contract PullPayment {

  using SafeMath for uint;
  
  mapping(address => uint) public payments;

  event LogRefundETH(address to, uint value);


  /**
  *  Store sent amount as credit to be pulled, called by payer 
  **/
  function asyncSend(address dest, uint amount) internal {
    payments[dest] = payments[dest].add(amount);
  }

  // withdraw accumulated balance, called by payee
  function withdrawPayments() {
    address payee = msg.sender;
    uint payment = payments[payee];
    
    if (payment == 0) {
      throw;
    }

    if (this.balance < payment) {
      throw;
    }

    payments[payee] = 0;

    if (!payee.send(payment)) {
      throw;
    }
    LogRefundETH(payee,payment);
  }
}
/*
 * PullPayment
 * Base contract supporting async send for pull payments.
 * Inherit from this contract and use asyncSend instead of send.
 */
function withdrawPayments() {
    address payee = msg.sender;
    uint payment = payments[payee];
    
    if (payment == 0) {
      throw;
    }

    if (this.balance < payment) {
      throw;
    }

    payments[payee] = 0;

    if (!payee.send(payment)) {
      throw;
    }
    LogRefundETH(payee,payment);
  }
// withdraw accumulated balance, called by payee