// SPDX-License-Identifier: MIT

pragma solidity =0.5.16;

interface IFireBirdFactory {
  event PairCreated(address indexed token0, address indexed token1, address pair, uint32 tokenWeight0, uint32 swapFee, uint256);

  function feeTo() external view returns (address);

  function formula() external view returns (address);

  function protocolFee() external view returns (uint256);

  function feeToSetter() external view returns (address);

  function getPair(
    address tokenA,
    address tokenB,
    uint32 tokenWeightA,
    uint32 swapFee
  ) external view returns (address pair);

  function allPairs(uint256) external view returns (address pair);

  function isPair(address) external view returns (bool);

  function allPairsLength() external view returns (uint256);

  function createPair(
    address tokenA,
    address tokenB,
    uint32 tokenWeightA,
    uint32 swapFee
  ) external returns (address pair);

  function getWeightsAndSwapFee(address pair)
    external
    view
    returns (
      uint32 tokenWeight0,
      uint32 tokenWeight1,
      uint32 swapFee
    );

  function setFeeTo(address) external;

  function setFeeToSetter(address) external;

  function setProtocolFee(uint256) external;
}

interface IFireBirdPair {
  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 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 PaidProtocolFee(uint112 collectedFee0, uint112 collectedFee1);
  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 getCollectedFees() external view returns (uint112 _collectedFee0, uint112 _collectedFee1);

  function getTokenWeights() external view returns (uint32 tokenWeight0, uint32 tokenWeight1);

  function getSwapFee() external view returns (uint32);

  function price0CumulativeLast() external view returns (uint256);

  function price1CumulativeLast() 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,
    uint32,
    uint32
  ) external;
}

/*
    Bancor Formula interface
*/
interface IFireBirdFormula {
  function getFactoryReserveAndWeights(
    address factory,
    address pair,
    address tokenA,
    uint8 dexId
  )
    external
    view
    returns (
      address tokenB,
      uint256 reserveA,
      uint256 reserveB,
      uint32 tokenWeightA,
      uint32 tokenWeightB,
      uint32 swapFee
    );

  function getFactoryWeightsAndSwapFee(
    address factory,
    address pair,
    uint8 dexId
  )
    external
    view
    returns (
      uint32 tokenWeight0,
      uint32 tokenWeight1,
      uint32 swapFee
    );

  function getAmountIn(
    uint256 amountOut,
    uint256 reserveIn,
    uint256 reserveOut,
    uint32 tokenWeightIn,
    uint32 tokenWeightOut,
    uint32 swapFee
  ) external view returns (uint256 amountIn);

  function getAmountOut(
    uint256 amountIn,
    uint256 reserveIn,
    uint256 reserveOut,
    uint32 tokenWeightIn,
    uint32 tokenWeightOut,
    uint32 swapFee
  ) external view returns (uint256 amountOut);

  function getFactoryAmountsIn(
    address factory,
    address tokenIn,
    address tokenOut,
    uint256 amountOut,
    address[] calldata path,
    uint8[] calldata dexIds
  ) external view returns (uint256[] memory amounts);

  function getFactoryAmountsOut(
    address factory,
    address tokenIn,
    address tokenOut,
    uint256 amountIn,
    address[] calldata path,
    uint8[] calldata dexIds
  ) external view returns (uint256[] memory amounts);

  function ensureConstantValue(
    uint256 reserve0,
    uint256 reserve1,
    uint256 balance0Adjusted,
    uint256 balance1Adjusted,
    uint32 tokenWeight0
  ) external view returns (bool);

  function getReserves(
    address pair,
    address tokenA,
    address tokenB
  ) external view returns (uint256 reserveA, uint256 reserveB);

  function getOtherToken(address pair, address tokenA) external view returns (address tokenB);

  function quote(
    uint256 amountA,
    uint256 reserveA,
    uint256 reserveB
  ) external pure returns (uint256 amountB);

  function sortTokens(address tokenA, address tokenB) external pure returns (address token0, address token1);

  function mintLiquidityFee(
    uint256 totalLiquidity,
    uint112 reserve0,
    uint112 reserve1,
    uint32 tokenWeight0,
    uint32 tokenWeight1,
    uint112 collectedFee0,
    uint112 collectedFee1
  ) external view returns (uint256 amount);
}

interface IFireBirdERC20 {
  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 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;
}

// 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");
  }

  function div(uint256 a, uint256 b) internal pure returns (uint256 c) {
    require(b > 0, "ds-math-division-by-zero");
    c = a / b;
  }
}

contract FireBirdERC20 is IFireBirdERC20 {
  using SafeMath for uint256;

  string public constant name = "FireBird Liquidity Provider";
  string public constant symbol = "FLP";
  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;

  constructor() public {
    uint256 chainId;
    assembly {
      chainId := chainid
    }
    DOMAIN_SEPARATOR = keccak256(
      abi.encode(keccak256("EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)"), keccak256(bytes(name)), keccak256(bytes("1")), chainId, address(this))
    );
  }

  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, "FLP: 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, "FLP: INVALID_SIGNATURE");
    _approve(owner, spender, value);
  }
}

