Refactor DymoLabeler classes

Fix a bug in which we had a constant for vertical margin, which is not true, since for every label width the margin is different.
Remove labeler state from DymoLabelerFunctions (it no longer initialized with current tape size).
Store default tape sizes in the labeler class, instead of in the GUI's code.

src/dymoprint/cli/cli.py

@@ -295,17 +295,16 @@ def run():
         else None
     )
 
+    dymo_labeler = DymoLabeler(tape_size_mm=args.tape_size_mm)
     render_engine = HorizontallyCombinedRenderEngine(render_engines)
     render_kwargs = dict(
         render_engine=render_engine,
         justify=args.justify,
         visible_horizontal_margin_px=margin_px,
-        labeler_margin_px=DymoLabeler.get_labeler_margin_px(),
+        labeler_margin_px=dymo_labeler.labeler_margin_px,
         max_width_px=max_payload_len_px,
         min_width_px=min_payload_len_px,
     )
-
-    dymo_labeler = DymoLabeler(tape_size_mm=args.tape_size_mm)
     render_context = RenderContext(height_px=dymo_labeler.height_px)
 
     # print or show the label

src/dymoprint/gui/gui.py

@@ -36,9 +36,6 @@
 
 
 class DymoPrintWindow(QWidget):
-    SUPPORTED_TAPE_SIZE_MM = (19, 12, 9, 6)
-    DEFAULT_TAPE_SIZE_MM_INDEX = 1
-
     print_label_bitmap: Optional[Image.Image]
     dymo_labeler: DymoLabeler
 
@@ -84,13 +81,19 @@ def init_elements(self):
         shadow.setBlurRadius(15)
         self.label_render.setGraphicsEffect(shadow)
 
-        h_margins_mm = round(DymoLabeler.LABELER_HORIZONTAL_MARGIN_MM)
+        self.dymo_labeler = DymoLabeler()
+        for tape_size_mm in self.dymo_labeler.SUPPORTED_TAPE_SIZES_MM:
+            self.tape_size_mm.addItem(str(tape_size_mm), tape_size_mm)
+        tape_size_index = self.dymo_labeler.SUPPORTED_TAPE_SIZES_MM.index(
+            self.dymo_labeler.tape_size_mm
+        )
+        self.tape_size_mm.setCurrentIndex(tape_size_index)
+
+        h_margins_mm = round(self.dymo_labeler.minimum_horizontal_margin_mm)
         self.horizontal_margin_mm.setMinimum(h_margins_mm)
         self.horizontal_margin_mm.setMaximum(100)
         self.horizontal_margin_mm.setValue(h_margins_mm)
-        for tape_size_mm in self.SUPPORTED_TAPE_SIZE_MM:
-            self.tape_size_mm.addItem(str(tape_size_mm), tape_size_mm)
-        self.tape_size_mm.setCurrentIndex(self.DEFAULT_TAPE_SIZE_MM_INDEX)
+
         self.min_label_width_mm.setMinimum(h_margins_mm * 2)
         self.min_label_width_mm.setMaximum(300)
         self.justify.addItems(["center", "left", "right"])
@@ -102,7 +105,6 @@ def init_elements(self):
             ["white", "black", "yellow", "blue", "red", "green"]
         )
 
-        self.dymo_labeler = DymoLabeler()
         self.update_params()
         self.label_list.populate()
 
@@ -185,6 +187,7 @@ def update_params(self):
         self.render_context.height_px = self.dymo_labeler.height_px
 
         self.label_list.update_params(
+            dymo_labeler=self.dymo_labeler,
             h_margin_mm=horizontal_margin_mm,
             min_label_width_mm=min_label_width_mm,
             render_context=self.render_context,

src/dymoprint/gui/q_dymo_labels_list.py

@@ -70,12 +70,14 @@ class QDymoLabelList(QListWidget):
     )
     render_context: Optional[RenderContext]
     itemWidget: TextDymoLabelWidget
+    dymo_labeler: DymoLabeler
     h_margin_mm: float
     min_label_width_mm: Optional[float]
     justify: str
 
     def __init__(self, parent=None):
         super().__init__(parent)
+        self.dymo_labeler = None
         self.margin_px = None
         self.min_label_width_mm = None
         self.justify = "center"
@@ -103,6 +105,7 @@ def dropEvent(self, e) -> None:
 
     def update_params(
         self,
+        dymo_labeler: DymoLabeler,
         h_margin_mm: float,
         min_label_width_mm: float,
         render_context: RenderContext,
@@ -112,11 +115,13 @@ def update_params(
 
         Args:
         ----
+            dymo_labeler: an instance of DymoLabeler object
             h_margin_mm: horizontal margin [mm]
             min_label_width_mm: minimum label width [mm]
             render_context (RenderContext): The new render context to use.
             justify: justification [center,left,right]
         """
+        self.dymo_labeler = dymo_labeler
         self.h_margin_mm = h_margin_mm
         self.min_label_width_mm = min_label_width_mm
         self.justify = justify
@@ -160,7 +165,7 @@ def render_preview(self):
             render_engine=self._payload_render_engine,
             justify=self.justify,
             visible_horizontal_margin_px=mm_to_px(self.h_margin_mm),
-            labeler_margin_px=DymoLabeler.get_labeler_margin_px(),
+            labeler_margin_px=self.dymo_labeler.labeler_margin_px,
             max_width_px=None,
             min_width_px=mm_to_px(self.min_label_width_mm),
         )
@@ -177,7 +182,7 @@ def render_print(self):
             render_engine=self._payload_render_engine,
             justify=self.justify,
             visible_horizontal_margin_px=mm_to_px(self.h_margin_mm),
-            labeler_margin_px=DymoLabeler.get_labeler_margin_px(),
+            labeler_margin_px=self.dymo_labeler.labeler_margin_px,
             max_width_px=None,
             min_width_px=mm_to_px(self.min_label_width_mm),
         )

src/dymoprint/lib/dymo_labeler.py

@@ -20,7 +20,6 @@
 from dymoprint.lib.utils import mm_to_px
 
 LOG = logging.getLogger(__name__)
-DEFAULT_TAPE_SIZE_MM = 12
 POSSIBLE_USB_ERRORS = (DymoUSBError, NoBackendError, USBError)
 
