Contract Address Details

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

import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";
import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import "@openzeppelin/contracts/security/ReentrancyGuard.sol";

contract GDrop is Ownable, ReentrancyGuard {
    using SafeERC20 for IERC20;
    
    // Base rate for percentage calculations (10000 = 100%)
    uint256 public constant BASE_RATE = 10000;

    // Maximum array length limit
    uint256 public constant MAX_RECIPIENTS = 200;

    // Fee token address (GD token)
    IERC20 public immutable feeToken;
    
    // Fee amount per address in GD tokens
    uint256 public feePerAddress;
    
    // Fee collector address
    address public feeCollector;
    
    // Fee switch (true=enabled, false=disabled)
    bool public feeEnabled;
    
    // GD token reward parameters
    uint256 public minRewardAddresses; // Minimum addresses required for reward
    uint256 public rewardPercentage;   // Reward percentage in basis points
    uint256 public maxRewardAmount;    // Maximum reward amount per transaction
    uint256 public cooldownBlocks;     // Cooldown period in blocks between rewards
    
    // User reward tracking
    mapping(address => uint256) public lastRewardBlock; // Last reward block for each user
    
    
    // Events
    event EtherDispersed(address indexed sender, address[] recipients, uint256[] values, uint256 feeAmount);
    event TokenDispersed(address indexed token, address indexed sender, address[] recipients, uint256[] values, uint256 feeAmount);
    event GDTokenDispersed(address indexed sender, address[] recipients, uint256[] values, uint256 rewardAmount);
    event FeeCollectorUpdated(address indexed oldCollector, address indexed newCollector);
    event FeeStatusUpdated(bool enabled);
    event FeePerAddressUpdated(uint256 oldAmount, uint256 newAmount);
    event RewardParametersUpdated(uint256 minAddresses, uint256 percentage);
    event MaxRewardAmountUpdated(uint256 oldAmount, uint256 newAmount);
    event CooldownBlocksUpdated(uint256 oldBlocks, uint256 newBlocks);
    event RewardPoolDeposited(address indexed depositor, uint256 amount);
    event RewardPoolWithdrawn(address indexed recipient, uint256 amount);
    
    // Custom errors
    error ArrayLengthMismatch();
    error TransferFailed();
    error InvalidAddress();
    error ValueMismatch();
    error InsufficientAllowance();
    error InsufficientFeeAllowance();
    error ZeroLength();
    error InvalidPercentage();
    error UnequalAmounts();
    error RewardCooldownActive();
    error TooManyRecipients();
    
    /**
     * @dev Constructor
     * @param _feeToken GD token address
     * @param _feeCollector Fee collector address
     */
    constructor(address _feeToken, address _feeCollector) {
        if (_feeToken == address(0) || _feeCollector == address(0)) revert InvalidAddress();
        feeToken = IERC20(_feeToken);
        feeCollector = _feeCollector;
        feeEnabled = true; // Fee enabled by default
        feePerAddress = 10_000 * 10**18; // Default: 10K GD tokens per address
        minRewardAddresses = 10; // Default: 10 addresses
        rewardPercentage = 1000; // Default: 10% (1000/10000)
        maxRewardAmount = 1_000_000 * 10**18; // Default: 1M GD tokens
        cooldownBlocks = 43200; // Default: 43200 blocks (~1 day)
    }
    
    /**
     * @dev Batch distribute ETH to multiple recipients
     * @notice Users need to:
     *         1. Send correct amount of ETH (msg.value = sum(values))
     *         2. Pre-approve GD tokens to this contract as fee
     * @param recipients Array of recipient addresses
     * @param values Array of corresponding ETH amounts
     */
    function gdropEther(address[] calldata recipients, uint256[] calldata values) external payable nonReentrant {
        if (recipients.length == 0) revert ZeroLength();
        if (recipients.length != values.length) revert ArrayLengthMismatch();
        if (recipients.length > MAX_RECIPIENTS) revert TooManyRecipients();
        
        // Check and charge fee (requires pre-approved GD tokens)
        uint256 feeAmount_ = _chargeFee(recipients.length);
        
        uint256 total;
        for (uint256 i = 0; i < recipients.length; i++) {
            if (recipients[i] == address(0)) revert InvalidAddress();
            total += values[i];
        }
        
        // Ensure sent ETH amount equals total amount
        if (msg.value != total) revert ValueMismatch();
        