// 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;
    }
  }
}

// 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);
  }
}

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);
}

interface IUniswapV2Callee {
  function uniswapV2Call(
    address sender,
    uint256 amount0,
    uint256 amount1,
    bytes calldata data
  ) external;
}

contract FireBirdPair is IFireBirdPair, FireBirdERC20 {
  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 private unlocked = 1;
  address public formula;

  uint112 private collectedFee0; // uses single storage slot, accessible via getReserves
  uint112 private collectedFee1; // uses single storage slot, accessible via getReserves
  uint32 private tokenWeight0;

  uint32 private swapFee;

  modifier lock() {
    require(unlocked == 1, "FLP: LOCKED");
    unlocked = 0;
    _;
    unlocked = 1;
  }

  function getReserves()
    public
    view
    returns (
      uint112 _reserve0,
      uint112 _reserve1,
      uint32 _blockTimestampLast
    )
  {
    _reserve0 = reserve0;
    _reserve1 = reserve1;
    _blockTimestampLast = blockTimestampLast;
  }

  function getCollectedFees() public view returns (uint112 _collectedFee0, uint112 _collectedFee1) {
    _collectedFee0 = collectedFee0;
    _collectedFee1 = collectedFee1;
  }

  function getTokenWeights() public view returns (uint32 _tokenWeight0, uint32 _tokenWeight1) {
    _tokenWeight0 = tokenWeight0;
    _tokenWeight1 = 100 - tokenWeight0;
  }

  function getSwapFee() public view returns (uint32 _swapFee) {
    _swapFee = swapFee;
  }

  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))), "FLP: TRANSFER_FAILED");
  }

  constructor() public {
    factory = msg.sender;
  }

  // called once by the factory at time of deployment
  function initialize(
    address _token0,
    address _token1,
    uint32 _tokenWeight0,
    uint32 _swapFee
  ) external {
    require(msg.sender == factory, "FLP: FORBIDDEN");
    // sufficient check
    token0 = _token0;
    token1 = _token1;
    tokenWeight0 = _tokenWeight0;
    swapFee = _swapFee;
    formula = IFireBirdFactory(factory).formula();
  }

  // update reserves and, on the first call per block, price accumulators
  function _update(
    uint256 balance0,
    uint256 balance1,
    uint112 _reserve0,
    uint112 _reserve1
  ) private {
    uint32 _tokenWeight0 = tokenWeight0;
    require(balance0 * (100 - _tokenWeight0) <= uint112(-1) && balance1 * _tokenWeight0 <= uint112(-1), "FLP: 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
      uint112 mReserve0 = _reserve0 * (100 - _tokenWeight0);
      uint112 mReserve1 = _reserve1 * _tokenWeight0;
      price0CumulativeLast += uint256(UQ112x112.encode(mReserve1).uqdiv(mReserve0)) * timeElapsed;
      price1CumulativeLast += uint256(UQ112x112.encode(mReserve0).uqdiv(mReserve1)) * timeElapsed;
    }
    reserve0 = uint112(balance0);
    reserve1 = uint112(balance1);
    blockTimestampLast = blockTimestamp;
    emit Sync(reserve0, reserve1);
  }

  function _mintFee(uint112 _reserve0, uint112 _reserve1) private returns (bool feeOn) {
    address feeTo = IFireBirdFactory(factory).feeTo();
    uint112 protocolFee = uint112(IFireBirdFactory(factory).protocolFee());
    feeOn = feeTo != address(0);
    (uint112 _collectedFee0, uint112 _collectedFee1) = getCollectedFees();
    if (protocolFee > 0 && feeOn && (_collectedFee0 > 0 || _collectedFee1 > 0)) {
      uint32 _tokenWeight0 = tokenWeight0;
      uint256 liquidity = IFireBirdFormula(formula).mintLiquidityFee(totalSupply, _reserve0, _reserve1, _tokenWeight0, 100 - _tokenWeight0, _collectedFee0 / protocolFee, _collectedFee1 / protocolFee);
      if (liquidity > 0) _mint(feeTo, liquidity);
    }
    if (_collectedFee0 > 0) collectedFee0 = 0;
    if (_collectedFee1 > 0) collectedFee1 = 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);
    _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, "FLP: INSUFFICIENT_LIQUIDITY_MINTED");
    _mint(to, liquidity);

