Deliverable 5

  function borrow(uint amount) public {
    uint creditScore = 750;
    require(creditScore > _minCreditScore, "Insufficient credit score");
    require(_borrower[msg.sender] == 0, "Can't borrow twice");
    require(_amountBorrowed + amount <= _totalAmount, "Not enough ether left to borrow");
    _borrower[msg.sender] = amount;
    uint costOfLoan = calculateInterest(amount, _numPayments) + amount;
    _borrowerExpectedPayment[msg.sender] = costOfLoan / _numPayments;
    _amountBorrowed += amount;
    if (isReady()) {
      _timeLoanStart = block.timestamp;
    }
    
  }
    
    function isReady() view public returns (bool) {
    return _totalAmount == _amountInvested && _totalAmount == _amountBorrowed;
  }

contract testSuite {

    Loan loan;
    function beforeAll() public {
        // instantiate contract
        loan = new Loan(1000, 5000, 12, 2592000, 650); 
        Assert.equal(uint(1), uint(1), "1 should be equal to 1");
    }


     // Test case to ensure borrower can't borrow twice
    function testBorrowTwice() public {
        loan = new Loan(1000, 5000, 12, 2592000, 650); 
        loan.borrow(100); // Borrow initial amount
        (bool success, ) = address(loan).call(abi.encodeWithSignature("borrow(uint256)", 100));
        Assert.ok(!success, "Borrower should not be able to borrow twice");
    }

    // Test case to ensure borrower can't borrow more than total amount available
    function testBorrowExceedTotalAmount() public {
        uint totalAmount = 500;
        (bool success, ) = address(loan).call{value: totalAmount + 1}(abi.encodeWithSignature("borrow(uint256)", totalAmount + 1));
        Assert.ok(!success, "Borrower should not be able to borrow more than total amount available");
    }
}

The calculateInterest(uint owed, uint numPayments) function: This function, named calculateInterest, is designed to compute the accrued interest on a loan based on the provided parameters.

  function calculateInterest(uint owed, uint numPayments) public view returns (uint) {
    if (numPayments <= 0) {
      return 0;
    }
    uint ratePerMilPayment = (_interestRatePerMil * _secondsBetweenPayments) / SECONDS_PER_YEAR;
    uint milAugmentInterest = owed * ((MILION + ratePerMilPayment) ** numPayments);
    uint newAmountOwed = milAugmentInterest / (MILION ** numPayments);
    return newAmountOwed - owed;
  }

Testing the calculateInterest(uint owed, uint numPayments) function: To write test cases for the calculateInterest function, we'll cover various scenarios to ensure its correctness. Here are some scenarios:

• Test case to ensure interest calculation is correct when numPayments is greater than 0.

contract testSuite {

    Loan loan;
    function beforeAll() public {
        // instantiate contract
        loan = new Loan(1000, 5000, 12, 2592000, 650); 
        Assert.equal(uint(1), uint(1), "1 should be equal to 1");
    }


    // Test case to ensure interest calculation is correct when numPayments is greater than 0
    function testCalculateInterestWithValidNumPayments() public {
        uint owed = 100; // Sample amount owed
        uint numPayments = 12; // Sample number of payments
        uint interestRatePerMil = 5000; // Sample interest rate per mil
        
        // Call the calculateInterest function and check the result
        uint calculatedInterest = loan.calculateInterest(owed, numPayments);
        uint expectedInterest = (1000 * ((1000000 + interestRatePerMil) ** 12)) / (1000000 ** 12) - 1000;

        Assert.equal(calculatedInterest, expectedInterest, "Interest calculation is incorrect");
    }
}

The withdraw(uint amount) function: This function allows an investor to withdraw a certain amount of ether from the contract.

  function withdraw(uint amount) public {
    uint current$$$=address(this).balance;
    require(current$$$ - amount >= 0, "Insufficient funds in the account");
    uint numPaymentsSinceLastCalculated = numPaymentsBetweenTimestamps(
      block.timestamp, _investorLastWithdraw[msg.sender]);
    uint investorBalance = _investors[msg.sender];
    investorBalance = investorBalance + calculateInterest(investorBalance,
      numPaymentsSinceLastCalculated);
    require(investorBalance >= amount, "Withdraw less or equal your investment");
    _investors[msg.sender] = investorBalance - amount;
    _investorLastWithdraw[msg.sender] = block.timestamp;
    payable(msg.sender).transfer(amount);

  }

Deploying the Loan Smart Contract:

Running the Test Suite:

Conclusion:These functions and some helper functions like isReady() (returns whether or not the loan has funded) concludes the implementation and unit testing of the Loan Smart Contract. Next, I will continue to examine the procedure of a borrower acquiring a loan and subsequently repaying it as defined in ALOE system [1]. We presume that the loan has already been established but has not yet received full funding or gathered the required number of borrowers. To monitor credit scores, we incorporate the following functions into the CreditBureau smart contract. The function updateScoreBorrow notifies the credit bureau of a loan being issued for a specified amount. Similarly, the function updateScoreRepayment informs the Credit Bureau smart contract that a loan has received a repayment payment of a certain amount. Furthermore, the function getScore retrieves the credit score of a client based on the given parameters such as the requested amount, interest rate per mil, number of payments, and seconds between payments.

References:

[1] T. H. Austin, K. Potika and C. Pollett, 'Autonomous Lending Organization on Ethereum with Credit Scoring,' 2023 Silicon Valley Cybersecurity Conference (SVCC), San Jose, CA, USA, 2023.