Favorites

  count: u64,
  created_at: u64,
  is_favorite: bool,
  updated_at: u64

  current_favorites: u64,
  favorites: sui::table::Table<address, Favorite>

  public fun add(
      favorites: &mut Favorites,
      key: address,
      timestamp: u64
  ): u64 {
      let does_exist = favorites.favorites.contains(key);
      let mut favorite_count = 1;

      if (does_exist) {
          let favorite = favorites.favorites.borrow_mut(key);

          assert!(!favorite.is_favorite, EAlreadyFavorited);

          favorite.count = favorite.count + 1;
          favorite.is_favorite = true;
          favorite.updated_at = timestamp;

          favorite_count = favorite.count;
      } else {
          let favorite = Favorite {
              count: favorite_count,
              created_at: timestamp,
              is_favorite: true,
              updated_at: timestamp
          };

          favorites.favorites.add(key, favorite);
      };

      favorites.current_favorites = favorites.current_favorites + 1;

      favorite_count
  }

  public fun assert_has_not_favorited(
      favorites: &Favorites,
      key: address
  ) {
      let is_favorite = is_favorite(
          favorites,
          key
      );

      assert!(!is_favorite, EAlreadyFavorited);
  }

  public fun create(
      ctx: &mut TxContext
  ): Favorites {
      let favorites = Favorites {
          current_favorites: 0,
          favorites: table::new(ctx)
      };

      favorites
  }

  public fun get_count(
      favorites: &Favorites,
      key: address
  ): u64 {
      favorites.favorites[key].count
  }

  public fun get_created_at(
      favorites: &Favorites,
      key: address
  ): u64 {
      favorites.favorites[key].created_at
  }

  public fun get_length(
      favorites: &Favorites
  ): u64 {
      favorites.current_favorites
  }

  public fun get_updated_at(
      favorites: &Favorites,
      key: address
  ): u64 {
      favorites.favorites[key].updated_at
  }

  public fun is_favorite(
      favorites: &Favorites,
      key: address
  ): bool {
      favorites.favorites.contains(key) &&
      favorites.favorites[key].is_favorite
  }

  public fun remove(
      favorites: &mut Favorites,
      key: address,
      timestamp: u64
  ): u64 {
      let favorite = favorites.favorites.borrow_mut(key);

      assert!(favorite.is_favorite, EIsNotFavorite);

      favorite.is_favorite = false;
      favorite.updated_at = timestamp;

      favorites.current_favorites = favorites.current_favorites - 1;

      favorite.count
  }