import argparse
import json
import sys
from pathlib import Path
from typing import Any


def pretty_json(text: str) -> str:
    """Parse JSON and return a consistently formatted representation."""
    value: Any = json.loads(text)
    return json.dumps(value, indent=2, ensure_ascii=False) + "\n"


def run_tests() -> None:
    """Run a couple of lightweight checks."""
    assert pretty_json('{"a":1}') == '{\n  "a": 1\n}\n'
    assert pretty_json("[true,null]") == "[\n  true,\n  null\n]\n"


def main() -> int:
    parser = argparse.ArgumentParser(description="Pretty-print JSON.")
    parser.add_argument("file", nargs="?", type=Path, help="JSON file; defaults to stdin")
    parser.add_argument("--test", action="store_true", help="run self-tests")
    args = parser.parse_args()

    if args.test:
        run_tests()
        return 0

    try:
        text = args.file.read_text(encoding="utf-8") if args.file else sys.stdin.read()
        sys.stdout.write(pretty_json(text))
    except (OSError, json.JSONDecodeError) as error:
        print(f"error: {error}", file=sys.stderr)
        return 1

    return 0


if __name__ == "__main__":
    raise SystemExit(main())