Contract Source Code:

// SPDX-License-Identifier: GPL-2.0-or-later
pragma solidity ^0.8.0;

import "./interfaces/IBanana.sol";
import "../utils/Ownable.sol";
import "../libraries/TransferHelper.sol";
import "../libraries/FullMath.sol";

contract Banana is IBanana, Ownable {
    using FullMath for uint256;

    string public constant override name = "Banana";
    string public constant override symbol = "BANA";
    uint8 public constant override decimals = 18;

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

    mapping(address => bool) public minters;

    constructor(address apeXToken_, uint256 redeemTime_) {
        owner = msg.sender;
        apeXToken = apeXToken_;
        redeemTime = redeemTime_;
        minters[msg.sender] = true;
    }

    function updateRedeemTime(uint256 redeemTime_) external onlyOwner {
        require(redeemTime_ > block.timestamp, "need over current time");
        emit RedeemTimeChanged(redeemTime, redeemTime_);
        redeemTime = redeemTime_;
    }

    function addMinter(address minter) external onlyOwner {
        minters[minter] = true;
    }

    function removeMinter(address minter) external onlyOwner {
        minters[minter] = false;
    }

    function mint(address to, uint256 apeXAmount) external override returns (uint256) {
        require(minters[msg.sender], "forbidden");
        require(apeXAmount > 0, "zero amount");

        uint256 apeXBalance = IERC20(apeXToken).balanceOf(address(this));
        uint256 mintAmount;
        if (totalSupply == 0) {
            mintAmount = apeXAmount * 1000;
        } else {
            mintAmount = apeXAmount.mulDiv(totalSupply, apeXBalance);
        }

        TransferHelper.safeTransferFrom(apeXToken, msg.sender, address(this), apeXAmount);
        _mint(to, mintAmount);
        return mintAmount;
    }

    function burn(uint256 amount) external override returns (bool) {
        _burn(msg.sender, amount);
        return true;
    }

    function burnFrom(address from, uint256 amount) external override returns (bool) {
        _spendAllowance(from, msg.sender, amount);
        _burn(from, amount);
        return true;
    }

    function redeem(uint256 amount) external override returns (uint256) {
        require(block.timestamp >= redeemTime, "unredeemable");
        require(balanceOf[msg.sender] >= amount, "not enough balance");

        uint256 totalApeX = IERC20(apeXToken).balanceOf(address(this));
        uint256 apeXAmount = amount.mulDiv(totalApeX, totalSupply);

        _burn(msg.sender, amount);
        TransferHelper.safeTransfer(apeXToken, msg.sender, apeXAmount);

        emit Redeem(msg.sender, amount, apeXAmount);
        return apeXAmount;
    }

    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) {
        _spendAllowance(from, msg.sender, value);
        _transfer(from, to, value);
        return true;
    }

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

    function _spendAllowance(
        address from,
        address spender,
        uint256 value
    ) internal virtual {
        uint256 currentAllowance = allowance[from][spender];
        if (currentAllowance != type(uint256).max) {
            require(currentAllowance >= value, "insufficient allowance");
            unchecked {
                _approve(owner, spender, currentAllowance - value);
            }
        }
    }

    function _mint(address to, uint256 value) internal {
        require(to != address(0), "zero address");
        totalSupply = totalSupply + value;
        balanceOf[to] = balanceOf[to] + value;
        emit Transfer(address(0), to, value);
    }

    function _burn(address from, uint256 value) internal {
        require(balanceOf[from] >= value, "balance of from < value");
        balanceOf[from] = balanceOf[from] - value;
        totalSupply = totalSupply - 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 {
        require(to != address(0), "can not tranfer to zero address");
        uint256 fromBalance = balanceOf[from];
        require(fromBalance >= value, "transfer amount exceeds balance");
        balanceOf[from] = fromBalance - value;
        balanceOf[to] = balanceOf[to] + value;
        emit Transfer(from, to, value);
    }
}

