from datetime import datetime


def _choose_name_of_file(user_input: dict) -> str:
    """
    Based on the full name of the desired subject and current date, \
    return the name of the PDF file.

    Args:
         `user_input`: the app's user input represented as a dict.
    Returns:
        `str`: the name of the PDF file which will be saved in the user-specified directory.
    """
    full_name = "".join([user_input["first_name"], user_input["last_name"]])
    time_str_to_output = datetime.now().replace(microsecond=0).isoformat()
    file_name_to_output = "_".join([full_name, time_str_to_output])
    return file_name_to_output