// File: contracts/TwapPair.sol



// SPDX-License-Identifier: GPL-3.0-or-later
// Deployed with donations via Gitcoin GR9

pragma solidity 0.7.6;

import './interfaces/ITwapPair.sol';
import './libraries/Reserves.sol';
import './TwapLPToken.sol';
import './libraries/Math.sol';
import './interfaces/IERC20.sol';
import './interfaces/ITwapFactory.sol';
import './interfaces/ITwapOracle.sol';

contract TwapPair is Reserves, TwapLPToken, ITwapPair {
    using SafeMath for uint256;

    uint256 private constant PRECISION = 10**18;

    uint256 public override mintFee = 0;
    uint256 public override burnFee = 0;
    uint256 public override swapFee = 0;

    uint256 public constant override MINIMUM_LIQUIDITY = 10**3;

    bytes4 private constant SELECTOR = bytes4(keccak256(bytes('transfer(address,uint256)')));

    address public immutable override factory;
    address public override token0;
    address public override token1;
    address public override oracle;
    address public override trader;

    uint256 private unlocked = 1;
    modifier lock() {
        require(unlocked == 1, 'TP06');
        unlocked = 0;
        _;
        unlocked = 1;
    }

    function isContract(address addr) private view returns (bool) {
        uint256 size;
        assembly {
            size := extcodesize(addr)
        }
        return size > 0;
    }

    function setMintFee(uint256 fee) external override {
        require(msg.sender == factory, 'TP00');
        require(fee != mintFee, 'TP01');
        mintFee = fee;
        emit SetMintFee(fee);
    }

    function setBurnFee(uint256 fee) external override {
        require(msg.sender == factory, 'TP00');
        require(fee != burnFee, 'TP01');
        burnFee = fee;
        emit SetBurnFee(fee);
    }

    function setSwapFee(uint256 fee) external override {
        require(msg.sender == factory, 'TP00');
        require(fee != swapFee, 'TP01');
        swapFee = fee;
        emit SetSwapFee(fee);
    }

    function setOracle(address _oracle) external override {
        require(msg.sender == factory, 'TP00');
        require(_oracle != oracle, 'TP01');
        require(_oracle != address(0), 'TP02');
        require(isContract(_oracle), 'TP1D');
        oracle = _oracle;
        emit SetOracle(_oracle);
    }

    function setTrader(address _trader) external override {
        require(msg.sender == factory, 'TP00');
        require(_trader != trader, 'TP01');
        // Allow trader to be set as address(0) to disable interaction
        trader = _trader;
        emit SetTrader(_trader);
    }

    function collect(address to) external override lock {
        require(msg.sender == factory, 'TP00');
        require(to != address(0), 'TP02');
        (uint256 fee0, uint256 fee1) = getFees();
        if (fee0 > 0) _safeTransfer(token0, to, fee0);
        if (fee1 > 0) _safeTransfer(token1, to, fee1);
        setFees(0, 0);
        _sync();
    }

    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))), 'TP05');
    }

    function canTrade(address user) private view returns (bool) {
        return user == trader || user == factory;
    }

    constructor() {
        factory = msg.sender;
    }

    // called once by the factory at time of deployment
    function initialize(
        address _token0,
        address _token1,
        address _oracle,
        address _trader
    ) external override {
        require(msg.sender == factory, 'TP00');
        require(_oracle != address(0), 'TP02');
        require(isContract(_oracle), 'TP1D');
        require(isContract(_token0) && isContract(_token1), 'TP10');
        token0 = _token0;
        token1 = _token1;
        oracle = _oracle;
        trader = _trader;
    }

    // this low-level function should be called from a contract which performs important safety checks
    function mint(address to) external override lock returns (uint256 liquidityOut) {
        require(canTrade(msg.sender), 'TP0C');
        require(to != address(0), 'TP02');
        (uint112 reserve0, uint112 reserve1) = getReserves();
        (uint256 balance0, uint256 balance1) = getBalances(token0, token1);
        uint256 amount0In = balance0.sub(reserve0);
        uint256 amount1In = balance1.sub(reserve1);

        uint256 _totalSupply = totalSupply; // gas savings
        if (_totalSupply == 0) {
            liquidityOut = Math.sqrt(amount0In.mul(amount1In)).sub(MINIMUM_LIQUIDITY);
            _mint(address(0), MINIMUM_LIQUIDITY); // permanently lock the first MINIMUM_LIQUIDITY tokens
        } else {
            liquidityOut = Math.min(amount0In.mul(_totalSupply) / reserve0, amount1In.mul(_totalSupply) / reserve1);
        }

