restruct contract repo

contracts/external/ERC20/NormalERC20.sol

@@ -0,0 +1,72 @@
+/*
+
+    Copyright 2020 DODO ZOO.
+    SPDX-License-Identifier: Apache-2.0
+
+*/
+
+pragma solidity 0.6.9;
+
+import {SafeMath} from "../../lib/SafeMath.sol";
+
+contract TestERC20 {
+    using SafeMath for uint256;
+
+    string public name;
+    uint8 public decimals;
+
+    mapping(address => uint256) balances;
+    mapping(address => mapping(address => uint256)) internal allowed;
+
+    event Transfer(address indexed from, address indexed to, uint256 amount);
+    event Approval(address indexed owner, address indexed spender, uint256 amount);
+
+    constructor(string memory _name, uint8 _decimals) public {
+        name = _name;
+        decimals = _decimals;
+    }
+
+    function transfer(address to, uint256 amount) public returns (bool) {
+        require(to != address(0), "TO_ADDRESS_IS_EMPTY");
+        require(amount <= balances[msg.sender], "BALANCE_NOT_ENOUGH");
+
+        balances[msg.sender] = balances[msg.sender].sub(amount);
+        balances[to] = balances[to].add(amount);
+        emit Transfer(msg.sender, to, amount);
+        return true;
+    }
+
+    function balanceOf(address owner) public view returns (uint256 balance) {
+        return balances[owner];
+    }
+
+    function transferFrom(
+        address from,
+        address to,
+        uint256 amount
+    ) public returns (bool) {
+        require(to != address(0), "TO_ADDRESS_IS_EMPTY");
+        require(amount <= balances[from], "BALANCE_NOT_ENOUGH");
+        require(amount <= allowed[from][msg.sender], "ALLOWANCE_NOT_ENOUGH");
+
+        balances[from] = balances[from].sub(amount);
+        balances[to] = balances[to].add(amount);
+        allowed[from][msg.sender] = allowed[from][msg.sender].sub(amount);
+        emit Transfer(from, to, amount);
+        return true;
+    }
+
+    function approve(address spender, uint256 amount) public returns (bool) {
+        allowed[msg.sender][spender] = amount;
+        emit Approval(msg.sender, spender, amount);
+        return true;
+    }
+
+    function allowance(address owner, address spender) public view returns (uint256) {
+        return allowed[owner][spender];
+    }
+
+    function mint(address account, uint256 amount) external {
+        balances[account] = balances[account].add(amount);
+    }
+}

contracts/external/ERC20/TestWETH.sol

@@ -0,0 +1,77 @@
+/*
+
+    Copyright 2020 DODO ZOO.
+    SPDX-License-Identifier: Apache-2.0
+
+*/
+
+pragma solidity 0.6.9;
+
+
+contract WETH9 {
+    string public name = "Wrapped Ether";
+    string public symbol = "WETH";
+    uint8 public decimals = 18;
+
+    event Approval(address indexed src, address indexed guy, uint256 wad);
+    event Transfer(address indexed src, address indexed dst, uint256 wad);
+    event Deposit(address indexed dst, uint256 wad);
+    event Withdrawal(address indexed src, uint256 wad);
+
+    mapping(address => uint256) public balanceOf;
+    mapping(address => mapping(address => uint256)) public allowance;
+
+    fallback() external payable {
+        deposit();
+    }
+
+    receive() external payable {
+        deposit();
+    }
+
+    function deposit() public payable {
+        balanceOf[msg.sender] += msg.value;
+        emit Deposit(msg.sender, msg.value);
+    }
+
+    function withdraw(uint256 wad) public {
+        require(balanceOf[msg.sender] >= wad);
+        balanceOf[msg.sender] -= wad;
+        msg.sender.transfer(wad);
+        emit Withdrawal(msg.sender, wad);
+    }
+
+    function totalSupply() public view returns (uint256) {
+        return address(this).balance;
+    }
+
+    function approve(address guy, uint256 wad) public returns (bool) {
+        allowance[msg.sender][guy] = wad;
+        emit Approval(msg.sender, guy, wad);
