pragma solidity ^0.4.25;


library SafeMath {

    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        if (a == 0) {
            return 0;
        }
        uint256 c = a * b;
        assert(c / a == b);
        return c;
    }

    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        // assert(b > 0); // Solidity automatically throws when dividing by 0
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold
        return c;       
    }       

    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        assert(b <= a);
        return a - b;
    }

    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        assert(c >= a);
        return c;
    }
}


contract Ownable {
    address public owner;
    address public newOwner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    constructor() public {
        owner = msg.sender;
        newOwner = address(0);
    }

    modifier onlyOwner() {
        require(msg.sender == owner);
        _;
    }
    modifier onlyNewOwner() {
        require(msg.sender != address(0));
        require(msg.sender == newOwner);
        _;
    }

    function transferOwnership(address _newOwner) public onlyOwner {
        require(_newOwner != address(0));
        newOwner = _newOwner;
    }

    function acceptOwnership() public onlyNewOwner returns(bool) {
        emit OwnershipTransferred(owner, newOwner);
        owner = newOwner;
    }
}

contract Pausable is Ownable {
  event Pause();
  event Unpause();

  bool public paused = false;

  modifier whenNotPaused() {
    require(!paused);
    _;
  }

  modifier whenPaused() {
    require(paused);
    _;
  }

  function pause() onlyOwner whenNotPaused public {
    paused = true;
    emit Pause();
  }

  function unpause() onlyOwner whenPaused public {
    paused = false;
    emit Unpause();
  }
}

contract ERC20 {
    function totalSupply() public view returns (uint256);
    function balanceOf(address who) public view returns (uint256);
    function allowance(address owner, address spender) public view returns (uint256);
    function transfer(address to, uint256 value) public returns (bool);
    function transferFrom(address from, address to, uint256 value) public returns (bool);
    function approve(address spender, uint256 value) public returns (bool);

    event Approval(address indexed owner, address indexed spender, uint256 value);
    event Transfer(address indexed from, address indexed to, uint256 value);
}


interface TokenRecipient {
    function receiveApproval(address _from, uint256 _value, address _token, bytes _extraData) external; 
}


contract DBSCToken is ERC20, Ownable, Pausable {
    
    using SafeMath for uint256;

    string public name;
    string public symbol;
    uint8 public decimals;
    uint256 internal initialSupply;
    uint256 internal totalSupply_;

    mapping(address => uint256) internal balances;
    mapping(address => bool) public frozen;
    mapping(address => mapping(address => uint256)) internal allowed;

    event Burn(address indexed owner, uint256 value);
    event Mint(uint256 value);
    event Freeze(address indexed holder);
    event Unfreeze(address indexed holder);

    modifier notFrozen(address _holder) {
        require(!frozen[_holder]);
        _;
    }

    constructor() public {
        name = "DBChain Token";
        symbol = "DBSC";
        decimals = 18;
        initialSupply = 2000000000;
        totalSupply_ = initialSupply * 10 ** uint(decimals);
        balances[owner] = totalSupply_;
        emit Transfer(address(0), owner, totalSupply_);
    }

    function () public payable {
        revert();
    }

    function totalSupply() public view returns (uint256) {
        return totalSupply_;
    }

    function transfer(address _to, uint256 _value) public whenNotPaused notFrozen(msg.sender) returns (bool) {
        require(_to != address(0));
        require(_value <= balances[msg.sender]);
        
        // SafeMath.sub will throw if there is not enough balance.
        balances[msg.sender] = balances[msg.sender].sub(_value);
        balances[_to] = balances[_to].add(_value);
        emit Transfer(msg.sender, _to, _value);
        return true;
    }

    function balanceOf(address _holder) public view returns (uint balance) {
        return balances[_holder];
    }
    
    function transferFrom(address _from, address _to, uint256 _value) public whenNotPaused notFrozen(_from)returns (bool) {
        require(_to != address(0));
        require(_value <= balances[_from]);
        require(_value <= allowed[_from][msg.sender]);
        

        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);
        return true;
    }

    function approve(address _spender, uint256 _value) public whenNotPaused returns (bool) {
        allowed[msg.sender][_spender] = _value;
        emit Approval(msg.sender, _spender, _value);
        return true;
    }
    
    function approveAndCall(address _spender, uint256 _value, bytes _extraData) public returns (bool success) {
        require(isContract(_spender));
        TokenRecipient spender = TokenRecipient(_spender);
        if (approve(_spender, _value)) {
            spender.receiveApproval(msg.sender, _value, this, _extraData);
            return true;
        }
    }

    function allowance(address _holder, address _spender) public view returns (uint256) {
        return allowed[_holder][_spender];
    }

    function freezeAccount(address _holder) public onlyOwner returns (bool) {
        require(!frozen[_holder]);
        frozen[_holder] = true;
        emit Freeze(_holder);
        return true;
    }

    function unfreezeAccount(address _holder) public onlyOwner returns (bool) {
        require(frozen[_holder]);
        frozen[_holder] = false;
        emit Unfreeze(_holder);
        return true;
    }

    function getNowTime() public view returns(uint256) {
      return now;
    }

    function claimToken(ERC20 token, address _to, uint256 _value) public onlyOwner returns (bool) {
        token.transfer(_to, _value);
        return true;
    }

    function burn(uint256 _value) public onlyOwner returns (bool success) {
        require(_value <= balances[msg.sender]);
        address burner = msg.sender;
        balances[burner] = balances[burner].sub(_value);
        totalSupply_ = totalSupply_.sub(_value);
        emit Burn(burner, _value);
        return true;
    }

    function mint( uint256 _amount) onlyOwner public returns (bool) {
        totalSupply_ = totalSupply_.add(_amount);
        balances[owner] = balances[owner].add(_amount);

        emit Transfer(address(0), owner, _amount);
        return true;
    }

    function isContract(address addr) internal view returns (bool) {
        uint size;
        assembly{size := extcodesize(addr)}
        return size > 0;
    }
}