        require(liquidityOut > 0, 'TP38');
        if (mintFee > 0) {
            uint256 fee = liquidityOut.mul(mintFee).div(PRECISION);
            liquidityOut = liquidityOut.sub(fee);
            _mint(factory, fee);
        }
        _mint(to, liquidityOut);

        setReserves(balance0, balance1);

        emit Mint(msg.sender, amount0In, amount1In, liquidityOut, to);
    }

    // this low-level function should be called from a contract which performs important safety checks
    function burn(address to) external override lock returns (uint256 amount0Out, uint256 amount1Out) {
        require(canTrade(msg.sender), 'TP0C');
        require(to != address(0), 'TP02');
        uint256 _totalSupply = totalSupply; // gas savings
        require(_totalSupply > 0, 'TP36');
        address _token0 = token0; // gas savings
        address _token1 = token1; // gas savings
        (uint256 balance0, uint256 balance1) = getBalances(token0, token1);
        uint256 liquidityIn = balanceOf[address(this)];

        if (msg.sender != factory && burnFee > 0) {
            uint256 fee = liquidityIn.mul(burnFee).div(PRECISION);
            liquidityIn = liquidityIn.sub(fee);
            _transfer(address(this), factory, fee);
        }
        _burn(address(this), liquidityIn);

        amount0Out = liquidityIn.mul(balance0) / _totalSupply; // using balances ensures pro-rata distribution
        amount1Out = liquidityIn.mul(balance1) / _totalSupply; // using balances ensures pro-rata distribution
        require(amount0Out > 0 && amount1Out > 0, 'TP39');

        _safeTransfer(_token0, to, amount0Out);
        _safeTransfer(_token1, to, amount1Out);

        (balance0, balance1) = getBalances(token0, token1);
        setReserves(balance0, balance1);

        emit Burn(msg.sender, amount0Out, amount1Out, liquidityIn, 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 override lock {
        require(canTrade(msg.sender), 'TP0C');
        require(to != address(0), 'TP02');
        require((amount0Out > 0 && amount1Out == 0) || (amount1Out > 0 && amount0Out == 0), 'TP31');
        (uint112 _reserve0, uint112 _reserve1) = getReserves();
        require(amount0Out < _reserve0 && amount1Out < _reserve1, 'TP07');

        {
            // scope for _token{0,1}, avoids stack too deep errors
            address _token0 = token0;
            address _token1 = token1;
            require(to != _token0 && to != _token1, 'TP2D');
            if (amount0Out > 0) _safeTransfer(_token0, to, amount0Out); // optimistically transfer tokens
            if (amount1Out > 0) _safeTransfer(_token1, to, amount1Out); // optimistically transfer tokens
        }
        (uint256 balance0, uint256 balance1) = getBalances(token0, token1);

        if (amount0Out > 0) {
            // trading token1 for token0
            require(balance1 > _reserve1, 'TP08');
            uint256 amount1In = balance1 - _reserve1;

            emit Swap(msg.sender, 0, amount1In, amount0Out, 0, to);

            uint256 fee1 = amount1In.mul(swapFee).div(PRECISION);
            uint256 balance1After = balance1.sub(fee1);
            uint256 balance0After = ITwapOracle(oracle).tradeY(balance1After, _reserve0, _reserve1, data);
            require(balance0 >= balance0After, 'TP2E');
            uint256 fee0 = balance0.sub(balance0After);
            addFees(fee0, fee1);
            setReserves(balance0After, balance1After);
        } else {
            // trading token0 for token1
            require(balance0 > _reserve0, 'TP08');
            uint256 amount0In = balance0 - _reserve0;

            emit Swap(msg.sender, amount0In, 0, 0, amount1Out, to);

            uint256 fee0 = amount0In.mul(swapFee).div(PRECISION);
            uint256 balance0After = balance0.sub(fee0);
            uint256 balance1After = ITwapOracle(oracle).tradeX(balance0After, _reserve0, _reserve1, data);
            require(balance1 >= balance1After, 'TP2E');
            uint256 fee1 = balance1.sub(balance1After);
            addFees(fee0, fee1);
            setReserves(balance0After, balance1After);
        }
    }

    function sync() external override lock {
        require(canTrade(msg.sender), 'TP0C');
        _sync();
    }