+        return true;
+    }
+
+    function transfer(address dst, uint256 wad) public returns (bool) {
+        return transferFrom(msg.sender, dst, wad);
+    }
+
+    function transferFrom(
+        address src,
+        address dst,
+        uint256 wad
+    ) public returns (bool) {
+        require(balanceOf[src] >= wad);
+
+        if (src != msg.sender && allowance[src][msg.sender] != uint256(-1)) {
+            require(allowance[src][msg.sender] >= wad);
+            allowance[src][msg.sender] -= wad;
+        }
+
+        balanceOf[src] -= wad;
+        balanceOf[dst] += wad;
+
+        Transfer(src, dst, wad);
+
+        return true;
+    }
+}

contracts/external/uniswap/UniswapV2.sol

@@ -0,0 +1,638 @@
+/*
+ Submitted for verification at Etherscan.io on 2020-05-05
+ SPDX-License-Identifier: Apache-2.0
+ */
+
+// File: contracts/interfaces/IUniswapV2Pair.sol
+
+pragma solidity >=0.5.0;
+
+interface IUniswapV2Pair {
+    event Approval(address indexed owner, address indexed spender, uint256 value);
+    event Transfer(address indexed from, address indexed to, uint256 value);
+
+    function name() external pure returns (string memory);
+
+    function symbol() external pure returns (string memory);
+
+    function decimals() external pure returns (uint8);
+
+    function totalSupply() external view returns (uint256);
+
+    function balanceOf(address owner) external view returns (uint256);
+
+    function allowance(address owner, address spender) external view returns (uint256);
+
+    function approve(address spender, uint256 value) external returns (bool);
+
+    function transfer(address to, uint256 value) external returns (bool);
+
+    function transferFrom(
+        address from,
+        address to,
+        uint256 value
+    ) external returns (bool);
+
+    function DOMAIN_SEPARATOR() external view returns (bytes32);
+
+    function PERMIT_TYPEHASH() external pure returns (bytes32);
+
+    function nonces(address owner) external view returns (uint256);
+
+    function permit(
+        address owner,
+        address spender,
+        uint256 value,
+        uint256 deadline,
+        uint8 v,
+        bytes32 r,
+        bytes32 s
+    ) external;
+
+    event Mint(address indexed sender, uint256 amount0, uint256 amount1);
+    event Burn(address indexed sender, uint256 amount0, uint256 amount1, address indexed to);
+    event Swap(
+        address indexed sender,
+        uint256 amount0In,
+        uint256 amount1In,
+        uint256 amount0Out,
+        uint256 amount1Out,
+        address indexed to
+    );
+    event Sync(uint112 reserve0, uint112 reserve1);
+
+    function MINIMUM_LIQUIDITY() external pure returns (uint256);
+
+    function factory() external view returns (address);
+
+    function token0() external view returns (address);
+
+    function token1() external view returns (address);
+
+    function getReserves()
+        external
+        view
+        returns (
+            uint112 reserve0,
+            uint112 reserve1,
+            uint32 blockTimestampLast
+        );
+
+    function price0CumulativeLast() external view returns (uint256);
+
+    function price1CumulativeLast() external view returns (uint256);
+
+    function kLast() external view returns (uint256);
+
+    function mint(address to) external returns (uint256 liquidity);
+
+    function burn(address to) external returns (uint256 amount0, uint256 amount1);
+
+    function swap(
+        uint256 amount0Out,
+        uint256 amount1Out,
+        address to,
+        bytes calldata data
+    ) external;
+
+    function skim(address to) external;
+
+    function sync() external;
+
+    function initialize(address, address) external;
+}
+
+// File: contracts/interfaces/IUniswapV2ERC20.sol
+
+pragma solidity >=0.5.0;
+
