#!/usr/bin/env python3

import argparse
import json
import sys
from typing import Any, TextIO


def pretty_print(source: TextIO, destination: TextIO) -> None:
    """Read JSON from source and write a consistently formatted version."""
    data: Any = json.load(source)
    json.dump(data, destination, indent=2, ensure_ascii=False)
    destination.write("\n")


def _run_tests() -> None:
    """Run a couple of lightweight sanity checks."""
    from io import StringIO

    output = StringIO()
    pretty_print(StringIO('{"name":"Ada","active":true}'), output)
    assert output.getvalue() == (
        '{\n  "name": "Ada",\n  "active": true\n}\n'
    )

    output = StringIO()
    pretty_print(StringIO("[1,null]"), output)
    assert output.getvalue() == "[\n  1,\n  null\n]\n"


def main() -> int:
    parser = argparse.ArgumentParser(description="Pretty-print JSON.")
    parser.add_argument(
        "file",
        nargs="?",
        type=argparse.FileType("r", encoding="utf-8"),
        default=sys.stdin,
        help="JSON file (defaults to standard input)",
    )
    parser.add_argument(
        "--test",
        action="store_true",
        help="run built-in tests",
    )
    args = parser.parse_args()

    if args.test:
        _run_tests()
        return 0

    try:
        pretty_print(args.file, sys.stdout)
    except json.JSONDecodeError as error:
        print(f"Invalid JSON: {error}", file=sys.stderr)
        return 1
    finally:
        if args.file is not sys.stdin:
            args.file.close()

    return 0


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