Smart Loan Contract for SmartFin

loan.sol

pragma solidity ^0.4.0;

contract Loan {
    uint principal;
    uint public total; // principal + interest rate
    uint interest;
    uint public dueDate;
    bool public isFunded;
    bool public isComplete;

    uint public amountPaid; // amount of the total that has been paid by borrower
    uint public collateralPaid; // amount paid in collateral -- TODO: collateral system is not implemented atm

    address backendAddr;
    address lenderAddr;
    address borrowerAddr;

    event ContractIsFunded(address lenderAddress, uint amount);
    event ContractIsComplete();
    event ListingIsCancelled();

    // Called by our backend to create the loan and get going
    function Loan(uint _principal, uint _interest, uint _numDays, address _lenderAddr) {
        backendAddr = msg.sender;
        lenderAddr = _lenderAddr;

        principal = _principal;
        interest = _interest;
        total = _interest + _principal;

        dueDate = now + _numDays * 1 days;

        isFunded = false;

        amountPaid = 0;
        collateralPaid = 0;

        isComplete = false;
    }

    // Called by the creditor to put their money into the loan
    function fund() payable {
        if(msg.sender != lenderAddr) throw;
        if(msg.value != principal) throw;
        if(isFunded) throw;

        isFunded = true;
        ContractIsFunded(msg.sender, msg.value);
    }

    // Cancel the loan but only if no one has borrowed
    function cancel() {
        if(msg.sender == lenderAddr && borrowerAddr != address(0)) {
            ListingIsCancelled();
            selfdestruct(msg.sender);
        }
    }

    // Tell contract where the loan is coming from
    function setBorrower(address _borrowerAddr) {
        if(borrowerAddr != address(0) || msg.sender != backendAddr) throw;

        borrowerAddr = _borrowerAddr;

        if(!borrowerAddr.send(principal))
            throw;
    }

    function pay() payable {
        // prevent overpayment
        //if (amountPaid >= total || amountPaid + msg.value > total)
        //  throw;

        amountPaid += msg.value;

        if(amountPaid >= total && collateralPaid > 0) {
            // Release collateral -- this loan is complete!
            if(!borrowerAddr.send(collateralPaid))
                throw;
        }

        isComplete = (amountPaid >= total);
        if (isComplete)
          ContractIsComplete();
    }

    function withdraw() {
        if(msg.sender != lenderAddr) throw;

        if(amountPaid > 0) {
            if(!lenderAddr.send(amountPaid))
                throw;
        }

        if(now > dueDate && amountPaid <= total) {
            // TODO: this isn't super accurate since someone could have partially
            // paid the loan
           if(!lenderAddr.send(collateralPaid))
            throw;
        }
    }
}