label_printer/print_area.py

"""
Query a Windows printer driver for its page and printable area.

Why this matters for the P-touch: the PT-E560BT driver reports its media as
65 x 24 mm, but its *printable* area is only about 61.1 x 18.06 mm, because the
print head cannot reach the edges. Anything drawn outside that window is cropped
by the driver, which is why a 63 x 20 mm design printed short.

Reading the values from the driver (rather than hardcoding them) means the layout
adapts automatically if the tape width or media size changes.

The 18 mm printable height is a hardware limit: the PT-E560BT has a 128 dot print
head at 180 dpi, and 128 / 180 * 25.4 = 18.06 mm. No layout can exceed it.
"""

from __future__ import annotations

from dataclasses import dataclass
from typing import Optional

# GetDeviceCaps indices (wingdi.h)
HORZSIZE, VERTSIZE = 4, 6
HORZRES, VERTRES = 8, 10
LOGPIXELSX, LOGPIXELSY = 88, 90
PHYSICALWIDTH, PHYSICALHEIGHT = 110, 111
PHYSICALOFFSETX, PHYSICALOFFSETY = 112, 113


@dataclass
class PrintArea:
    """Page and printable-area geometry of a printer driver, in millimetres."""

    printer: str
    dpi_x: int
    dpi_y: int
    # Physical media
    media_width_mm: float
    media_height_mm: float
    # Area the head can actually reach
    printable_width_mm: float
    printable_height_mm: float
    # Where the printable area starts, relative to the physical page corner
    offset_x_mm: float
    offset_y_mm: float

    def describe(self) -> str:
        return (
            f"{self.printer}: media {self.media_width_mm:.2f} x {self.media_height_mm:.2f} mm, "
            f"printable {self.printable_width_mm:.2f} x {self.printable_height_mm:.2f} mm "
            f"at ({self.offset_x_mm:.2f}, {self.offset_y_mm:.2f}) mm, "
            f"{self.dpi_x}x{self.dpi_y} dpi"
        )


def _mm(dots: float, dpi: float) -> float:
    return dots / dpi * 25.4 if dpi else 0.0


def query_print_area(printer_name: str) -> Optional[PrintArea]:
    """Read a printer's page and printable geometry.

    Returns None when the information is unavailable (non-Windows platform, the
    printer is missing, or pywin32 is not installed). Callers must fall back to
    configured defaults in that case.
    """
    try:
        import win32ui
    except ImportError:
        return None

    try:
        dc = win32ui.CreateDC()
        dc.CreatePrinterDC(printer_name)
    except Exception as exc:  # noqa: BLE001 - caller falls back to defaults
        print(f"Could not query print area for '{printer_name}': {exc}")
        return None

    try:
        dpi_x = dc.GetDeviceCaps(LOGPIXELSX) or 180
        dpi_y = dc.GetDeviceCaps(LOGPIXELSY) or 180
        return PrintArea(
            printer=printer_name,
            dpi_x=dpi_x,
            dpi_y=dpi_y,
            media_width_mm=_mm(dc.GetDeviceCaps(PHYSICALWIDTH), dpi_x),
            media_height_mm=_mm(dc.GetDeviceCaps(PHYSICALHEIGHT), dpi_y),
            printable_width_mm=_mm(dc.GetDeviceCaps(HORZRES), dpi_x),
            printable_height_mm=_mm(dc.GetDeviceCaps(VERTRES), dpi_y),
            offset_x_mm=_mm(dc.GetDeviceCaps(PHYSICALOFFSETX), dpi_x),
            offset_y_mm=_mm(dc.GetDeviceCaps(PHYSICALOFFSETY), dpi_y),
        )
    except Exception as exc:  # noqa: BLE001
        print(f"GetDeviceCaps failed for '{printer_name}': {exc}")
        return None
    finally:
        try:
            dc.DeleteDC()
        except Exception:  # noqa: BLE001
            pass


def apply_to_config(config, printer_name: str, margin_mm: float = 0.1) -> bool:
    """Resize a LabelConfig to the printer's printable area.

    The label content is set to the printable area (minus a small safety margin)
    so nothing the driver cannot reach is ever drawn.

    Args:
        config: a LabelConfig instance, modified in place
        printer_name: printer to query
        margin_mm: shrink each dimension by this much to stay clear of rounding

    Returns:
        bool: True if the config was updated
    """
    area = query_print_area(printer_name)
    if area is None:
        return False

    config.media_width_mm = round(area.media_width_mm, 2)
    config.media_height_mm = round(area.media_height_mm, 2)
    config.page_width_mm = round(area.printable_width_mm - margin_mm, 2)
    config.page_height_mm = round(area.printable_height_mm - margin_mm, 2)
    config.gutter_mm = 0.0  # the content box is now the printable area itself
    config.match_driver_media = True

    # Keep the three columns tiling the new width, preserving their proportions.
    total = config.col_logo_mm + config.col_text_mm + config.col_code_mm
    if total > 0:
        scale = config.page_width_mm / total
        config.col_logo_mm = round(config.col_logo_mm * scale, 2)
        config.col_text_mm = round(config.col_text_mm * scale, 2)
    return True