;; ============================================================================
;; STACKS DEX - Constant Product AMM Pool Contract (Clarity 3)
;; ============================================================================
;;
;; This contract implements a minimal constant-product AMM (x * y = k) for
;; swapping between two SIP-010 fungible tokens on Stacks (Bitcoin L2).
;;
;; Key Features:
;; - Single swap direction: Token X -> Token Y
;; - 0.30% fee deducted from input, sent to fee-recipient (set at init)
;; - Slippage protection via min-dy parameter
;; - Deadline protection via block-height check
;; - No admin functions, no upgradability
;;
;; AMM Formula:
;; Given reserves (x, y) and input dx:
;; fee = dx * 30 / 10000
;; dx_to_pool = dx - fee
;; dy = (y * dx_to_pool) / (x + dx_to_pool)
;;
;; The fee (0.30%) is sent to the fee recipient (whoever initializes the pool).
;; ============================================================================
;; ============================================================================
;; TRAITS
;; ============================================================================
;; SIP-010 Fungible Token Trait
(use-trait ft-trait .sip-010-trait-ft-standard-v2-c5.sip-010-trait)
;; ============================================================================
;; CONSTANTS
;; ============================================================================
;; Fee configuration: 30 basis points = 0.30%
(define-constant FEE_BPS u30)
(define-constant BPS_DENOM u10000)
;; Error codes
(define-constant ERR_ZERO_INPUT (err u100))
(define-constant ERR_ZERO_RESERVES (err u101))
(define-constant ERR_DEADLINE_EXPIRED (err u102))
(define-constant ERR_SLIPPAGE_EXCEEDED (err u103))
(define-constant ERR_INSUFFICIENT_LIQUIDITY (err u104))
(define-constant ERR_TRANSFER_X_FAILED (err u105))
(define-constant ERR_TRANSFER_Y_FAILED (err u106))
(define-constant ERR_FEE_TRANSFER_FAILED (err u107))
(define-constant ERR_ALREADY_INITIALIZED (err u200))
(define-constant ERR_NOT_INITIALIZED (err u201))
;; ============================================================================
;; DATA VARIABLES
;; ============================================================================
;; Fee recipient - set to tx-sender when pool is initialized
;; This is whoever calls initialize-pool first (should be deployer/you)
(define-data-var fee-recipient (optional principal) none)
;; Pool reserves - tracks the current balance of each token in the pool
(define-data-var reserve-x uint u0)
(define-data-var reserve-y uint u0)
;; Total fees collected (for tracking)
(define-data-var total-fees-collected uint u0)
;; ============================================================================
;; READ-ONLY FUNCTIONS
;; ============================================================================
;; Get current pool reserves
(define-read-only (get-reserves)
{
x: (var-get reserve-x),
y: (var-get reserve-y),
}
)
;; Get fee configuration and recipient
(define-read-only (get-fee-info)
{
fee-bps: FEE_BPS,
denom: BPS_DENOM,
recipient: (var-get fee-recipient),
}
)
;; Get total fees collected
(define-read-only (get-total-fees)
(var-get total-fees-collected)
)
;; Quote: Calculate output amount for a given input
;;
;; Parameters:
;; dx: Amount of token X to swap (in smallest units)
;;
;; Returns: Amount of token Y that would be received (ok uint) or error
(define-read-only (quote-x-for-y (dx uint))
(let (
(rx (var-get reserve-x))
(ry (var-get reserve-y))
)
;; Validate inputs
(asserts! (> dx u0) ERR_ZERO_INPUT)
(asserts! (and (> rx u0) (> ry u0)) ERR_ZERO_RESERVES)
(let (
;; Calculate fee: fee = dx * 30 / 10000
(fee (/ (* dx FEE_BPS) BPS_DENOM))
;; Amount going to pool after fee
(dx-to-pool (- dx fee))
;; AMM formula: dy = (ry * dx_to_pool) / (rx + dx_to_pool)
(numerator (* ry dx-to-pool))
(denominator (+ rx dx-to-pool))
(dy (/ numerator denominator))
)
;; Ensure we're not draining the pool
(asserts! (< dy ry) ERR_INSUFFICIENT_LIQUIDITY)
(ok dy)
)
)
)
;; Calculate the fee amount for a given input
(define-read-only (calculate-fee (dx uint))
(/ (* dx FEE_BPS) BPS_DENOM)
)
;; ============================================================================
;; PUBLIC FUNCTIONS
;; ============================================================================
;; Swap Token X for Token Y
;;
;; Executes a swap using the constant-product AMM formula.
;; The fee (0.30%) is sent directly to the fee-recipient (set at initialization).
