BestPrice.sol

interface IUniswap {
    function getEthToTokenInputPrice(uint256 eth_sold) external view returns(uint256);
    function getEthToTokenOutputPrice(uint256 tokens_bought) external view returns(uint256);
    function getTokenToEthInputPrice(uint256 tokens_sold) external view returns(uint256);
    function getTokenToEthOutputPrice(uint256 eth_bought) external view returns(uint256);
}

interface IBancor {
    function getReturnByPath(address[] calldata _path, uint256 _amount) external view
        returns (uint256 amount, uint256 conversion_fee);
}

interface IKyber {
    function getExpectedRate(address src, address dest, uint srcQty) external view
        returns (uint expectedRate, uint slippageRate);
}

contract BestPrice {
    address constant KYBER_NETWORK_ETH_ADDRESS = 0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE;

    function _getBestPrice(
        address fromToken,
        address toToken,
        address[] calldata path,
        uint256 amount,
        uint256 parts,
        IUniswap uniswap,
        IBancor bancor,
        IKyber kyber
    )
        external
        view
        returns(uint256[7] memory res)
    {
        uint256[] memory uniswapReturns = new uint256[](parts + 1);
        uint256[] memory bancorReturns = new uint256[](parts + 1);
        uint256[] memory kyberReturns = new uint256[](parts + 1);
        
        for (uint i = 1; i <= parts; i++) {
            if (address(uniswap) != address(0)) {
                uniswapReturns[i] = _getUniswapRate(uniswap, fromToken, amount * i / parts);
            }
            if (address(bancor) != address(0)) {
                (bancorReturns[i],) = bancor.getReturnByPath(path, amount * i / parts);
            }
            if (address(kyber) != address(0)) {
                (kyberReturns[i],) = kyber.getExpectedRate(fromToken, toToken, amount * i / parts);
            }
        }
        
        res[3] = uniswapReturns[parts];
        res[4] = bancorReturns[parts];
        res[5] = kyberReturns[parts];
    
        for (uint i = 0; i < parts; i++) {
            for (uint j = i; j < parts; j++) {
                uint256 theReturn = uniswapReturns[i] + bancorReturns[j - i] + kyberReturns[parts - 1 - j];
                if (theReturn > res[6]) {
                    res[0] = i;
                    res[1] = j - i;
                    res[2] = parts - 1 - j;
                    res[6] = theReturn;
                }  
            }
        }
    }
    
    function _getUniswapRate(
        IUniswap uniswap,
        address fromToken,
        uint256 amount
    )
        internal
        view
        returns(uint256)
    {
        if (fromToken == address(0) || fromToken == KYBER_NETWORK_ETH_ADDRESS) {
            return uniswap.getEthToTokenInputPrice(amount);
        }
        return uniswap.getTokenToEthInputPrice(amount);
    }
}