fix: correct Blynclight BitField offsets and move state policy to _on (#708)

OffBit, DimBit, FlashBit, and SpeedField had bit offsets one higher
than correct. Worked by accident due to the Word layout, but the
off-by-one was wrong per the protocol spec.

Moves off/dim/flash state management from __bytes__ (a serialization
method with side effects) into _on where it belongs. The off bit is
now set when _on receives a black color, and cleared when lit. Flash
and dim are cleared on turn-off.

__bytes__ is now a pure serializer with no side effects.

Tests updated to exercise state through _on instead of bytes().

Relates to: busylight-core #61 (Blynclight off-bit state)
Dispatch #75

Authored by Jny

Author: JnyJny

packages/busylight-core/src/busylight_core/vendors/embrava/blynclight_base.py

@@ -20,11 +20,6 @@ def state(self) -> "BlynclightState":
 
     def __bytes__(self) -> bytes:
         """Return the device state as bytes for USB communication."""
-        if not self.is_lit:
-            self.state.off = True
-            self.state.flash = False
-            self.state.dim = False
-
         return bytes([0, *bytes(self.state), 0xFF, 0x22])
 
     @property
@@ -45,6 +40,12 @@ def _on(self, color: tuple[int, int, int], led: int = 0) -> None:
         """
         with self.batch_update():
             self.color = color
+            if not self.is_lit:
+                self.state.off = True
+                self.state.dim = False
+                self.state.flash = False
+            else:
+                self.state.off = False
 
     def dim(self) -> None:
         """Dim the current light color."""

packages/busylight-core/src/busylight_core/vendors/embrava/implementation/blynclight_fields.py

@@ -33,28 +33,28 @@ class OffBit(BitField):
     """1-bit field to turn light off, clear to turn light on."""
 
     def __init__(self) -> None:
-        super().__init__(17, 1)
+        super().__init__(16, 1)
 
 
 class DimBit(BitField):
     """1-bit field to dim light, clear to brighten light."""
 
     def __init__(self) -> None:
-        super().__init__(18, 1)
+        super().__init__(17, 1)
 
 
 class FlashBit(BitField):
     """1-bit field to flash light, clear to stop flashing."""
 
     def __init__(self) -> None:
-        super().__init__(19, 1)
+        super().__init__(18, 1)
 
 
 class SpeedField(BitField):
     """3-bit field to set flash speed: 1=slow, 2=medium, 4=fast."""
 
     def __init__(self) -> None:
-        super().__init__(20, 3)
+        super().__init__(19, 3)
 
 
 class RepeatBit(BitField):

packages/busylight-core/tests/test_vendor_embrava_blynclight.py

@@ -88,45 +88,48 @@ def test_bytes_conversion_light_on(self) -> None:
             assert len(result) == 9  # Expected struct size
             assert blynclight.state.off == 0  # Should set off=False when lit
 
-    def test_bytes_conversion_light_off(self) -> None:
-        """Test __bytes__ method when light is off."""
+    def test_on_sets_off_bit_when_color_is_black(self) -> None:
+        """Test on() sets off=True when color is black (not lit)."""
         mock_hardware = create_mock_blynclight_hardware()
 
-        with patch.object(mock_hardware, "acquire"), patch.object(Blynclight, "reset"):
+        with (
+            patch.object(mock_hardware, "acquire"),
+            patch.object(Blynclight, "reset"),
+            patch.object(Blynclight, "update"),
+        ):
             blynclight = Blynclight(mock_hardware)
-            blynclight.color = (0, 0, 0)  # Set RGB to zero - this makes is_lit False
-
-            result = bytes(blynclight)
+            blynclight.on((0, 0, 0))  # Black color - not lit
 
-            assert isinstance(result, bytes)
-            assert blynclight.state.off == 1  # Should set off=True when not lit
+            assert blynclight.state.off == 1
 
-    def test_bytes_flash_disabled_when_off(self) -> None:
-        """Test that flash is disabled when light is off."""
+    def test_on_clears_flash_when_off(self) -> None:
+        """Test that on() clears flash when light is off."""
         mock_hardware = create_mock_blynclight_hardware()
 
-        with patch.object(mock_hardware, "acquire"), patch.object(Blynclight, "reset"):
+        with (
+            patch.object(mock_hardware, "acquire"),
+            patch.object(Blynclight, "reset"),
+            patch.object(Blynclight, "update"),
+        ):
             blynclight = Blynclight(mock_hardware)
             blynclight.state.flash = True
-            blynclight.color = (0, 0, 0)  # Set RGB to zero - this makes is_lit False
-
-            bytes(blynclight)
+            blynclight.on((0, 0, 0))  # Black color - not lit
 
-            # Flash should be disabled when light is off
             assert blynclight.state.flash == 0
 
-    def test_bytes_dim_disabled_when_off(self) -> None:
-        """Test that dim is disabled when light is off."""
+    def test_on_clears_dim_when_off(self) -> None:
+        """Test that on() clears dim when light is off."""
         mock_hardware = create_mock_blynclight_hardware()
 
-        with patch.object(mock_hardware, "acquire"), patch.object(Blynclight, "reset"):
+        with (
+            patch.object(mock_hardware, "acquire"),
+            patch.object(Blynclight, "reset"),
+            patch.object(Blynclight, "update"),
+        ):
             blynclight = Blynclight(mock_hardware)
             blynclight.state.dim = True
-            blynclight.color = (0, 0, 0)  # Set RGB to zero - this makes is_lit False
-
-            bytes(blynclight)
+            blynclight.on((0, 0, 0))  # Black color - not lit
 
-            # Dim should be disabled when light is off
             assert blynclight.state.dim == 0
 
     def test_bytes_flash_preserved_when_on(self) -> None:
@@ -326,17 +329,18 @@ def test_state_interactions(self) -> None:
         """Test interactions between different state settings."""
         mock_hardware = create_mock_blynclight_hardware()
 
-        with patch.object(mock_hardware, "acquire"), patch.object(Blynclight, "reset"):
+        with (
+            patch.object(mock_hardware, "acquire"),
+            patch.object(Blynclight, "reset"),
+            patch.object(Blynclight, "update"),
+        ):
             blynclight = Blynclight(mock_hardware)
 
-            # Test flash and dim both set, then light turned off
+            # Test flash and dim both set, then light turned off via on()
             blynclight.state.flash = True
             blynclight.state.dim = True
-            blynclight.color = (0, 0, 0)  # Set color to zero to make is_lit False
-
-            bytes(blynclight)
+            blynclight.on((0, 0, 0))  # Turn off clears flash and dim
 
-            # Both should be disabled when light is off
             assert blynclight.state.flash == 0
             assert blynclight.state.dim == 0