public class UserPreferences
{
    private IDataProvider _dataProvider;
    private UserPreferencesDefaults _defaults;
    private PreferencesContainer _container;

    public CommonPreferences Common => _container.Common;
    public SettingsPreferences Settings => _container.Settings;
    public ControlsPreferences Controls => _container.Controls;

    public UserPreferences(IDataProvider dataProvider, UserPreferencesDefaults defaults)
    {
        _dataProvider = dataProvider;
        _defaults = defaults;
        LoadPreferences();
    }

    public void SaveChanges()
    {
        SavePreferences();
        _dataProvider.Apply();
    }

    private void LoadPreferences()
    {
        if (_dataProvider.Contains("preferences"))
        {
            var jsonText = _dataProvider.GetString("preferences");
            _container = JsonConvert.DeserializeObject<PreferencesContainer>(jsonText);
        }
        else
        {
            _container = new PreferencesContainer()
            {
                Common = _defaults.Common,
                Settings = _defaults.Settings,
                Controls = _defaults.Controls
            };
        }
    }
    private void SavePreferences()
    {
        _dataProvider.PutString(key, JsonConvert.SerializeObject(_container));
    }

    private class PreferencesContainer
    {
        public int Version = 1;
        public CommonPreferences Common;
        public SettingsPreferences Settings;
        public ControlsPreferences Controls;
    }
}