    // force reserves to match balances
    function _sync() internal {
        syncReserves(token0, token1);
        uint256 tokens = balanceOf[address(this)];
        if (tokens > 0) {
            _transfer(address(this), factory, tokens);
        }
    }

    function getSwapAmount0In(uint256 amount1Out, bytes calldata data)
        public
        view
        override
        returns (uint256 swapAmount0In)
    {
        (uint112 reserve0, uint112 reserve1) = getReserves();
        uint256 balance1After = uint256(reserve1).sub(amount1Out);
        uint256 balance0After = ITwapOracle(oracle).tradeY(balance1After, reserve0, reserve1, data);
        return balance0After.sub(uint256(reserve0)).mul(PRECISION).ceil_div(PRECISION.sub(swapFee));
    }

    function getSwapAmount1In(uint256 amount0Out, bytes calldata data)
        public
        view
        override
        returns (uint256 swapAmount1In)
    {
        (uint112 reserve0, uint112 reserve1) = getReserves();
        uint256 balance0After = uint256(reserve0).sub(amount0Out);
        uint256 balance1After = ITwapOracle(oracle).tradeX(balance0After, reserve0, reserve1, data);
        return balance1After.add(1).sub(uint256(reserve1)).mul(PRECISION).ceil_div(PRECISION.sub(swapFee));
    }

    function getSwapAmount0Out(uint256 amount1In, bytes calldata data)
        public
        view
        override
        returns (uint256 swapAmount0Out)
    {
        (uint112 reserve0, uint112 reserve1) = getReserves();
        uint256 fee = amount1In.mul(swapFee).div(PRECISION);
        uint256 balance0After = ITwapOracle(oracle).tradeY(
            uint256(reserve1).add(amount1In).sub(fee),
            reserve0,
            reserve1,
            data
        );
        return uint256(reserve0).sub(balance0After);
    }

    function getSwapAmount1Out(uint256 amount0In, bytes calldata data)
        public
        view
        override
        returns (uint256 swapAmount1Out)
    {
        (uint112 reserve0, uint112 reserve1) = getReserves();
        uint256 fee = amount0In.mul(swapFee).div(PRECISION);
        uint256 balance1After = ITwapOracle(oracle).tradeX(
            uint256(reserve0).add(amount0In).sub(fee),
            reserve0,
            reserve1,
            data
        );
        return uint256(reserve1).sub(balance1After);
    }

    function getDepositAmount0In(uint256 amount0, bytes calldata data) external view override returns (uint256) {
        (uint112 reserve0, uint112 reserve1) = getReserves();
        return ITwapOracle(oracle).depositTradeXIn(amount0, reserve0, reserve1, data);
    }

    function getDepositAmount1In(uint256 amount1, bytes calldata data) external view override returns (uint256) {
        (uint112 reserve0, uint112 reserve1) = getReserves();
        return ITwapOracle(oracle).depositTradeYIn(amount1, reserve0, reserve1, data);
    }
}

// File: contracts/interfaces/ITwapPair.sol



// SPDX-License-Identifier: GPL-3.0-or-later
// Deployed with donations via Gitcoin GR9

pragma solidity 0.7.6;

import './ITwapERC20.sol';
import './IReserves.sol';

interface ITwapPair is ITwapERC20, IReserves {
    event Mint(address indexed sender, uint256 amount0In, uint256 amount1In, uint256 liquidityOut, address indexed to);
    event Burn(address indexed sender, uint256 amount0Out, uint256 amount1Out, uint256 liquidityIn, address indexed to);
    event Swap(
        address indexed sender,
        uint256 amount0In,
        uint256 amount1In,
        uint256 amount0Out,
        uint256 amount1Out,
        address indexed to
    );
    event SetMintFee(uint256 fee);
    event SetBurnFee(uint256 fee);
    event SetSwapFee(uint256 fee);
    event SetOracle(address account);
    event SetTrader(address trader);

