/*

    Copyright 2020 Kollateral LLC.

    Licensed under the Apache License, Version 2.0 (the "License");
    you may not use this file except in compliance with the License.
    You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

    Unless required by applicable law or agreed to in writing, software
    distributed under the License is distributed on an "AS IS" BASIS,
    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    See the License for the specific language governing permissions and
    limitations under the License.

*/

// SPDX-License-Identifier: Apache-2.0
pragma solidity ^0.7.0;

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

abstract contract UnlimitedApprovalErc20 is ERC20 {
    using SafeMath for uint256;

    function transferFrom(
        address sender,
        address recipient,
        uint256 amount
    ) public virtual override returns (bool) {
        _transfer(sender, recipient, amount);
        if (allowance(sender, _msgSender()) != uint256(-1)) {
            _approve(
                sender,
                _msgSender(),
                allowance(sender, _msgSender()).sub(
                    amount,
                    "UnlimitedApprovalErc20: transfer amount exceeds allowance"
                )
            );
        }
        return true;
    }
}