backend.py

"""Send a rendered receipt image to an ESC/POS printer over USB."""

import logging
import threading

from PIL import Image

import config

logger = logging.getLogger(__name__)

# One USB device, one job at a time. The bot prints from worker threads
# (asyncio.to_thread), so two messages can land here at once — serialize them
# or they fight over the same device.
_print_lock = threading.Lock()


def print_image(img: Image.Image) -> None:
    """Open the USB printer, print one bitmap, feed and cut."""
    if config.USB_VID is None or config.USB_PID is None:
        raise RuntimeError(
            "Printer not configured: set PRINTER_USB_VID and PRINTER_USB_PID "
            "(find them with `lsusb`)."
        )

    from escpos.printer import Usb

    with _print_lock:
        printer = Usb(config.USB_VID, config.USB_PID)
        try:
            printer.image(img)
            printer.cut()
        finally:
            printer.close()

    logger.info(f"Printed image {img.width}x{img.height}")