pragma solidity ^0.4.23;

/**
 * @title ERC20 interface
 */
contract ERC20 {
  function totalSupply() 
    public view returns (uint256);

  function balanceOf(address who) 
    public view returns (uint256);

  function transfer(address to, uint256 value) 
    public returns (bool);

  function allowance(address owner, address spender)
    public view returns (uint256);

  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);
}



/**
 * @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;

  event OwnershipTransferred(
    address indexed previousOwner,
    address indexed newOwner
  );


  /**
   * @dev The Ownable constructor sets the original `owner` of the contract to the sender
   * account.
   */
  constructor() public {
    owner = msg.sender;
  }

  /**
   * @dev Throws if called by any account other than the owner.
   */
  modifier onlyOwner() {
    require(msg.sender == owner);
    _;
  }

  /**
   * @dev Allows 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 {
    require(newOwner != address(0));
    emit OwnershipTransferred(owner, newOwner);
    owner = newOwner;
  }

}

/**
 * @title ERC827 interface, an extension of ERC20 token standard
 *
 * @dev Interface of a ERC827 token, following the ERC20 standard with extra
 * @dev methods to transfer value and data and execute calls in transfers and
 * @dev approvals.
 */
contract ERC827 is ERC20 {
  function approveAndCall(
    address _spender,
    uint256 _value,
    bytes _data
  )
    public
    payable
    returns (bool);

  function transferAndCall(
    address _to,
    uint256 _value,
    bytes _data
  )
    public
    payable
    returns (bool);

  function transferFromAndCall(
    address _from,
    address _to,
    uint256 _value,
    bytes _data
  )
    public
    payable
    returns (bool);
}

/**
 * @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 c) {
    if (a == 0) {
      return 0;
    }
    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 a / b;
  }

  /**
  * @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);
    return a - b;
  }

  /**
  * @dev Adds two numbers, throws on overflow.
  */
  function add(uint256 a, uint256 b) internal pure returns (uint256 c) {
    c = a + b;
    assert(c >= a);
    return c;
  }
}


/**
 * @title Standard ERC20 token
 *
 */
contract ERC20Token is ERC20{

  using SafeMath for uint256;

  mapping (address => mapping (address => uint256)) internal allowed; 

  mapping(address => uint256) balances;

  uint256 totalSupply_;

  /**
  * @dev total number of tokens in existence
  */
  function totalSupply() public view returns (uint256) {
    return totalSupply_;
  }

  /**
  * @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 returns (bool) {
    require(_to != address(0));
    require(_value <= balances[msg.sender]);

    balances[msg.sender] = balances[msg.sender].sub(_value);
    balances[_to] = balances[_to].add(_value);
    emit Transfer(msg.sender, _to, _value);
    return true;
  }

  /**
  * @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 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
    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.
   */
  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];
  }

  /**
   * @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,
    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;
  }

  /**
   * @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,
    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;
  }

}



/**
 * @title ERC827, an extension of ERC20 token standard
 *
 * @dev Implementation the ERC827, following the ERC20 standard with extra
 * @dev methods to transfer value and data and execute calls in transfers and
 * @dev approvals.
 *
 * @dev Uses OpenZeppelin StandardToken.
 */
contract ERC827Token is ERC827, ERC20Token {

  /**
   * @dev Addition to ERC20 token methods. It allows to
   * @dev approve the transfer of value and execute a call with the sent data.
   *
   * @dev Beware that changing an allowance with this method brings the risk that
   * @dev someone may use both the old and the new allowance by unfortunate
   * @dev transaction ordering. One possible solution to mitigate this race condition
   * @dev is to first reduce the spender's allowance to 0 and set the desired value
   * @dev afterwards:
   * @dev https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
   *
   * @param _spender The address that will spend the funds.
   * @param _value The amount of tokens to be spent.
   * @param _data ABI-encoded contract call to call `_to` address.
   *
   * @return true if the call function was executed successfully
   */
  function approveAndCall(
    address _spender,
    uint256 _value,
    bytes _data
  )
    public
    payable
    returns (bool)
  {
    require(_spender != address(this));

    super.approve(_spender, _value);

    // solium-disable-next-line security/no-call-value
    require(_spender.call.value(msg.value)(_data));

    return true;
  }

  /**
   * @dev Addition to ERC20 token methods. Transfer tokens to a specified
   * @dev address and execute a call with the sent data on the same transaction
   *
   * @param _to address The address which you want to transfer to
   * @param _value uint256 the amout of tokens to be transfered
   * @param _data ABI-encoded contract call to call `_to` address.
   *
   * @return true if the call function was executed successfully
   */
  function transferAndCall(
    address _to,
    uint256 _value,
    bytes _data
  )
    public
    payable
    returns (bool)
  {
    require(_to != address(this));

    super.transfer(_to, _value);

    require(_to.call.value(msg.value)(_data));
    return true;
  }

  /**
   * @dev Addition to ERC20 token methods. Transfer tokens from one address to
   * @dev another and make a contract call on the same transaction
   *
   * @param _from The address which you want to send tokens from
   * @param _to The address which you want to transfer to
   * @param _value The amout of tokens to be transferred
   * @param _data ABI-encoded contract call to call `_to` address.
   *
   * @return true if the call function was executed successfully
   */
  function transferFromAndCall(
    address _from,
    address _to,
    uint256 _value,
    bytes _data
  )
    public payable returns (bool)
  {
    require(_to != address(this));

