#!/usr/bin/env python3
"""Validate the stable JSON contract returned by GET /health."""

import argparse
import json
import sys
from datetime import datetime
from pathlib import Path


def validate(value):
    if not isinstance(value, dict):
        return "health response must be a JSON object"
    missing = sorted({"status", "timestamp", "uptime", "checks"} - value.keys())
    if missing:
        return f"health response missing fields: {', '.join(missing)}"
    if value["status"] != "healthy":
        return f"unexpected health status: {value['status']}"
    try:
        datetime.fromisoformat(value["timestamp"].replace("Z", "+00:00"))
    except (AttributeError, ValueError):
        return "timestamp must be RFC3339"
    if not isinstance(value["uptime"], str) or not value["uptime"]:
        return "uptime must be a non-empty string"
    if not isinstance(value["checks"], dict) or value["checks"].get("database") != "healthy":
        return "database health check must be healthy"
    return None


def main(argv=None):
    parser = argparse.ArgumentParser()
    parser.add_argument("path", nargs="?", help="JSON file; stdin when omitted")
    args = parser.parse_args(argv)
    try:
        raw = Path(args.path).read_text(encoding="utf-8") if args.path else sys.stdin.read()
        error = validate(json.loads(raw))
    except (OSError, json.JSONDecodeError) as exc:
        error = f"invalid health JSON: {exc}"
    if error:
        print(error, file=sys.stderr)
        return 1
    print("health JSON contract: ok")
    return 0


if __name__ == "__main__":
    sys.exit(main())