        // Distribute ETH
        for (uint256 i = 0; i < recipients.length; i++) {
            (bool success, ) = recipients[i].call{value: values[i]}("");
            if (!success) revert TransferFailed();
        }
        
        emit EtherDispersed(msg.sender, recipients, values, feeAmount_);
    }
    
    /**
     * @dev Batch distribute ERC20 tokens to multiple recipients
     * @param token ERC20 token address
     * @param recipients Array of recipient addresses
     * @param values Array of corresponding token amounts
     */
    function gdropToken(IERC20 token, address[] calldata recipients, uint256[] calldata values) external nonReentrant {
        if (recipients.length == 0) revert ZeroLength();
        if (recipients.length != values.length) revert ArrayLengthMismatch();
        if (recipients.length > MAX_RECIPIENTS) revert TooManyRecipients();
        if (address(token) == address(0)) revert InvalidAddress();
        
        // Check and charge fee
        uint256 feeAmount_ = _chargeFee(recipients.length);
        
        uint256 total;
        for (uint256 i = 0; i < recipients.length; i++) {
            if (recipients[i] == address(0)) revert InvalidAddress();
            total += values[i];
        }
        
        // Check allowance
        if (token.allowance(msg.sender, address(this)) < total) revert InsufficientAllowance();
        
        // Transfer tokens using SafeERC20
        token.safeTransferFrom(msg.sender, address(this), total);
        
        // Distribute tokens
        for (uint256 i = 0; i < recipients.length; i++) {
            token.safeTransfer(recipients[i], values[i]);
        }
        
        emit TokenDispersed(address(token), msg.sender, recipients, values, feeAmount_);
    }
    
    /**
     * @dev Batch distribute GD tokens with reward mechanism
     * @notice Reward conditions:
     *         1. Send to more than {minRewardAddresses} unique addresses
     *         2. Each address must receive the same amount
     *         3. Meeting conditions grants {rewardPercentage}% reward
     *         4. No fee charged for GD token distribution
     * @param recipients Array of recipient addresses
     * @param values Array of corresponding GD token amounts
     */
    function gdropGD(address[] calldata recipients, uint256[] calldata values) external nonReentrant {
        if (recipients.length == 0) revert ZeroLength();
        if (recipients.length != values.length) revert ArrayLengthMismatch();
        if (recipients.length > MAX_RECIPIENTS) revert TooManyRecipients();
        
        // Validate addresses and calculate total amount
        uint256 total;
        for (uint256 i = 0; i < recipients.length; i++) {
            if (recipients[i] == address(0)) revert InvalidAddress();
            total += values[i];
        }
        
        // Check allowance
        if (feeToken.allowance(msg.sender, address(this)) < total) revert InsufficientAllowance();
        
        // Calculate reward using _calculateReward (handles cooldown internally)
        uint256 rewardAmount = _calculateReward(recipients, values, total);
        
        // Adjust reward amount based on available pool balance
        if (rewardAmount > 0) {
            uint256 contractBalance = feeToken.balanceOf(address(this));
            if (contractBalance < rewardAmount) {
                // If pool balance is insufficient, set reward to 0 to avoid state inconsistency
                rewardAmount = 0;
            }
        }
        
        // Transfer GD tokens to contract
        feeToken.safeTransferFrom(msg.sender, address(this), total);
        
        // Distribute GD tokens
        for (uint256 i = 0; i < recipients.length; i++) {
            feeToken.safeTransfer(recipients[i], values[i]);
        }
        
        // Grant reward and update state atomically
        if (rewardAmount > 0) {
            // Update cooldown timestamp before sending reward
            lastRewardBlock[msg.sender] = block.number;
            feeToken.safeTransfer(msg.sender, rewardAmount);
        }
        
        emit GDTokenDispersed(msg.sender, recipients, values, rewardAmount);
    }
    
    /**
     * @dev Calculate GD token transfer reward (internal, no cooldown check)
     * @param recipients Array of recipient addresses
     * @param values Array of corresponding amounts
     * @param total Total amount
     * @return Reward amount
     */
    function _calculateRewardInternal(
        address[] calldata recipients, 
        uint256[] calldata values, 
        uint256 total
    ) internal view returns (uint256) {
        // Basic validation
        if (recipients.length == 0 || values.length == 0) return 0;
        if (recipients.length != values.length) return 0;
        if (total == 0) return 0;
        
