import json

def main():
    """
    Opens a HAR archive file "data.har" and prints a list of files (URLs)
    found in the archive.
    """
    har_file_path = "data.har"
    try:
        with open(har_file_path, 'r', encoding='utf-8') as f:
            har_data = json.load(f)
    except FileNotFoundError:
        print(f"Error: The file '{har_file_path}' was not found.")
        return
    except json.JSONDecodeError:
        print(f"Error: Could not decode JSON from the file '{har_file_path}'.")
        return
    except Exception as e:
        print(f"An unexpected error occurred while reading the file: {e}")
        return

    try:
        entries = har_data.get('log', {}).get('entries', [])
        if not entries:
            print("No entries found in the HAR file.")
            return

        print("Files found in the HAR archive:")
        for entry in entries:
            request = entry.get('request', {})
            url = request.get('url')
            if url:
                print(url)
            else:
                print("Entry found with no request URL.")
    except AttributeError:
        print("Error: The HAR file does not have the expected structure ('log' or 'entries' missing).")
    except Exception as e:
        print(f"An unexpected error occurred while processing HAR entries: {e}")


if __name__ == "__main__":
    main()