contract Freezable is Ownable {

  event AccountFrozen(address indexed _account);
  event AccountUnfrozen(address indexed _account);

  // frozen status of all accounts
  mapping(address=>bool) public frozenAccounts;


   /**
   * @dev Modifier to make a function callable only when the address is frozen.
   */
  modifier whenAccountFrozen(address _account) {
    require(frozenAccounts[_account] == true);
    _;
  }

  /**
   * @dev Modifier to make a function callable only when the address is not frozen.
   */
  modifier whenAccountNotFrozen(address _account) {
    require(frozenAccounts[_account] == false);
    _;
  }


  /**
   * @dev Function to freeze an account from transactions
   */
  function freeze(address _account)
    external
    onlyOwner
    whenAccountNotFrozen(_account)
    returns (bool)
  {
    frozenAccounts[_account] = true;
    emit AccountFrozen(_account);
    return true;
  }

  /**
   * @dev Function to unfreeze an account form frozen state
   */
  function unfreeze(address _account)
    external
    onlyOwner
    whenAccountFrozen(_account)
    returns (bool)
  {
    frozenAccounts[_account] = false;
    emit AccountUnfrozen(_account);
    return true;
  }


  /**
   * @dev A user can choose to freeze her account (not unfreezable)
   */
  function freezeMyAccount()
    external
    whenAccountNotFrozen(msg.sender)
    returns (bool)
  {
    // require(msg.sender != owner);       // Only the owner cannot freeze herself

    frozenAccounts[msg.sender] = true;
    emit AccountFrozen(msg.sender);
    return true;
  }
}
/// @title An inheritable extension for a contract to freeze accessibility of any specific addresses
/// @author Jeff Hu
/// @notice Have a contract inherited from this to use the modifiers: whenAccountFrozen(), whenAccountNotFrozen()
/// @dev Concern: Ownable may cause multiple owners; You need to pass in msg.sender when using modifiers
function unfreeze(address _account)
  external
  onlyOwner
  whenAccountFrozen(_account)
  returns (bool)
{
  frozenAccounts[_account] = false;
  emit AccountUnfrozen(_account);
  return true;
}

/**
 * @dev Function to unfreeze an account form frozen state
 */