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

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/security/Pausable.sol";
import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/math/SafeMath.sol";

contract NFUEL is ERC20, Pausable, Ownable {
    using SafeMath for uint256;

    address public minter;
    uint256 public cap;
    uint256 public gasRefundPercentage;

    event Mint(address indexed to, uint256 amount);
    event GasRefund(address indexed to, uint256 amount);

    constructor(uint256 _cap, uint256 _gasRefundPercentage) ERC20("GasToken", "NFUEL") {
        minter = msg.sender;
        cap = _cap;
        gasRefundPercentage = _gasRefundPercentage;
    }

    modifier onlyMinter() {
        require(msg.sender == minter, "Only the minter can call this");
        _;
    }

    modifier notExceedsCap(uint256 amount) {
        require(totalSupply().add(amount) <= cap, "Exceeds the token cap");
        _;
    }

    function mint(address to, uint256 amount) external onlyMinter notExceedsCap(amount) {
        _mint(to, amount);
        emit Mint(to, amount);
    }

    function setMinter(address newMinter) external onlyOwner {
        minter = newMinter;
    }

    function setCap(uint256 _cap) external onlyOwner {
        cap = _cap;
    }

    function setGasRefundPercentage(uint256 percentage) external onlyOwner {
        require(percentage <= 100, "Invalid percentage");
        gasRefundPercentage = percentage;
    }

    function pause() external onlyOwner {
        _pause();
    }

    function unpause() external onlyOwner {
        _unpause();
    }

    function refundGas(address to, uint256 amount) external whenNotPaused {
        require(msg.sender == minter, "Only the minter can refund gas");
        uint256 refundAmount = amount.mul(gasRefundPercentage).div(100);
        _mint(to, refundAmount);
        emit GasRefund(to, refundAmount);
    }

    receive() external payable {
        mint(msg.sender, msg.value);
    }
}