Simple Staleness Flagger

Staleness.sol

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "https://github.com/smartcontractkit/chainlink/blob/develop/evm-contracts/src/v0.8/interfaces/AggregatorV3Interface.sol";

contract Staleness {
    
    uint public immutable interval;
    
    mapping(AggregatorV3Interface => bool) public staleFlag;
    
    constructor(uint updateInterval) {
        interval = updateInterval;
    }
    
    function checkIfStale(AggregatorV3Interface priceFeed) public view returns (bool) {
        (,,,uint timeStamp,) = priceFeed.latestRoundData();
        return (block.timestamp - timeStamp) > interval;
    }
    
    function raiseFlag(AggregatorV3Interface priceFeed) public {
        require(checkIfStale(priceFeed), "Not stale");
        require(!staleFlag[priceFeed], "Already flagged");
        staleFlag[priceFeed] = true;
    }
    
    function lowerFlag(AggregatorV3Interface priceFeed) public {
        require(!checkIfStale(priceFeed), "Still stale");
        require(staleFlag[priceFeed], "Not flagged");
        staleFlag[priceFeed] = false;
    }
}