        // Check if all amounts are equal
        if (recipients.length > 1) {
            uint256 firstAmount = values[0];
            for (uint256 i = 1; i < values.length; i++) {
                if (values[i] != firstAmount) {
                    return 0; // Unequal amounts, no reward
                }
            }
        }
        
        // Count unique addresses
        uint256 uniqueCount = _countUniqueAddresses(recipients);
        
        // Check if minimum address requirement is met
        if (uniqueCount >= minRewardAddresses) {
            uint256 calculatedReward = (total * rewardPercentage) / BASE_RATE;
            // Apply maximum reward limit
            return calculatedReward > maxRewardAmount ? maxRewardAmount : calculatedReward;
        }
        
        return 0;
    }
    
    /**
     * @dev Calculate GD token transfer reward (with cooldown check for external use)
     * @param recipients Array of recipient addresses
     * @param values Array of corresponding amounts
     * @param total Total amount
     * @return Reward amount
     */
    function _calculateReward(
        address[] calldata recipients, 
        uint256[] calldata values, 
        uint256 total
    ) internal view returns (uint256) {
        // Check cooldown period
        if (lastRewardBlock[msg.sender] + cooldownBlocks > block.number) {
            return 0; // Still in cooldown period
        }
        
        return _calculateRewardInternal(recipients, values, total);
    }
    
    /**
     * @dev Count unique addresses after deduplication
     * @param recipients Array of addresses
     * @return Number of unique addresses
     */
    function _countUniqueAddresses(address[] calldata recipients) internal pure returns (uint256) {
        if (recipients.length == 0) return 0;
        if (recipients.length == 1) return 1;
        
        uint256 uniqueCount = 0;
        
        // Use O(n²) algorithm for exact counting - acceptable for max 200 addresses
        for (uint256 i = 0; i < recipients.length; i++) {
            bool isDuplicate = false;
            // Check if current address appeared before
            for (uint256 j = 0; j < i; j++) {
                if (recipients[i] == recipients[j]) {
                    isDuplicate = true;
                    break;
                }
            }
            if (!isDuplicate) {
                uniqueCount++;
            }
        }
        
        return uniqueCount;
    }
    
    /**
     * @dev Internal function: charge fee
     * @param recipientCount Number of recipients
     * @return Actual fee amount charged
     */
    function _chargeFee(uint256 recipientCount) internal returns (uint256) {
        if (!feeEnabled) {
            return 0; // Fee disabled
        }
        
        // Check if user has approved sufficient GD tokens as fee
        if (feeToken.allowance(msg.sender, address(this)) < feePerAddress * recipientCount) {
            revert InsufficientFeeAllowance();
        }
        
        // Transfer fee to fee collector
        feeToken.safeTransferFrom(msg.sender, feeCollector, feePerAddress * recipientCount);
        return feePerAddress * recipientCount;
    }
    
    /**
     * @dev Set fee enabled status (owner only)
     * @param _enabled Whether fee is enabled
     */
    function setFeeEnabled(bool _enabled) external onlyOwner {
        feeEnabled = _enabled;
        emit FeeStatusUpdated(_enabled);
    }
    
    /**
     * @dev Set fee amount per address (owner only)
     * @param _feePerAddress New fee amount per address in GD tokens
     */
    function setFeePerAddress(uint256 _feePerAddress) external onlyOwner {
        uint256 oldAmount = feePerAddress;
        feePerAddress = _feePerAddress;
        emit FeePerAddressUpdated(oldAmount, _feePerAddress);
    }
    

    /**
     * @dev Set reward parameters (owner only)
     * @param _minAddresses Minimum addresses required for reward
     * @param _percentage Reward percentage in basis points (10000 = 100%)
     */
    function setRewardParameters(uint256 _minAddresses, uint256 _percentage) external onlyOwner {
        if (_percentage > BASE_RATE) revert InvalidPercentage(); // Maximum 100%
        minRewardAddresses = _minAddresses;
        rewardPercentage = _percentage;
        emit RewardParametersUpdated(_minAddresses, _percentage);
    }
    
    /**
     * @dev Set max reward amount (owner only)
     * @param _maxRewardAmount New max reward amount in GD tokens
     */
    function setMaxRewardAmount(uint256 _maxRewardAmount) external onlyOwner {
        uint256 oldAmount = maxRewardAmount;
        maxRewardAmount = _maxRewardAmount;
        emit MaxRewardAmountUpdated(oldAmount, _maxRewardAmount);
    }
    