// SPDX-License-Identifier: GPL-2.0-or-later
pragma solidity ^0.8.0;

import "../../interfaces/IERC20.sol";

interface IBanana is IERC20 {
    event RedeemTimeChanged(uint256 oldRedeemTime, uint256 newRedeemTime);
    event Redeem(address indexed user, uint256 burntAmount, uint256 apeXAmount);

    function apeXToken() external view returns (address);
    function redeemTime() external view returns (uint256);

    function mint(address to, uint256 apeXAmount) external returns (uint256);
    function burn(uint256 amount) external returns (bool);
    function burnFrom(address from, uint256 amount) external returns (bool);
    function redeem(uint256 amount) external returns (uint256);
}

// SPDX-License-Identifier: GPL-2.0-or-later
pragma solidity ^0.8.0;

abstract contract Ownable {
    address public owner;
    address public pendingOwner;

    event NewOwner(address indexed oldOwner, address indexed newOwner);
    event NewPendingOwner(address indexed oldPendingOwner, address indexed newPendingOwner);

    modifier onlyOwner() {
        require(msg.sender == owner, "Ownable: REQUIRE_OWNER");
        _;
    }

    function setPendingOwner(address newPendingOwner) external onlyOwner {
        require(pendingOwner != newPendingOwner, "Ownable: ALREADY_SET");
        emit NewPendingOwner(pendingOwner, newPendingOwner);
        pendingOwner = newPendingOwner;
    }

    function acceptOwner() external {
        require(msg.sender == pendingOwner, "Ownable: REQUIRE_PENDING_OWNER");
        address oldOwner = owner;
        address oldPendingOwner = pendingOwner;
        owner = pendingOwner;
        pendingOwner = address(0);
        emit NewOwner(oldOwner, owner);
        emit NewPendingOwner(oldPendingOwner, pendingOwner);
    }
}

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

// helper methods for interacting with ERC20 tokens and sending ETH that do not consistently return true/false
library TransferHelper {
    function safeApprove(
        address token,
        address to,
        uint256 value
    ) internal {
        // bytes4(keccak256(bytes('approve(address,uint256)')));
        (bool success, bytes memory data) = token.call(abi.encodeWithSelector(0x095ea7b3, to, value));
        require(
            success && (data.length == 0 || abi.decode(data, (bool))),
            "TransferHelper::safeApprove: approve failed"
        );
    }

    function safeTransfer(
        address token,
        address to,
        uint256 value
    ) internal {
        // bytes4(keccak256(bytes('transfer(address,uint256)')));
        (bool success, bytes memory data) = token.call(abi.encodeWithSelector(0xa9059cbb, to, value));
        require(
            success && (data.length == 0 || abi.decode(data, (bool))),
            "TransferHelper::safeTransfer: transfer failed"
        );
    }

    function safeTransferFrom(
        address token,
        address from,
        address to,
        uint256 value
    ) internal {
        // bytes4(keccak256(bytes('transferFrom(address,address,uint256)')));
        (bool success, bytes memory data) = token.call(abi.encodeWithSelector(0x23b872dd, from, to, value));
        require(
            success && (data.length == 0 || abi.decode(data, (bool))),
            "TransferHelper::transferFrom: transferFrom failed"
        );
    }

    function safeTransferETH(address to, uint256 value) internal {
        (bool success, ) = to.call{value: value}(new bytes(0));
        require(success, "TransferHelper::safeTransferETH: ETH transfer failed");
    }
}

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

/// @title Contains 512-bit math functions
/// @notice Facilitates multiplication and division that can have overflow of an intermediate value without any loss of precision
/// @dev Handles "phantom overflow" i.e., allows multiplication and division where an intermediate value overflows 256 bits
library FullMath {
    /// @notice Calculates floor(a×b÷denominator) with full precision. Throws if result overflows a uint256 or denominator == 0
    /// @param a The multiplicand
    /// @param b The multiplier
    /// @param denominator The divisor
    /// @return result The 256-bit result
    /// @dev Credit to Remco Bloemen under MIT license https://xn--2-umb.com/21/muldiv
    function mulDiv(
        uint256 a,
        uint256 b,
        uint256 denominator
    ) internal pure returns (uint256 result) {
        // 512-bit multiply [prod1 prod0] = a * b
        // Compute the product mod 2**256 and mod 2**256 - 1
        // then use the Chinese Remainder Theorem to reconstruct
        // the 512 bit result. The result is stored in two 256
        // variables such that product = prod1 * 2**256 + prod0
        uint256 prod0; // Least significant 256 bits of the product
        uint256 prod1; // Most significant 256 bits of the product