+interface IUniswapV2ERC20 {
+    event Approval(address indexed owner, address indexed spender, uint256 value);
+    event Transfer(address indexed from, address indexed to, uint256 value);
+
+    function name() external pure returns (string memory);
+
+    function symbol() external pure returns (string memory);
+
+    function decimals() external pure returns (uint8);
+
+    function totalSupply() external view returns (uint256);
+
+    function balanceOf(address owner) external view returns (uint256);
+
+    function allowance(address owner, address spender) external view returns (uint256);
+
+    function approve(address spender, uint256 value) external returns (bool);
+
+    function transfer(address to, uint256 value) external returns (bool);
+
+    function transferFrom(
+        address from,
+        address to,
+        uint256 value
+    ) external returns (bool);
+
+    function DOMAIN_SEPARATOR() external view returns (bytes32);
+
+    function PERMIT_TYPEHASH() external pure returns (bytes32);
+
+    function nonces(address owner) external view returns (uint256);
+
+    function permit(
+        address owner,
+        address spender,
+        uint256 value,
+        uint256 deadline,
+        uint8 v,
+        bytes32 r,
+        bytes32 s
+    ) external;
+}
+
+// File: contracts/libraries/SafeMath.sol
+
+pragma solidity 0.6.9;
+
+// a library for performing overflow-safe math, courtesy of DappHub (https://github.com/dapphub/ds-math)
+
+library SafeMath {
+    function add(uint256 x, uint256 y) internal pure returns (uint256 z) {
+        require((z = x + y) >= x, "ds-math-add-overflow");
+    }
+
+    function sub(uint256 x, uint256 y) internal pure returns (uint256 z) {
+        require((z = x - y) <= x, "ds-math-sub-underflow");
+    }
+
+    function mul(uint256 x, uint256 y) internal pure returns (uint256 z) {
+        require(y == 0 || (z = x * y) / y == x, "ds-math-mul-overflow");
+    }
+}
+
+// File: contracts/UniswapV2ERC20.sol
+
+pragma solidity 0.6.9;
+
+contract UniswapV2ERC20 {
+    using SafeMath for uint256;
+
+    string public constant name = "Uniswap V2";
+    string public constant symbol = "UNI-V2";
+    uint8 public constant decimals = 18;
+    uint256 public totalSupply;
+    mapping(address => uint256) public balanceOf;
+    mapping(address => mapping(address => uint256)) public allowance;
+
+    bytes32 public DOMAIN_SEPARATOR;
+    // keccak256("Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)");
+    bytes32
+        public constant PERMIT_TYPEHASH = 0x6e71edae12b1b97f4d1f60370fef10105fa2faae0126114a169c64845d6126c9;
+    mapping(address => uint256) public nonces;
+
+    event Approval(address indexed owner, address indexed spender, uint256 value);
+    event Transfer(address indexed from, address indexed to, uint256 value);
+
+    function _mint(address to, uint256 value) internal {
+        totalSupply = totalSupply.add(value);
+        balanceOf[to] = balanceOf[to].add(value);
+        emit Transfer(address(0), to, value);
+    }
+
+    function _burn(address from, uint256 value) internal {
+        balanceOf[from] = balanceOf[from].sub(value);
+        totalSupply = totalSupply.sub(value);
+        emit Transfer(from, address(0), value);
+    }
+
+    function _approve(
+        address owner,
+        address spender,
+        uint256 value
+    ) private {
+        allowance[owner][spender] = value;
+        emit Approval(owner, spender, value);
+    }
+
+    function _transfer(
+        address from,
+        address to,
+        uint256 value
+    ) private {
+        balanceOf[from] = balanceOf[from].sub(value);
+        balanceOf[to] = balanceOf[to].add(value);
+        emit Transfer(from, to, value);
+    }
+
+    function approve(address spender, uint256 value) external returns (bool) {