    /**
     * @dev Set cooldown blocks (owner only)
     * @param _cooldownBlocks New cooldown blocks
     */
    function setCooldownBlocks(uint256 _cooldownBlocks) external onlyOwner {
        uint256 oldBlocks = cooldownBlocks;
        cooldownBlocks = _cooldownBlocks;
        emit CooldownBlocksUpdated(oldBlocks, _cooldownBlocks);
    }
    
    /**
     * @dev Update fee collector address (owner only)
     * @param _newCollector New fee collector address
     */
    function updateFeeCollector(address _newCollector) external onlyOwner {
        if (_newCollector == address(0)) revert InvalidAddress();
        address oldCollector = feeCollector;
        feeCollector = _newCollector;
        emit FeeCollectorUpdated(oldCollector, _newCollector);
    }
    
    /**
     * @dev Recover funds (owner only)
     * @param _tokenAddress Token address (0 address means ETH)
     * @param _amount Amount to recover (0 means all available balance)
     */
    function recoverFunds(address _tokenAddress, uint256 _amount) external onlyOwner nonReentrant {
        if (_tokenAddress == address(0)) {
            // Recover ETH
            uint256 balance = address(this).balance;
            uint256 amountToRecover = _amount == 0 ? balance : (_amount < balance ? _amount : balance);
            require(amountToRecover > 0, "No ETH to recover");
            
            (bool success,) = payable(owner()).call{value: amountToRecover}("");
            require(success, "ETH transfer failed");
        } else {
            // Recover other tokens
            IERC20 token = IERC20(_tokenAddress);
            uint256 balance = token.balanceOf(address(this));
            uint256 amountToRecover = _amount == 0 ? balance : (_amount < balance ? _amount : balance);
            require(amountToRecover > 0, "No tokens to recover");
            
            token.safeTransfer(owner(), amountToRecover);
        }
    }
    
    /**
     * @dev Get detailed contract information
     */
    function getContractInfo() external view returns (
        address feeTokenAddress,
        uint256 feePerAddress_,
        address feeCollectorAddress,
        bool isFeeEnabled,
        uint256 minAddresses,
        uint256 rewardPercentage_,
        uint256 maxRewardAmount_,
        uint256 cooldownBlocks_
    ) {
        return (
            address(feeToken),
            feePerAddress,
            feeCollector,
            feeEnabled,
            minRewardAddresses,
            rewardPercentage,
            maxRewardAmount,
            cooldownBlocks
        );
    }
    
    /**
     * @dev Get fee information (backward compatibility)
     */
    function getFeeInfo() external view returns (address, uint256, address) {
        return (address(feeToken), feePerAddress, feeCollector);
    }
    
    /**
     * @dev Calculate total fee for given recipient count
     * @param recipientCount Number of recipients
     * @return Total fee amount
     */
    function calculateTotalFee(uint256 recipientCount) external view returns (uint256) {
        if (!feeEnabled) {
            return 0;
        }
        return feePerAddress * recipientCount;
    }
    
    /**
     * @dev Deposit GD tokens to reward pool (anyone can deposit)
     * @param amount Amount of GD tokens to deposit
     */
    function depositRewardPool(uint256 amount) external nonReentrant {
        if (amount == 0) revert ZeroLength();
        
        // Transfer GD tokens from user to contract
        feeToken.safeTransferFrom(msg.sender, address(this), amount);
        
        emit RewardPoolDeposited(msg.sender, amount);
    }
    
    /**
     * @dev Withdraw GD tokens from reward pool (owner only)
     * @param amount Amount to withdraw (0 means all available balance)
     */
    function withdrawRewardPool(uint256 amount) external onlyOwner nonReentrant {
        uint256 balance = feeToken.balanceOf(address(this));
        uint256 amountToWithdraw = amount == 0 ? balance : (amount < balance ? amount : balance);
        
        if (amountToWithdraw == 0) revert ZeroLength();
        
        feeToken.safeTransfer(owner(), amountToWithdraw);
        
        emit RewardPoolWithdrawn(owner(), amountToWithdraw);
    }
    
    /**
     * @dev Get reward pool balance
     * @return Current GD token balance in the contract
     */
    function getRewardPoolBalance() external view returns (uint256) {
        return feeToken.balanceOf(address(this));
    }
    
