FlashKub.sol

// SPDX-License-Identifier: MIT
// author: yoyoismee.eth -- it's opensource but also feel free to send me coffee/beer.          

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pragma solidity 0.8.14;
import "@openzeppelin/contracts/security/ReentrancyGuard.sol";
import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";

interface IFlashLoanReceiver {

    function executeOperation(address _reserve, uint256 _amount, uint256 _fee, bytes calldata _params) external;
}

// flash kub protocol
contract FlashKub is ReentrancyGuard{
    using SafeERC20 for IERC20;

    IERC20 constant KUSDT = IERC20(0x7d984C24d2499D840eB3b7016077164e15E5faA6);
    mapping(address => uint256) share;
    uint feeBips = 9; // 0.09 % fees
    uint256 totalShare;

    function deposit(uint amount) external nonReentrant{
        uint initialBal = KUSDT.balanceOf(address(this));
        if (totalShare == 0){
            totalShare = amount;
            share[msg.sender] += amount;
        }else{
            uint newShare = amount * initialBal / totalShare;
            totalShare += newShare;
            share[msg.sender] += newShare;
        }
        KUSDT.safeTransferFrom(msg.sender,address(this), amount);
        
    }

    function flashloan(address _receiver, address _reserve, uint256 _amount, bytes memory _params) external{
        _flashLoan(_receiver,_reserve,_amount,_params);

    }
    function flashloan(address _receiver, uint _amount, bytes memory _params) external{
        _flashLoan(_receiver,address(KUSDT),_amount,_params);
    }
    function flashloan( uint _amount, bytes memory _params) external{
        _flashLoan(msg.sender,address(KUSDT),_amount,_params);
    }

    function withdraw(uint amount) external nonReentrant{
        require(amount <= share[msg.sender]);
        uint initialBal = KUSDT.balanceOf(address(this));
        uint toSend = amount * initialBal / totalShare;
        totalShare -= amount;
        share[msg.sender] -= amount;
        KUSDT.safeTransfer(msg.sender, toSend);
    }

    function _flashLoan(address _receiver, address _reserve, uint256 _amount, bytes memory _params)
        public
        nonReentrant
    {

        uint256 availableLiquidityBefore = KUSDT.balanceOf(address(this));

        require(
            availableLiquidityBefore >= _amount,
            "There is not enough liquidity available to borrow"
        );

        //calculate amount fee
        uint256 amountFee = _amount * feeBips / 10000;

        //get the FlashLoanReceiver instance
        IFlashLoanReceiver receiver = IFlashLoanReceiver(_receiver);

        //transfer funds to the receiver
        KUSDT.safeTransfer(_receiver, _amount);

        //execute action of the receiver
        receiver.executeOperation(address(KUSDT), _amount, amountFee, _params);

        //check that the actual balance of the core contract includes the returned amount
        uint256 availableLiquidityAfter  = KUSDT.balanceOf(address(this));

        require(
            availableLiquidityAfter == availableLiquidityBefore + amountFee,
            "The actual balance of the protocol is inconsistent"
        );

    }

}