// 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;
        // solhint-disable-next-line no-inline-assembly
        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");

        // solhint-disable-next-line avoid-low-level-calls, avoid-call-value
        (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");

        // solhint-disable-next-line avoid-low-level-calls
        (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");

        // solhint-disable-next-line avoid-low-level-calls
        (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");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.delegatecall(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    function _verifyCallResult(bool success, bytes memory returndata, string memory errorMessage) private 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

                // solhint-disable-next-line no-inline-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) {
        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
        return msg.data;
    }
}

// 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;

interface IERC677Receiver {
  function onTokenTransfer(address _sender, uint _value, bytes calldata _data) external;
}

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

interface IVoters {
  function snapshot() external returns (uint);
  function totalSupplyAt(uint snapshotId) external view returns (uint);
  function votesAt(address account, uint snapshotId) external view returns (uint);
  function balanceOf(address account) external view returns (uint);
  function balanceOfAt(address account, uint snapshotId) external view returns (uint);
  function donate(uint amount) external;
}

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "@openzeppelin/contracts/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 (address owner) {
        _owner = owner;
        emit OwnershipTransferred(address(0), owner);
    }

    /**
     * @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 {
        emit OwnershipTransferred(_owner, address(0));
        _owner = 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");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = 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;

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'
        // solhint-disable-next-line max-line-length
        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
            // solhint-disable-next-line max-line-length
            require(abi.decode(returndata, (bool)), "SafeERC20: ERC20 operation did not succeed");
        }
    }
}

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

import "@openzeppelin/contracts/security/ReentrancyGuard.sol";
import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";
import "./utils/Ownable.sol";
import "./interfaces/IVoters.sol";
import "./interfaces/IERC677Receiver.sol";

contract SaleDutch is Ownable, ReentrancyGuard, IERC677Receiver {
    using SafeERC20 for IERC20;

    // Information of each user's participation
    struct UserInfo {
        // How many tokens the user has provided
        uint amount;
        // Wether this user has already claimed their share of tokens, defaults to false
        bool claimedTokens;
    }

    // The raising token
    IERC20 public paymentToken;
    // The offering token
    IERC20 public offeringToken;
    // The time (unix seconds) when sale starts
    uint public startTime;
    // The time (unix security) when sale ends
    uint public endTime;
    // Price to start the sale at (offeringToken per 1e18 of paymentToken)
    uint public startPrice;
    // Reserve price (as amount per 1e18 of token invested)
    uint public endPrice;
    // Amount of tokens offered for sale
    uint public offeringAmount;
    // Maximum a user can contribute
    uint public perUserCap;
    // Voting token minimum balance to participate
    uint public votingMinimum;
    // Voting token address
    IVoters public votingToken;
    // Voting token snapshot id to use for balances (optional)
    uint public votingSnapshotId;
    // Wether deposits are paused
    bool public paused;
    // Wether the sale is finalized
    bool public finalized;
    // Total amount of raising tokens that have already been raised
    uint public totalAmount;
    // User's participation info
    mapping(address => UserInfo) public userInfo;
    // Participants list
    address[] public addressList;


    event Deposit(address indexed user, uint amount);
    event HarvestTokens(address indexed user, uint amount);
    event HarvestRefund(address indexed user, uint amount);

    constructor(
        address _paymentToken,
        address _offeringToken,
        uint _startTime,
        uint _endTime,
        uint _startPrice,
        uint _endPrice,
        uint _offeringAmount,
        uint _perUserCap,
        address _owner
    ) Ownable(_owner) {
        paymentToken = IERC20(_paymentToken);
        offeringToken = IERC20(_offeringToken);
        startTime = _startTime;
        endTime = _endTime;
        startPrice = _startPrice;
        endPrice = _endPrice;
        offeringAmount = _offeringAmount;
        perUserCap = _perUserCap;
        require(_paymentToken != _offeringToken, 'payment != offering');
        require(_startTime > block.timestamp, 'start > now');
        require(_startTime < _endTime, 'start < end');
        require(_startTime < 10000000000, 'start time not unix');
        require(_endTime < 10000000000, 'start time not unix');
        require(_startPrice > 0, 'start price > 0');
        require(_endPrice > 0, 'end price > 0');
        require(_offeringAmount > 0, 'offering amount > 0');
    }

    function configureVotingToken(uint minimum, address token, uint snapshotId) public onlyOwner {
        votingMinimum = minimum;
        votingToken = IVoters(token);
        votingSnapshotId = snapshotId;
    }

    function togglePaused() public onlyOwner {
        paused = !paused;
    }

    function finalize() public {
        require(msg.sender == owner() || block.timestamp > endTime + 7 days, 'no allowed');
        finalized = true;
    }