    /**
     * @dev Check if user is in cooldown period
     * @param user User address to check
     * @return inCooldown Whether user is in cooldown
     * @return remainingBlocks Remaining blocks until cooldown ends (0 if not in cooldown)
     */
    function getUserCooldownStatus(address user) external view returns (bool inCooldown, uint256 remainingBlocks) {
        uint256 lastBlock = lastRewardBlock[user];
        uint256 cooldownEndBlock = lastBlock + cooldownBlocks;
        
        if (cooldownEndBlock > block.number) {
            return (true, cooldownEndBlock - block.number);
        } else {
            return (false, 0);
        }
    }
    
    /**
     * @dev Estimate reward amount for given parameters (without executing)
     * @param user User address
     * @param recipients Array of recipient addresses
     * @param values Array of corresponding amounts
     * @return estimatedReward Estimated reward amount (0 if conditions not met)
     * @return reason Reason if no reward (0: eligible, 1: cooldown, 2: unequal amounts, 3: insufficient addresses)
     */
    function estimateReward(
        address user,
        address[] calldata recipients, 
        uint256[] calldata values
    ) external view returns (uint256 estimatedReward, uint8 reason) {
        // Check cooldown period
        if (lastRewardBlock[user] + cooldownBlocks > block.number) {
            return (0, 1); // Cooldown active
        }
        
        // Check if all amounts are equal
        if (recipients.length > 1) {
            uint256 firstAmount = values[0];
            for (uint256 i = 1; i < values.length; i++) {
                if (values[i] != firstAmount) {
                    return (0, 2); // Unequal amounts
                }
            }
        }
        
        // Count unique addresses
        uint256 uniqueCount = _countUniqueAddresses(recipients);
        
        // Check if minimum address requirement is met
        if (uniqueCount < minRewardAddresses) {
            return (0, 3); // Insufficient addresses
        }
        
        // Calculate total
        uint256 total = 0;
        for (uint256 i = 0; i < values.length; i++) {
            total += values[i];
        }
        
        // Use the same logic as gdropGD function
        uint256 calculatedReward = (total * rewardPercentage) / BASE_RATE;
        uint256 finalReward = calculatedReward > maxRewardAmount ? maxRewardAmount : calculatedReward;
        
        return (finalReward, 0); // Eligible for reward
    }
} 
        

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "../utils/Context.sol";

/**
 * @dev Contract module which provides a basic access control mechanism, where
 * there is an account (an owner) that can be granted exclusive access to
 * specific functions.
 *
 * By default, the owner account will be the one that deploys the contract. This
 * can later be changed with {transferOwnership}.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be applied to your functions to restrict their use to
 * the owner.
 */
abstract contract Ownable is Context {
    address private _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor() {
        _setOwner(_msgSender());
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view virtual returns (address) {
        return _owner;
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(owner() == _msgSender(), "Ownable: caller is not the owner");
        _;
    }

    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions anymore. Can only be called by the current owner.
     *
     * NOTE: Renouncing ownership will leave the contract without an owner,
     * thereby removing any functionality that is only available to the owner.
     */
    function renounceOwnership() public virtual onlyOwner {
        _setOwner(address(0));
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Can only be called by the current owner.
     */
    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        _setOwner(newOwner);
    }

    function _setOwner(address newOwner) private {
        address oldOwner = _owner;
        _owner = newOwner;
        emit OwnershipTransferred(oldOwner, newOwner);
    }
}
          

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

/**
 * @dev Contract module that helps prevent reentrant calls to a function.
 *
 * Inheriting from `ReentrancyGuard` will make the {nonReentrant} modifier
 * available, which can be applied to functions to make sure there are no nested
 * (reentrant) calls to them.
 *
 * Note that because there is a single `nonReentrant` guard, functions marked as
 * `nonReentrant` may not call one another. This can be worked around by making
 * those functions `private`, and then adding `external` `nonReentrant` entry
 * points to them.
 *
 * TIP: If you would like to learn more about reentrancy and alternative ways
 * to protect against it, check out our blog post
 * https://blog.openzeppelin.com/reentrancy-after-istanbul/[Reentrancy After Istanbul].
 */
abstract contract ReentrancyGuard {
    // Booleans are more expensive than uint256 or any type that takes up a full
    // word because each write operation emits an extra SLOAD to first read the
    // slot's contents, replace the bits taken up by the boolean, and then write
    // back. This is the compiler's defense against contract upgrades and
    // pointer aliasing, and it cannot be disabled.

