/**
 * @notice Loads _numTokens ERC20 tokens into the voting contract for one-to-one voting rights
 * @dev Assumes that msg.sender has approved voting contract to spend on their behalf
 * @param _numTokens The number of votingTokens desired in exchange for ERC20 tokens
 */
function requestVotingRights(uint256 _numTokens) public {
  require(token.balanceOf(msg.sender) >= _numTokens, "Cannot stake more than you have");
  voteTokenBalance[msg.sender] = voteTokenBalance[msg.sender].add(_numTokens);

  // Transfer tokens to voting contract
  // User must approve tokens to voting contract in advance token.approve(voting)
  require(token.transferFrom(msg.sender, this, _numTokens));
  emit _VotingRightsGranted(_numTokens, msg.sender);
}

/**
 * @notice Withdraw _numTokens ERC20 tokens from the voting contract, revoking these voting rights
 * @param _numTokens The number of ERC20 tokens desired in exchange for voting rights
 */
function withdrawVotingRights(uint256 _numTokens) external {
  // withdrawing tokens only not locked should be available
  require(voteTokenBalance[msg.sender] >= _numTokens, "Cannot withdraw more than used in the polls");
  voteTokenBalance[msg.sender] = voteTokenBalance[msg.sender].sub(_numTokens);
  require(token.transfer(msg.sender, _numTokens));
  emit _VotingRightsWithdrawn(_numTokens, msg.sender);
}

/**
 * @dev Unlocks tokens locked in unrevealed vote where poll has ended
 * @param _pollID Integer identifier associated with the target poll
 */
function rescueTokens(uint _pollID) public {
  require(isExpired(pollMap[_pollID].revealEndDate), "The poll has not ended");
  require(dllMap[msg.sender].contains(_pollID));

  uint256 numTokens = getNumTokens(msg.sender, _pollID);

  dllMap[msg.sender].remove(_pollID);

  // No partial lock, add _numTokens back to the voting rights
  // Tokens are now available to withdraw or for another vote
  voteTokenBalance[msg.sender] = voteTokenBalance[msg.sender].add(numTokens);

  emit _TokensRescued(_pollID, msg.sender);
}