pragma solidity ^0.5.0;

interface IERC20 {
  /**
   * @dev Returns the amount of tokens in existence.
   */
  function totalSupply() external view returns (uint256);

  /**
   * @dev Returns the amount of tokens owned by `account`.
   */
  function balanceOf(address account) external view returns (uint256);

  /**
   * @dev Moves `amount` tokens from the caller's account to `recipient`.
   *
   * Returns a boolean value indicating whether the operation succeeded.
   *
   * Emits a `Transfer` event.
   */
  function transfer(address recipient, uint256 amount) external returns (bool);

  /**
   * @dev Returns the remaining number of tokens that `spender` will be
   * allowed to spend on behalf of `owner` through `transferFrom`. This is
   * zero by default.
   *
   * This value changes when `approve` or `transferFrom` are called.
   */
  function allowance(address owner, address spender) external view returns (uint256);

  /**
   * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
   *
   * Returns a boolean value indicating whether the operation succeeded.
   *
   * > 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
   *
   * Emits an `Approval` event.
   */
  function approve(address spender, uint256 amount) external returns (bool);

  /**
   * @dev Moves `amount` tokens from `sender` to `recipient` using the
   * allowance mechanism. `amount` is then deducted from the caller's
   * allowance.
   *
   * Returns a boolean value indicating whether the operation succeeded.
   *
   * Emits a `Transfer` event.
   */
  function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);

  /**
   * @dev Emitted when `value` tokens are moved from one account (`from`) to
   * another (`to`).
   *
   * Note that `value` may be zero.
   */
  event Transfer(address indexed from, address indexed to, uint256 value);

  /**
   * @dev Emitted when the allowance of a `spender` for an `owner` is set by
   * a call to `approve`. `value` is the new allowance.
   */
  event Approval(address indexed owner, address indexed spender, uint256 value);
}


/**
 * @dev Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */
library SafeMath {
  /**
   * @dev Returns the addition of two unsigned integers, reverting on
   * overflow.
   *
   * Counterpart to Solidity's `+` operator.
   *
   * Requirements:
   * - Addition cannot overflow.
   */
  function add(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a + b;
    require(c >= a, "SafeMath: addition overflow");

    return c;
  }

  /**
   * @dev Returns the subtraction of two unsigned integers, reverting on
   * overflow (when the result is negative).
   *
   * Counterpart to Solidity's `-` operator.
   *
   * Requirements:
   * - Subtraction cannot overflow.
   */
  function sub(uint256 a, uint256 b) internal pure returns (uint256) {
    require(b <= a, "SafeMath: subtraction overflow");
    uint256 c = a - b;

    return c;
  }

  /**
   * @dev Returns the multiplication of two unsigned integers, reverting on
   * overflow.
   *
   * Counterpart to Solidity's `*` operator.
   *
   * Requirements:
   * - Multiplication cannot 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: multiplication overflow");

    return c;
  }

  /**
   * @dev Returns the integer division of two unsigned integers. Reverts on
   * division by zero. The result is rounded towards zero.
   *
   * Counterpart to Solidity's `/` operator. Note: this function uses a
   * `revert` opcode (which leaves remaining gas untouched) while Solidity
   * uses an invalid opcode to revert (consuming all remaining gas).
   *
   * Requirements:
   * - The divisor cannot be zero.
   */
  function div(uint256 a, uint256 b) internal pure returns (uint256) {
    // Solidity only automatically asserts when dividing by 0
    require(b > 0, "SafeMath: division by zero");
    uint256 c = a / b;
    // assert(a == b * c + a % b); // There is no case in which this doesn't hold

    return c;
  }

  /**
   * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
   * Reverts when dividing by zero.
   *
   * Counterpart to Solidity's `%` operator. This function uses a `revert`
   * opcode (which leaves remaining gas untouched) while Solidity uses an
   * invalid opcode to revert (consuming all remaining gas).
   *
   * Requirements:
   * - The divisor cannot be zero.
   */
  function mod(uint256 a, uint256 b) internal pure returns (uint256) {
    require(b != 0, "SafeMath: modulo by zero");
    return a % b;
  }
}


