushes it to the frontend."""
 
         self._read_weight()
+        self.last_sent_value = self.data['value']
         event_manager.device_changed(self)
 
     def _set_zero_action(self, data):
@@ -183,10 +185,11 @@ def _read_weight(self):
         self._connection.write(protocol.measureCommand + protocol.commandTerminator)
         answer = self._get_raw_response(self._connection)
         match = re.search(self._protocol.measureRegexp, answer)
-        self.data = {
-            'value': float(match.group(1)) if match else None,
-            'status': self._status
-        }
+        if match:
+            self.data = {
+                'value': float(match.group(1)),
+                'status': self._status
+            }
 
     # Ensures compatibility with older versions of Odoo
     def _scale_read_old_route(self):
@@ -200,7 +203,8 @@ def _take_measure(self):
 
         with self._device_lock:
             self._read_weight()
-            if self.data['value'] is not None or self._status['status'] == self.STATUS_ERROR:
+            if self.data['value'] != self.last_sent_value or self._status['status'] == self.STATUS_ERROR:
+                self.last_sent_value = self.data['value']
                 event_manager.device_changed(self)
 
 
@@ -274,7 +278,8 @@ def _take_measure(self):
             with self._device_lock:
                 self._read_weight()
                 self._check_last_weight_time()
-                if self.data['value'] is not None or self._status['status'] == self.STATUS_ERROR:
+                if self.data['value'] != self.last_sent_value or self._status['status'] == self.STATUS_ERROR:
+                    self.last_sent_value = self.data['value']
                     event_manager.device_changed(self)
         else:
             time.sleep(0.5)