Decentralized Stablecoin

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.18;

import {ERC20, ERC20Burnable} from "@openzeppelin/contracts/token/ERC20/extensions/ERC20Burnable.sol";
import {Ownable} from "@openzeppelin/contracts/access/Ownable.sol";

/**
 * @title DecentralizedStableCoin
 * @notice ERC20 token that only DSCEngine can mint/burn
 * @dev Ownership is transferred to DSCEngine after deployment
 */
contract DecentralizedStableCoin is ERC20Burnable, Ownable {
    error DecentralizedStableCoin__AmountMustBeMoreThanZero();
    error DecentralizedStableCoin__BurnAmountExceedsBalance();

    constructor(address initialOwner)
        ERC20("DecentralizedStableCoin", "DSC")
        Ownable(initialOwner)
    {}

    // Only DSCEngine (owner) can mint
    function mint(address _to, uint256 _amount) external onlyOwner returns (bool) {
        if (_to == address(0)) revert DecentralizedStableCoin__NotZeroAddress();
        if (_amount <= 0) revert DecentralizedStableCoin__AmountMustBeMoreThanZero();
        _mint(_to, _amount);
        return true;
    }

    // Only DSCEngine (owner) can burn
    function burn(uint256 _amount) public override onlyOwner {
        if (_amount <= 0) revert DecentralizedStableCoin__AmountMustBeMoreThanZero();
        if (_amount > balanceOf(msg.sender)) {
            revert DecentralizedStableCoin__BurnAmountExceedsBalance();
        }
        super.burn(_amount);
    }
}

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.18;

import {AggregatorV3Interface} from "@chainlink/contracts/src/v0.8/interfaces/AggregatorV3Interface.sol";

/**
 * @title OracleLib
 * @notice Wraps Chainlink price feeds with staleness checks
 * @dev Reverts if price data is older than 3 hours
 */
library OracleLib {
    error OracleLib__StalePrice();

    uint256 private constant TIMEOUT = 3 hours;

    function staleCheckLatestRoundData(AggregatorV3Interface feed)
        public view returns (uint80, int256, uint256, uint256, uint80)
    {
        (
            uint80 roundId,
            int256 answer,
            uint256 startedAt,
            uint256 updatedAt,
            uint80 answeredInRound
        ) = feed.latestRoundData();

        // Check 1: Price must have been updated
        if (updatedAt == 0 || answeredInRound < roundId) {
            revert OracleLib__StalePrice();
        }

        // Check 2: Price must be fresh (within 3 hours)
        uint256 secondsSince = block.timestamp - updatedAt;
        if (secondsSince > TIMEOUT) revert OracleLib__StalePrice();

        return (roundId, answer, startedAt, updatedAt, answeredInRound);
    }
}