    super.transferFrom(_from, _to, _value);

    require(_to.call.value(msg.value)(_data));
    return true;
  }

  /**
   * @dev Addition to StandardToken methods. Increase the amount of tokens that
   * @dev an owner allowed to a spender and execute a call with the sent data.
   *
   * @dev approve should be called when allowed[_spender] == 0. To increment
   * @dev allowed value is better to use this function to avoid 2 calls (and wait until
   * @dev the first transaction is mined)
   * @dev From MonolithDAO Token.sol
   *
   * @param _spender The address which will spend the funds.
   * @param _addedValue The amount of tokens to increase the allowance by.
   * @param _data ABI-encoded contract call to call `_spender` address.
   */
  function increaseApprovalAndCall(
    address _spender,
    uint _addedValue,
    bytes _data
  )
    public
    payable
    returns (bool)
  {
    require(_spender != address(this));

    super.increaseApproval(_spender, _addedValue);

    require(_spender.call.value(msg.value)(_data));

    return true;
  }

  /**
   * @dev Addition to StandardToken methods. Decrease the amount of tokens that
   * @dev an owner allowed to a spender and execute a call with the sent data.
   *
   * @dev approve should be called when allowed[_spender] == 0. To decrement
   * @dev allowed value is better to use this function to avoid 2 calls (and wait until
   * @dev the first transaction is mined)
   * @dev From MonolithDAO Token.sol
   *
   * @param _spender The address which will spend the funds.
   * @param _subtractedValue The amount of tokens to decrease the allowance by.
   * @param _data ABI-encoded contract call to call `_spender` address.
   */
  function decreaseApprovalAndCall(
    address _spender,
    uint _subtractedValue,
    bytes _data
  )
    public
    payable
    returns (bool)
  {
    require(_spender != address(this));

    super.decreaseApproval(_spender, _subtractedValue);

    require(_spender.call.value(msg.value)(_data));

    return true;
  }

}



/**
 * @title  Burnable and Pause Token
 * @dev    StandardToken modified with pausable transfers.
 **/
contract PauseBurnableERC827Token is ERC827Token, Ownable{
  using SafeMath for uint256;

  event Pause();
  event Unpause();
  event PauseOperatorTransferred(address indexed previousOperator,address indexed newOperator);

 
  event Burn(address indexed burner, uint256 value);

  bool    public paused = false;
  address public pauseOperator;

  /**
   * @dev Throws if called by any account other than the owner.
   */
  modifier onlyPauseOperator() {
    require(msg.sender == pauseOperator || msg.sender == owner);
    _;
  }

  /**
   * @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 The constructor sets the original `owner` of the contract to the sender
   * account.
   */
  constructor() public {
    pauseOperator = msg.sender;
  } 

    /**
   * @dev called by the operator to set the new operator to pause the token
   */
  function transferPauseOperator(address newPauseOperator) onlyPauseOperator public {
    require(newPauseOperator != address(0));
    emit PauseOperatorTransferred(pauseOperator, newPauseOperator);
    pauseOperator = newPauseOperator;
  }

  /**
   * @dev called by the owner to pause, triggers stopped state
   */
  function pause() onlyPauseOperator whenNotPaused public {
    paused = true;
    emit Pause();
  }

  /**
   * @dev called by the owner to unpause, returns to normal state
   */
  function unpause() onlyPauseOperator whenPaused public {
    paused = false;
    emit Unpause();
  }

  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);
  }  

  /**
  * @dev Burns a specific amount of tokens.
  * @param _value The amount of token to be burned.
  */
  function burn(uint256 _value) 
    public whenNotPaused 
  {
      _burn(msg.sender, _value);
  }

  function _burn(address _who, uint256 _value) internal{
      require(_value <= balances[_who]);
      // 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);                      // Subtract from the sender
      totalSupply_ = totalSupply_.sub(_value);     
      
      emit Burn(_who, _value);
      emit Transfer(_who, address(0), _value);
  }

  /**
  * @dev Burns 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 whenNotPaused 
  {
      require(_value <= allowed[_from][msg.sender]);
      allowed[_from][msg.sender] = allowed[_from][msg.sender].sub(_value);
      _burn(_from, _value);
  }  
}
  

/**
 * @title the Blockchain Quotations Token for BQI.COM
 *  
 * @dev Uses OpenZeppelin Lib.
 */
contract BQT is PauseBurnableERC827Token {  
        string  public constant name     = "BQT";
        string  public constant symbol   = "BQT"; 
        uint8   public constant decimals = 18;
        uint256 public constant INITIAL_SUPPLY = 1000000000 * (10 ** uint256(decimals));

        /**
        * @dev Constructor that gives msg.sender all of existing tokens.
        */
        constructor() public {
            totalSupply_ = INITIAL_SUPPLY;
            balances[msg.sender] = INITIAL_SUPPLY;
            emit Transfer(0x0, msg.sender, INITIAL_SUPPLY);
        } 
}