+        _approve(msg.sender, spender, value);
+        return true;
+    }
+
+    function transfer(address to, uint256 value) external returns (bool) {
+        _transfer(msg.sender, to, value);
+        return true;
+    }
+
+    function transferFrom(
+        address from,
+        address to,
+        uint256 value
+    ) external returns (bool) {
+        if (allowance[from][msg.sender] != uint256(-1)) {
+            allowance[from][msg.sender] = allowance[from][msg.sender].sub(value);
+        }
+        _transfer(from, to, value);
+        return true;
+    }
+
+    function permit(
+        address owner,
+        address spender,
+        uint256 value,
+        uint256 deadline,
+        uint8 v,
+        bytes32 r,
+        bytes32 s
+    ) external {
+        require(deadline >= block.timestamp, "UniswapV2: EXPIRED");
+        bytes32 digest = keccak256(
+            abi.encodePacked(
+                "\x19\x01",
+                DOMAIN_SEPARATOR,
+                keccak256(
+                    abi.encode(PERMIT_TYPEHASH, owner, spender, value, nonces[owner]++, deadline)
+                )
+            )
+        );
+        address recoveredAddress = ecrecover(digest, v, r, s);
+        require(
+            recoveredAddress != address(0) && recoveredAddress == owner,
+            "UniswapV2: INVALID_SIGNATURE"
+        );
+        _approve(owner, spender, value);
+    }
+}
+
+// File: contracts/libraries/Math.sol
+
+pragma solidity 0.6.9;
+
+// a library for performing various math operations
+
+library Math {
+    function min(uint256 x, uint256 y) internal pure returns (uint256 z) {
+        z = x < y ? x : y;
+    }
+
+    // babylonian method (https://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Babylonian_method)
+    function sqrt(uint256 y) internal pure returns (uint256 z) {
+        if (y > 3) {
+            z = y;
+            uint256 x = y / 2 + 1;
+            while (x < z) {
+                z = x;
+                x = (y / x + x) / 2;
+            }
+        } else if (y != 0) {
+            z = 1;
+        }
+    }
+}
+
+// File: contracts/libraries/UQ112x112.sol
+
+pragma solidity 0.6.9;
+
+// a library for handling binary fixed point numbers (https://en.wikipedia.org/wiki/Q_(number_format))
+
+// range: [0, 2**112 - 1]
+// resolution: 1 / 2**112
+
+library UQ112x112 {
+    uint224 constant Q112 = 2**112;
+
+    // encode a uint112 as a UQ112x112
+    function encode(uint112 y) internal pure returns (uint224 z) {
+        z = uint224(y) * Q112; // never overflows
+    }
+
+    // divide a UQ112x112 by a uint112, returning a UQ112x112
+    function uqdiv(uint224 x, uint112 y) internal pure returns (uint224 z) {
+        z = x / uint224(y);
+    }
+}
+
+// File: contracts/interfaces/IERC20.sol
+
+pragma solidity >=0.5.0;
+
+interface IERC20 {
+    event Approval(address indexed owner, address indexed spender, uint256 value);
+    event Transfer(address indexed from, address indexed to, uint256 value);
+
+    function name() external view returns (string memory);
+
+    function symbol() external view returns (string memory);
+
+    function decimals() external view returns (uint8);
+
+    function totalSupply() external view returns (uint256);
+
+    function balanceOf(address owner) external view returns (uint256);
+
+    function allowance(address owner, address spender) external view returns (uint256);
+
+    function approve(address spender, uint256 value) external returns (bool);
+
+    function transfer(address to, uint256 value) external returns (bool);
+
+    function transferFrom(
+        address from,
+        address to,
+        uint256 value
+    ) external returns (bool);
+}
+
+// File: contracts/interfaces/IUniswapV2Factory.sol
+
+pragma solidity >=0.5.0;
+
