feat(router): add constant-product swap router

src/FluxRouter.sol

@@ -0,0 +1,158 @@
+// SPDX-License-Identifier: MIT
+pragma solidity 0.8.36;
+
+import {IFluxFactory} from "./interfaces/IFluxFactory.sol";
+import {IFluxPair} from "./interfaces/IFluxPair.sol";
+import {IErc20} from "./interfaces/IErc20.sol";
+import {FluxLibrary} from "./libraries/FluxLibrary.sol";
+
+/// @title User-facing entrypoint for liquidity and multi-hop swaps.
+contract FluxRouter {
+    address public immutable factory;
+
+    modifier ensure(uint256 deadline) {
+        require(deadline >= block.timestamp, "FluxRouter: EXPIRED");
+        _;
+    }
+
+    constructor(address factoryAddress) {
+        factory = factoryAddress;
+    }
+
+    function _safeTransferFrom(address token, address from, address to, uint256 value) private {
+        (bool success, bytes memory returndata) =
+            token.call(abi.encodeWithSelector(IErc20.transferFrom.selector, from, to, value));
+        require(
+            success && (returndata.length == 0 || abi.decode(returndata, (bool))), "FluxRouter: TRANSFER_FROM_FAILED"
+        );
+    }
+
+    function _addLiquidity(
+        address tokenA,
+        address tokenB,
+        uint256 amountADesired,
+        uint256 amountBDesired,
+        uint256 amountAMin,
+        uint256 amountBMin
+    ) private returns (uint256 amountA, uint256 amountB) {
+        if (IFluxFactory(factory).getPair(tokenA, tokenB) == address(0)) {
+            IFluxFactory(factory).createPair(tokenA, tokenB);
+        }
+        (uint256 reserveA, uint256 reserveB) = FluxLibrary.getReserves(factory, tokenA, tokenB);
+        if (reserveA == 0 && reserveB == 0) {
+            (amountA, amountB) = (amountADesired, amountBDesired);
+        } else {
+            uint256 amountBOptimal = FluxLibrary.quote(amountADesired, reserveA, reserveB);
+            if (amountBOptimal <= amountBDesired) {
+                require(amountBOptimal >= amountBMin, "FluxRouter: INSUFFICIENT_B_AMOUNT");
+                (amountA, amountB) = (amountADesired, amountBOptimal);
+            } else {
+                uint256 amountAOptimal = FluxLibrary.quote(amountBDesired, reserveB, reserveA);
+                assert(amountAOptimal <= amountADesired);
+                require(amountAOptimal >= amountAMin, "FluxRouter: INSUFFICIENT_A_AMOUNT");
+                (amountA, amountB) = (amountAOptimal, amountBDesired);
+            }
+        }
+    }
+
+    function addLiquidity(
+        address tokenA,
+        address tokenB,
+        uint256 amountADesired,
+        uint256 amountBDesired,
+        uint256 amountAMin,
+        uint256 amountBMin,
+        address to,
+        uint256 deadline
+    ) external ensure(deadline) returns (uint256 amountA, uint256 amountB, uint256 liquidity) {
+        (amountA, amountB) = _addLiquidity(tokenA, tokenB, amountADesired, amountBDesired, amountAMin, amountBMin);
+        address pair = FluxLibrary.pairFor(factory, tokenA, tokenB);
+        _safeTransferFrom(tokenA, msg.sender, pair, amountA);
+        _safeTransferFrom(tokenB, msg.sender, pair, amountB);
+        liquidity = IFluxPair(pair).mint(to);
+    }
+
+    function removeLiquidity(
+        address tokenA,
+        address tokenB,
+        uint256 liquidity,
+        uint256 amountAMin,
+        uint256 amountBMin,
+        address to,
+        uint256 deadline
+    ) public ensure(deadline) returns (uint256 amountA, uint256 amountB) {
