Integration testing

;; Error constants for various failure scenarios.
(define-constant err-overborrow (err u300))

;; The interest rate for loans, represented as 10% (out of a base of 100).
(define-data-var loan-interest-rate uint u10) ;; Representing 10% interest rate


;; Holds the total amount of deposits in the contract, initialized to 0.
(define-data-var total-deposits uint u0)

;; Maps a user's principal address to their deposited amount.
(define-map deposits { owner: principal } { amount: uint })

;; Maps a borrower's principal address to their loan details: amount and the last interaction block.
(define-map loans principal { amount: uint, last-interaction-block: uint })

;; Public function for users to deposit STX into the contract.
;; Updates their balance and the total deposits in the contract.
(define-public (deposit (amount uint))
  (let
    (
      ;; Fetch the current balance or default to 0 if none exists.
      (current-balance (default-to u0 (get amount (map-get? deposits { owner: tx-sender }))))
    )
    ;; Transfer the STX from sender = "ST1PQHQKV0RJXZFY1DGX8MNSNYVE3VGZJSRTPGZGM" to recipient = "ST1PQHQKV0RJXZFY1DGX8MNSNYVE3VGZJSRTPGZGM.defi (ie: contract identifier on the chain!)".
    (try! (stx-transfer? amount tx-sender (as-contract tx-sender)))
    ;; Update the user's deposit amount in the map.
    (map-set deposits { owner: tx-sender } { amount: (+ current-balance amount) })
    ;; Update the total deposits variable.
    (var-set total-deposits (+ (var-get total-deposits) amount))
    ;; Return success.
    (ok true)
  )
)

;; Public function for users to borrow STX based on their deposits.
(define-public (borrow (amount uint))
  (let
    (
      ;; Fetch user's deposit or default to 0.
      (user-deposit (default-to u0 (get amount (map-get? deposits { owner: tx-sender }))))
      ;; Calculate the maximum amount the user is allowed to borrow. (which will be upto HALF of what they deposited)
      (allowed-borrow (/ user-deposit u2))
      ;; Fetch current loan details or default to initial values.
      (current-loan-details (default-to { amount: u0, last-interaction-block: u0 } (map-get? loans tx-sender )))
      ;; Calculate accrued interest on the current loan.
      (accrued-interest (calculate-accrued-interest (get amount current-loan-details) (get last-interaction-block current-loan-details)))
      ;; Calculate the total amount due including interest.
      (total-due (+ (get amount current-loan-details) (unwrap-panic accrued-interest)))
      ;; Calculate the new loan total after borrowing additional amount.
      (new-loan (+ amount))
    )
    ;; Ensure the requested borrow amount does not exceed the allowed amount.
    (asserts! (<= new-loan allowed-borrow) err-overborrow)
    ;; Transfer the borrowed STX to the user.
    (let
      (
        (recipient tx-sender)
      )
      (try! (as-contract (stx-transfer? amount tx-sender recipient)))
    )
    ;; Update the user's loan details in the map.
    (map-set loans tx-sender { amount: new-loan, last-interaction-block: block-height })
    ;; Return success.
    (ok true)
  )
)

;; Read-only function to get the total balance by tx-sender
(define-read-only (get-balance-by-sender)
  (ok (map-get? deposits { owner: tx-sender }))
)

;; Read-only function to get the total amount owed by the user.
(define-read-only (get-amount-owed)
  (let
    (
      ;; Fetch current loan details or default to initial values.
      (current-loan-details (default-to { amount: u0, last-interaction-block: u0 } (map-get? loans tx-sender )))
      ;; Calculate accrued interest on the current loan.
      (accrued-interest (calculate-accrued-interest (get amount current-loan-details) (get last-interaction-block current-loan-details)))
      ;; Calculate the total amount due including interest.
      (total-due (+ (get amount current-loan-details) (unwrap-panic accrued-interest)))
    )
    ;; Return the total amount due.
    (ok total-due)
  )
)

;; Private function to calculate the accrued interest on a loan.
(define-private (calculate-accrued-interest (principal uint) (start-block uint))
  (let
    (
      ;; Calculate the number of blocks elapsed since the last interaction.
      (elapsed-blocks (- block-height start-block))
      ;; Calculate the interest based on the principal, rate, and elapsed time.
      (interest (/ (* principal (var-get loan-interest-rate) elapsed-blocks) u10000))
    )
    ;; Ensure the loan started in the past (not at block 0).
    (asserts! (not (is-eq start-block u0)) (ok u0))
    ;; Return the calculated interest.
    (ok interest)
  )
)

import { describe, it, expect } from 'vitest';
import { Cl } from '@stacks/transactions';

const accounts = simnet.getAccounts();
const wallet1 = accounts.get('wallet_1')!;

describe('stx-defi', () => {
  it('borrows 10 and verifies the amount owed to be 10', () => {
    simnet.callPublicFn('defi', 'deposit', [Cl.uint(1000)], wallet1);
    const totalDeposits = simnet.getDataVar('defi', 'total-deposits');
    expect(totalDeposits).toBeUint(1000);

    simnet.callPublicFn('defi', 'borrow', [Cl.uint(10)], wallet1);
    const { result } = simnet.callReadOnlyFn('defi', 'get-amount-owed', [], wallet1);
    expect(result).toBeOk(Cl.uint(10));
  });
});