/**
 * @dev Implementation of the `IERC20` interface.
 *
 * This implementation is agnostic to the way tokens are created. This means
 * that a supply mechanism has to be added in a derived contract using `_mint`.
 * For a generic mechanism see `ERC20Mintable`.
 *
 * *For a detailed writeup see our guide [How to implement supply
 * mechanisms](https://forum.zeppelin.solutions/t/how-to-implement-erc20-supply-mechanisms/226).*
 *
 * We have followed general OpenZeppelin guidelines: functions revert instead
 * of returning `false` on failure. This behavior is nonetheless conventional
 * and does not conflict with the expectations of ERC20 applications.
 *
 * Additionally, an `Approval` event is emitted on calls to `transferFrom`.
 * This allows applications to reconstruct the allowance for all accounts just
 * by listening to said events. Other implementations of the EIP may not emit
 * these events, as it isn't required by the specification.
 *
 * Finally, the non-standard `decreaseAllowance` and `increaseAllowance`
 * functions have been added to mitigate the well-known issues around setting
 * allowances. See `IERC20.approve`.
 */
contract ERC20 is IERC20 {
  using SafeMath for uint256;

  mapping (address => uint256) private _balances;

  mapping (address => mapping (address => uint256)) private _allowances;

  uint256 private _totalSupply;

  /**
   * @dev See `IERC20.totalSupply`.
   */
  function totalSupply() public view returns (uint256) {
    return _totalSupply;
  }

  /**
   * @dev See `IERC20.balanceOf`.
   */
  function balanceOf(address account) public view returns (uint256) {
    return _balances[account];
  }

  /**
   * @dev See `IERC20.transfer`.
   *
   * Requirements:
   *
   * - `recipient` cannot be the zero address.
   * - the caller must have a balance of at least `amount`.
   */
  function transfer(address recipient, uint256 amount) public returns (bool) {
    _transfer(msg.sender, recipient, amount);
    return true;
  }

  /**
   * @dev See `IERC20.allowance`.
   */
  function allowance(address owner, address spender) public view returns (uint256) {
    return _allowances[owner][spender];
  }

  /**
   * @dev See `IERC20.approve`.
   *
   * Requirements:
   *
   * - `spender` cannot be the zero address.
   */
  function approve(address spender, uint256 value) public returns (bool) {
    _approve(msg.sender, spender, value);
    return true;
  }

  /**
   * @dev See `IERC20.transferFrom`.
   *
   * Emits an `Approval` event indicating the updated allowance. This is not
   * required by the EIP. See the note at the beginning of `ERC20`;
   *
   * Requirements:
   * - `sender` and `recipient` cannot be the zero address.
   * - `sender` must have a balance of at least `value`.
   * - the caller must have allowance for `sender`'s tokens of at least
   * `amount`.
   */
  function transferFrom(address sender, address recipient, uint256 amount) public returns (bool) {
    _transfer(sender, recipient, amount);
    _approve(sender, msg.sender, _allowances[sender][msg.sender].sub(amount));
    return true;
  }

  /**
   * @dev Atomically increases the allowance granted to `spender` by the caller.
   *
   * This is an alternative to `approve` that can be used as a mitigation for
   * problems described in `IERC20.approve`.
   *
   * Emits an `Approval` event indicating the updated allowance.
   *
   * Requirements:
   *
   * - `spender` cannot be the zero address.
   */
  function increaseAllowance(address spender, uint256 addedValue) public returns (bool) {
    _approve(msg.sender, spender, _allowances[msg.sender][spender].add(addedValue));
    return true;
  }

  /**
   * @dev Atomically decreases the allowance granted to `spender` by the caller.
   *
   * This is an alternative to `approve` that can be used as a mitigation for
   * problems described in `IERC20.approve`.
   *
   * Emits an `Approval` event indicating the updated allowance.
   *
   * Requirements:
   *
   * - `spender` cannot be the zero address.
   * - `spender` must have allowance for the caller of at least
   * `subtractedValue`.
   */
  function decreaseAllowance(address spender, uint256 subtractedValue) public returns (bool) {
    _approve(msg.sender, spender, _allowances[msg.sender][spender].sub(subtractedValue));
    return true;
  }

  /**
   * @dev Moves tokens `amount` from `sender` to `recipient`.
   *
   * This is internal function is equivalent to `transfer`, and can be used to
   * e.g. implement automatic token fees, slashing mechanisms, etc.
   *
   * Emits a `Transfer` event.
   *
   * Requirements:
   *
   * - `sender` cannot be the zero address.
   * - `recipient` cannot be the zero address.
   * - `sender` must have a balance of at least `amount`.
   */
  function _transfer(address sender, address recipient, uint256 amount) internal {
    require(sender != address(0), "ERC20: transfer from the zero address");
    require(recipient != address(0), "ERC20: transfer to the zero address");

