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contracts...UtilityToken.sol

// SPDX-License-Identifier: UNLICENSED
pragma solidity >=0.8.0;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";


contract UtilityToken is ERC20 {
    address public managerAddress;
    uint internal _totalSupply;
    mapping(address => uint256) internal _balances;

    event TransferFee(address indexed from, address indexed to, uint256 value);
    event Reset(address indexed reseter, uint amount);

    constructor(uint _initialSupply) ERC20("UtilityToken", "UT") {
        // Assume that msg.sender is ManagerContract.
        managerAddress = msg.sender;
        _mint(managerAddress, _initialSupply);
    }

    // .transfer OR ._beforeTokenTransfer
    // https://docs.openzeppelin.com/contracts/4.x/extending-contracts#using-hooks
    function _transfer(
        address from,
        address to,
        uint amount
    ) override internal virtual {
        super._transfer(from, to, amount * 90 / 100);
        super._transfer(from, managerAddress, amount * 10/100);
        emit TransferFee(from, managerAddress, amount * 10/100);
    }

    // Hard Reset
    function _beforeReset() internal virtual {}
    function _afterReset() internal virtual {}
    function _reset(uint _initialSupply) internal virtual {
        _beforeReset();
        // delete _balances;
        // emit Reset(msg.sender(), _totalSupply);
        _totalSupply = 0;
        _mint(msg.sender, _initialSupply);
        _afterReset();

        // TODO: allowances mapping 도 다 리셋해야 함.
    }
    function reset(uint _initialSupply) public virtual returns(bool) {
        _reset(_initialSupply);
        return true;
    }
}