        // todo unchecked
        unchecked {
            assembly {
                let mm := mulmod(a, b, not(0))
                prod0 := mul(a, b)
                prod1 := sub(sub(mm, prod0), lt(mm, prod0))
            }

            // Handle non-overflow cases, 256 by 256 division
            if (prod1 == 0) {
                require(denominator > 0);
                assembly {
                    result := div(prod0, denominator)
                }
                return result;
            }

            // Make sure the result is less than 2**256.
            // Also prevents denominator == 0
            require(denominator > prod1);

            ///////////////////////////////////////////////
            // 512 by 256 division.
            ///////////////////////////////////////////////

            // Make division exact by subtracting the remainder from [prod1 prod0]
            // Compute remainder using mulmod
            uint256 remainder;
            assembly {
                remainder := mulmod(a, b, denominator)
            }
            // Subtract 256 bit number from 512 bit number
            assembly {
                prod1 := sub(prod1, gt(remainder, prod0))
                prod0 := sub(prod0, remainder)
            }

            // Factor powers of two out of denominator
            // Compute largest power of two divisor of denominator.
            // Always >= 1.
            uint256 twos = (~denominator + 1) & denominator;
            // Divide denominator by power of two
            assembly {
                denominator := div(denominator, twos)
            }

            // Divide [prod1 prod0] by the factors of two
            assembly {
                prod0 := div(prod0, twos)
            }
            // Shift in bits from prod1 into prod0. For this we need
            // to flip `twos` such that it is 2**256 / twos.
            // If twos is zero, then it becomes one
            assembly {
                twos := add(div(sub(0, twos), twos), 1)
            }

            prod0 |= prod1 * twos;

            // Invert denominator mod 2**256
            // Now that denominator is an odd number, it has an inverse
            // modulo 2**256 such that denominator * inv = 1 mod 2**256.
            // Compute the inverse by starting with a seed that is correct
            // correct for four bits. That is, denominator * inv = 1 mod 2**4
            uint256 inv = (3 * denominator) ^ 2;
            // Now use Newton-Raphson iteration to improve the precision.
            // Thanks to Hensel's lifting lemma, this also works in modular
            // arithmetic, doubling the correct bits in each step.

            inv *= 2 - denominator * inv; // inverse mod 2**8
            inv *= 2 - denominator * inv; // inverse mod 2**16
            inv *= 2 - denominator * inv; // inverse mod 2**32
            inv *= 2 - denominator * inv; // inverse mod 2**64
            inv *= 2 - denominator * inv; // inverse mod 2**128
            inv *= 2 - denominator * inv; // inverse mod 2**256

            // Because the division is now exact we can divide by multiplying
            // with the modular inverse of denominator. This will give us the
            // correct result modulo 2**256. Since the precoditions guarantee
            // that the outcome is less than 2**256, this is the final result.
            // We don't need to compute the high bits of the result and prod1
            // is no longer required.
            result = prod0 * inv;
            return result;
        }
    }

    /// @notice Calculates ceil(a×b÷denominator) with full precision. Throws if result overflows a uint256 or denominator == 0
    /// @param a The multiplicand
    /// @param b The multiplier
    /// @param denominator The divisor
    /// @return result The 256-bit result
    function mulDivRoundingUp(
        uint256 a,
        uint256 b,
        uint256 denominator
    ) internal pure returns (uint256 result) {
        result = mulDiv(a, b, denominator);
        if (mulmod(a, b, denominator) > 0) {
            require(result < type(uint256).max);
            result++;
        }
    }
}

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

interface IERC20 {
    event Approval(address indexed owner, address indexed spender, uint256 value);
    event Transfer(address indexed from, address indexed to, uint256 value);

    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 totalSupply() external view returns (uint256);

    function balanceOf(address owner) external view returns (uint256);

    function name() external view returns (string memory);

    function symbol() external view returns (string memory);

    function decimals() external pure returns (uint8);
}