pragma solidity ^0.6.0;
// SPDX-License-Identifier: UNLICENSED

// ----------------------------------------------------------------------------
// 'FORMS' SALE 3 CONTRACT
// ----------------------------------------------------------------------------

// ----------------------------------------------------------------------------
// SafeMath library
// ----------------------------------------------------------------------------

/**
 * @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(uint a, uint m) internal pure returns (uint r) {
        return (a + m - 1) / m * m;
    }
}

// ----------------------------------------------------------------------------
// ERC Token Standard #20 Interface
// ----------------------------------------------------------------------------
abstract contract IFORMS {
    function transfer(address to, uint256 tokens) public virtual returns (bool success);
    function setTokenLock (uint256 lockedTokens, uint256 cliffTime, address purchaser) public virtual;
    function burnTokens(uint256 _amount) public virtual;
    function balanceOf(address tokenOwner) public virtual view returns (uint256 balance);
}

contract FORMS_SALE_3{
    
    using SafeMath for uint256;
    
    string public tokenPrice = '0.000256 ether';
    address public FORMS_TOKEN_ADDRESS;
    uint256 public saleEndDate = 0;
    address payable owner = 0xA6a3E445E613FF022a3001091C7bE274B6a409B0;
    
    modifier onlyOwner {
        require(owner == msg.sender, "UnAuthorized");
        _;
    }
    
    function setTokenAddress(address _tokenAddress) external onlyOwner{
        require(FORMS_TOKEN_ADDRESS == address(0), "TOKEN ADDRESS ALREADY CONFIGURED");
        FORMS_TOKEN_ADDRESS = _tokenAddress;
    }
    
    function startSale() external onlyOwner{
        require(saleEndDate == 0, "SALE ALREADY STARTED");
        saleEndDate = block.timestamp.add(2 days);
    }
    
    receive() external payable{
        // checks if sale is started or not
        require(saleEndDate > 0, "Sale has not started");
        
        // check minimum condition
        require(msg.value >= 0.1 ether, "Not enough investment");
        
        uint256 remainingSaleTokens = IFORMS(FORMS_TOKEN_ADDRESS).balanceOf(address(this));
        
        // check if burning is needed
        if(remainingSaleTokens > 0 && block.timestamp > saleEndDate)
            IFORMS(FORMS_TOKEN_ADDRESS).burnTokens(remainingSaleTokens);
            
        // checks if sale is finished
        require(IFORMS(FORMS_TOKEN_ADDRESS).balanceOf(address(this)) > 0, "Sale is finished");
        
        // receive ethers
        uint tokens = getTokenAmount(msg.value);
        
        // transfer tokens
        IFORMS(FORMS_TOKEN_ADDRESS).transfer(msg.sender, tokens);
        
        // send received funds to the owner
        owner.transfer(msg.value);
    }
    
    function getTokenAmount(uint256 amount) private pure returns(uint256){
        return amount.mul(3906); // 1 ether = 3906 tokens approx
    }
}