stx-defi.clar

;; Define the contract's data variables

;; 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 })

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

;; Represents the reserve funds in the pool, initialized to 0.
(define-data-var pool-reserve uint u0)

;; 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

;; Error constants for various failure scenarios.
(define-constant err-no-interest (err u100))
(define-constant err-overpay (err u200))
(define-constant err-overborrow (err u300))

;; 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.stx-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: burn-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 balance 
(define-read-only (get-balance)
    (ok (var-get total-deposits))
)

;; 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)
    )
)

;; Public function for users to repay their STX loans.
(define-public (repay (amount uint))
    (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 since the last interaction.
        (accrued-interest (unwrap! (calculate-accrued-interest (get amount current-loan-details) (get last-interaction-block current-loan-details)) err-no-interest))
        ;; Calculate the total amount due including accrued interest.
        (total-due (+ (get amount current-loan-details) accrued-interest))
    )
        ;; Ensure the repayment amount is not more than the total due.
        (asserts! (>= total-due amount) err-overpay)
        ;; Transfer the repayment amount from the user to the contract.
        (try! (stx-transfer? amount tx-sender (as-contract tx-sender)))
        ;; Update the user's loan details in the map with the new total due.
        (map-set loans tx-sender { amount: (- total-due amount), last-interaction-block: burn-block-height })
        ;; Update the pool reserve with the paid interest.
        (var-set pool-reserve (+ (var-get pool-reserve) accrued-interest))
        ;; Return success.
        (ok true)
    )
)

;; Public function for users to claim their yield based on the pool reserve and their deposits.
(define-public (claim-yield)
    (let (
        ;; Fetch user's deposit amount or default to 0.
        (user-deposit (default-to u0 (get amount (map-get? deposits { owner: tx-sender }))))
        ;; Calculate the yield amount based on user's share of the pool.
        (yield-amount (/ (* (var-get pool-reserve) user-deposit) (var-get total-deposits)))
    )
        ;; Transfer the yield amount from the contract to the user.
        (let ((recipient tx-sender))
            (try! (as-contract (stx-transfer? yield-amount tx-sender recipient)))
        )
        ;; Update the pool reserve by subtracting the claimed yield.
        (var-set pool-reserve (- (var-get pool-reserve) yield-amount))
        ;; Return success.
        (ok true)
    )
)

;; 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 (- burn-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)
    )
)