pragma solidity ^0.5.0;

/**
 * @dev The contract has an owner address, and provides basic authorization control whitch
 * simplifies the implementation of user permissions. This contract is based on the source code
 * at https://goo.gl/n2ZGVt.
 */
contract Ownable {
  address public owner;

  /**
   * @dev An event which is triggered when the owner is changed.
   * @param previousOwner The address of the previous owner.
   * @param newOwner The address of the new owner.
   */
  event OwnershipTransferred(
    address indexed previousOwner,
    address indexed newOwner
  );

  /**
   * @dev The constructor sets the original `owner` of the contract to the sender account.
   */
  constructor()
    public
  {
    owner = msg.sender;
  }

  /**
   * @dev Throws if called by any account other than the owner.
   */
  modifier onlyOwner() {
    require(msg.sender == owner);
    _;
  }

  /**
   * @dev Allows the current owner to transfer control of the contract to a newOwner.
   * @param _newOwner The address to transfer ownership to.
   */
  function transferOwnership(
    address _newOwner
  )
    onlyOwner
    public
  {
    require(_newOwner != address(0));
    emit OwnershipTransferred(owner, _newOwner);
    owner = _newOwner;
  }

}