    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 oracle() external view returns (address);

    function trader() external view returns (address);

    function mintFee() external view returns (uint256);

    function setMintFee(uint256 fee) external;

    function mint(address to) external returns (uint256 liquidity);

    function burnFee() external view returns (uint256);

    function setBurnFee(uint256 fee) external;

    function burn(address to) external returns (uint256 amount0, uint256 amount1);

    function swapFee() external view returns (uint256);

    function setSwapFee(uint256 fee) external;

    function setOracle(address account) external;

    function setTrader(address account) external;

    function collect(address to) external;

    function swap(
        uint256 amount0Out,
        uint256 amount1Out,
        address to,
        bytes calldata data
    ) external;

    function sync() external;

    function initialize(
        address _token0,
        address _token1,
        address _oracle,
        address _trader
    ) external;

    function getSwapAmount0In(uint256 amount1Out, bytes calldata data) external view returns (uint256 swapAmount0In);

    function getSwapAmount1In(uint256 amount0Out, bytes calldata data) external view returns (uint256 swapAmount1In);

    function getSwapAmount0Out(uint256 amount1In, bytes calldata data) external view returns (uint256 swapAmount0Out);

    function getSwapAmount1Out(uint256 amount0In, bytes calldata data) external view returns (uint256 swapAmount1Out);

    function getDepositAmount0In(uint256 amount0, bytes calldata data) external view returns (uint256 depositAmount0In);

    function getDepositAmount1In(uint256 amount1, bytes calldata data) external view returns (uint256 depositAmount1In);
}

// File: contracts/libraries/Reserves.sol



// SPDX-License-Identifier: GPL-3.0-or-later
// Deployed with donations via Gitcoin GR9

pragma solidity 0.7.6;

import '../interfaces/IReserves.sol';
import '../interfaces/IERC20.sol';
import '../libraries/SafeMath.sol';

contract Reserves is IReserves {
    using SafeMath for uint256;

    uint112 private reserve0;
    uint112 private reserve1;

    uint112 private fee0;
    uint112 private fee1;

    function getReserves() public view override returns (uint112, uint112) {
        return (reserve0, reserve1);
    }

    function setReserves(uint256 balance0MinusFee, uint256 balance1MinusFee) internal {
        require(balance0MinusFee != 0 && balance1MinusFee != 0, 'RS09');
        reserve0 = balance0MinusFee.toUint112();
        reserve1 = balance1MinusFee.toUint112();
    }

    function syncReserves(address token0, address token1) internal {
        uint256 balance0 = IERC20(token0).balanceOf(address(this));
        uint256 balance1 = IERC20(token1).balanceOf(address(this));

        uint256 oldBalance0 = uint256(reserve0) + fee0;
        uint256 oldBalance1 = uint256(reserve1) + fee1;

        if (balance0 != oldBalance0 || balance1 != oldBalance1) {
            if (oldBalance0 != 0) {
                fee0 = (balance0.mul(fee0).div(oldBalance0)).toUint112();
            }
            if (oldBalance1 != 0) {
                fee1 = (balance1.mul(fee1).div(oldBalance1)).toUint112();
            }

            setReserves(balance0.sub(fee0), balance1.sub(fee1));
        }
    }

    function getFees() public view override returns (uint256, uint256) {
        return (fee0, fee1);
    }

    function addFees(uint256 _fee0, uint256 _fee1) internal {
        setFees(_fee0.add(fee0), _fee1.add(fee1));
    }

    function setFees(uint256 _fee0, uint256 _fee1) internal {
        fee0 = _fee0.toUint112();
        fee1 = _fee1.toUint112();
    }

    function getBalances(address token0, address token1) internal returns (uint256, uint256) {
        uint256 balance0 = IERC20(token0).balanceOf(address(this));
        uint256 balance1 = IERC20(token1).balanceOf(address(this));
        if (fee0 > balance0) {
            fee0 = uint112(balance0);
        }
        if (fee1 > balance1) {
            fee1 = uint112(balance1);
        }
        return (balance0.sub(fee0), balance1.sub(fee1));
    }
}

// File: contracts/TwapLPToken.sol



// SPDX-License-Identifier: GPL-3.0-or-later
// Deployed with donations via Gitcoin GR9

pragma solidity 0.7.6;

import './libraries/AbstractERC20.sol';

contract TwapLPToken is AbstractERC20 {
    constructor() {
        name = 'Twap LP';
        symbol = 'TWAP-LP';
        decimals = 18;
    }
}

// File: contracts/libraries/Math.sol



// SPDX-License-Identifier: GPL-3.0-or-later
// Deployed with donations via Gitcoin GR9

pragma solidity 0.7.6;

// 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;
    }

    function max(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/interfaces/IERC20.sol



// SPDX-License-Identifier: GPL-3.0-or-later
// Deployed with donations via Gitcoin GR9

pragma solidity 0.7.6;

