"""PDF417 barcode decoding for boarding pass photos.

zxing-cpp is used as the primary (and only) decoder: it ships prebuilt wheels
for common platforms and has more reliable PDF417 support on real-world
skewed/glare phone photos than pyzbar/zbar. Kept behind this single function
so the library can be swapped later without touching call sites, per the
brief's note that decoder reliability should be validated against real
captures rather than assumed.
"""

import io

import zxingcpp
from PIL import Image, ImageOps

MIN_DIMENSION = 800
MAX_DIMENSION = 3000

# IATA Resolution 792 (BCBP) permits any of these 2D symbologies - PDF417 is
# typical for printed passes, Aztec/QR/DataMatrix are common for on-screen
# mobile passes (e.g. Emirates' app uses Aztec).
BARCODE_FORMATS = (
    zxingcpp.BarcodeFormat.PDF417
    | zxingcpp.BarcodeFormat.Aztec
    | zxingcpp.BarcodeFormat.QRCode
    | zxingcpp.BarcodeFormat.DataMatrix
)


def _prepare(img: Image.Image) -> Image.Image:
    img = ImageOps.exif_transpose(img)
    img = img.convert("L")
    w, h = img.size
    if min(w, h) < MIN_DIMENSION:
        scale = MIN_DIMENSION / min(w, h)
        img = img.resize((int(w * scale), int(h * scale)), Image.LANCZOS)
    elif max(w, h) > MAX_DIMENSION:
        scale = MAX_DIMENSION / max(w, h)
        img = img.resize((int(w * scale), int(h * scale)), Image.LANCZOS)
    return img


def decode_boarding_pass(image_bytes: bytes) -> str | None:
    try:
        img = Image.open(io.BytesIO(image_bytes))
        img = _prepare(img)
    except Exception:
        return None

    results = zxingcpp.read_barcodes(img, formats=BARCODE_FORMATS)
    if results:
        return results[0].text

    # One retry with autocontrast - cheap, catches glare/low-contrast photos.
    contrasted = ImageOps.autocontrast(img)
    results = zxingcpp.read_barcodes(contrasted, formats=BARCODE_FORMATS)
    if results:
        return results[0].text

    return None