#!/usr/bin/env python3
"""calc.py — command-line calculator.

Usage: python calc.py "<expression>"

Prints the result to stdout and exits 0.
Prints an error message to stderr and exits 1 on bad input.
"""
import sys

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


def _fmt(val) -> str:
    """Format a numeric result: whole-valued floats print without '.0'."""
    if isinstance(val, float) and val.is_integer():
        return str(int(val))
    return str(val)


def main() -> None:
    if len(sys.argv) != 2:
        print(f"usage: python calc.py \"<expression>\"", file=sys.stderr)
        sys.exit(1)

    expr = sys.argv[1]
    try:
        tokens = tokenize(expr)
        ast = parse(tokens)
        result = evaluate(ast)
        print(_fmt(result))
    except (LexError, ParseError, EvalError) as exc:
        print(f"error: {exc}", file=sys.stderr)
        sys.exit(1)


if __name__ == "__main__":
    main()