chainlinkOptions.sol

pragma solidity ^0.6.7;

import "https://github.com/smartcontractkit/chainlink/blob/develop/evm-contracts/src/v0.6/interfaces/LinkTokenInterface.sol";
import "https://github.com/smartcontractkit/chainlink/blob/master/evm-contracts/src/v0.6/interfaces/AggregatorV3Interface.sol";
import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/math/SafeMath.sol";

contract chainlinkOptions {
    //Overflow safe operators
    using SafeMath for uint;
    //Pricefeed interfaces
    AggregatorV3Interface internal ethFeed;
    AggregatorV3Interface internal linkFeed;
    //Interface for LINK token functions
    LinkTokenInterface internal LINK;
    uint ethPrice;
    uint linkPrice;
    //Precomputing hash of strings
    bytes32 ethHash = keccak256(abi.encodePacked("ETH"));
    bytes32 linkHash = keccak256(abi.encodePacked("LINK"));
    address payable contractAddr;
    
    //Options stored in arrays of structs
    struct option {
        uint strike; //Price in USD (18 decimal places) option allows buyer to purchase tokens at
        uint premium; //Fee in contract token that option writer charges
        uint expiry; //Unix timestamp of expiration time
        uint amount; //Amount of tokens the option contract is for
        bool exercised; //Has option been exercised
        bool canceled; //Has option been canceled
        uint id; //Unique ID of option, also array index
        uint latestCost; //Helper to show last updated cost to exercise
        address payable writer; //Issuer of option
        address payable buyer; //Buyer of option
    }
    option[] public ethOpts;
    option[] public linkOpts;

    //Kovan feeds: https://docs.chain.link/docs/reference-contracts
    constructor() public {
        //ETH/USD Kovan feed
        ethFeed = AggregatorV3Interface(0x9326BFA02ADD2366b30bacB125260Af641031331);
        //LINK/USD Kovan feed
        linkFeed = AggregatorV3Interface(0x396c5E36DD0a0F5a5D33dae44368D4193f69a1F0);
        //LINK token address on Kovan
        LINK = LinkTokenInterface(0xa36085F69e2889c224210F603D836748e7dC0088);
        contractAddr = payable(address(this));
    }

    //Returns the latest ETH price
    function getEthPrice() public view returns (uint) {
        (
            uint80 roundID, 
            int price,
            uint startedAt,
            uint timeStamp,
            uint80 answeredInRound
        ) = ethFeed.latestRoundData();
        // If the round is not complete yet, timestamp is 0
        require(timeStamp > 0, "Round not complete");
        //Price should never be negative thus cast int to unit is ok
        //Price is 8 decimal places and will require 1e10 correction later to 18 places
        return uint(price);
    }
    
    //Returns the latest LINK price
    function getLinkPrice() public view returns (uint) {
        (
            uint80 roundID, 
            int price,
            uint startedAt,
            uint timeStamp,
            uint80 answeredInRound
        ) = linkFeed.latestRoundData();
        // If the round is not complete yet, timestamp is 0
        require(timeStamp > 0, "Round not complete");
        //Price should never be negative thus cast int to unit is ok
        //Price is 8 decimal places and will require 1e10 correction later to 18 places
        return uint(price);
    }
    
    //Updates prices to latest
    function updatePrices() internal {
        ethPrice = getEthPrice();
        linkPrice = getLinkPrice();
    }
    
    //Allows user to write a covered call option
    //Takes which token, a strike price(USD per token w/18 decimal places), premium(same unit as token), expiration time(unix) and how many tokens the contract is for
    function writeOption(string memory token, uint strike, uint premium, uint expiry, uint tknAmt) public payable {
        bytes32 tokenHash = keccak256(abi.encodePacked(token));
        require(tokenHash == ethHash || tokenHash == linkHash, "Only ETH and LINK tokens are supported");
        updatePrices();
        if (tokenHash == ethHash) {
            require(msg.value == tknAmt, "Incorrect amount of ETH supplied"); 
            uint latestCost = strike.mul(tknAmt).div(ethPrice.mul(10**10)); //current cost to exercise in ETH, decimal places corrected
            ethOpts.push(option(strike, premium, expiry, tknAmt, false, false, ethOpts.length, latestCost, msg.sender, address(0)));
        } else {
            require(LINK.transferFrom(msg.sender, contractAddr, tknAmt), "Incorrect amount of LINK supplied");
            uint latestCost = strike.mul(tknAmt).div(linkPrice.mul(10**10));
            linkOpts.push(option(strike, premium, expiry, tknAmt, false, false, linkOpts.length, latestCost, msg.sender, address(0)));
        }
    }
    
    //Allows option writer to cancel and get their funds back from an unpurchased option
    function cancelOption(string memory token, uint ID) public payable {
        bytes32 tokenHash = keccak256(abi.encodePacked(token));
        require(tokenHash == ethHash || tokenHash == linkHash, "Only ETH and LINK tokens are supported");
        if (tokenHash == ethHash) {
            require(msg.sender == ethOpts[ID].writer, "You did not write this option");
            //Must not have already been canceled or bought
            require(!ethOpts[ID].canceled && ethOpts[ID].buyer == address(0), "This option cannot be canceled");
            ethOpts[ID].writer.transfer(ethOpts[ID].amount);
            ethOpts[ID].canceled = true;
        } else {
            require(msg.sender == linkOpts[ID].writer, "You did not write this option");
            require(!linkOpts[ID].canceled && linkOpts[ID].buyer == address(0), "This option cannot be canceled");
            require(LINK.transferFrom(address(this), linkOpts[ID].writer, linkOpts[ID].amount), "Incorrect amount of LINK sent");
            linkOpts[ID].canceled = true;
        }
    }
    
