# SPDX-License-Identifier: MIT
"""Learning project: bounded local task-status reporting, not a general JSON validator."""
import argparse
import json
import sys
from pathlib import Path

MAX_BYTES = 65536
MAX_RECORDS = 1000


def reject_constant(value):
    raise ValueError("non-standard JSON constant")


def unique_object(pairs):
    result = {}
    for key, value in pairs:
        if key in result:
            raise ValueError("duplicate JSON key")
        result[key] = value
    return result


def summarise(records):
    if not isinstance(records, list) or len(records) > MAX_RECORDS:
        raise ValueError("expected at most 1000 records")
    counts = {"closed": 0, "open": 0}
    for record in records:
        if not isinstance(record, dict) or set(record) != {"title", "status"}:
            raise ValueError("expected title and status only")
        title, status = record["title"], record["status"]
        if not isinstance(title, str) or not title.strip() or len(title) > 100:
            raise ValueError("expected a nonblank title of at most 100 characters")
        if not isinstance(status, str) or status not in counts:
            raise ValueError("expected open or closed status")
        counts[status] += 1
    return {"records": len(records), "by_status": counts}


def read_records(path):
    with Path(path).open("rb") as handle:
        raw = handle.read(MAX_BYTES + 1)
    if len(raw) > MAX_BYTES:
        raise ValueError("input exceeds 65536 bytes")
    return json.loads(raw.decode("utf-8"), parse_constant=reject_constant,
                      object_pairs_hook=unique_object)


def main(argv=None):
    parser = argparse.ArgumentParser(description="Summarise a small local task list.")
    parser.add_argument("input", help="UTF-8 JSON file, at most 65536 bytes")
    args = parser.parse_args(argv)
    try:
        result = summarise(read_records(args.input))
    except (OSError, UnicodeError, ValueError, RecursionError):
        print("error: invalid or unreadable task file", file=sys.stderr)
        return 2
    print(json.dumps(result, sort_keys=True, allow_nan=False))
    return 0


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