#!/usr/bin/env python3
"""Top-level CLI: python calc.py "<expression>"

Prints the result to stdout and exits 0 on success.
Prints an error message to stderr and exits 1 on any parse / eval error.
"""
import sys

from calc.lexer import tokenize, LexError
from calc.parser import parse, ParseError
from calc.evaluator import evaluate, EvalError


def main() -> None:
    if len(sys.argv) != 2:
        print("usage: calc.py <expression>", file=sys.stderr)
        sys.exit(1)
    expr = sys.argv[1]
    try:
        result = evaluate(parse(tokenize(expr)))
        print(result)
    except (LexError, ParseError, EvalError) as exc:
        print(f"error: {exc}", file=sys.stderr)
        sys.exit(1)


if __name__ == "__main__":
    main()