ERC777Receiver.sol

//SPDX-License-Identifier: MIT
pragma solidity ^0.7.0;

import "@openzeppelin/contracts/token/ERC777/IERC777.sol";
import "@openzeppelin/contracts/token/ERC777/IERC777Recipient.sol";
import "@openzeppelin/contracts/introspection/IERC1820Registry.sol";

abstract contract ERC777Receiver is IERC777Recipient {
  IERC1820Registry constant internal ERC1820_REGISTRY = IERC1820Registry(0x1820a4B7618BdE71Dce8cdc73aAB6C95905faD24);

  constructor() {
    ERC1820_REGISTRY.setInterfaceImplementer(address(this), keccak256("ERC777TokensRecipient"), address(this));
  }

  function _tokensReceived(IERC777 token, address from, uint256 amount, bytes memory data) internal virtual;

  function tokensReceived(
    address /*operator*/,
    address from,
    address /*to*/,
    uint256 amount,
    bytes calldata userData,
    bytes calldata /*operatorData*/
  ) external override {
    _tokensReceived(IERC777(msg.sender), from, amount, userData);
  }
}