function craftUrl(uint256[] memory _cryptos, bool _isCoin)
      public
      view
    returns (string memory url)
    {
        if (_isCoin) url = coinUrl;
        else url = cashUrl;

        for (uint256 i = 0; i < _cryptos.length; i++) {
            uint256 id = _cryptos[i];

            
            for (uint256 j = 0; j < _cryptos.length; j++) {
                if (i == j) break;
                require(id != _cryptos[j]);
            }

            require(bytes(cryptoSymbols[id]).length > 0);
            url = url.toSlice().concat(cryptoSymbols[id].toSlice());
        }
        return url;
    }