Lesson 9: Implementing Single Swap to Auto Fund VRF Subscription

[raymondfam]

function fulfillRandomWords(
        uint256, /* requestId */
        uint256[] memory randomWords
    ) internal override {
        uint256 indexOfWinner = randomWords[0] % s_players.length;
        address payable recentWinner = s_players[indexOfWinner];
        s_recentWinner = recentWinner;
        s_players = new address payable[](0);
        s_raffleState = RaffleState.OPEN;
        s_lastTimeStamp = block.timestamp;
        uint256 ethAmountToBuyLink = address(this).balance / 100 * 5;
        i_wethToken.deposit{ value: ethAmountToBuyLink }();
        uint256 wethBalance = i_wethToken.balanceOf(address(this));
        buyLink(wethBalance);
        uint256 linkBalance = i_linkToken.balanceOf(address(this));
        topUpVRFSubscription(linkBalance);
        (bool success, ) = recentWinner.call{value: address(this).balance}("");
        // require(success, "Transfer failed");
        if (!success) {
            revert Raffle__TransferFailed();
        }
        emit WinnerPicked(recentWinner);
    }

    function topUpVRFSubscription(uint256 amount) internal {
        i_linkToken.transferAndCall(address(i_vrfCoordinator), amount, abi.encode(i_subscriptionId));
    }

    function buyLink(uint256 amountIn) internal returns (uint256 amountOut) {
        
        // Approve the router to spend DAI.
        TransferHelper.safeApprove(WETH_ADDRESS, address(i_swapRouter), amountIn);

        // Naively set amountOutMinimum to 0. In production, use an oracle or other data source to choose a safer value for amountOutMinimum.
        // We also set the sqrtPriceLimitx96 to be 0 to ensure we swap our exact input amount.
        ISwapRouter.ExactInputSingleParams memory params =
            ISwapRouter.ExactInputSingleParams({
                tokenIn: WETH_ADDRESS,
                tokenOut: LINK_ADDRESS,
                fee: 3000,
                recipient: address(this),
                deadline: block.timestamp + 15,
                amountIn: amountIn,
                amountOutMinimum: 0,
                sqrtPriceLimitX96: 0
            });

        // The call to `exactInputSingle` executes the swap.
        amountOut = i_swapRouter.exactInputSingle(params);
    }

The refactored function fulfillRandomWords would revert with an error showing up on Rinkeby etherscan (Internal Txns) when running the staging test:

https://rinkeby.etherscan.io/address/0xAbA0228feF6De3A8320FC4487792D698F9EA8c39#internaltx

Could anyone help look into this problem, or we simply cannot have the contract calling the ISwapRouter contract considering the tx.origin is Chainlink VRF in this instance? Thanks.