Crowdfunding Smart Contract Example

Crowdfund.sol.js

pragma solidity 0.5.2;

contract Crowdfunding {
    
    address payable beneficiary;
    uint goalInEther;
    uint deadline;
    
    mapping (address => uint) public contributions;
    
    address[] public contributors;
    
    event NewContribution(address _who, uint _amount, uint _timestamp);
    event RefundIssued(address _who, uint _amount, uint _timestamp);
    event BeneficiaryPaid(address _beneficiary, uint _amount, uint _timestamp);
    
    constructor(address payable _beneficiary, uint _goalInEther, uint _durationInHours) public {
        beneficiary = _beneficiary;
        goalInEther = _goalInEther * 1 ether;
        deadline = now + (_durationInHours * 1 hours);
    }
    
    function contribute() public payable {
        require(now < deadline);
        if (contributions[msg.sender] == 0) contributors.push(msg.sender);
        contributions[msg.sender] += msg.value;
        emit NewContribution(msg.sender, msg.value, now);
    }
    
    function refund() public {
        require(now > deadline &&
                address(this).balance < goalInEther
                );
        uint amountToSend = contributions[msg.sender];
        contributions[msg.sender] = 0;
        msg.sender.transfer(amountToSend);
        emit RefundIssued(msg.sender, amountToSend, now);
    }
    
    function payBeneficary() public {
        require(now > deadline &&
                address(this).balance >= goalInEther
                );
        beneficiary.transfer(address(this).balance);
        emit BeneficiaryPaid(beneficiary, address(this).balance, now);
    }
}