Add uniswap v2 path finder algo

contracts/protocols/uniswapV2.sol

@@ -85,6 +85,22 @@ contract UniswapHelpers is Helpers {
         _sell = sell == getEthAddr() ? TokenInterface(getAddressWETH()) : TokenInterface(sell);
     }
 
+    function checkPaths(
+        IUniswapV2Router02 router,
+        address[] memory paths
+    ) internal view returns(bool isValid) {
+        isValid = true;
+        for (uint i; i < paths.length - 1; i++) {
+            if (paths[i] == paths[i + 1]) {
+                return false;
+            }
+            address pair = IUniswapV2Factory(router.factory()).getPair(paths[i], paths[i + 1]);
+            if (pair == address(0)) {
+                return false;
+            }
+        }
+    }
+
     function getExpectedBuyAmt(
         address buyAddr,
         address sellAddr,
@@ -173,6 +189,40 @@ contract UniswapHelpers is Helpers {
         amtA = wmul(_tokenA.balanceOf(exchangeAddr), share);
         amtB = wmul(_tokenB.balanceOf(exchangeAddr), share);
     }
+
+    function _getExpectedBuyAmtByPath(
+        address[] memory paths,
+        uint sellAmt
+    ) internal view returns(uint buyAmt) {
+        IUniswapV2Router02 router = IUniswapV2Router02(getUniswapAddr());
+
+        if (checkPaths(router, paths)) {
+            uint[] memory amts = router.getAmountsOut(
+                sellAmt,
+                paths
+            );
+            buyAmt = amts[amts.length - 1];
+        } else {
+            buyAmt = 0;
+        }
+    }
+
+    function _getExpectedSellAmtByPath(
+        address[] memory paths,
+        uint buyAmt
+    ) internal view returns(uint sellAmt) {
+        IUniswapV2Router02 router = IUniswapV2Router02(getUniswapAddr());
+
+        if (checkPaths(router, paths)) {
+           uint[] memory amts = router.getAmountsIn(
+                buyAmt,
+                paths
+            );
+            sellAmt = amts[0];
+        } else {
+            sellAmt = uint(-1);
+        }
+    }
 }
 
 
@@ -293,6 +343,134 @@ contract Resolver is UniswapHelpers {
         }
         return poolData;
     }
+
+    function getOptimalSellPath(
+        address buyAddr,
+        address sellAddr,
+        address[] memory tokens,
+        uint sellAmt,
+        uint slippage
+    ) public view returns (address[] memory paths, uint buyAmt, uint unitAmt)
+    {
+        (TokenInterface _buyAddr, TokenInterface _sellAddr) = changeEthAddress(buyAddr, sellAddr);
+
+        address[] memory _path = new address[](2);
+        _path[0] = address(_sellAddr);
+        _path[1] = address(_buyAddr);
+
+        paths = _path;
+        buyAmt = _getExpectedBuyAmtByPath(_path, sellAmt);
+
+        _path = new address[](3);
+        _path[0] = address(_sellAddr);
+        _path[2] = address(_buyAddr);
+
+        uint i;
+        uint j;
+        uint _buyAmt;
+
+        for(i = 0; i < tokens.length; i++) {
+            _path[1] = tokens[i];
+
+            _buyAmt = _getExpectedBuyAmtByPath(_path, sellAmt);
+
+            if (_buyAmt > buyAmt) {
+                buyAmt = _buyAmt;
+                paths = new address[](3);
+                paths[0] = _path[0];
+                paths[1] = _path[1];
+                paths[2] = _path[2];
+            }
+        }
+
+        _path = new address[](4);
+        _path[0] = address(_sellAddr);
+        _path[3] = address(_buyAddr);
+
+        for(i = 0; i < tokens.length; i++) {
+            for(j = 0; j < tokens.length; j++) {
+                _path[1] = tokens[i];
+                _path[2] = tokens[j];
+
+                _buyAmt = _getExpectedBuyAmtByPath(_path, sellAmt);
+
+                if (_buyAmt > buyAmt) {
+                    buyAmt = _buyAmt;
+                    paths = new address[](4);
+                    paths[0] = _path[0];
+                    paths[1] = _path[1];
+                    paths[2] = _path[2];
+                    paths[3] = _path[3];
+                }
+            }
+        }
+
+        unitAmt = getBuyUnitAmt(_buyAddr, buyAmt, _sellAddr, sellAmt, slippage);
+    }
+
+    function getOptimalBuyPath(
+        address buyAddr,
+        address sellAddr,
+        address[] memory tokens,
+        uint buyAmt,
+        uint slippage
+    ) public view returns (address[] memory paths, uint sellAmt, uint unitAmt)
+    {
+        (TokenInterface _buyAddr, TokenInterface _sellAddr) = changeEthAddress(buyAddr, sellAddr);
+
+        address[] memory _path = new address[](2);
+        _path[0] = address(_sellAddr);
+        _path[1] = address(_buyAddr);
+
+        paths = _path;
+        sellAmt = _getExpectedSellAmtByPath(_path, buyAmt);
+
+        _path = new address[](3);
+        _path[0] = address(_sellAddr);
+        _path[2] = address(_buyAddr);
+
+        uint i;
+        uint j;
+        uint _sellAmt;
+
+        for(i = 0; i < tokens.length; i++) {
+            _path[1] = tokens[i];
+
+            _sellAmt = _getExpectedSellAmtByPath(_path, buyAmt);
+
+            if (_sellAmt < sellAmt) {
+                sellAmt = _sellAmt;
+                paths = new address[](3);
+                paths[0] = _path[0];
+                paths[1] = _path[1];
+                paths[2] = _path[2];
+            }
+        }
+
+        _path = new address[](4);
+        _path[0] = address(_sellAddr);
+        _path[3] = address(_buyAddr);
+
+        for(i = 0; i < tokens.length; i++) {
+            for(j = 0; j < tokens.length; j++) {
+                _path[1] = tokens[i];
+                _path[2] = tokens[j];
+
+                _sellAmt = _getExpectedSellAmtByPath(_path, buyAmt);
+
+                if (_sellAmt < sellAmt) {
+                    sellAmt = _sellAmt;
+                    paths = new address[](4);
+                    paths[0] = _path[0];
+                    paths[1] = _path[1];
+                    paths[2] = _path[2];
+                    paths[3] = _path[3];
+                }
+            }
+        }
+
+        unitAmt = getSellUnitAmt(_sellAddr, sellAmt, _buyAddr, buyAmt, slippage);
+    }
 }