Resolver.js

pragma solidity >=0.5.0;

import './Proxy.sol';
import "openzeppelin-solidity/contracts/ownership/Ownable.sol";


// @title is where Proxy can lookup users version preference and update valid implementations
// @notice resolver is ownable
contract Resolver is Ownable{

  Proxy public proxy;

  mapping (address => address) public userVersion;
  mapping (address => bool) public validImplementation;

  // @notice proxy creates this contract and sets the owner
  constructor(address owner)
  public {
      proxy = Proxy(msg.sender);
      transferOwnership(owner);
  }

  // @notice user can set his preferred version of the contract here
  function setUserVersion(address addr)
  public {
      require(validImplementation[addr]);
      userVersion[msg.sender] = addr;
  }

  // @notice authorizes contracts to act as the implementation for Proxy
  function setValidImplementation(address addr, bool valid)
  public
  returns (bool) {
      require(msg.sender == address(proxy));
      validImplementation[addr] = valid;
      return true;
  }

  // @notice get the version preferred by this user
  function getUserVersion(address user)
  public
  view
  returns (address){
      if (userVersion[user] == address(0))
         return proxy.implementation();
      else
         return userVersion[user];
  }
}