#!/usr/bin/env python3
"""
JSON to CSV Converter - A simple utility to convert JSON files to CSV format.
Usage: python3 json_to_csv.py <input.json> <output.csv>
"""

import json
import csv
import sys
from pathlib import Path


def flatten_dict(d, parent_key='', sep='_'):
    """Flatten nested dictionary for CSV compatibility."""
    items = []
    for k, v in d.items():
        new_key = f"{parent_key}{sep}{k}" if parent_key else k
        if isinstance(v, dict):
            items.extend(flatten_dict(v, new_key, sep).items())
        elif isinstance(v, list):
            items.append((new_key, json.dumps(v)))
        else:
            items.append((new_key, v))
    return dict(items)


def convert_json_to_csv(json_path, csv_path):
    """Convert JSON file to CSV."""
    with open(json_path, 'r') as f:
        data = json.load(f)

    if isinstance(data, list):
        records = [flatten_dict(record) for record in data] if data else []
    elif isinstance(data, dict):
        records = [flatten_dict(data)]
    else:
        raise ValueError("JSON must contain objects or array of objects")

    if not records:
        with open(csv_path, 'w') as f:
            pass
        return

    fieldnames = sorted(set(key for record in records for key in record.keys()))

    with open(csv_path, 'w', newline='') as f:
        writer = csv.DictWriter(f, fieldnames=fieldnames)
        writer.writeheader()
        writer.writerows(records)

    return {
        'input_path': str(json_path),
        'output_path': str(csv_path),
        'records_processed': len(records),
        'columns': fieldnames
    }


if __name__ == '__main__':
    if len(sys.argv) != 3:
        print("Usage: python3 json_to_csv.py <input.json> <output.csv>")
        sys.exit(1)

    result = convert_json_to_csv(sys.argv[1], sys.argv[2])
    print(json.dumps(result, indent=2))