barcode_print.py

#!/usr/bin/env python3
"""Print a scannable Code 39 barcode on the S01 thermal printer.

Code 39 encodes digits, uppercase letters, and a few symbols (- . space $ / + %).
Real barcode-scanner apps can read these. Handy for labelling cables, boxes,
shelves, or anything you want to track.

Examples:
    python barcode_print.py --text "PRT-0042"
    python barcode_print.py --text "SHELF A3"
    python barcode_print.py                     # random sample code
    python barcode_print.py --no-print
"""
from __future__ import annotations

import argparse
from pathlib import Path
import random
import string

from PIL import Image, ImageDraw

from print_common import ROOT, Card, font

# Code 39: 9 elements per char (bar/space alternating, starting bar); n=narrow, w=wide
CODE39 = {
    "0": "nnnwwnwnn", "1": "wnnwnnnnw", "2": "nnwwnnnnw", "3": "wnwwnnnnn",
    "4": "nnnwwnnnw", "5": "wnnwwnnnn", "6": "nnwwwnnnn", "7": "nnnwnnwnw",
    "8": "wnnwnnwnn", "9": "nnwwnnwnn", "A": "wnnnnwnnw", "B": "nnwnnwnnw",
    "C": "wnwnnwnnn", "D": "nnnnwwnnw", "E": "wnnnwwnnn", "F": "nnwnwwnnn",
    "G": "nnnnnwwnw", "H": "wnnnnwwnn", "I": "nnwnnwwnn", "J": "nnnnwwwnn",
    "K": "wnnnnnnww", "L": "nnwnnnnww", "M": "wnwnnnnwn", "N": "nnnnwnnww",
    "O": "wnnnwnnwn", "P": "nnwnwnnwn", "Q": "nnnnnnwww", "R": "wnnnnnwwn",
    "S": "nnwnnnwwn", "T": "nnnnwnwwn", "U": "wwnnnnnnw", "V": "nwwnnnnnw",
    "W": "wwwnnnnnn", "X": "nwnnwnnnw", "Y": "wwnnwnnnn", "Z": "nwwnwnnnn",
    "-": "nwnnnnwnw", ".": "wwnnnnwnn", " ": "nwwnnnwnn", "$": "nwnwnwnnn",
    "/": "nwnwnnnwn", "+": "nwnnnwnwn", "%": "nnnwnwnwn", "*": "nwnnwnwnn",
}


def build_segments(text: str):
    """Return list of (is_bar, width_units) for *text* framed by start/stop '*'."""
    chars = ["*"] + list(text) + ["*"]
    segs = []
    for ci, ch in enumerate(chars):
        for ei, el in enumerate(CODE39[ch]):
            segs.append((ei % 2 == 0, 3 if el == "w" else 1))  # even index = bar
        if ci != len(chars) - 1:
            segs.append((False, 1))  # narrow inter-character space
    return segs


def render(text: str, target_w: int, height: int = 90) -> Image.Image:
    segs = build_segments(text)
    total = sum(w for _, w in segs)
    quiet = 12  # quiet-zone units each side
    u = max(1, target_w // (total + 2 * quiet))
    bar_px = total * u
    w = bar_px + 2 * quiet * u
    img = Image.new("L", (w, height), 255)
    d = ImageDraw.Draw(img)
    x = quiet * u
    for is_bar, width in segs:
        if is_bar:
            d.rectangle((x, 0, x + width * u - 1, height - 1), fill=0)
        x += width * u
    return img


def main() -> int:
    parser = argparse.ArgumentParser(description="Print a scannable Code 39 barcode on the S01 thermal printer.")
    parser.add_argument("--text", default=None, help="Text to encode (default: random sample code).")
    parser.add_argument("--out", type=Path, default=ROOT / "barcode.png")
    parser.add_argument("--darkness", type=int, choices=range(1, 6), default=3)
    parser.add_argument("--bottom-feed", type=int, default=24)
    parser.add_argument("--no-print", action="store_true")
    args = parser.parse_args()

    text = (args.text or "PRT-" + "".join(random.choice(string.digits) for _ in range(4))).upper()
    bad = [c for c in text if c not in CODE39 or c == "*"]
    if bad:
        raise SystemExit(f"Code 39 can't encode: {''.join(sorted(set(bad)))}. "
                         "Allowed: 0-9 A-Z space - . $ / + %")
    print(f"Encoding Code 39: {text}")

    card = Card()
    card.title("BARCODE")
    card.line("Code 39", size=12, bold=False, center=True)
    card.gap(8).image(render(text, card.inner_w), border=False)
    card.gap(4).line(text, size=18, bold=True, center=True)
    card.footer("code 39", "scan me")
    return card.finish(args.out, args.bottom_feed, args.darkness, do_print=not args.no_print)


if __name__ == "__main__":
    raise SystemExit(main())