// SPDX-License-Identifier: GPL-3.0-only

pragma solidity ^0.5.0;

import "./external/OZIERC20.sol";
import "./external/OZSafeMath.sol";

contract NXMToken is OZIERC20 {
  using OZSafeMath for uint256;

  event WhiteListed(address indexed member);

  event BlackListed(address indexed member);

  mapping(address => uint256) private _balances;

  mapping(address => mapping(address => uint256)) private _allowed;

  mapping(address => bool) public whiteListed;

  mapping(address => uint) public isLockedForMV;

  uint256 private _totalSupply;

  string public name = "NXM";
  string public symbol = "NXM";
  uint8 public decimals = 18;
  address public operator;

  modifier canTransfer(address _to) {
    require(whiteListed[_to]);
    _;
  }

  modifier onlyOperator() {
    if (operator != address(0))
      require(msg.sender == operator);
    _;
  }

  constructor(address _founderAddress, uint _initialSupply) public {
    _mint(_founderAddress, _initialSupply);
  }

  /**
  * @dev Total number of tokens in existence
  */
  function totalSupply() public view returns (uint256) {
    return _totalSupply;
  }

  /**
  * @dev Gets the balance of the specified address.
  * @param owner The address to query the balance of.
  * @return An uint256 representing the amount owned by the passed address.
  */
  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 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) {
    require(spender != address(0));

    _allowed[msg.sender][spender] = value;
    emit Approval(msg.sender, spender, value);
    return true;
  }

  /**
  * @dev Increase the amount of tokens that an owner allowed to a spender.
  * approve should be called when allowed_[_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
  * @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)
  {
    require(spender != address(0));

    _allowed[msg.sender][spender] = (
    _allowed[msg.sender][spender].add(addedValue));
    emit Approval(msg.sender, spender, _allowed[msg.sender][spender]);
    return true;
  }

  /**
  * @dev Decrease the amount of tokens that an owner allowed to a spender.
  * approve should be called when allowed_[_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
  * @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)
  {
    require(spender != address(0));

    _allowed[msg.sender][spender] = (
    _allowed[msg.sender][spender].sub(subtractedValue));
    emit Approval(msg.sender, spender, _allowed[msg.sender][spender]);
    return true;
  }

  /**
  * @dev Adds a user to whitelist
  * @param _member address to add to whitelist
  */
  function addToWhiteList(address _member) public onlyOperator returns (bool) {
    whiteListed[_member] = true;
    emit WhiteListed(_member);
    return true;
  }

  /**
  * @dev removes a user from whitelist
  * @param _member address to remove from whitelist
  */
  function removeFromWhiteList(address _member) public onlyOperator returns (bool) {
    whiteListed[_member] = false;
    emit BlackListed(_member);
    return true;
  }

  /**
  * @dev change operator address
  * @param _newOperator address of new operator
  */
  function changeOperator(address _newOperator) public onlyOperator returns (bool) {
    operator = _newOperator;
    return true;
  }

  /**
  * @dev burns an amount of the tokens of the message sender
  * account.
  * @param amount The amount that will be burnt.
  */
  function burn(uint256 amount) public returns (bool) {
    _burn(msg.sender, amount);
    return true;
  }

  /**
  * @dev Burns a specific amount of tokens from the target address and decrements allowance
  * @param from address The address which you want to send tokens from
  * @param value uint256 The amount of token to be burned
  */
  function burnFrom(address from, uint256 value) public returns (bool) {
    _burnFrom(from, value);
    return true;
  }

  /**
  * @dev function that mints an amount of the token and assigns it to
  * an account.
  * @param account The account that will receive the created tokens.
  * @param amount The amount that will be created.
  */
  function mint(address account, uint256 amount) public onlyOperator {
    _mint(account, amount);
  }

  /**
  * @dev Transfer token for a specified address
  * @param to The address to transfer to.
  * @param value The amount to be transferred.
  */
  function transfer(address to, uint256 value) public canTransfer(to) returns (bool) {

    require(isLockedForMV[msg.sender] < now); // if not voted under governance
    require(value <= _balances[msg.sender]);
    _transfer(to, value);
    return true;
  }

  /**
  * @dev Transfer tokens to the operator from the specified address
  * @param from The address to transfer from.
  * @param value The amount to be transferred.
  */
  function operatorTransfer(address from, uint256 value) public onlyOperator returns (bool) {
    require(value <= _balances[from]);
    _transferFrom(from, operator, value);
    return true;
  }

  /**
  * @dev Transfer tokens from one address to another
  * @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
  canTransfer(to)
  returns (bool)
  {
    require(isLockedForMV[from] < now); // if not voted under governance
    require(value <= _balances[from]);
    require(value <= _allowed[from][msg.sender]);
    _transferFrom(from, to, value);
    return true;
  }

  /**
   * @dev Lock the user's tokens
   * @param _of user's address.
   */
  function lockForMemberVote(address _of, uint _days) public onlyOperator {
    if (_days.add(now) > isLockedForMV[_of])
      isLockedForMV[_of] = _days.add(now);
  }

  /**
  * @dev Transfer token for a specified address
  * @param to The address to transfer to.
  * @param value The amount to be transferred.
  */
  function _transfer(address to, uint256 value) internal {
    _balances[msg.sender] = _balances[msg.sender].sub(value);
    _balances[to] = _balances[to].add(value);
    emit Transfer(msg.sender, to, value);
  }

  /**
  * @dev Transfer tokens from one address to another
  * @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
  )
  internal
  {
    _balances[from] = _balances[from].sub(value);
    _balances[to] = _balances[to].add(value);
    _allowed[from][msg.sender] = _allowed[from][msg.sender].sub(value);
    emit Transfer(from, to, value);
  }

  /**
  * @dev Internal function that mints an amount of the token and assigns it to
  * an account. This encapsulates the modification of balances such that the
  * proper events are emitted.
  * @param account The account that will receive the created tokens.
  * @param amount The amount that will be created.
  */
  function _mint(address account, uint256 amount) internal {
    require(account != address(0));
    _totalSupply = _totalSupply.add(amount);
    _balances[account] = _balances[account].add(amount);
    emit Transfer(address(0), account, amount);
  }

  /**
  * @dev Internal function that burns an amount of the token of a given
  * account.
  * @param account The account whose tokens will be burnt.
  * @param amount The amount that will be burnt.
  */
  function _burn(address account, uint256 amount) internal {
    require(amount <= _balances[account]);

    _totalSupply = _totalSupply.sub(amount);
    _balances[account] = _balances[account].sub(amount);
    emit Transfer(account, address(0), amount);
  }

  /**
  * @dev Internal function that burns an amount of the token of a given
  * account, deducting from the sender's allowance for said account. Uses the
  * internal burn function.
  * @param account The account whose tokens will be burnt.
  * @param value The amount that will be burnt.
  */
  function _burnFrom(address account, uint256 value) internal {
    require(value <= _allowed[account][msg.sender]);

    // Should https://github.com/OpenZeppelin/zeppelin-solidity/issues/707 be accepted,
    // this function needs to emit an event with the updated approval.
    _allowed[account][msg.sender] = _allowed[account][msg.sender].sub(
      value);
    _burn(account, value);
  }
}