pragma solidity ^0.5.1;

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 ERC20 {
  event Transfer(address indexed from, address indexed to, uint256 value);
  event Approval(address indexed owner, address indexed spender, uint256 value);
  
  uint256 public totalSupply;
  
  function balanceOf(address who) 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);
  function allowance(address owner, address spender) public view returns (uint256);
}

contract StandardToken is ERC20 {
  using SafeMath for uint256;

  mapping (address => uint256) balances;

  mapping (address => mapping (address => uint256)) internal allowed;


  function balanceOf(address _owner) public view returns (uint256 balance) {
    return balances[_owner];
  }
  
  function transfer(address _to, uint256 _value) public 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 transferFrom(address _from, address _to, uint256 _value) public 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;
  }

  /**
   * @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) {
    allowed[msg.sender][_spender] = _value;
    emit Approval(msg.sender, _spender, _value);
    return true;
  }

  /**
   * @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];
  }

  /**
   * 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
   */
  function increaseApproval(address _spender, uint _addedValue) public returns (bool) {
    allowed[msg.sender][_spender] = allowed[msg.sender][_spender].add(_addedValue);
    emit Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
    return true;
  }

  function decreaseApproval(address _spender, uint _subtractedValue) public returns (bool) {
    uint oldValue = allowed[msg.sender][_spender];
    if (_subtractedValue > oldValue) {
      allowed[msg.sender][_spender] = 0;
    } else {
      allowed[msg.sender][_spender] = oldValue.sub(_subtractedValue);
    }
    emit Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
    return true;
  }

}


contract Ownable {
  address public owner;

  event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

  modifier onlyOwner() {
    require(msg.sender == owner);
    _;
  }

  function transferOwnership(address newOwner) public onlyOwner {
    require(newOwner != address(0));
    emit OwnershipTransferred(owner, newOwner);
    owner = newOwner;
  }
  
}

contract Pausable is Ownable {
  event PausePublic(bool newState);
  event PauseOwnerAdmin(bool newState);

  bool public pausedPublic = true;
  bool public pausedOwnerAdmin = false;

  address public admin;

  modifier whenNotPaused() {
    if(pausedPublic) {
      if(!pausedOwnerAdmin) {
        require(msg.sender == admin || msg.sender == owner);
      } else {
        revert();
      }
    }
    _;
  }

  function pause(bool newPausedPublic, bool newPausedOwnerAdmin) onlyOwner public {
    require(!(newPausedPublic == false && newPausedOwnerAdmin == true));

    pausedPublic = newPausedPublic;
    pausedOwnerAdmin = newPausedOwnerAdmin;

    emit PausePublic(newPausedPublic);
    emit PauseOwnerAdmin(newPausedOwnerAdmin);
  }
  
}

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 increaseApproval(address _spender, uint _addedValue) public whenNotPaused returns (bool success) {
    return super.increaseApproval(_spender, _addedValue);
  }

  function decreaseApproval(address _spender, uint _subtractedValue) public whenNotPaused returns (bool success) {
    return super.decreaseApproval(_spender, _subtractedValue);
  }
}


contract BangkaToken is PausableToken {
    string  public  constant name = "Bangka Token";
    string  public  constant symbol = "BGT";
    uint8   public  constant decimals = 18;

    modifier validDestination( address to )
    {
        require(to != address(0x0));
        require(to != address(this));
        _;
    }

    constructor ( address _admin, address _owner, uint _totalTokenAmount ) public
    {
        admin = _admin;
        owner = _owner;

        totalSupply = _totalTokenAmount;
        balances[_owner] = _totalTokenAmount;
        
        emit Transfer(address(0x0), _owner, _totalTokenAmount);
    }

    function transfer(address _to, uint _value) validDestination(_to) public returns (bool) 
    {
        return super.transfer(_to, _value);
    }

    function transferFrom(address _from, address _to, uint _value) validDestination(_to) public returns (bool) 
    {
        return super.transferFrom(_from, _to, _value);
    }

    event Burn(address indexed _burner, uint _value);

    function burn(uint _value) public returns (bool)
    {
        balances[msg.sender] = balances[msg.sender].sub(_value);
        totalSupply = totalSupply.sub(_value);
        emit Burn(msg.sender, _value);
        emit Transfer(msg.sender, address(0x0), _value);
        return true;
    }

    // save some gas by making only one contract call
    function burnFrom(address _from, uint256 _value) public returns (bool) 
    {
        assert( transferFrom( _from, msg.sender, _value ) );
        return burn(_value);
    }

    function emergencyERC20Drain( ERC20 token, uint amount ) onlyOwner public {
        // owner can drain tokens that are sent here by mistake
        token.transfer( owner, amount );
    }

    event AdminTransferred(address indexed previousAdmin, address indexed newAdmin);

    function changeAdmin(address newAdmin) onlyOwner public {
        // owner can re-assign the admin
        emit AdminTransferred(admin, newAdmin);
        admin = newAdmin;
    }
}