CollectableDust.sol

// SPDX-License-Identifier: MIT
pragma solidity >=0.8.4 <0.9.0;

import '@openzeppelin/contracts/utils/structs/EnumerableSet.sol';
import '@openzeppelin/contracts/token/ERC20/IERC20.sol';
import '@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol';

import '../interfaces/utils/ICollectableDust.sol';

abstract contract CollectableDust is ICollectableDust {
  using SafeERC20 for IERC20;
  using EnumerableSet for EnumerableSet.AddressSet;

  address public constant ETH_ADDRESS = 0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE;
  EnumerableSet.AddressSet internal protocolTokens;

  constructor() {}

  function _addProtocolToken(address _token) internal {
    require(!protocolTokens.contains(_token), 'collectable-dust/token-is-part-of-the-protocol');
    protocolTokens.add(_token);
  }

  function _removeProtocolToken(address _token) internal {
    require(protocolTokens.contains(_token), 'collectable-dust/token-not-part-of-the-protocol');
    protocolTokens.remove(_token);
  }

  function _sendDust(
    address _to,
    address _token,
    uint256 _amount
  ) internal {
    require(_to != address(0), 'collectable-dust/cant-send-dust-to-zero-address');
    require(!protocolTokens.contains(_token), 'collectable-dust/token-is-part-of-the-protocol');
    if (_token == ETH_ADDRESS) {
      payable(_to).transfer(_amount);
    } else {
      IERC20(_token).safeTransfer(_to, _amount);
    }
    emit DustSent(_to, _token, _amount);
  }
}