+interface IUniswapV2Factory {
+    event PairCreated(address indexed token0, address indexed token1, address pair, uint256);
+
+    function feeTo() external view returns (address);
+
+    function feeToSetter() external view returns (address);
+
+    function getPair(address tokenA, address tokenB) external view returns (address pair);
+
+    function allPairs(uint256) external view returns (address pair);
+
+    function allPairsLength() external view returns (uint256);
+
+    function createPair(address tokenA, address tokenB) external returns (address pair);
+
+    function setFeeTo(address) external;
+
+    function setFeeToSetter(address) external;
+}
+
+// File: contracts/interfaces/IUniswapV2Callee.sol
+
+pragma solidity >=0.5.0;
+
+interface IUniswapV2Callee {
+    function uniswapV2Call(
+        address sender,
+        uint256 amount0,
+        uint256 amount1,
+        bytes calldata data
+    ) external;
+}
+
+// File: contracts/UniswapV2Pair.sol
+
+pragma solidity 0.6.9;
+
+contract UniswapV2Pair is UniswapV2ERC20 {
+    using SafeMath for uint256;
+    using UQ112x112 for uint224;
+
+    uint256 public constant MINIMUM_LIQUIDITY = 10**3;
+    bytes4 private constant SELECTOR = bytes4(keccak256(bytes("transfer(address,uint256)")));
+
+    address public factory;
+    address public token0;
+    address public token1;
+
+    uint112 private reserve0; // uses single storage slot, accessible via getReserves
+    uint112 private reserve1; // uses single storage slot, accessible via getReserves
+    uint32 private blockTimestampLast; // uses single storage slot, accessible via getReserves
+
+    uint256 public price0CumulativeLast;
+    uint256 public price1CumulativeLast;
+    uint256 public kLast; // reserve0 * reserve1, as of immediately after the most recent liquidity event
+
+    uint256 private unlocked = 1;
+    modifier lock() {
+        require(unlocked == 1, "UniswapV2: LOCKED");
+        unlocked = 0;
+        _;
+        unlocked = 1;
+    }
+
+    function getReserves()
+        public
+        view
+        returns (
+            uint112 _reserve0,
+            uint112 _reserve1,
+            uint32 _blockTimestampLast
+        )
+    {
+        _reserve0 = reserve0;
+        _reserve1 = reserve1;
+        _blockTimestampLast = blockTimestampLast;
+    }
+
+    function _safeTransfer(
+        address token,
+        address to,
+        uint256 value
+    ) private {
+        (bool success, bytes memory data) = token.call(abi.encodeWithSelector(SELECTOR, to, value));
+        require(
+            success && (data.length == 0 || abi.decode(data, (bool))),
+            "UniswapV2: TRANSFER_FAILED"
+        );
+    }
+
+    event Mint(address indexed sender, uint256 amount0, uint256 amount1);
+    event Burn(address indexed sender, uint256 amount0, uint256 amount1, address indexed to);
+    event Swap(
+        address indexed sender,
+        uint256 amount0In,
+        uint256 amount1In,
+        uint256 amount0Out,
+        uint256 amount1Out,
+        address indexed to
+    );
+    event Sync(uint112 reserve0, uint112 reserve1);
+
+    constructor() public {
+        factory = msg.sender;
+    }
+
+    // called once by the factory at time of deployment
+    function initialize(address _token0, address _token1) external {
+        require(msg.sender == factory, "UniswapV2: FORBIDDEN"); // sufficient check
+        token0 = _token0;
+        token1 = _token1;
+    }
+
+    // update reserves and, on the first call per block, price accumulators
+    function _update(
+        uint256 balance0,
+        uint256 balance1,
+        uint112 _reserve0,
+        uint112 _reserve1
+    ) private {
+        require(balance0 <= uint112(-1) && balance1 <= uint112(-1), "UniswapV2: OVERFLOW");
