public class PreferencesHelperImpl implements PreferencesHelper {

  private final Gson gson;
  private final SharedPreferences preferences;

  public PreferencesHelperImpl(Gson gson, SharedPreferences sharedPreferences) {
    this.gson = gson;
    this.preferences = sharedPreferences;
  }

  @Override public void putAccessToken(AccessToken accessToken) {
    String json = gson.toJson(accessToken);
    preferences.edit().putString("access-token", json).apply();
  }

  @Override public AccessToken getAccessToken() {
    String json = preferences.getString("access-token", null);
    AccessToken accessToken = null;
    if (!StringUtils.isEmpty(json)) {
      try {
        accessToken = gson.fromJson(json, AccessToken.class);
      } catch (JsonSyntaxException e) {
        return null;
      }
    }
    return accessToken;
  }
}