pragma solidity ^0.6.0;

// SPDX-License-Identifier: UNLICENSED

/**
 * @dev Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     *
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;

        return c;
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     *
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return div(a, b, "SafeMath: division by zero");
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return mod(a, b, "SafeMath: modulo by zero");
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts with custom message when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }

    function ceil(uint256 a, uint256 m) internal pure returns (uint256 r) {
        return (a + m - 1) / m * m;
    }
}

// ----------------------------------------------------------------------------
// Owned contract
// ----------------------------------------------------------------------------
contract Owned {
    address payable public owner;

    event OwnershipTransferred(address indexed _from, address indexed _to);

    constructor() public {
        owner = msg.sender;
    }

    modifier onlyOwner {
        require(msg.sender == owner, "Only allowed by owner");
        _;
    }

    function transferOwnership(address payable _newOwner) external onlyOwner {
        require(_newOwner != address(0),"Invalid address passed");
        owner = _newOwner;
        emit OwnershipTransferred(msg.sender, _newOwner);
    }
}

// ----------------------------------------------------------------------------
// ERC Token Standard #20 Interface
// https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20-token-standard.md
// ----------------------------------------------------------------------------
/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    function transfer(address recipient, uint256 amount) external returns (bool);
    function balanceOf(address account) external view returns (uint256);
}

contract PreSale is Owned {
    using SafeMath for uint256;
    
    address public tokenAddress;
    uint256 public constant startSale = 1613502000; // 16 Feb 2021, 7pm GMT
    uint256 public constant endSale =   1614106800; // 23 Feb 2021, 7pm GMT
    uint256 public constant claimDate = 1614110400; // 23 Feb 2021, 8pm GMT
    uint256 public purchasedTokens;
        
    mapping(address => uint256) public investor;
    
    constructor() public {
        owner = 0xa97F07bc8155f729bfF5B5312cf42b6bA7c4fCB9;
    }
    
    function SetTokenAddress(address _tokenAddress) external onlyOwner {
        tokenAddress = _tokenAddress;
    }
    
    receive() external payable{
        Invest();
    }
    
    function Invest() public payable{
        require( now > startSale && now < endSale , "Sale is closed");
        uint256 tokens = getTokenAmount(msg.value);
        investor[msg.sender] += tokens;
        purchasedTokens = purchasedTokens + tokens;
        owner.transfer(msg.value);
    }

    function getTokenAmount(uint256 amount) internal view returns(uint256){
        uint256 _tokens = 0;
        if (now <= startSale + 3 days){
            _tokens = amount * 100;
        }
        if (now > startSale + 3 days){
            _tokens = amount * 80;
        }
        return _tokens;
    }

    function ClaimTokens() external returns(bool){
        require(now >= claimDate, "Token claim date not reached");
        require(investor[msg.sender] > 0, "Not an investor");
        uint256 tokens = investor[msg.sender];
        investor[msg.sender] = 0;
        require(IERC20(tokenAddress).transfer(msg.sender, tokens));
        return true;
    }
    
    function getUnSoldTokens() onlyOwner external{
        require(block.timestamp > endSale, "sale is not closed");
        // check unsold tokens
        uint256 tokensInContract = IERC20(tokenAddress).balanceOf(address(this));
        require(tokensInContract > 0, "no unsold tokens in contract");
        require(IERC20(tokenAddress).transfer(owner, tokensInContract), "transfer of token failed");
    }
}