openzeppelin-contracts/contracts/payment/escrow/RefundEscrow.sol

pragma solidity ^0.4.24;

import "./ConditionalEscrow.sol";

/**
 * @title RefundEscrow
 * @dev Escrow that holds funds for a beneficiary, deposited from multiple
 * parties.
 * @dev Intended usage: See Escrow.sol. Same usage guidelines apply here.
 * @dev The primary account (that is, the contract that instantiates this
 * contract) may deposit, close the deposit period, and allow for either
 * withdrawal by the beneficiary, or refunds to the depositors. All interactions
 * with RefundEscrow will be made through the primary contract. See the
 * RefundableCrowdsale contract for an example of RefundEscrow’s use.
 */
contract RefundEscrow is ConditionalEscrow {
  enum State { Active, Refunding, Closed }

  event RefundsClosed();
  event RefundsEnabled();

  State private _state;
  address private _beneficiary;

  /**
   * @dev Constructor.
   * @param beneficiary The beneficiary of the deposits.
   */
  constructor(address beneficiary) public {
    require(beneficiary != address(0));
    _beneficiary = beneficiary;
    _state = State.Active;
  }

  /**
   * @return the current state of the escrow.
   */
  function state() public view returns (State) {
    return _state;
  }

  /**
   * @return the beneficiary of the escrow.
   */
  function beneficiary() public view returns (address) {
    return _beneficiary;
  }

  /**
   * @dev Stores funds that may later be refunded.
   * @param refundee The address funds will be sent to if a refund occurs.
   */
  function deposit(address refundee) public payable {
    require(_state == State.Active);
    super.deposit(refundee);
  }

  /**
   * @dev Allows for the beneficiary to withdraw their funds, rejecting
   * further deposits.
   */
  function close() public onlyPrimary {
    require(_state == State.Active);
    _state = State.Closed;
    emit RefundsClosed();
  }

  /**
   * @dev Allows for refunds to take place, rejecting further deposits.
   */
  function enableRefunds() public onlyPrimary {
    require(_state == State.Active);
    _state = State.Refunding;
    emit RefundsEnabled();
  }

  /**
   * @dev Withdraws the beneficiary's funds.
   */
  function beneficiaryWithdraw() public {
    require(_state == State.Closed);
    _beneficiary.transfer(address(this).balance);
  }

  /**
   * @dev Returns whether refundees can withdraw their deposits (be refunded).
   */
  function withdrawalAllowed(address payee) public view returns (bool) {
    return _state == State.Refunding;
  }
}