Fee.sol

The contract fetches real-time price feed from Chainlink Oracles and converts the gas fee amount to an equivalent token price.

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admin

mapping(address => bool) admins;

Key-value pair map that keeps track of the contract admin.

Parameter	Type
key	address	input addresses
value	bool	True: the address is an admin, False: otherwise

priceContracts

mapping(bytes => address) public priceContracts;

Key-value pair map that stores the address of a Chainlink pricefeed oracle contract.

Parameter	Type
key	bytes	The input price feed index, with the format: <network>-<token>-eth. For example, to query the USDC/ETH price from the Mainnet, enter main-usdc-eth
value	address	The Chainlink oracle address

tokensMap

mapping(address => bytes) public tokensMap;

Key-value pair mapping tokens to their contract addresses.

Parameter	Type
key	address	The ERC20 token address
value	bytes	The input price feed index, as defined in priceContracts

constructor()

constructor() public;

Assigns the deployer as a default admin, and pre-assigns the following price feed:

• main-usdc-eth
• main-uni-eth
• kovan-usdc-eth

onlyAdmin()

modifier onlyAdmin();

Verifies msg.sender is a contract admin.

modifyAdmin()

function modifyAdmin(address input, bool isAdmin) public onlyAdmin();

Adds or removes admin privilege to or from the input address.

Parameter	Type
input	address	The input address to be given or revoked admin privilege
isAdmin	bool	true: assigns admin, false: revokes admin

addPriceFeed()

function addPriceFeed(
    string memory priceIndex, 
    address feed, 
    address token
) public onlyAdmin();

Adds a new price feed, then maps to the token address. It can only be invoked by an admin. To find more oracle addresses, check out the Chainlink docs.

Parameter	Type
priceIndex	string	The input price feed index, as defined in priceContracts
feed	address	The address of the Chainlink price feed
token	address	The ERC20 token address

gasPrice()

function getPrice(address token) public view returns (int256);

Gets the real time price data from Chainlink in 18 decimals.

Parameter	Type
token	address	The ERC20 Token address

calculateGasInTokens()

function calculateGasInTokens(
    address token, 
    uint256 gas, 
    uint256 weiPerToken
) public view returns (uint256)

Returns the amount of tokens equivalent to the gas fee.

Parameter	Type
token	address	The ERC20 token address
gas	uint256	The gas fee
weiPerToken	uint256	The Wei amount per token