feat(factory): add constant-product pair factory

src/FluxFactory.sol

@@ -0,0 +1,48 @@
+// SPDX-License-Identifier: MIT
+pragma solidity 0.8.36;
+
+import {FluxPair} from "./FluxPair.sol";
+import {IFluxFactory} from "./interfaces/IFluxFactory.sol";
+
+/// @title Deploys and registers constant-product pairs at deterministic CREATE2 addresses.
+contract FluxFactory is IFluxFactory {
+    address public feeTo;
+    address public feeToSetter;
+
+    mapping(address => mapping(address => address)) public getPair;
+    address[] public allPairs;
+
+    constructor(address setter) {
+        feeToSetter = setter;
+    }
+
+    function allPairsLength() external view returns (uint256) {
+        return allPairs.length;
+    }
+
+    function createPair(address tokenA, address tokenB) external returns (address pair) {
+        require(tokenA != tokenB, "Flux: IDENTICAL_ADDRESSES");
+        (address token0, address token1) = tokenA < tokenB ? (tokenA, tokenB) : (tokenB, tokenA);
+        require(token0 != address(0), "Flux: ZERO_ADDRESS");
+        require(getPair[token0][token1] == address(0), "Flux: PAIR_EXISTS");
+
+        bytes32 salt = keccak256(abi.encodePacked(token0, token1));
+        pair = address(new FluxPair{salt: salt}());
+        FluxPair(pair).initialize(token0, token1);
+
+        getPair[token0][token1] = pair;
+        getPair[token1][token0] = pair;
+        allPairs.push(pair);
+        emit PairCreated(token0, token1, pair, allPairs.length);
+    }
+
+    function setFeeTo(address to) external {
+        require(msg.sender == feeToSetter, "Flux: FORBIDDEN");
+        feeTo = to;
+    }
+
+    function setFeeToSetter(address setter) external {
+        require(msg.sender == feeToSetter, "Flux: FORBIDDEN");
+        feeToSetter = setter;
+    }
+}