;;
;; Parameters:
;; token-x: SIP-010 token contract for input token
;; token-y: SIP-010 token contract for output token
;; dx: Amount of token X to swap (in smallest units)
;; min-dy: Minimum acceptable output (slippage protection)
;; recipient: Address to receive output tokens
;; deadline: Maximum block height for execution
;;
;; Returns: { dx: uint, dy: uint, fee: uint, recipient: principal }
(define-public (swap-x-for-y
(token-x <ft-trait>)
(token-y <ft-trait>)
(dx uint)
(min-dy uint)
(recipient principal)
(deadline uint)
)
(let (
(rx (var-get reserve-x))
(ry (var-get reserve-y))
(sender tx-sender)
(fee-addr (unwrap! (var-get fee-recipient) ERR_NOT_INITIALIZED))
)
;; ========================================
;; VALIDATION
;; ========================================
;; Check deadline hasn't passed
(asserts! (<= stacks-block-height deadline) ERR_DEADLINE_EXPIRED)
;; Check input is non-zero
(asserts! (> dx u0) ERR_ZERO_INPUT)
;; Check pool has liquidity
(asserts! (and (> rx u0) (> ry u0)) ERR_ZERO_RESERVES)
;; ========================================
;; CALCULATE FEE AND OUTPUT
;; ========================================
(let (
;; Calculate fee: fee = dx * 30 / 10000 (0.30%)
(fee (/ (* dx FEE_BPS) BPS_DENOM))
;; Amount going to pool after fee deduction
(dx-to-pool (- dx fee))
;; AMM formula: dy = (ry * dx_to_pool) / (rx + dx_to_pool)
(numerator (* ry dx-to-pool))
(denominator (+ rx dx-to-pool))
(dy (/ numerator denominator))
)
;; ========================================
;; SLIPPAGE CHECK
;; ========================================
;; Ensure output meets minimum requirement
(asserts! (>= dy min-dy) ERR_SLIPPAGE_EXCEEDED)
;; Ensure we're not draining the pool
(asserts! (< dy ry) ERR_INSUFFICIENT_LIQUIDITY)
;; ========================================
;; EXECUTE TRANSFERS
;; ========================================
;; 1. Transfer fee from sender to fee-recipient (your wallet)
(if (> fee u0)
(unwrap! (contract-call? token-x transfer fee sender fee-addr none)
ERR_FEE_TRANSFER_FAILED
)
true
)
;; 2. Transfer remaining token X from sender to this contract (pool)
(unwrap!
(contract-call? token-x transfer dx-to-pool sender
(as-contract tx-sender) none
)
ERR_TRANSFER_X_FAILED
)
;; 3. Transfer token Y from this contract to recipient
(unwrap!
(as-contract (contract-call? token-y transfer dy tx-sender recipient none))
ERR_TRANSFER_Y_FAILED
)
;; ========================================
;; UPDATE STATE
;; ========================================
;; Update reserves (only dx-to-pool goes into reserves, fee goes to your wallet)
(var-set reserve-x (+ rx dx-to-pool))
(var-set reserve-y (- ry dy))
;; Track total fees collected
(var-set total-fees-collected (+ (var-get total-fees-collected) fee))
;; Return swap details including fee
(ok {
dx: dx,
dy: dy,
fee: fee,
recipient: recipient,
})
)
)
)
;; ============================================================================
;; INITIALIZATION
;; ============================================================================
;; Initialize pool with liquidity
;; Can only be called once (when reserves are zero)
;; The caller (tx-sender) becomes the fee recipient for all future swaps
;; Typically called by the deployer to seed initial liquidity
(define-public (initialize-pool
(token-x <ft-trait>)
(token-y <ft-trait>)
(amount-x uint)
(amount-y uint)
)
(begin
;; Only allow initialization once (when reserves are zero)
(asserts! (and (is-eq (var-get reserve-x) u0) (is-eq (var-get reserve-y) u0))
ERR_ALREADY_INITIALIZED
)
;; Set the fee recipient to whoever initializes the pool (YOU)
(var-set fee-recipient (some tx-sender))
;; Transfer initial liquidity from sender to contract
(unwrap!
(contract-call? token-x transfer amount-x tx-sender (as-contract tx-sender)
none
)
ERR_TRANSFER_X_FAILED
)
(unwrap!
(contract-call? token-y transfer amount-y tx-sender (as-contract tx-sender)
none
)
ERR_TRANSFER_Y_FAILED
)
;; Set initial reserves
(var-set reserve-x amount-x)
(var-set reserve-y amount-y)
(ok {
x: amount-x,
y: amount-y,
fee-recipient: tx-sender,
})
)
)
;; ============================================================================
;; CONTRACT INFO
;; ============================================================================
;; Get contract information
(define-read-only (get-contract-info)
{
name: "stacks-dex-pool-c4",
version: "1.0.0",
fee-bps: FEE_BPS,
fee-recipient: (var-get fee-recipient),
reserve-x: (var-get reserve-x),
reserve-y: (var-get reserve-y),
total-fees: (var-get total-fees-collected),
}
)