fun getAddedToBackend(favouriteSymbol: String): Observable<UpdateFavouritesMutation> {
        return Observable.zip(Observable.just(favouriteSymbol), BackendService.favouriteAssets,
            BiFunction<String, MutableList<String>, Pair<String, MutableList<String>>> { symbol, favouritesList ->
                Pair(symbol, getAddOrRemove(symbol, favouritesList))
            }).flatMap {
            val favsMutation = UpdateFavouritesMutation.builder().favourites(it.second).build()
            BackendService.updateFavouritesAssets(favsMutation)
        }.execute()
    }

    private fun getAddOrRemove(
        favouriteSymbol: String, currentFavourites: MutableList<String>
    ): MutableList<String> {
        if (currentFavourites.contains(favouriteSymbol)) {
            currentFavourites.remove(favouriteSymbol)
            return currentFavourites
        } else {
            currentFavourites.add(favouriteSymbol)
            return currentFavourites
        }
    }