Contract Source Code:

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

import "@openzeppelin/contracts/access/Ownable.sol";

contract S16Presale is Ownable {
    address private admin; //address of the s16 owner

    mapping(address => bool) public regForPresaleMint;

    uint256 public preSaleRegisterPrice = 0.016 ether;
    uint256 private PRE_SALE_REG_TIME = 1643414400; // Presale Time till 28th JAN 2021 07: 00 PM
    address[] public preSaleRegisterUserList;

    fallback() external payable {
        require(admin != address(0x0), "S16Presale: zero address error");
        require(
            block.timestamp <= PRE_SALE_REG_TIME,
            "S16Presale: preSale registration times end"
        );
        require(msg.value >= preSaleRegisterPrice, "transfer ether error");
        require(regForPresaleMint[msg.sender] == false, "already registered for presale");
        payable(admin).transfer(msg.value);
        regForPresaleMint[msg.sender] = true;
        preSaleRegisterUserList.push(msg.sender);
    }

    function changePreSaleTime(uint256 _PRE_SALE_REG_TIME) external onlyOwner {
        require(_PRE_SALE_REG_TIME > 0, "S16Presale: time update error");
        PRE_SALE_REG_TIME = _PRE_SALE_REG_TIME;
    }

    function setOwnerAddress(address _admin) external onlyOwner {
        require(_admin != address(0x0), "S16Presale: zero address error");
        admin = _admin;
    }

    function isRegisterforPresale(address _wallet)
        external
        view
        returns (bool)
    {
        return regForPresaleMint[_wallet];
    }

    function getETHBalance(address _wallet) external view returns (uint256) {
        return _wallet.balance;
    }

    function getPresaleRegisterUserList()
        external
        view
        returns (address[] memory)
    {
        return preSaleRegisterUserList;
    }

    function getPresaleTime() external view returns (uint) {
        return PRE_SALE_REG_TIME;
    }
}

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (access/Ownable.sol)

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() {
        _transferOwnership(_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 {
        _transferOwnership(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");
        _transferOwnership(newOwner);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Internal function without access restriction.
     */
    function _transferOwnership(address newOwner) internal virtual {
        address oldOwner = _owner;
        _owner = newOwner;
        emit OwnershipTransferred(oldOwner, newOwner);
    }
}

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (utils/Context.sol)

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;
    }
}