    _update(balance0, balance1, _reserve0, _reserve1);
    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)];
    _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, "FLP: 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);
    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, "FLP: INSUFFICIENT_OUTPUT_AMOUNT");
    uint112 _reserve0 = reserve0; // gas savings
    uint112 _reserve1 = reserve1; // gas savings
    require(amount0Out < _reserve0 && amount1Out < _reserve1, "FLP: 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, "FLP: 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, "FLP: INSUFFICIENT_INPUT_AMOUNT");
    {
      // scope for reserve{0,1}Adjusted, avoids stack too deep errors
      uint256 balance0Adjusted = balance0.mul(10000);
      uint256 balance1Adjusted = balance1.mul(10000);
      {
        // avoids stack too deep errors
        if (amount0In > 0) {
          uint256 amount0InFee = amount0In.mul(swapFee);
          balance0Adjusted = balance0Adjusted.sub(amount0InFee);
          collectedFee0 = uint112(uint256(collectedFee0).add(amount0InFee));
        }
        if (amount1In > 0) {
          uint256 amount1InFee = amount1In.mul(swapFee);
          balance1Adjusted = balance1Adjusted.sub(amount1InFee);
          collectedFee1 = uint112(uint256(collectedFee1).add(amount1InFee));
        }
        uint32 _tokenWeight0 = tokenWeight0; // gas savings
        if (_tokenWeight0 == 50) {
          // gas savings for pair 50/50
          require(balance0Adjusted.mul(balance1Adjusted) >= uint256(_reserve0).mul(_reserve1).mul(10000**2), "FLP: K");
        } else {
          require(IFireBirdFormula(formula).ensureConstantValue(uint256(_reserve0).mul(10000), uint256(_reserve1).mul(10000), balance0Adjusted, balance1Adjusted, _tokenWeight0), "FLP: 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);
  }
}

contract FireBirdFactory is IFireBirdFactory {
  address public feeTo;
  address public formula;
  uint256 public protocolFee;
  address public feeToSetter;

  mapping(bytes32 => address) private _pairSalts;
  address[] public allPairs;
  mapping(address => uint64) private _pairs;

  constructor(address _feeToSetter, address _formula) public {
    feeToSetter = _feeToSetter;
    formula = _formula;
  }

  function isPair(address b) external view returns (bool) {
    return _pairs[b] > 0;
  }

  function allPairsLength() external view returns (uint256) {
    return allPairs.length;
  }

  function getPair(
    address tokenA,
    address tokenB,
    uint32 tokenWeightA,
    uint32 swapFee
  ) external view returns (address pair) {
    (address token0, address token1, uint32 tokenWeight0) = tokenA < tokenB ? (tokenA, tokenB, tokenWeightA) : (tokenB, tokenA, 100 - tokenWeightA);
    bytes32 salt = keccak256(abi.encodePacked(token0, token1, tokenWeight0, swapFee));
    pair = _pairSalts[salt];
  }

  function createPair(
    address tokenA,
    address tokenB,
    uint32 tokenWeightA,
    uint32 swapFee
  ) external returns (address pair) {
    require(tokenA != tokenB, "FLP: IDENTICAL_ADDRESSES");
    require(tokenWeightA >= 2 && tokenWeightA <= 98 && (tokenWeightA % 2) == 0, "FLP: INVALID_TOKEN_WEIGHT");
    // swap fee from [0.01% - 20%]
    require(swapFee >= 1 && swapFee <= 2000, "FLP: INVALID_SWAP_FEE");
    (address token0, address token1, uint32 tokenWeight0) = tokenA < tokenB ? (tokenA, tokenB, tokenWeightA) : (tokenB, tokenA, 100 - tokenWeightA);
    require(token0 != address(0), "FLP: ZERO_ADDRESS");
    // single check is sufficient
    bytes memory bytecode = type(FireBirdPair).creationCode;
    bytes32 salt = keccak256(abi.encodePacked(token0, token1, tokenWeight0, swapFee));
    require(_pairSalts[salt] == address(0), "FLP: PAIR_EXISTS");
    assembly {
      pair := create2(0, add(bytecode, 32), mload(bytecode), salt)
    }
    IFireBirdPair(pair).initialize(token0, token1, tokenWeight0, swapFee);
    _pairSalts[salt] = address(pair);
    allPairs.push(pair);
    uint64 weightAndFee = uint64(swapFee);
    weightAndFee |= uint64(tokenWeight0) << 32;
    _pairs[address(pair)] = weightAndFee;
    emit PairCreated(token0, token1, pair, tokenWeight0, swapFee, allPairs.length);
  }

  function setFeeTo(address _feeTo) external {
    require(msg.sender == feeToSetter, "FLP: FORBIDDEN");
    feeTo = _feeTo;
  }

  function setFeeToSetter(address _feeToSetter) external {
    require(msg.sender == feeToSetter, "FLP: FORBIDDEN");
    feeToSetter = _feeToSetter;
  }

  function setProtocolFee(uint256 _protocolFee) external {
    require(msg.sender == feeToSetter, "FLP: FORBIDDEN");
    require(_protocolFee == 0 || (_protocolFee >= 10000 && _protocolFee <= 100000), "FLP: Invalid Protocol fee");
    protocolFee = _protocolFee;
  }

  function getWeightsAndSwapFee(address pair)
    public
    view
    returns (
      uint32 tokenWeight0,
      uint32 tokenWeight1,
      uint32 swapFee
    )
  {
    uint64 weightAndFee = _pairs[pair];
    if (weightAndFee > 0) {
      swapFee = uint32(weightAndFee);
      tokenWeight0 = uint32(weightAndFee >> 32);
      tokenWeight1 = 100 - tokenWeight0;
    } else {
      // Default is 0.3%
      return (50, 50, 30);
    }
  }
}