Single hop swap

contracts/SingleHopSwap.sol

@@ -0,0 +1,67 @@
+pragma solidity 0.8.11;
+
+// Efficient single hop swap without relying on UniswapV2Lib
+
+import "@rari-capital/solmate/src/utils/SafeTransferLib.sol";
+
+interface IUniswapV2Pair {
+    function swap(uint amount0Out, uint amount1Out, address to, bytes calldata data) external;
+    function getReserves() external view returns (uint112 reserve0, uint112 reserve1, uint32 blockTimestampLast);
+}
+
+contract Swapper {
+
+    using SafeTransferLib for ERC20;
+
+    address public immutable factory;
+
+    constructor(address _factory) {
+        factory = _factory;
+    }
+
+    function swap(
+        address tokenIn,
+        address tokenOut,
+        uint256 amountIn,
+        uint256 amountOutMin
+    ) external returns (uint256 outAmount) {
+
+        address pair = _pairFor(tokenIn, tokenOut);
+
+        ERC20(tokenIn).safeTransfer(pair, amountIn);
+
+        (uint256 reserve0, uint256 reserve1, ) = IUniswapV2Pair(pair).getReserves();
+
+        if (tokenIn < tokenOut) {
+            outAmount = _getAmountOut(amountIn, reserve0, reserve1);
+            IUniswapV2Pair(pair).swap(0, outAmount, address(this), "");
+        } else {
+            outAmount = _getAmountOut(amountIn, reserve1, reserve0);
+            IUniswapV2Pair(pair).swap(outAmount, 0, address(this), "");
+        }
+
+        require(outAmount > amountOutMin);
+    }
+
+    function _getAmountOut(
+        uint256 amountIn,
+        uint256 reserveIn,
+        uint256 reserveOut
+    ) internal pure returns (uint256) {
+        uint256 amountInWithFee = amountIn * 997;
+        uint256 numerator = amountInWithFee * reserveOut;
+        uint256 denominator = reserveIn * 1000 + amountInWithFee;
+        return numerator / denominator;
+    }
+
+    function _pairFor(address tokenA, address tokenB) internal view returns (address) {
+        (address token0, address token1) = tokenA < tokenB ? (tokenA, tokenB) : (tokenB, tokenA);
+        return address(uint160(uint256(keccak256(abi.encodePacked(
+            hex'ff',
+            factory,
+            keccak256(abi.encodePacked(token0, token1)),
+            hex'e18a34eb0e04b04f7a0ac29a6e80748dca96319b42c54d679cb821dca90c6303'
+        )))));
+    }
+
+}

package.json

@@ -86,5 +86,8 @@
     "ts-node": "^10.4.0",
     "typechain": "^6.1.0",
     "typescript": "^4.5.0"
+  },
+  "dependencies": {
+    "@rari-capital/solmate": "^6.2.0"
   }
 }

yarn.lock

@@ -782,6 +782,11 @@
   resolved "https://registry.yarnpkg.com/@openzeppelin/contracts/-/contracts-4.4.1.tgz#3382db2cd83ab565ed9626765e7da92944b45de8"
   integrity sha512-o+pHCf/yMLSlV5MkDQEzEQL402i6SoRnktru+0rdSxVEFZcTzzGhZCAtZjUFyKGazMSv1TilzMg+RbED1N8XHQ==
 
+"@rari-capital/solmate@^6.2.0":
+  version "6.2.0"
+  resolved "https://registry.yarnpkg.com/@rari-capital/solmate/-/solmate-6.2.0.tgz#4f70dc236606c27ec2cb1b4261dd830235d01fe4"
+  integrity sha512-g94F+Ra9ixyJyNgvnOIufNjUz488uEG0nxIEEtJ7+g+tA1XGUupRB2kB5b+VO7WYO26RNOVD2fW6xE4e14iWpg==
+
 "@resolver-engine/core@^0.3.3":
   version "0.3.3"
   resolved "https://registry.yarnpkg.com/@resolver-engine/core/-/core-0.3.3.tgz#590f77d85d45bc7ecc4e06c654f41345db6ca967"