CrowdSale.sol

pragma solidity ^0.5.0;

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.
     *
     * NOTE: This is a feature of the next version of OpenZeppelin Contracts.
     * @dev Get it via `npm install @openzeppelin/contracts@next`.
     */
    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.
     * NOTE: This is a feature of the next version of OpenZeppelin Contracts.
     * @dev Get it via `npm install @openzeppelin/contracts@next`.
     */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        // Solidity only automatically asserts when dividing by 0
        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.
     *
     * NOTE: This is a feature of the next version of OpenZeppelin Contracts.
     * @dev Get it via `npm install @openzeppelin/contracts@next`.
     */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}
contract CrowdSale{

    using SafeMath for uint256;
    mapping (address=> uint256) public contributions;
    uint256 public totalRaised;
    uint256 public maxAmount;
    uint256 public saleEndTimeStamp;
    bool public saleActive;
    address public admin;

    // constructor to enable basic parameters of the crowdsale
    constructor(uint256 _maxAmount, bool _saleActive, uint256 _saleEndTimeStamp) public {
        admin = msg.sender;
        // Max amount limit
        maxAmount = _maxAmount;
        // Sale status on launch
        saleActive = _saleActive;
        // Sale end time
        saleEndTimeStamp = _saleEndTimeStamp;
    }
    
    // Function to deposit ETH for the crowdsale
    function contribute() public payable returns (bool){
        require(msg.value > 0, "Deposit ETH along with the function");
        require(msg.value + totalRaised < maxAmount, "Crowdsale limit reached");
        require(saleActive, "Sale hasn't started or has ended");
        require(now < saleEndTimeStamp, "Sale has ended");
        contributions[msg.sender] = msg.value;
        totalRaised = totalRaised.add(msg.value);
        return true;
    }
    
    // Function contributers can use to withdraw their money at all times
    function withdraw() public returns (bool){
        require(contributions[msg.sender] > 0, "No deposits made");
        // refund their funds
        msg.sender.transfer(contributions[msg.sender]);
        // remove their contributions from the log
        totalRaised = totalRaised.sub(contributions[msg.sender]);
        contributions[msg.sender]= 0;
        return true;
    }
    // Function to end crowdsale and distribute funds to admin
    function endCrowdSale() public onlyAdmin{
        saleActive = false;
        msg.sender.transfer(totalRaised);
    }
    // Function to resume/pause crowdsale
    function changeCrowdSaleStatus(bool _status) public onlyAdmin{
        saleActive = _status;
    }
    // Function to check total amount raised
    function totalAmountRaised() public view returns (uint256){
        return totalRaised;
    }
    // Sets permissions for certain function
    modifier onlyAdmin() {
        require(msg.sender == admin);
        _;
    }
    
}