    function getAddressListLength() external view returns (uint) {
        return addressList.length;
    }

    function getParams() external view returns (uint, uint, uint, uint, uint, uint, uint, uint, uint, bool, bool) {
        return (startTime, endTime, startPrice, endPrice,
                offeringAmount, perUserCap, totalAmount,
                currentPrice(), clearingPrice(), paused, finalized);
    }

    function priceChange() public view returns (uint) {
        return (startPrice - endPrice) / (endTime - startTime);
    }

    function currentPrice() public view returns (uint) {
        if (block.timestamp <= startTime) return startPrice;
        if (block.timestamp >= endTime) return endPrice;
        return startPrice - ((block.timestamp - startTime) * priceChange());
    }

    function tokenPrice() public view returns (uint) {
        return (totalAmount * 1e18) / offeringAmount;
    }

    function clearingPrice() public view returns (uint) {
        if (tokenPrice() > currentPrice()) return tokenPrice();
        return currentPrice();
    }

    function saleSuccessful() public view returns (bool) {
        return tokenPrice() >= clearingPrice();
    }

    function commitmentSize(uint amount) public view returns (uint) {
      uint max = (offeringAmount * clearingPrice()) / 1e18;
      if (totalAmount + amount > max) {
        return max - totalAmount;
      }
      return amount;
    }

    function _deposit(address user, uint amount) private nonReentrant {
      require(!paused, 'paused');
      require(block.timestamp >= startTime && block.timestamp <= endTime, 'sale not active');
      require(amount > 0, 'need amount > 0');
      require(perUserCap == 0 || amount <= perUserCap, 'over per user cap');
      require(userInfo[user].amount == 0, 'already participated');

      if (votingMinimum > 0) {
          if (votingSnapshotId == 0) {
              require(votingToken.balanceOf(user) >= votingMinimum, "under minimum locked");
          } else {
              require(votingToken.balanceOfAt(user, votingSnapshotId) >= votingMinimum, "under minimum locked");
          }
      }

      uint cappedAmount = commitmentSize(amount);
      require(cappedAmount > 0, 'sale fully commited');

      // Refund user's overpayment
      if (amount - cappedAmount > 0) {
          paymentToken.transfer(user, amount - cappedAmount);
      }

      addressList.push(user);
      userInfo[user].amount = cappedAmount;
      totalAmount += cappedAmount;
      emit Deposit(user, cappedAmount);
    }

    function deposit(uint amount) external {
        _transferFrom(msg.sender, amount);
        _deposit(msg.sender, amount);
    }

    function onTokenTransfer(address user, uint amount, bytes calldata _data) external override {
        require(msg.sender == address(paymentToken), "onTokenTransfer: not paymentToken");
        _deposit(user, amount);
    }

    function harvestTokens() public nonReentrant {
      require(!paused, 'paused');
      require(block.timestamp > endTime, 'sale not ended');

      if (saleSuccessful()) {
          require(finalized, 'not finalized');
          require(userInfo[msg.sender].amount > 0, 'have you participated?');
          require(!userInfo[msg.sender].claimedTokens, 'already claimed');

          uint amount = getOfferingAmount(msg.sender);
          require(amount > 0, 'nothing to claim');
          offeringToken.safeTransfer(msg.sender, amount);
          userInfo[msg.sender].claimedTokens = true;
          emit HarvestTokens(msg.sender, amount);
      } else {
          uint amount = userInfo[msg.sender].amount;
          userInfo[msg.sender].amount = 0;
          paymentToken.safeTransfer(msg.sender, amount);
          emit HarvestRefund(msg.sender, amount);
      }
    }

    // Amount of offering token a user will receive
    function getOfferingAmount(address _user) public view returns (uint) {
        return (userInfo[_user].amount * offeringAmount) / totalAmount;
    }

    function withdrawToken(address token, uint amount) public onlyOwner {
        IERC20(token).safeTransfer(msg.sender, amount);
    }

    function _transferFrom(address from, uint amount) private {
        uint balanceBefore = paymentToken.balanceOf(address(this));
        paymentToken.safeTransferFrom(from, address(this), amount);
        uint balanceAfter = paymentToken.balanceOf(address(this));
        require(balanceAfter - balanceBefore == amount, "_transferFrom: balance change does not match amount");
    }
}

{
  "compilationTarget": {
    "contracts/SaleDutch.sol": "SaleDutch"
  },
  "evmVersion": "london",
  "libraries": {},
  "metadata": {
    "bytecodeHash": "ipfs"
  },
  "optimizer": {
    "enabled": true,
    "runs": 200
  },
  "remappings": []
}