+        uint32 blockTimestamp = uint32(block.timestamp % 2**32);
+        uint32 timeElapsed = blockTimestamp - blockTimestampLast; // overflow is desired
+        if (timeElapsed > 0 && _reserve0 != 0 && _reserve1 != 0) {
+            // * never overflows, and + overflow is desired
+            price0CumulativeLast +=
+                uint256(UQ112x112.encode(_reserve1).uqdiv(_reserve0)) *
+                timeElapsed;
+            price1CumulativeLast +=
+                uint256(UQ112x112.encode(_reserve0).uqdiv(_reserve1)) *
+                timeElapsed;
+        }
+        reserve0 = uint112(balance0);
+        reserve1 = uint112(balance1);
+        blockTimestampLast = blockTimestamp;
+        emit Sync(reserve0, reserve1);
+    }
+
+    // if fee is on, mint liquidity equivalent to 1/6th of the growth in sqrt(k)
+    function _mintFee(uint112 _reserve0, uint112 _reserve1) private returns (bool feeOn) {
+        address feeTo = IUniswapV2Factory(factory).feeTo();
+        feeOn = feeTo != address(0);
+        uint256 _kLast = kLast; // gas savings
+        if (feeOn) {
+            if (_kLast != 0) {
+                uint256 rootK = Math.sqrt(uint256(_reserve0).mul(_reserve1));
+                uint256 rootKLast = Math.sqrt(_kLast);
+                if (rootK > rootKLast) {
+                    uint256 numerator = totalSupply.mul(rootK.sub(rootKLast));
+                    uint256 denominator = rootK.mul(5).add(rootKLast);
+                    uint256 liquidity = numerator / denominator;
+                    if (liquidity > 0) _mint(feeTo, liquidity);
+                }
+            }
+        } else if (_kLast != 0) {
+            kLast = 0;
+        }
+    }
+
+    // this low-level function should be called from a contract which performs important safety checks
+    function mint(address to) external lock returns (uint256 liquidity) {
+        (uint112 _reserve0, uint112 _reserve1, ) = getReserves(); // gas savings
+        uint256 balance0 = IERC20(token0).balanceOf(address(this));
+        uint256 balance1 = IERC20(token1).balanceOf(address(this));
+        uint256 amount0 = balance0.sub(_reserve0);
+        uint256 amount1 = balance1.sub(_reserve1);
+
+        bool feeOn = _mintFee(_reserve0, _reserve1);
+        uint256 _totalSupply = totalSupply; // gas savings, must be defined here since totalSupply can update in _mintFee
+        if (_totalSupply == 0) {
+            liquidity = Math.sqrt(amount0.mul(amount1)).sub(MINIMUM_LIQUIDITY);
+            _mint(address(0), MINIMUM_LIQUIDITY); // permanently lock the first MINIMUM_LIQUIDITY tokens
+        } else {
+            liquidity = Math.min(
+                amount0.mul(_totalSupply) / _reserve0,
+                amount1.mul(_totalSupply) / _reserve1
+            );
+        }
+        require(liquidity > 0, "UniswapV2: INSUFFICIENT_LIQUIDITY_MINTED");
+        _mint(to, liquidity);
+
+        _update(balance0, balance1, _reserve0, _reserve1);
+        if (feeOn) kLast = uint256(reserve0).mul(reserve1); // reserve0 and reserve1 are up-to-date
+        emit Mint(msg.sender, amount0, amount1);
+    }
+
+    // this low-level function should be called from a contract which performs important safety checks
+    function burn(address to) external lock returns (uint256 amount0, uint256 amount1) {
+        (uint112 _reserve0, uint112 _reserve1, ) = getReserves(); // gas savings
+        address _token0 = token0; // gas savings
+        address _token1 = token1; // gas savings
+        uint256 balance0 = IERC20(_token0).balanceOf(address(this));
+        uint256 balance1 = IERC20(_token1).balanceOf(address(this));
+        uint256 liquidity = balanceOf[address(this)];
+
+        bool feeOn = _mintFee(_reserve0, _reserve1);
+        uint256 _totalSupply = totalSupply; // gas savings, must be defined here since totalSupply can update in _mintFee