    //Purchase a call option, needs desired token, ID of option and payment
    function buyOption(string memory token, uint ID) public payable {
        bytes32 tokenHash = keccak256(abi.encodePacked(token));
        require(tokenHash == ethHash || tokenHash == linkHash, "Only ETH and LINK tokens are supported");
        updatePrices();
        if (tokenHash == ethHash) {
            require(!ethOpts[ID].canceled && ethOpts[ID].expiry > now, "Option is canceled/expired and cannot be bought");
            //Transfer premium payment from buyer
            require(msg.value == ethOpts[ID].premium, "Incorrect amount of ETH sent for premium");
            //Transfer premium payment to writer
            ethOpts[ID].writer.transfer(ethOpts[ID].premium);
            ethOpts[ID].buyer = msg.sender;
        } else {
            require(!linkOpts[ID].canceled && linkOpts[ID].expiry > now, "Option is canceled/expired and cannot be bought");
            //Transfer premium payment from buyer to writer
            require(LINK.transferFrom(msg.sender, linkOpts[ID].writer, linkOpts[ID].premium), "Incorrect amount of LINK sent for premium");
            linkOpts[ID].buyer = msg.sender;
        }
    }
    
    //Exercise your call option, needs desired token, ID of option and payment
    function exercise(string memory token, uint ID) public payable {
        //If not expired and not already exercised, allow option owner to exercise
        //To exercise, the strike value*amount equivalent paid to writer (from buyer) and amount of tokens in the contract paid to buyer
        bytes32 tokenHash = keccak256(abi.encodePacked(token));
        require(tokenHash == ethHash || tokenHash == linkHash, "Only ETH and LINK tokens are supported");
        if (tokenHash == ethHash) {
            require(ethOpts[ID].buyer == msg.sender, "You do not own this option");
            require(!ethOpts[ID].exercised, "Option has already been exercised");
            require(ethOpts[ID].expiry > now, "Option is expired");
            //Conditions are met, proceed to payouts
            updatePrices();
            //Cost to exercise
            uint exerciseVal = ethOpts[ID].strike*ethOpts[ID].amount;
            //Equivalent ETH value using Chainlink feed
            uint equivEth = exerciseVal.div(ethPrice.mul(10**10)); //move decimal 10 places right to account for 8 places of pricefeed
            //Buyer exercises option by paying strike*amount equivalent ETH value
            require(msg.value == equivEth, "Incorrect LINK amount sent to exercise");
            //Pay writer the exercise cost
            ethOpts[ID].writer.transfer(equivEth);
            //Pay buyer contract amount of ETH
            msg.sender.transfer(ethOpts[ID].amount);
            ethOpts[ID].exercised = true;
            
        } else {
            require(linkOpts[ID].buyer == msg.sender, "You do not own this option");
            require(!linkOpts[ID].exercised, "Option has already been exercised");
            require(linkOpts[ID].expiry > now, "Option is expired");
            updatePrices();
            uint exerciseVal = linkOpts[ID].strike*linkOpts[ID].amount;
            uint equivLink = exerciseVal.div(linkPrice.mul(10**10));
            //Buyer exercises option, exercise cost paid to writer
            require(LINK.transferFrom(msg.sender, linkOpts[ID].writer, equivLink), "Incorrect LINK amount sent to exercise");
            //Pay buyer contract amount of LINK
            require(LINK.transfer(msg.sender, linkOpts[ID].amount), "Error: buyer was not paid");
            linkOpts[ID].exercised = true;
        }
    }
    
    //Allows writer to retrieve funds from an expired, non-exercised, non-canceled option
    function retrieveExpiredFunds(string memory token, uint ID) public payable {
        bytes32 tokenHash = keccak256(abi.encodePacked(token));
        require(tokenHash == ethHash || tokenHash == linkHash, "Only ETH and LINK tokens are supported");
        if (tokenHash == ethHash) {
            require(msg.sender == ethOpts[ID].writer, "You did not write this option");
            //Must be expired, not exercised and not canceled
            require(ethOpts[ID].expiry <= now && !ethOpts[ID].exercised && !ethOpts[ID].canceled, "This option is not eligible for withdraw");
            ethOpts[ID].writer.transfer(ethOpts[ID].amount);
            //Repurposing canceled flag to prevent more than one withdraw
            ethOpts[ID].canceled = true;
        } else {
            require(msg.sender == linkOpts[ID].writer, "You did not write this option");
            require(linkOpts[ID].expiry <= now && !linkOpts[ID].exercised && !linkOpts[ID].canceled, "This option is not eligible for withdraw");
            require(LINK.transferFrom(address(this), linkOpts[ID].writer, linkOpts[ID].amount), "Incorrect amount of LINK sent");
            linkOpts[ID].canceled = true;
        }
    }
    
    //This is a helper function to help the user see what the cost to exercise an option is currently before they do so
    //Updates lastestCost member of option which is publicly viewable
    function updateExerciseCost(string memory token, uint ID) public {
        bytes32 tokenHash = keccak256(abi.encodePacked(token));
        require(tokenHash == ethHash || tokenHash == linkHash, "Only ETH and LINK tokens are supported");
        updatePrices();
        if (tokenHash == ethHash) {
            ethOpts[ID].latestCost = ethOpts[ID].strike.mul(ethOpts[ID].amount).div(ethPrice.mul(10**10));
        } else {
            linkOpts[ID].latestCost = linkOpts[ID].strike.mul(linkOpts[ID].amount).div(linkPrice.mul(10**10));
        }
    }
}