    _balances[sender] = _balances[sender].sub(amount);
    _balances[recipient] = _balances[recipient].add(amount);
    emit Transfer(sender, recipient, amount);
  }

  /** @dev Creates `amount` tokens and assigns them to `account`, increasing
   * the total supply.
   *
   * Emits a `Transfer` event with `from` set to the zero address.
   *
   * Requirements
   *
   * - `to` cannot be the zero address.
   */
  function _mint(address account, uint256 amount) internal {
    require(account != address(0), "ERC20: mint to the zero address");

    _totalSupply = _totalSupply.add(amount);
    _balances[account] = _balances[account].add(amount);
    emit Transfer(address(0), account, amount);
  }

  /**
  * @dev Destoys `amount` tokens from `account`, reducing the
  * total supply.
  *
  * Emits a `Transfer` event with `to` set to the zero address.
  *
  * Requirements
  *
  * - `account` cannot be the zero address.
  * - `account` must have at least `amount` tokens.
  */
  function _burn(address account, uint256 value) internal {
    require(account != address(0), "ERC20: burn from the zero address");

    _totalSupply = _totalSupply.sub(value);
    _balances[account] = _balances[account].sub(value);
    emit Transfer(account, address(0), value);
  }

  /**
   * @dev Sets `amount` as the allowance of `spender` over the `owner`s tokens.
   *
   * This is internal function is equivalent to `approve`, and can be used to
   * e.g. set automatic allowances for certain subsystems, etc.
   *
   * Emits an `Approval` event.
   *
   * Requirements:
   *
   * - `owner` cannot be the zero address.
   * - `spender` cannot be the zero address.
   */
  function _approve(address owner, address spender, uint256 value) internal {
    require(owner != address(0), "ERC20: approve from the zero address");
    require(spender != address(0), "ERC20: approve to the zero address");

    _allowances[owner][spender] = value;
    emit Approval(owner, spender, value);
  }

  /**
   * @dev Destoys `amount` tokens from `account`.`amount` is then deducted
   * from the caller's allowance.
   *
   * See `_burn` and `_approve`.
   */
  function _burnFrom(address account, uint256 amount) internal {
    _burn(account, amount);
    _approve(account, msg.sender, _allowances[account][msg.sender].sub(amount));
  }
}

/**
 * @dev Optional functions from the ERC20 standard.
 */
contract ERC20Detailed is IERC20 {
  string private _name;
  string private _symbol;
  uint8 private _decimals;

  /**
   * @dev Sets the values for `name`, `symbol`, and `decimals`. All three of
   * these values are immutable: they can only be set once during
   * construction.
   */
  constructor (string memory name, string memory symbol, uint8 decimals) public {
    _name = name;
    _symbol = symbol;
    _decimals = decimals;
  }

  /**
   * @dev Returns the name of the token.
   */
  function name() public view returns (string memory) {
    return _name;
  }

  /**
   * @dev Returns the symbol of the token, usually a shorter version of the
   * name.
   */
  function symbol() public view returns (string memory) {
    return _symbol;
  }

  /**
   * @dev Returns the number of decimals used to get its user representation.
   * For example, if `decimals` equals `2`, a balance of `505` tokens should
   * be displayed to a user as `5,05` (`505 / 10 ** 2`).
   *
   * Tokens usually opt for a value of 18, imitating the relationship between
   * Ether and Wei.
   *
   * > Note that this information is only used for _display_ purposes: it in
   * no way affects any of the arithmetic of the contract, including
   * `IERC20.balanceOf` and `IERC20.transfer`.
   */
  function decimals() public view returns (uint8) {
    return _decimals;
  }
}


/**
 * @title Roles
 * @dev Library for managing addresses assigned to a Role.
 */
library Roles {
  struct Role {
    mapping (address => bool) bearer;
  }

  /**
   * @dev Give an account access to this role.
   */
  function add(Role storage role, address account) internal {
    require(!has(role, account), "Roles: account already has role");
    role.bearer[account] = true;
  }

  /**
   * @dev Remove an account's access to this role.
   */
  function remove(Role storage role, address account) internal {
    require(has(role, account), "Roles: account does not have role");
    role.bearer[account] = false;
  }