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/ITwapFactory.sol



// SPDX-License-Identifier: GPL-3.0-or-later
// Deployed with donations via Gitcoin GR9

pragma solidity 0.7.6;

interface ITwapFactory {
    event PairCreated(address indexed token0, address indexed token1, address pair, uint256);
    event OwnerSet(address owner);

    function owner() 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,
        address oracle,
        address trader
    ) external returns (address pair);

    function setOwner(address) external;

    function setMintFee(
        address tokenA,
        address tokenB,
        uint256 fee
    ) external;

    function setBurnFee(
        address tokenA,
        address tokenB,
        uint256 fee
    ) external;

    function setSwapFee(
        address tokenA,
        address tokenB,
        uint256 fee
    ) external;

    function setOracle(
        address tokenA,
        address tokenB,
        address oracle
    ) external;

    function setTrader(
        address tokenA,
        address tokenB,
        address trader
    ) external;

    function collect(
        address tokenA,
        address tokenB,
        address to
    ) external;

    function withdraw(
        address tokenA,
        address tokenB,
        uint256 amount,
        address to
    ) external;
}

// File: contracts/interfaces/ITwapOracle.sol



// SPDX-License-Identifier: GPL-3.0-or-later
// Deployed with donations via Gitcoin GR9

pragma solidity 0.7.6;

interface ITwapOracle {
    event OwnerSet(address owner);
    event UniswapPairSet(address uniswapPair);

    function decimalsConverter() external view returns (int256);

    function xDecimals() external view returns (uint8);

    function yDecimals() external view returns (uint8);

    function owner() external view returns (address);

    function uniswapPair() external view returns (address);

    function getPriceInfo() external view returns (uint256 priceAccumulator, uint32 priceTimestamp);

    function getSpotPrice() external view returns (uint256);

    function getAveragePrice(uint256 priceAccumulator, uint32 priceTimestamp) external view returns (uint256);

    function setOwner(address _owner) external;

    function setUniswapPair(address _uniswapPair) external;

    function tradeX(
        uint256 xAfter,
        uint256 xBefore,
        uint256 yBefore,
        bytes calldata data
    ) external view returns (uint256 yAfter);

    function tradeY(
        uint256 yAfter,
        uint256 yBefore,
        uint256 xBefore,
        bytes calldata data
    ) external view returns (uint256 xAfter);

    function depositTradeXIn(
        uint256 xLeft,
        uint256 xBefore,
        uint256 yBefore,
        bytes calldata data
    ) external view returns (uint256 xIn);

    function depositTradeYIn(
        uint256 yLeft,
        uint256 yBefore,
        uint256 xBefore,
        bytes calldata data
    ) external view returns (uint256 yIn);
}

// File: contracts/interfaces/ITwapERC20.sol



// SPDX-License-Identifier: GPL-3.0-or-later
// Deployed with donations via Gitcoin GR9

pragma solidity 0.7.6;

import './IERC20.sol';

interface ITwapERC20 is IERC20 {
    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;

    function increaseAllowance(address spender, uint256 addedValue) external returns (bool);

    function decreaseAllowance(address spender, uint256 subtractedValue) external returns (bool);
}

// File: contracts/interfaces/IReserves.sol



// SPDX-License-Identifier: GPL-3.0-or-later
// Deployed with donations via Gitcoin GR9

pragma solidity 0.7.6;

interface IReserves {
    function getReserves() external view returns (uint112 reserve0, uint112 reserve1);

    function getFees() external view returns (uint256 fee0, uint256 fee1);
}

// File: contracts/libraries/SafeMath.sol



// SPDX-License-Identifier: GPL-3.0-or-later
// Deployed with donations via Gitcoin GR9

pragma solidity 0.7.6;

// a library for performing overflow-safe math, courtesy of DappHub (https://github.com/dapphub/ds-math)

library SafeMath {
    int256 private constant _INT256_MIN = -2**255;

    function add(uint256 x, uint256 y) internal pure returns (uint256 z) {
        require((z = x + y) >= x, 'SM4E');
    }

    function sub(uint256 x, uint256 y) internal pure returns (uint256 z) {
        z = sub(x, y, 'SM12');
    }

    function sub(
        uint256 x,
        uint256 y,
        string memory message
    ) internal pure returns (uint256 z) {
        require((z = x - y) <= x, message);
    }

    function mul(uint256 x, uint256 y) internal pure returns (uint256 z) {
        require(y == 0 || (z = x * y) / y == x, 'SM2A');
    }

