wip: buy with stable/cusd

[sirpy]

Description

about: #290

[sourcery-ai]

Hey - I've found 3 issues, and left some high level feedback:

• In BuyGDCloneV2.swap, the Bought event emitted in the cUSD/stable branch still uses celo as the token address, which will mislead consumers of the event and should be updated to emit the correct token (likely CUSD or stable).
• In swapCusd, gasCosts are carved out from the contract’s CUSD balance but the refund is paid in stable, which will fail or behave unexpectedly when stable != CUSD; consider refunding from the same token the gas was reserved in or explicitly ensuring sufficient stable balance for the refund.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- In `BuyGDCloneV2.swap`, the `Bought` event emitted in the cUSD/stable branch still uses `celo` as the token address, which will mislead consumers of the event and should be updated to emit the correct token (likely `CUSD` or `stable`).
- In `swapCusd`, `gasCosts` are carved out from the contract’s `CUSD` balance but the refund is paid in `stable`, which will fail or behave unexpectedly when `stable != CUSD`; consider refunding from the same token the gas was reserved in or explicitly ensuring sufficient `stable` balance for the refund.

## Individual Comments

### Comment 1
<location> `contracts/utils/BuyGDClone.sol:93-101` </location>
<code_context>
 		uint256 gasCosts;
+		uint24[] memory fees = new uint24[](1);
+		fees[0] = 100;
 		if (refundGas != owner) {
-			(gasCosts, ) = oracle.quoteAllAvailablePoolsWithTimePeriod(
+			(gasCosts, ) = oracle.quoteSpecificFeeTiersWithTimePeriod(
</code_context>

<issue_to_address>
**issue (bug_risk):** Gas refund is taken from CUSD balance but paid out in `stable`, which can mis-account funds when `stable != CUSD`.

`swapCusd` subtracts `gasCosts` from the CUSD balance (`amountIn = ERC20(CUSD).balanceOf(address(this)) - gasCosts;`) but sends the refund in `stable` (`ERC20(stable).transfer(refundGas, gasCosts)`). When `stable != CUSD`, this reduces CUSD while spending an unreserved amount of `stable`, which can desync balances and underfund future swaps. Consider either refunding in CUSD or charging gas costs from `stable` consistently.
</issue_to_address>

### Comment 2
<location> `contracts/utils/BuyGDClone.sol:72` </location>
<code_context>
 			return bought;
 		}
-		balance = ERC20(cusd).balanceOf(address(this));
+		balance = ERC20(CUSD).balanceOf(address(this));
 		if (balance > 0) {
 			bought = swapCusd(_minAmount, refundGas);
</code_context>

<issue_to_address>
**issue (bug_risk):** `swap` only checks CUSD balance, even though the contract now supports a generic `stable` token.

The second branch still checks `ERC20(CUSD).balanceOf(address(this))` and calls `swapCusd`, so if `stable` is set to a different token and only that token is funded, this path never runs and those funds are never swapped. Either restrict the docstring to CUSD only, or update this branch to work off `stable` (and a corresponding `swapStable`) when `stable != CUSD`.
</issue_to_address>

### Comment 3
<location> `contracts/utils/BuyGDClone.sol:34` </location>
<code_context>

 	constructor(
 		ISwapRouter _router,
-		address _cusd,
+		address _stable,
 		address _gd,
</code_context>

<issue_to_address>
**nitpick:** Constructor parameter name `_cusd` in `DonateGDClone` is now misleading since it represents a generic stable token.

The parameter is still named `_cusd` in `DonateGDClone` while it now represents a generic stable token and is passed through to `BuyGDCloneV2`. Please rename it to `_stable` to align with `BuyGDCloneV2` and avoid confusion when deploying with non-cUSD stablecoins.
</issue_to_address>

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[sourcery-ai]

nitpick: Constructor parameter name _cusd in DonateGDClone is now misleading since it represents a generic stable token.

The parameter is still named _cusd in DonateGDClone while it now represents a generic stable token and is passed through to BuyGDCloneV2. Please rename it to _stable to align with BuyGDCloneV2 and avoid confusion when deploying with non-cUSD stablecoins.

[openzeppelin-code]

wip: buy with stable/cusd

Generated at commit: d201e1475962239f2582e379e0d218430c957213

🚨 Report Summary

	Severity Level	Results
Contracts	Critical High Medium Low Note Total	3 5 0 16 44 68
Dependencies	Critical High Medium Low Note Total	0 0 1 0 130 131

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For more details view the full report in OpenZeppelin Code Inspector