from typing import Dict


def define_demographics_popularity(data: Dict) -> Dict:
    """Get biggest demographics groups.
    Args:
        data (Dict): all demographics data for video.
    Returns:
        Dict.
    """
    age_band_views_percentages, gender_views_percentages = (
        data["age_band_views_percentages"],
        data["gender_views_percentages"],
    )

    gender_views_percentages = {v: k for k, v in gender_views_percentages.items()}
    max_gender_band = max(gender_views_percentages.keys())
    gender_most_popular = gender_views_percentages[max_gender_band]

    age_band_views_percentages = {v: k for k, v in age_band_views_percentages.items() if gender_most_popular in k}
    max_age_band = max(age_band_views_percentages.keys())
    age_band_most_popular = age_band_views_percentages[max_age_band]

    return {
        "gender_most_popular": gender_most_popular,
        "gender_percentage": max_gender_band,
        "age_band_most_popular": age_band_most_popular,
        "age_band_percentage": max_age_band,
    }