    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b > 0, 'SM43');
        uint256 c = a / b;
        return c;
    }

    function ceil_div(uint256 a, uint256 b) internal pure returns (uint256 c) {
        c = div(a, b);
        if (c == mul(a, b)) {
            return c;
        } else {
            return add(c, 1);
        }
    }

    function toUint32(uint256 n) internal pure returns (uint32) {
        require(n <= type(uint32).max, 'SM50');
        return uint32(n);
    }

    function toUint112(uint256 n) internal pure returns (uint112) {
        require(n <= type(uint112).max, 'SM51');
        return uint112(n);
    }

    function toInt256(uint256 unsigned) internal pure returns (int256 signed) {
        require(unsigned <= uint256(type(int256).max), 'SM34');
        signed = int256(unsigned);
    }

    // int256

    function add(int256 a, int256 b) internal pure returns (int256) {
        int256 c = a + b;
        require((b >= 0 && c >= a) || (b < 0 && c < a), 'SM4D');

        return c;
    }

    function sub(int256 a, int256 b) internal pure returns (int256) {
        int256 c = a - b;
        require((b >= 0 && c <= a) || (b < 0 && c > a), 'SM11');

        return c;
    }

    function mul(int256 a, int256 b) internal pure returns (int256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
        if (a == 0) {
            return 0;
        }

        require(!(a == -1 && b == _INT256_MIN), 'SM29');

        int256 c = a * b;
        require(c / a == b, 'SM29');

        return c;
    }

    function div(int256 a, int256 b) internal pure returns (int256) {
        require(b != 0, 'SM43');
        require(!(b == -1 && a == _INT256_MIN), 'SM42');

        int256 c = a / b;

        return c;
    }
}

// File: contracts/libraries/AbstractERC20.sol



// SPDX-License-Identifier: GPL-3.0-or-later
// Deployed with donations via Gitcoin GR9

pragma solidity 0.7.6;

import '../interfaces/ITwapERC20.sol';
import './SafeMath.sol';

abstract contract AbstractERC20 is ITwapERC20 {
    using SafeMath for uint256;

    string public override name;
    string public override symbol;
    uint8 public override decimals;

    uint256 public override totalSupply;
    mapping(address => uint256) public override balanceOf;
    mapping(address => mapping(address => uint256)) public override allowance;

    bytes32 public constant DOMAIN_TYPEHASH =
        keccak256('EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)');
    // keccak256("Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)");
    bytes32 public constant override PERMIT_TYPEHASH =
        0x6e71edae12b1b97f4d1f60370fef10105fa2faae0126114a169c64845d6126c9;
    mapping(address => uint256) public override nonces;

    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
    ) internal {
        allowance[owner][spender] = value;
        emit Approval(owner, spender, value);
    }

    function _transfer(
        address from,
        address to,
        uint256 value
    ) internal {
        balanceOf[from] = balanceOf[from].sub(value);
        balanceOf[to] = balanceOf[to].add(value);
        emit Transfer(from, to, value);
    }

    function approve(address spender, uint256 value) external override returns (bool) {
        _approve(msg.sender, spender, value);
        return true;
    }

    function increaseAllowance(address spender, uint256 addedValue) external override returns (bool) {
        _approve(msg.sender, spender, allowance[msg.sender][spender].add(addedValue));
        return true;
    }

    function decreaseAllowance(address spender, uint256 subtractedValue) external override returns (bool) {
        uint256 currentAllowance = allowance[msg.sender][spender];
        require(currentAllowance >= subtractedValue, 'TA48');
        _approve(msg.sender, spender, currentAllowance.sub(subtractedValue));
        return true;
    }

    function transfer(address to, uint256 value) external override returns (bool) {
        _transfer(msg.sender, to, value);
        return true;
    }

    function transferFrom(
        address from,
        address to,
        uint256 value
    ) external override 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 override {
        require(deadline >= block.timestamp, 'TA04');
        bytes32 digest = keccak256(
            abi.encodePacked(
                '\x19\x01',
                getDomainSeparator(),
                keccak256(abi.encode(PERMIT_TYPEHASH, owner, spender, value, nonces[owner]++, deadline))
            )
        );
        address recoveredAddress = ecrecover(digest, v, r, s);
        require(recoveredAddress != address(0) && recoveredAddress == owner, 'TA2F');
        _approve(owner, spender, value);
    }

    function getDomainSeparator() public view returns (bytes32) {
        uint256 chainId;
        assembly {
            chainId := chainid()
        }
        return
            keccak256(
                abi.encode(DOMAIN_TYPEHASH, keccak256(bytes(name)), keccak256(bytes('1')), chainId, address(this))
            );
    }
}