PAAL AI - Audit

The "swapExactTokensForETH" function calculates the "actualReceived" amount by comparing the token balance in the contract before and after the swap, which is a correct and recommended way to obtain the "amountIn". However, the "swapExactTokensForTokens" function doesn't follow the same practice, which means the amountIn value could be off if the token is a special ERC20 token, such as a deflationary token.

The code utilizes `address(this)` when calculating the `initialBalance` and `afterBalance`. This logic is incorrect because the tokens are sent to the `sender` address. The current calculation will result in the `amountOut` becoming a zero value. ```sol uint256 initialBalance = tokenOutContract.balanceOf(address(this)); ... // Calculate the amount of tokenOut received uint256 afterBalance = tokenOutContract.balanceOf(address(this)); amountOut = afterBalance - initialBalance; ```

There are no upper boundaries for **swappingFee** which is used to **calculate the swap fee**. It is possible to set the total fee up to any arbitrary amount.

In the smart contract's event emission logic, there's an inconsistency observed in the representation of `amountIn` across different transaction types. Specifically, the `Buy` and `Sell` events emit the `amountIn` value before the deduction of any transaction fees. These events are structured as follows: - `event Buy(address indexed sender, uint256 amountIn, address indexed tokenOut, uint256 amountOut);` - `event Sell(address indexed sender, address indexed tokenIn, uint256 amountIn, uint256 amountOut);` In contrast, the `SellTokensForTokens` event uses `amountInAfterFee` instead of the gross `amountIn`: - `event SellTokensForTokens(address indexed sender, address indexed tokenIn, address indexed tokenOut, uint256 amountInAfterFee, uint256 amountOut);` This discrepancy leads to a lack of uniformity in how the input amounts are reported, potentially causing confusion when interpreting the events, especially for off-chain services and analyses that rely on these events for transaction data.

An inconsistency in the fee calculation methodology was identified. The functions `swapExactTokensForETH` and `swapExactETHForTokens` calculate the transaction fee using the formula `uint256 fee = (msg.value * swappingFee) / swappingFeeDivisior;`, which utilizes a dynamic fee rate determined by the `swappingFee` and `swappingFeeDivisior` variables. Conversely, the `swapExactTokenForToken` function employs a static fee calculation method: `uint256 fee = (amountIn * swappingFee) / 1000000;`, which effectively hardcodes the fee rate to a specific value, assumed to be 1% based on the comment.

In the `swapExactETHForTokens` function, the function "swapExactETHForTokensSupportingFeeOnTransferTokens" accepts the native token, such as ETH, instead of the wrapped version (e.g., WETH). Therefore, performing the approval operations is not necessary. ```sol // Approve the router to spend the tokens for the swap weth.safeApprove(address(router), amountIn); ```