 
@@ -51,8 +50,6 @@ class DymoLabelerFunctions:
     <https://download.dymo.com/dymo/technical-data-sheets/LW%20450%20Series%20Technical%20Reference.pdf>
     """
 
-    tape_size_mm: int
-
     # Max number of print lines to send before waiting for a response. This helps
     # to avoid timeouts due to differences between data transfer and
     # printer speeds. I added this because I kept getting "IOError: [Errno
@@ -69,10 +66,8 @@ def __init__(
         devout: usb.core.Endpoint,
         devin: usb.core.Endpoint,
         synwait: int | None = None,
-        tape_size_mm: int | None = None,
     ):
         """Initialize the LabelManager object (HLF)."""
-        self._tape_size_mm = tape_size_mm
         self._cmd: list[int] = []
         self._response = False
         self._bytesPerLine = None
@@ -83,13 +78,11 @@ def __init__(
         self._synwait = synwait
 
     @classmethod
-    def _max_bytes_per_line(cls, tape_size_mm: int | None = None) -> int:
-        if not tape_size_mm:
-            tape_size_mm = DEFAULT_TAPE_SIZE_MM
+    def _max_bytes_per_line(cls, tape_size_mm: int) -> int:
         return int(8 * tape_size_mm / 12)
 
     @classmethod
-    def height_px(cls, tape_size_mm: int | None = None):
+    def height_px(cls, tape_size_mm: int):
         return cls._max_bytes_per_line(tape_size_mm) * 8
 
     def _send_command(self):
@@ -155,9 +148,9 @@ def _status_request(self):
         self._build_command(cmd)
         self._response = True
 
-    def _dot_tab(self, value):
+    def _dot_tab(self, value, tape_size_mm: int):
         """Set the bias text height, in bytes (MLF)."""
-        if value < 0 or value > self._max_bytes_per_line(self._tape_size_mm):
+        if value < 0 or value > self._max_bytes_per_line(tape_size_mm):
             raise ValueError
         cmd = [ESC, ord("B"), value]
         self._build_command(cmd)
@@ -190,11 +183,11 @@ def _line(self, value):
         cmd = [SYN, *value]
         self._build_command(cmd)
 
-    def _chain_mark(self):
+    def _chain_mark(self, tape_size_mm: int):
         """Set Chain Mark (MLF)."""
-        self._dot_tab(0)
-        self._bytes_per_line(self._max_bytes_per_line(self._tape_size_mm))
-        self._line([0x99] * self._max_bytes_per_line(self._tape_size_mm))
+        self._dot_tab(0, tape_size_mm)
+        self._bytes_per_line(self._max_bytes_per_line(tape_size_mm))
+        self._line([0x99] * self._max_bytes_per_line(tape_size_mm))
 
     def _skip_lines(self, value):
         """Set number of lines of white to print (MLF)."""
@@ -245,13 +238,16 @@ class DymoLabeler:
     device: DetectedDevice
     tape_size_mm: int
 
-    LABELER_HORIZONTAL_MARGIN_MM = 8.1
-    LABELER_VERTICAL_MARGIN_MM = 1.9
+    LABELER_DISTANCE_BETWEEN_PRINT_HEAD_AND_CUTTER_MM = 8.1
+    LABELER_PRINT_HEAD_HEIGHT_MM = 8.2
+    SUPPORTED_TAPE_SIZES_MM = (19, 12, 9, 6)
+    DEFAULT_TAPE_SIZE_MM = 12
 
     def __init__(
         self,
         tape_size_mm: int = DEFAULT_TAPE_SIZE_MM,
     ):
+        assert tape_size_mm in self.SUPPORTED_TAPE_SIZES_MM
         self.tape_size_mm = tape_size_mm
         self.device = None
 
@@ -268,14 +264,18 @@ def _functions(self):
             devout=self.device.devout,
             devin=self.device.devin,
             synwait=64,
-            tape_size_mm=self.tape_size_mm,
         )
 
-    @classmethod
-    def get_labeler_margin_px(cls) -> tuple[float, float]:
+    @property
+    def minimum_horizontal_margin_mm(self):
+        return self.LABELER_DISTANCE_BETWEEN_PRINT_HEAD_AND_CUTTER_MM
+
+    @property
+    def labeler_margin_px(self) -> tuple[float, float]:
+        vertical_margin_mm = (self.tape_size_mm - self.LABELER_PRINT_HEAD_HEIGHT_MM) / 2
         return (
-            mm_to_px(cls.LABELER_HORIZONTAL_MARGIN_MM),
-            mm_to_px(cls.LABELER_VERTICAL_MARGIN_MM),
+            mm_to_px(self.minimum_horizontal_margin_mm),
+            mm_to_px(vertical_margin_mm),
         )
 
     def detect(self):