pragma solidity 0.5.8;

/**
 * @title SafeMath 
 * @dev Unsigned math operations with safety checks that revert on error.
 */
library SafeMath {
    /**
     * @dev Multiplie two unsigned integers, revert 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);

        return c;
    }

    /**
     * @dev Integer division of two unsigned integers truncating the quotient, revert 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);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    /**
     * @dev Subtract two unsigned integers, revert on underflow (i.e. if subtrahend is greater than minuend).
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b <= a);
        uint256 c = a - b;

        return c;
    }

    /**
     * @dev Add two unsigned integers, revert on overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a);

        return c;
    }
}

/**
 * @title ERC20 interface
 * @dev See https://eips.ethereum.org/EIPS/eip-20
 */
interface IERC20 {
    function transfer(address to, uint256 value) external returns (bool); 

    function approve(address spender, uint256 value) external returns (bool); 

    function transferFrom(address from, address to, uint256 value) external returns (bool); 

    function totalSupply() external view returns (uint256); 

    function balanceOf(address who) external view returns (uint256);

    function allowance(address owner, address spender) external view returns (uint256); 

    event Transfer(address indexed from, address indexed to, uint256 value); 

    event Approval(address indexed owner, address indexed spender, uint256 value); 
}

/**
 * @title Ownable
 * @dev The Ownable contract has an owner address, and provides basic authorization control
 * functions, this simplifies the implementation of "user permissions".
 */
contract Ownable {
    address internal _owner; 

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner); 

    /**
     * @return the address of the owner.
     */
    function owner() public view returns (address) {
        return _owner;
    }

    /**
     * @dev Revert if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(isOwner(), "The caller must be owner");
        _;
    }

    /**
     * @return true if `msg.sender` is the owner of the contract.
     */
    function isOwner() public view returns (bool) {
        return msg.sender == _owner;
    }

    /**
     * @dev Allow the current owner to relinquish control of the contract.
     * It will not be possible to call the functions with the `onlyOwner`
     * modifier anymore.
     * @notice Renouncing ownership will leave the contract without an owner,
     * thereby removing any functionality that is only available to the owner.
     */
    function renounceOwnership() public onlyOwner {
        emit OwnershipTransferred(_owner, address(0));
        _owner = address(0);
    }

    /**
     * @dev Allow the current owner to transfer control of the contract to a newOwner.
     * @param newOwner The address to transfer ownership to.
     */
    function transferOwnership(address newOwner) public onlyOwner {
        _transferOwnership(newOwner); 
    }

    /**
     * @dev Transfer control of the contract to a newOwner.
     * @param newOwner The address to transfer ownership to.
     */
    function _transferOwnership(address newOwner) internal {
        require(newOwner != address(0), "Cannot transfer control of the contract to the zero address");
        emit OwnershipTransferred(_owner, newOwner); 
        _owner = newOwner; 
    }
}

/**
 * @title Standard ERC20 token
 * @dev Implementation of the basic standard token.
 */
contract StandardToken is IERC20 {
    using SafeMath for uint256; 
    
    mapping (address => uint256) internal _balances; 
    mapping (address => mapping (address => uint256)) internal _allowed; 
    
    uint256 internal _totalSupply; 
    
    /**
     * @dev Total number of tokens in existence.
     */
    function totalSupply() public view returns (uint256) {
        return _totalSupply; 
    }

    /**
     * @dev Get 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 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 The address which owns the funds.
     * @param spender 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 tokens 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 The address which you want to send tokens from.
     * @param to The address which you want to transfer to.
     * @param value 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 tokens for a specified address.
     * @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(to != address(0), "Cannot transfer to the zero address"); 
        _balances[from] = _balances[from].sub(value); 
        _balances[to] = _balances[to].add(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), "Cannot approve to the zero address"); 
        require(owner != address(0), "Setter cannot be the zero address"); 
	    _allowed[owner][spender] = value;
        emit Approval(owner, spender, value); 
    }

}

/**
 * @title Pausable
 * @dev Base contract which allows children to implement an emergency stop mechanism.
 */
contract Pausable is Ownable {
    event Pause(); 
    event Unpause(); 
    
    bool public paused = false; 
    


    /**
     * @dev Modifier to make a function callable only when the contract is not paused.
     */
    modifier whenNotPaused() {
        require(!paused, "Only when the contract is not paused"); 
        _;
    }

    /**
     * @dev Modifier to make a function callable only when the contract is paused.
     */
    modifier whenPaused() {
        require(paused, "Only when the contract is paused"); 
        _;
    }

    /**
     * @dev Called by the owner to pause, trigger stopped state.
     */
    function pause() public onlyOwner whenNotPaused {
        paused = true; 
        emit Pause(); 
    }

    /**
     * @dev Called by the owner to unpause, return to normal state.
     */
    function unpause() public onlyOwner whenPaused {
        paused = false; 
        emit Unpause(); 
    }
}

/**
 * @title PausableToken
 * @dev ERC20 modified with pausable transfers.
 */
contract PausableToken is StandardToken, 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 success) {
        return super.increaseAllowance(_spender, _addedValue); 
    }
    
    function decreaseAllowance(address _spender, uint _subtractedValue) public whenNotPaused returns (bool success) {
        return super.decreaseAllowance(_spender, _subtractedValue); 
    }
}

/**
 * @title BurnableToken
 * @dev Implement the function of ERC20 token burning.
 */
contract BurnableToken is StandardToken {

    /**
    * @dev Burn a specific amount of tokens.
    * @param _value The amount of token to be burned.
    */
    function burn(uint256 _value) public {
        _burn(msg.sender, _value);
    }

    /**
    * @dev Burn 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 {
        _approve(_from, msg.sender, _allowed[_from][msg.sender].sub(_value));
        _burn(_from, _value);
    }

    function _burn(address _who, uint256 _value) internal {
        require(_value <= _balances[_who], "Not enough token balance");
        // no need to require value <= totalSupply, since that would imply the
        // sender's balance is greater than the totalSupply, which *should* be an assertion failure
        _balances[_who] = _balances[_who].sub(_value);
        _totalSupply = _totalSupply.sub(_value);
        emit Transfer(_who, address(0), _value);
    }
}

contract VFDToken is BurnableToken, PausableToken {
    string public constant name = "Micro Payment Shield";  
    string public constant symbol = "VFD";  
    uint8 public constant decimals = 18;
    uint256 internal constant INIT_TOTALSUPPLY = 65000000; 
    
    /**
     * @dev Constructor, initialize the basic information of contract.
     */
    constructor() public {
        _owner = 0x2CcaFDD16aA603Bbc8026711dd2E838616c010c3;
        emit OwnershipTransferred(address(0), _owner);
        _totalSupply = INIT_TOTALSUPPLY * 10 ** uint256(decimals);
        _balances[_owner] = _totalSupply;
        emit Transfer(address(0), _owner, _totalSupply);
    }
}