from __future__ import annotations

import re
from pathlib import Path

REGEX = re.compile(r"^Serial\s+:\s+([0-9a-f]+)$", re.MULTILINE)

# with regex
def get_serial(as_hex: bool = False) -> int | str:
    cpuinfo = Path("/proc/cpuinfo").read_text()
    match = REGEX.search(cpuinfo)
    if not match:
        raise RuntimeError("This is not a Raspberry Pi")

    serial = int(match.group(1), 16)

    if as_hex:
        serial = hex(serial)

    return serial


# no regex
def get_serial(as_hex: bool = False) -> int | str:
    with open("/proc/cpuinfo") as fd:
        for line in fd:
            if line.startswith("Serial"):
                serial = int(line.rpartition(":")[2], 16)
                break
        else:
            # This branch is only reached, if the
            # for-loop has been finished
            # a break in the for loop will not execute this branch
            raise RuntimeError("This is not a Raspberry Pi")

    if as_hex:
        serial = hex(serial)

    return serial


if __name__ == "__main__":
    try:
        print(get_serial())
        print(get_serial(as_hex=True))
    except RuntimeError as err:
        raise SystemExit(err.args[0])