    // The values being non-zero value makes deployment a bit more expensive,
    // but in exchange the refund on every call to nonReentrant will be lower in
    // amount. Since refunds are capped to a percentage of the total
    // transaction's gas, it is best to keep them low in cases like this one, to
    // increase the likelihood of the full refund coming into effect.
    uint256 private constant _NOT_ENTERED = 1;
    uint256 private constant _ENTERED = 2;

    uint256 private _status;

    constructor() {
        _status = _NOT_ENTERED;
    }

    /**
     * @dev Prevents a contract from calling itself, directly or indirectly.
     * Calling a `nonReentrant` function from another `nonReentrant`
     * function is not supported. It is possible to prevent this from happening
     * by making the `nonReentrant` function external, and make it call a
     * `private` function that does the actual work.
     */
    modifier nonReentrant() {
        // On the first call to nonReentrant, _notEntered will be true
        require(_status != _ENTERED, "ReentrancyGuard: reentrant call");

        // Any calls to nonReentrant after this point will fail
        _status = _ENTERED;

        _;

        // By storing the original value once again, a refund is triggered (see
        // https://eips.ethereum.org/EIPS/eip-2200)
        _status = _NOT_ENTERED;
    }
}
          

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Moves `amount` tokens from the caller's account to `recipient`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `sender` to `recipient` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(
        address sender,
        address recipient,
        uint256 amount
    ) external returns (bool);

    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);
}
          

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "../IERC20.sol";
import "../../../utils/Address.sol";

/**
 * @title SafeERC20
 * @dev Wrappers around ERC20 operations that throw on failure (when the token
 * contract returns false). Tokens that return no value (and instead revert or
 * throw on failure) are also supported, non-reverting calls are assumed to be
 * successful.
 * To use this library you can add a `using SafeERC20 for IERC20;` statement to your contract,
 * which allows you to call the safe operations as `token.safeTransfer(...)`, etc.
 */
library SafeERC20 {
    using Address for address;

    function safeTransfer(
        IERC20 token,
        address to,
        uint256 value
    ) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transfer.selector, to, value));
    }

    function safeTransferFrom(
        IERC20 token,
        address from,
        address to,
        uint256 value
    ) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transferFrom.selector, from, to, value));
    }

    /**
     * @dev Deprecated. This function has issues similar to the ones found in
     * {IERC20-approve}, and its usage is discouraged.
     *
     * Whenever possible, use {safeIncreaseAllowance} and
     * {safeDecreaseAllowance} instead.
     */
    function safeApprove(
        IERC20 token,
        address spender,
        uint256 value
    ) internal {
        // safeApprove should only be called when setting an initial allowance,
        // or when resetting it to zero. To increase and decrease it, use
        // 'safeIncreaseAllowance' and 'safeDecreaseAllowance'
        require(
            (value == 0) || (token.allowance(address(this), spender) == 0),
            "SafeERC20: approve from non-zero to non-zero allowance"
        );
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, value));
    }

    function safeIncreaseAllowance(
        IERC20 token,
        address spender,
        uint256 value
    ) internal {
        uint256 newAllowance = token.allowance(address(this), spender) + value;
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    function safeDecreaseAllowance(
        IERC20 token,
        address spender,
        uint256 value
    ) internal {
        unchecked {
            uint256 oldAllowance = token.allowance(address(this), spender);
            require(oldAllowance >= value, "SafeERC20: decreased allowance below zero");
            uint256 newAllowance = oldAllowance - value;
            _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
        }
    }

    /**
     * @dev Imitates a Solidity high-level call (i.e. a regular function call to a contract), relaxing the requirement
     * on the return value: the return value is optional (but if data is returned, it must not be false).
     * @param token The token targeted by the call.
     * @param data The call data (encoded using abi.encode or one of its variants).
     */
    function _callOptionalReturn(IERC20 token, bytes memory data) private {
        // We need to perform a low level call here, to bypass Solidity's return data size checking mechanism, since
        // we're implementing it ourselves. We use {Address.functionCall} to perform this call, which verifies that
        // the target address contains contract code and also asserts for success in the low-level call.

        bytes memory returndata = address(token).functionCall(data, "SafeERC20: low-level call failed");
        if (returndata.length > 0) {
            // Return data is optional
            require(abi.decode(returndata, (bool)), "SafeERC20: ERC20 operation did not succeed");
        }
    }
}
          

