AuricAMM

src/AuricAMM.sol — toy constant-product (x·y = k) AMM for an AUR/ETH pair.

NOT AUDITED. Not safe for mainnet. Intended for learning only.

Constructor

constructor(address _token)

Sets the immutable token (ERC-20). The contract receives ETH natively.

Requirement: Auric's taxBps must be 0 when using this pool. Fee-on-transfer tokens break the invariant.

Pool Model

LP shares are tracked internally — there is no separate ERC-20 LP token.

addLiquidity

function addLiquidity(uint256 tokenAmount) external payable returns (uint256 sharesOut)

Caller sends ETH via msg.value and approves tokenAmount AUR before calling.

For subsequent deposits, msg.value drives the scale. The required token amount is derived from the current ratio (requiredToken = ethAmount * reserveToken / reserveEth). If requiredToken > tokenAmount, reverts with SlippageExceeded() — the caller's tokenAmount acts as a slippage cap.

removeLiquidity

function removeLiquidity(uint256 sharesToBurn) external returns (uint256 tokenOut, uint256 ethOut)

Burns sharesToBurn and returns the proportional share of both reserves:

tokenOut = sharesToBurn * reserveToken / totalShares
ethOut   = sharesToBurn * reserveEth   / totalShares

Reverts with InsufficientShares() if caller holds fewer shares than sharesToBurn.

swapETHForTokens

function swapETHForTokens(uint256 minTokenOut) external payable returns (uint256 tokenOut)

Sends ETH, receives AUR. Reverts with SlippageExceeded() if tokenOut < minTokenOut.

swapTokensForETH

function swapTokensForETH(uint256 tokenIn, uint256 minEthOut) external returns (uint256 ethOut)

Sends AUR (must be pre-approved), receives ETH. Reverts with SlippageExceeded() if ethOut < minEthOut.

Fee Mechanism

0.3% fee stays in the pool on every swap. No fee on liquidity add/remove.

FEE_NUMERATOR   = 997
FEE_DENOMINATOR = 1000

Output formula:

amountOut = reserveOut * (amountIn * 997) / (reserveIn * 1000 + amountIn * 997)

The full amountIn is added to reserveIn, but only amountIn * 997 counts in the numerator. This means reserveIn * reserveOut strictly increases after every swap, accruing fee income to LPs proportionally to their shares.

View

function getAmountOut(uint256 amountIn, uint256 reserveIn, uint256 reserveOut) external pure returns (uint256)

Public wrapper for the output formula. Useful for off-chain quote computation.

Events

Custom Errors