"""Issue #26 / #17 item 4: the one integer rule for knobs and flags.

lib_int.sh's mam_int / mam_int_knob run this file, and the loop runner's
_positive_int is positive_int below, so bash and Python share one
implementation. Surrounding ASCII blanks are allowed, then ASCII digits only,
read as DECIMAL (bash would read 0700 as octal 448), and
minimum <= n <= 999999999. The per-knob minimum lives in
tests/test_issue26_ints.py.

Stdlib only and Python 3.9: lib_int.sh runs it as a script (python3 -I),
where lib_py is not importable.

  ints.py int <value> <min>                    print n, or exit 1
  ints.py knob <name> <value> <default> <min>  print n; empty gives <default>,
                                               invalid gives <default> + a warning
"""
from __future__ import annotations

import sys
from typing import List, Optional

_BLANKS = " \t\n\r\v\f"


def positive_int(text: Optional[str], minimum: int = 1) -> Optional[int]:
    """n when `text` is a decimal integer >= minimum (and <= 999999999), else None."""
    s = (text or "").strip(_BLANKS)
    if not s or not s.isascii() or not s.isdigit():
        return None
    s = s.lstrip("0") or "0"
    if len(s) > 9:  # bounded before int(), which refuses > 4300 digits
        return None
    n = int(s)
    return n if n >= minimum else None


def knob(name: str, raw: str, default: str, minimum: int) -> str:
    """mam_int_knob: the value of $name by the rule, <default> when empty or invalid."""
    if not raw:
        return default
    n = positive_int(raw, minimum)
    if n is not None:
        return str(n)
    print(f"WARNING: {name}={raw} ignored (not a decimal integer >= {minimum}); using {default}", file=sys.stderr)
    return default


def main(argv: List[str]) -> int:
    if len(argv) == 3 and argv[0] == "int":
        n = positive_int(argv[1], int(argv[2]))
        if n is None:
            return 1
        print(n)
        return 0
    if len(argv) == 5 and argv[0] == "knob":
        print(knob(argv[1], argv[2], argv[3], int(argv[4])))
        return 0
    print("usage: ints.py int <value> <min> | knob <name> <value> <default> <min>", file=sys.stderr)
    return 2


if __name__ == "__main__":
    sys.exit(main(sys.argv[1:]))