import json
import sys

def extract_urls_to_file(json_data, output_filename="urls.txt"):
    """Extracts URLs from server data and writes them to a text file.

    Args:
        json_data: The JSON object containing the server data.
        output_filename: The name of the output text file (default: urls.txt).
    """

    try:
        servers = json_data.get("servers", [])
        with open(output_filename, 'w', encoding='utf-8') as outfile:
            for server in servers:
                url = server.get("url")
                if url:
                    outfile.write(url.strip() + '\n')

    except (IOError, json.JSONDecodeError) as e:
        print(f"An error occurred: {e}")


if __name__ == "__main__":
    if len(sys.argv) > 1:
        json_filename = sys.argv[1]
        try:
            with open(json_filename, 'r', encoding='utf-8') as f:
                json_data = json.load(f)
        except FileNotFoundError:
            print(f"Error: File '{json_filename}' not found.")
            sys.exit(1)
        except json.JSONDecodeError:
            print(f"Error: Invalid JSON format in '{json_filename}'.")
            sys.exit(1)
        
        if len(sys.argv) > 2:
            output_filename = sys.argv[2]
            extract_urls_to_file(json_data, output_filename)
            print(f"URLs extracted to '{output_filename}'")
        else:
            extract_urls_to_file(json_data)
            print("URLs extracted to 'urls.txt'")


    else:
        print("Usage: python script_name.py <json_filename> <output_filename>(optional)")
        default_json = {"servers": []}
        extract_urls_to_file(default_json)
        print("URLs (from default JSON) extracted to 'urls.txt'")