+        address pair = FluxLibrary.pairFor(factory, tokenA, tokenB);
+        IFluxPair(pair).transferFrom(msg.sender, pair, liquidity);
+        (uint256 amount0, uint256 amount1) = IFluxPair(pair).burn(to);
+        (address token0,) = FluxLibrary.sortTokens(tokenA, tokenB);
+        (amountA, amountB) = tokenA == token0 ? (amount0, amount1) : (amount1, amount0);
+        require(amountA >= amountAMin, "FluxRouter: INSUFFICIENT_A_AMOUNT");
+        require(amountB >= amountBMin, "FluxRouter: INSUFFICIENT_B_AMOUNT");
+    }
+
+    function _swap(uint256[] memory amounts, address[] memory path, address to) private {
+        for (uint256 i; i < path.length - 1; i++) {
+            (address input, address output) = (path[i], path[i + 1]);
+            (address token0,) = FluxLibrary.sortTokens(input, output);
+            uint256 amountOut = amounts[i + 1];
+            (uint256 amount0Out, uint256 amount1Out) =
+                input == token0 ? (uint256(0), amountOut) : (amountOut, uint256(0));
+            address recipient = i < path.length - 2 ? FluxLibrary.pairFor(factory, output, path[i + 2]) : to;
+            IFluxPair(FluxLibrary.pairFor(factory, input, output)).swap(amount0Out, amount1Out, recipient, new bytes(0));
+        }
+    }
+
+    function swapExactTokensForTokens(
+        uint256 amountIn,
+        uint256 amountOutMin,
+        address[] calldata path,
+        address to,
+        uint256 deadline
+    ) external ensure(deadline) returns (uint256[] memory amounts) {
+        amounts = FluxLibrary.getAmountsOut(factory, amountIn, path);
+        require(amounts[amounts.length - 1] >= amountOutMin, "FluxRouter: INSUFFICIENT_OUTPUT_AMOUNT");
+        _safeTransferFrom(path[0], msg.sender, FluxLibrary.pairFor(factory, path[0], path[1]), amounts[0]);
+        _swap(amounts, path, to);
+    }
+
+    function swapTokensForExactTokens(
+        uint256 amountOut,
+        uint256 amountInMax,
+        address[] calldata path,
+        address to,
+        uint256 deadline
+    ) external ensure(deadline) returns (uint256[] memory amounts) {
+        amounts = FluxLibrary.getAmountsIn(factory, amountOut, path);
+        require(amounts[0] <= amountInMax, "FluxRouter: EXCESSIVE_INPUT_AMOUNT");
+        _safeTransferFrom(path[0], msg.sender, FluxLibrary.pairFor(factory, path[0], path[1]), amounts[0]);
+        _swap(amounts, path, to);
+    }
+
+    function quote(uint256 amountA, uint256 reserveA, uint256 reserveB) external pure returns (uint256 amountB) {
+        return FluxLibrary.quote(amountA, reserveA, reserveB);
+    }
+
+    function getAmountOut(uint256 amountIn, uint256 reserveIn, uint256 reserveOut)
+        external
+        pure
+        returns (uint256 amountOut)
+    {
+        return FluxLibrary.getAmountOut(amountIn, reserveIn, reserveOut);
+    }
+
+    function getAmountIn(uint256 amountOut, uint256 reserveIn, uint256 reserveOut)
+        external
+        pure
+        returns (uint256 amountIn)
+    {
+        return FluxLibrary.getAmountIn(amountOut, reserveIn, reserveOut);
+    }
+
+    function getAmountsOut(uint256 amountIn, address[] calldata path) external view returns (uint256[] memory amounts) {
+        return FluxLibrary.getAmountsOut(factory, amountIn, path);
+    }
+
+    function getAmountsIn(uint256 amountOut, address[] calldata path) external view returns (uint256[] memory amounts) {
+        return FluxLibrary.getAmountsIn(factory, amountOut, path);
+    }
+}