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In this tutorial we use several helpers to common tasks. Here you can find a link to those helpers:

Swap Helper Lib

SwapHelperLib.sol
library SwapHelperLib {
uint16 internal constant MAX_DEADLINE = 200;
//...
error WrongGasContract();
error NotEnoughToPayGasFee();
error CantBeIdenticalAddresses();
error CantBeZeroAddress();
//...
// returns sorted token addresses, used to handle return values from pairs sorted in this order
function sortTokens(address tokenA, address tokenB) internal pure returns (address token0, address token1) {
if (tokenA == tokenB) revert CantBeIdenticalAddresses();
(token0, token1) = tokenA < tokenB ? (tokenA, tokenB) : (tokenB, tokenA);
if (token0 == address(0)) revert CantBeZeroAddress();
}
//...
// calculates the CREATE2 address for a pair without making any external calls
function uniswapv2PairFor(address factory, address tokenA, address tokenB) public pure returns (address pair) {
(address token0, address token1) = sortTokens(tokenA, tokenB);
pair = address(
uint160(
uint256(
keccak256(
abi.encodePacked(
hex"ff",
factory,
keccak256(abi.encodePacked(token0, token1)),
hex"96e8ac4277198ff8b6f785478aa9a39f403cb768dd02cbee326c3e7da348845f" // init code hash
)
)
)
)
);
}
//...
function _doWithdrawal(address targetZRC20, uint256 amount, bytes32 receipient) internal {
(address gasZRC20, uint256 gasFee) = IZRC20(targetZRC20).withdrawGasFee();
if (gasZRC20 != targetZRC20) revert WrongGasContract();
if (gasFee >= amount) revert NotEnoughToPayGasFee();
IZRC20(targetZRC20).approve(targetZRC20, gasFee);
IZRC20(targetZRC20).withdraw(abi.encodePacked(receipient), amount - gasFee);
}
//...
function _existsPairPool(address uniswapV2Factory, address zrc20A, address zrc20B) internal view returns (bool) {
address uniswapPool = uniswapv2PairFor(uniswapV2Factory, zrc20A, zrc20B);
return IZRC20(zrc20A).balanceOf(uniswapPool) > 0 && IZRC20(zrc20B).balanceOf(uniswapPool) > 0;
}
//...
function _doSwap(
address zetaToken,
address uniswapV2Factory,
address uniswapV2Router,
address zrc20,
uint256 amount,
address targetZRC20,
uint256 minAmountOut
) internal returns (uint256) {
bool existsPairPool = _existsPairPool(uniswapV2Factory, zrc20, targetZRC20);
address[] memory path;
if (existsPairPool) {
path = new address[](2);
path[0] = zrc20;
path[1] = targetZRC20;
} else {
path = new address[](3);
path[0] = zrc20;
path[1] = zetaToken;
path[2] = targetZRC20;
}
IZRC20(zrc20).approve(address(uniswapV2Router), amount);
uint256[] memory amounts = IUniswapV2Router01(uniswapV2Router).swapExactTokensForTokens(
amount,
minAmountOut,
path,
address(this),
block.timestamp + MAX_DEADLINE
);
return amounts[path.length - 1];
}
}

Bytes Helper Lib

BytesHelperLib.sol
library BytesHelperLib {
function bytesToAddress(bytes calldata data, uint256 offset) internal pure returns (address output) {
bytes memory b = data[offset:offset + 20];
assembly {
output := mload(add(b, 20))
}
}
//...
function bytesToUint32(bytes calldata data, uint256 offset) internal pure returns (uint32 output) {
bytes memory b = data[offset:offset + 4];
assembly {
output := mload(add(b, 4))
}
}
//...
function addressToBytes(address someAddress) internal pure returns (bytes32) {
return bytes32(uint256(uint160(someAddress)));
}
}