Almost done with uniswap resolver

contracts/protocols/uniswapV2.sol

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+pragma solidity ^0.6.0;
+pragma experimental ABIEncoderV2;
+
+interface IUniswapV2Router01 {
+    function factory() external pure returns (address);
+    function WETH() external pure returns (address);
+    function quote(uint amountA, uint reserveA, uint reserveB) external pure returns (uint amountB);
+    function getAmountOut(uint amountIn, uint reserveIn, uint reserveOut) external pure returns (uint amountOut);
+    function getAmountIn(uint amountOut, uint reserveIn, uint reserveOut) external pure returns (uint amountIn);
+    function getAmountsOut(uint amountIn, address[] calldata path) external view returns (uint[] memory amounts);
+    function getAmountsIn(uint amountOut, address[] calldata path) external view returns (uint[] memory amounts);
+}
+
+interface IUniswapV2Factory {
+  function getPair(address tokenA, address tokenB) external view returns (address pair);
+  function allPairs(uint) external view returns (address pair);
+  function allPairsLength() external view returns (uint);
+
+  function feeTo() external view returns (address);
+  function feeToSetter() external view returns (address);
+
+  function createPair(address tokenA, address tokenB) external returns (address pair);
+}
+
+interface TokenInterface {
+    function allowance(address, address) external view returns (uint);
+    function balanceOf(address) external view returns (uint);
+    function approve(address, uint) external;
+    function transfer(address, uint) external returns (bool);
+    function decimals() external view returns (uint);
+}
+
+contract DSMath {
+
+    function add(uint x, uint y) internal pure returns (uint z) {
+        require((z = x + y) >= x, "math-not-safe");
+    }
+
+    function mul(uint x, uint y) internal pure returns (uint z) {
+        require(y == 0 || (z = x * y) / y == x, "math-not-safe");
+    }
+
+    function sub(uint x, uint y) internal pure returns (uint z) {
+        require((z = x - y) <= x, "sub-overflow");
+    }
+
+    uint constant WAD = 10 ** 18;
+
+    function wmul(uint x, uint y) internal pure returns (uint z) {
+        z = add(mul(x, y), WAD / 2) / WAD;
+    }
+
+    function wdiv(uint x, uint y) internal pure returns (uint z) {
+        z = add(mul(x, WAD), y / 2) / y;
+    }
+
+}
+
+
+contract Helpers is DSMath {
+    /**
+     * @dev get Ethereum address
+     */
+    function getEthAddr() public pure returns (address) {
+        return 0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE;
+    }
+}
+
+contract UniswapHelpers is Helpers {
+    /**
+     * @dev Return WETH address
+     */
+    function getAddressWETH() internal pure returns (address) {
+        return 0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2;
+    }
+
+    /**
+     * @dev Return uniswap v2 router Address
+     */
+    function getUniswapAddr() internal pure returns (address) {
+        return 0x794e6e91555438aFc3ccF1c5076A74F42133d08D; //Mainnet
+    }
+
+    function convert18ToDec(uint _dec, uint256 _amt) internal pure returns (uint256 amt) {
+        amt = (_amt / 10 ** (18 - _dec));
+    }
+
+    function convertTo18(uint _dec, uint256 _amt) internal pure returns (uint256 amt) {
+        amt = mul(_amt, 10 ** (18 - _dec));
+    }
+
+    function changeEthAddress(address buy, address sell) internal pure returns(TokenInterface _buy, TokenInterface _sell){
+        _buy = buy == getEthAddr() ? TokenInterface(getAddressWETH()) : TokenInterface(buy);
+        _sell = sell == getEthAddr() ? TokenInterface(getAddressWETH()) : TokenInterface(sell);
+    }
+
+    function getExpectedBuyAmt(
+        address buyAddr,
+        address sellAddr,
+        uint sellAmt
+    ) internal view returns(uint buyAmt) {
+        IUniswapV2Router01 router = IUniswapV2Router01(getUniswapAddr());
+        address[] memory paths = new address[](2);
+        paths[0] = address(sellAddr);
+        paths[1] = address(buyAddr);
+        uint[] memory amts = router.getAmountsOut(
+            sellAmt,
+            paths
+        );
+        buyAmt = amts[1];
+    }
+
+    function getExpectedSellAmt(
+        address buyAddr,
+        address sellAddr,
+        uint buyAmt
+    ) internal view returns(uint sellAmt) {
+        IUniswapV2Router01 router = IUniswapV2Router01(getUniswapAddr());
+        address[] memory paths = new address[](2);
+        paths[0] = address(sellAddr);
+        paths[1] = address(buyAddr);
+        uint[] memory amts = router.getAmountsOut(
+            buyAmt,
+            paths
+        );
+        sellAmt = amts[1];
+    }
+
+    function checkPair(
+        IUniswapV2Router01 router,
+        address[] memory paths
+    ) internal view {
+        address pair = IUniswapV2Factory(router.factory()).getPair(paths[0], paths[1]);
+        require(pair != address(0), "No-exchange-address");
+    }
+
+    function getBuyUnitAmt(
+        TokenInterface buyAddr,
+        uint expectedAmt,
+        TokenInterface sellAddr,
+        uint sellAmt,
+        uint slippage
+    ) internal view returns (uint unitAmt) {
+        uint _sellAmt = convertTo18((sellAddr).decimals(), sellAmt);
+        uint _buyAmt = convertTo18(buyAddr.decimals(), expectedAmt);
+        unitAmt = wdiv(_buyAmt, _sellAmt);
+        unitAmt = wmul(unitAmt, sub(WAD, slippage));
+    }
+
+    function getSellUnitAmt(
+        TokenInterface sellAddr,
+        uint expectedAmt,
+        TokenInterface buyAddr,
+        uint buyAmt,
+        uint slippage
+    ) internal view returns (uint unitAmt) {
+        uint _buyAmt = convertTo18(buyAddr.decimals(), buyAmt);
+        uint _sellAmt = convertTo18(sellAddr.decimals(), expectedAmt);
+        unitAmt = wdiv(_sellAmt, _buyAmt);
+        unitAmt = wmul(unitAmt, add(WAD, slippage));
+    }
+
+}
+
+
+contract Resolver is UniswapHelpers {
+
+    function getBuyAmount(address buyAddr, address sellAddr, uint sellAmt, uint slippage) public view returns (uint expectedRate, uint unitAmt) {
+        (TokenInterface _buyAddr, TokenInterface _sellAddr) = changeEthAddress(buyAddr, sellAddr);
+        expectedRate = getExpectedSellAmt(address(_buyAddr), address(_sellAddr), sellAmt);
+        unitAmt = getBuyUnitAmt(_buyAddr, expectedRate, _sellAddr, sellAmt, slippage);
+    }
+
+    function getSellAmount(address buyAddr, address sellAddr, uint buyAmt, uint slippage) public view returns (uint expectedRate, uint unitAmt) {
+        (TokenInterface _buyAddr, TokenInterface _sellAddr) = changeEthAddress(buyAddr, sellAddr);
+        expectedRate = getExpectedSellAmt(address(_buyAddr), address(_sellAddr), buyAmt);
+        unitAmt = getSellUnitAmt(_sellAddr, expectedRate, _buyAddr, buyAmt, slippage);
+    }
+}
+
+
+contract InstaUniswapV2Resolver is Resolver {
+    string public constant name = "UniswapV2-Resolver-v1";
+}
+