+        amount0 = liquidity.mul(balance0) / _totalSupply; // using balances ensures pro-rata distribution
+        amount1 = liquidity.mul(balance1) / _totalSupply; // using balances ensures pro-rata distribution
+        require(amount0 > 0 && amount1 > 0, "UniswapV2: INSUFFICIENT_LIQUIDITY_BURNED");
+        _burn(address(this), liquidity);
+        _safeTransfer(_token0, to, amount0);
+        _safeTransfer(_token1, to, amount1);
+        balance0 = IERC20(_token0).balanceOf(address(this));
+        balance1 = IERC20(_token1).balanceOf(address(this));
+
+        _update(balance0, balance1, _reserve0, _reserve1);
+        if (feeOn) kLast = uint256(reserve0).mul(reserve1); // reserve0 and reserve1 are up-to-date
+        emit Burn(msg.sender, amount0, amount1, to);
+    }
+
+    // this low-level function should be called from a contract which performs important safety checks
+    function swap(
+        uint256 amount0Out,
+        uint256 amount1Out,
+        address to,
+        bytes calldata data
+    ) external lock {
+        require(amount0Out > 0 || amount1Out > 0, "UniswapV2: INSUFFICIENT_OUTPUT_AMOUNT");
+        (uint112 _reserve0, uint112 _reserve1, ) = getReserves(); // gas savings
+        require(
+            amount0Out < _reserve0 && amount1Out < _reserve1,
+            "UniswapV2: INSUFFICIENT_LIQUIDITY"
+        );
+
+        uint256 balance0;
+        uint256 balance1;
+        {
+            // scope for _token{0,1}, avoids stack too deep errors
+            address _token0 = token0;
+            address _token1 = token1;
+            require(to != _token0 && to != _token1, "UniswapV2: INVALID_TO");
+            if (amount0Out > 0) _safeTransfer(_token0, to, amount0Out); // optimistically transfer tokens
+            if (amount1Out > 0) _safeTransfer(_token1, to, amount1Out); // optimistically transfer tokens
+            if (data.length > 0)
+                IUniswapV2Callee(to).uniswapV2Call(msg.sender, amount0Out, amount1Out, data);
+            balance0 = IERC20(_token0).balanceOf(address(this));
+            balance1 = IERC20(_token1).balanceOf(address(this));
+        }
+        uint256 amount0In = balance0 > _reserve0 - amount0Out
+            ? balance0 - (_reserve0 - amount0Out)
+            : 0;
+        uint256 amount1In = balance1 > _reserve1 - amount1Out
+            ? balance1 - (_reserve1 - amount1Out)
+            : 0;
+        require(amount0In > 0 || amount1In > 0, "UniswapV2: INSUFFICIENT_INPUT_AMOUNT");
+        {
+            // scope for reserve{0,1}Adjusted, avoids stack too deep errors
+            uint256 balance0Adjusted = balance0.mul(1000).sub(amount0In.mul(3));
+            uint256 balance1Adjusted = balance1.mul(1000).sub(amount1In.mul(3));
+            require(
+                balance0Adjusted.mul(balance1Adjusted) >=
+                    uint256(_reserve0).mul(_reserve1).mul(1000**2),
+                "UniswapV2: K"
+            );
+        }
+
+        _update(balance0, balance1, _reserve0, _reserve1);
+        emit Swap(msg.sender, amount0In, amount1In, amount0Out, amount1Out, to);
+    }
+
+    // force balances to match reserves
+    function skim(address to) external lock {
+        address _token0 = token0; // gas savings
+        address _token1 = token1; // gas savings
+        _safeTransfer(_token0, to, IERC20(_token0).balanceOf(address(this)).sub(reserve0));
+        _safeTransfer(_token1, to, IERC20(_token1).balanceOf(address(this)).sub(reserve1));
+    }
+
+    // force reserves to match balances
+    function sync() external lock {
+        _update(
+            IERC20(token0).balanceOf(address(this)),
+            IERC20(token1).balanceOf(address(this)),
+            reserve0,
+            reserve1
+        );
+    }
+}