  /**
   * @dev Check if an account has this role.
   * @return bool
   */
  function has(Role storage role, address account) internal view returns (bool) {
    require(account != address(0), "Roles: account is the zero address");
    return role.bearer[account];
  }
}


contract PauserRole {
  using Roles for Roles.Role;

  event PauserAdded(address indexed account);
  event PauserRemoved(address indexed account);

  Roles.Role private _pausers;

  constructor () internal {
    _addPauser(msg.sender);
  }

  modifier onlyPauser() {
    require(isPauser(msg.sender), "PauserRole: caller does not have the Pauser role");
    _;
  }

  function isPauser(address account) public view returns (bool) {
    return _pausers.has(account);
  }

  function addPauser(address account) public onlyPauser {
    _addPauser(account);
  }

  function renouncePauser() public {
    _removePauser(msg.sender);
  }

  function _addPauser(address account) internal {
    _pausers.add(account);
    emit PauserAdded(account);
  }

  function _removePauser(address account) internal {
    _pausers.remove(account);
    emit PauserRemoved(account);
  }
}


/**
 * @dev Contract module which allows children to implement an emergency stop
 * mechanism that can be triggered by an authorized account.
 *
 * This module is used through inheritance. It will make available the
 * modifiers `whenNotPaused` and `whenPaused`, which can be applied to
 * the functions of your contract. Note that they will not be pausable by
 * simply including this module, only once the modifiers are put in place.
 */
contract Pausable is PauserRole {
  /**
   * @dev Emitted when the pause is triggered by a pauser (`account`).
   */
  event Paused(address account);

  /**
   * @dev Emitted when the pause is lifted by a pauser (`account`).
   */
  event Unpaused(address account);

  bool private _paused;

  /**
   * @dev Initializes the contract in unpaused state. Assigns the Pauser role
   * to the deployer.
   */
  constructor () internal {
    _paused = false;
  }

  /**
   * @dev Returns true if the contract is paused, and false otherwise.
   */
  function paused() public view returns (bool) {
    return _paused;
  }

  /**
   * @dev Modifier to make a function callable only when the contract is not paused.
   */
  modifier whenNotPaused() {
    require(!_paused, "Pausable: paused");
    _;
  }

  /**
   * @dev Modifier to make a function callable only when the contract is paused.
   */
  modifier whenPaused() {
    require(_paused, "Pausable: not paused");
    _;
  }

  /**
   * @dev Called by a pauser to pause, triggers stopped state.
   */
  function pause() public onlyPauser whenNotPaused {
    _paused = true;
    emit Paused(msg.sender);
  }

  /**
   * @dev Called by a pauser to unpause, returns to normal state.
   */
  function unpause() public onlyPauser whenPaused {
    _paused = false;
    emit Unpaused(msg.sender);
  }
}

/**
 * @title Pausable token
 * @dev ERC20 modified with pausable transfers.
 */
contract ERC20Pausable is ERC20, Pausable {
  function transfer(address to, uint256 value) public whenNotPaused returns (bool) {
    return super.transfer(to, value);
  }

  function transferFrom(address from, address to, uint256 value) public whenNotPaused returns (bool) {
    return super.transferFrom(from, to, value);
  }

  function approve(address spender, uint256 value) public whenNotPaused returns (bool) {
    return super.approve(spender, value);
  }

  function increaseAllowance(address spender, uint addedValue) public whenNotPaused returns (bool) {
    return super.increaseAllowance(spender, addedValue);
  }

  function decreaseAllowance(address spender, uint subtractedValue) public whenNotPaused returns (bool) {
    return super.decreaseAllowance(spender, subtractedValue);
  }
}


/**
 * @dev Extension of `ERC20` that allows token holders to destroy both their own
 * tokens and those that they have an allowance for, in a way that can be
 * recognized off-chain (via event analysis).
 */
contract ERC20Burnable is ERC20 {
  /**
   * @dev Destoys `amount` tokens from the caller.
   *
   * See `ERC20._burn`.
   */
  function burn(uint256 amount) public {
    _burn(msg.sender, amount);
  }

  /**
   * @dev See `ERC20._burnFrom`.
   */
  function burnFrom(address account, uint256 amount) public {
    _burnFrom(account, amount);
  }
}

contract NafenToken is ERC20Pausable, ERC20Detailed, ERC20Burnable {
  uint private INITIAL_SUPPLY = 8123731e18;
  constructor () public ERC20Detailed("NafenToken", "NFN", 18) {
    _mint(msg.sender, INITIAL_SUPPLY);
  }
}