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

/**
 * @dev Collection of functions related to the address type
 */
library Address {
    /**
     * @dev Returns true if `account` is a contract.
     *
     * [IMPORTANT]
     * ====
     * It is unsafe to assume that an address for which this function returns
     * false is an externally-owned account (EOA) and not a contract.
     *
     * Among others, `isContract` will return false for the following
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies on extcodesize, which returns 0 for contracts in
        // construction, since the code is only stored at the end of the
        // constructor execution.

        uint256 size;
        assembly {
            size := extcodesize(account)
        }
        return size > 0;
    }

    /**
     * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
     * `recipient`, forwarding all available gas and reverting on errors.
     *
     * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
     * of certain opcodes, possibly making contracts go over the 2300 gas limit
     * imposed by `transfer`, making them unable to receive funds via
     * `transfer`. {sendValue} removes this limitation.
     *
     * https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
     *
     * IMPORTANT: because control is transferred to `recipient`, care must be
     * taken to not create reentrancy vulnerabilities. Consider using
     * {ReentrancyGuard} or the
     * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
     */
    function sendValue(address payable recipient, uint256 amount) internal {
        require(address(this).balance >= amount, "Address: insufficient balance");

        (bool success, ) = recipient.call{value: amount}("");
        require(success, "Address: unable to send value, recipient may have reverted");
    }

    /**
     * @dev Performs a Solidity function call using a low level `call`. A
     * plain `call` is an unsafe replacement for a function call: use this
     * function instead.
     *
     * If `target` reverts with a revert reason, it is bubbled up by this
     * function (like regular Solidity function calls).
     *
     * Returns the raw returned data. To convert to the expected return value,
     * use https://solidity.readthedocs.io/en/latest/units-and-global-variables.html?highlight=abi.decode#abi-encoding-and-decoding-functions[`abi.decode`].
     *
     * Requirements:
     *
     * - `target` must be a contract.
     * - calling `target` with `data` must not revert.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data) internal returns (bytes memory) {
        return functionCall(target, data, "Address: low-level call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`], but with
     * `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCall(
        address target,
        bytes memory data,
        string memory errorMessage
    ) internal returns (bytes memory) {
        return functionCallWithValue(target, data, 0, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but also transferring `value` wei to `target`.
     *
     * Requirements:
     *
     * - the calling contract must have an ETH balance of at least `value`.
     * - the called Solidity function must be `payable`.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(
        address target,
        bytes memory data,
        uint256 value
    ) internal returns (bytes memory) {
        return functionCallWithValue(target, data, value, "Address: low-level call with value failed");
    }

    /**
     * @dev Same as {xref-Address-functionCallWithValue-address-bytes-uint256-}[`functionCallWithValue`], but
     * with `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(
        address target,
        bytes memory data,
        uint256 value,
        string memory errorMessage
    ) internal returns (bytes memory) {
        require(address(this).balance >= value, "Address: insufficient balance for call");
        require(isContract(target), "Address: call to non-contract");

        (bool success, bytes memory returndata) = target.call{value: value}(data);
        return verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(address target, bytes memory data) internal view returns (bytes memory) {
        return functionStaticCall(target, data, "Address: low-level static call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(
        address target,
        bytes memory data,
        string memory errorMessage
    ) internal view returns (bytes memory) {
        require(isContract(target), "Address: static call to non-contract");

        (bool success, bytes memory returndata) = target.staticcall(data);
        return verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(address target, bytes memory data) internal returns (bytes memory) {
        return functionDelegateCall(target, data, "Address: low-level delegate call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(
        address target,
        bytes memory data,
        string memory errorMessage
    ) internal returns (bytes memory) {
        require(isContract(target), "Address: delegate call to non-contract");

        (bool success, bytes memory returndata) = target.delegatecall(data);
        return verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Tool to verifies that a low level call was successful, and revert if it wasn't, either by bubbling the
     * revert reason using the provided one.
     *
     * _Available since v4.3._
     */
    function verifyCallResult(
        bool success,
        bytes memory returndata,
        string memory errorMessage
    ) internal pure returns (bytes memory) {
        if (success) {
            return returndata;
        } else {
            // Look for revert reason and bubble it up if present
            if (returndata.length > 0) {
                // The easiest way to bubble the revert reason is using memory via assembly

                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }
}
          

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

/**
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
abstract contract Context {
    function _msgSender() internal view virtual returns (address) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes calldata) {
        return msg.data;
    }
}