pragma solidity ^0.4.18;

/**
 * @title SafeMath
 * @dev Math operations with safety checks that throw on error
 */
library SafeMath {

  	/**
  	 * @dev Multiplies two numbers, throws on overflow.
  	*/
  	function mul(uint256 _a, uint256 _b) internal pure returns (uint256) {
    	// Gas optimization: this is cheaper than asserting '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;
    	assert(c / _a == _b);

    	return c;
  	}

  	/**
  	 * @dev Integer division of two numbers, truncating the quotient.
  	 */
  	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;
  	}

  	/**
  	 * @dev Subtracts two numbers, throws on overflow (i.e. if subtrahend is greater than minuend).
  	 */
  	function sub(uint256 _a, uint256 _b) internal pure returns (uint256) {
    	assert(_b <= _a);
    	uint256 c = _a - _b;

    	return c;
  	}

  	/**
  	 * @dev Adds two numbers, throws on overflow.
  	 */
  	function add(uint256 _a, uint256 _b) internal pure returns (uint256) {
    	uint256 c = _a + _b;
    	assert(c >= _a);

    	return c;
  	}
}

/**
 * @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 public owner;

    address internal newOwner;

    event OwnerUpdate(address _prevOwner, address _newOwner);

  	/**
   	 * @dev The Ownable constructor sets the original `owner` of the contract to the sender
   	 * account.
   	 */
    constructor() public {
        owner = msg.sender;
        newOwner = address(0);
    }

  	/**
   	 * @dev Throws if called by any account other than the owner.
   	 */
    modifier onlyOwner() {
        require(msg.sender == owner);
        _;
    }

    /*
     * @dev Change the owner.
     * @param _newOwner The new owner.
     */
    function changeOwner(address _newOwner) public onlyOwner {
        require(_newOwner != owner);
        newOwner = _newOwner;
    }

    /*
     * @dev Accept the ownership.
     */
    function acceptOwnership() public {
        require(msg.sender == newOwner);
        
        emit OwnerUpdate(owner, newOwner);
        owner = newOwner;
        newOwner = address(0);
    }
}

/**
 * @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);
    	_;
  	}

  	/**
   	 * @dev Modifier to make a function callable only when the contract is paused.
   	 */
  	modifier whenPaused() {
    	require(paused);
    	_;
  	}

  	/**
   	 * @dev called by the owner to pause, triggers stopped state
   	 */
  	function pause() public onlyOwner whenNotPaused {
    	paused = true;
    	emit Pause();
  	}

  	/**
   	 * @dev called by the owner to unpause, returns to normal state
   	 */
  	function unpause() public onlyOwner whenPaused {
    	paused = false;
    	emit Unpause();
  	}
}

/**
 * @title ERC20 interface
 * @dev see https://github.com/ethereum/EIPs/issues/20
 */
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 approve(address _spender, uint256 _value) public returns (bool);

  	function transferFrom(address _from, address _to, uint256 _value) public returns (bool);

  	event Transfer(address indexed from, address indexed to, uint256 value);

  	event Approval(address indexed owner, address indexed spender, uint256 value);
}

/**
 * @title Standard ERC20 token
 *
 * @dev Implementation of the basic standard token.
 * https://github.com/ethereum/EIPs/issues/20
 */
contract StandardToken is ERC20, Pausable {
	
    using SafeMath for uint256;
    
    mapping(address => uint256) balances;
    
    mapping(address => mapping(address => uint256)) internal allowed;
    
    uint256 totalSupply_;
    
  	/**
     * @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 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 whenNotPaused returns (uint256) {
        return allowed[_owner][_spender];
    }
    
  	/**
  	 * @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 whenNotPaused returns (bool) {
    	require(_value <= balances[msg.sender]);
    	require(_to != address(0));
    
        balances[msg.sender] = balances[msg.sender].sub(_value);
        balances[_to] = balances[_to].add(_value);
        emit 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 whenNotPaused returns (bool) {
        allowed[msg.sender][_spender] = _value;
        emit Approval(msg.sender, _spender, _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 whenNotPaused returns (bool) {
	    require(_value <= balances[_from]);
	    require(_value <= allowed[_from][msg.sender]);
	    require(_to != address(0));    	

        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 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 increaseApproval(address _spender, uint256 _addedValue) public whenNotPaused returns (bool) {
        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 decreaseApproval(address _spender, uint256 _subtractedValue) public whenNotPaused returns (bool) {
    	uint256 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;
    }

  	/**
   	 * @dev Decrease the amount of tokens that an owner allowed to a spender by spender self.
   	 * approve should be called when allowed[msg.sender] == 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 _from The address which will transfer the funds from.
   	 * @param _subtractedValue The amount of tokens to decrease the allowance by.
   	 */
    function spenderDecreaseApproval(address _from, uint256 _subtractedValue) public whenNotPaused returns (bool) {
    	uint256 oldValue = allowed[_from][msg.sender];
        if (_subtractedValue >= oldValue) {
            allowed[_from][msg.sender] = 0;
        } else {
            allowed[_from][msg.sender] = oldValue.sub(_subtractedValue);
        }

        emit Approval(_from, msg.sender, allowed[_from][msg.sender]);
        return true;
    }
}

/**
 * @title BCL token.
 * @dev Issued by blockchainlock.io
 */
contract BCLToken is StandardToken {
    string public name = "Blockchainlock Token";
    string public symbol = "BCL";
    uint8 public decimals = 18;

  	/**
   	 * @dev The BCLToken constructor
   	 */
    constructor() public {
        totalSupply_ = 360 * (10**26);			// 36 billions
        balances[msg.sender] = totalSupply_; 	// Give the creator all initial tokens
    }
}