// File: zeppelin-solidity/contracts/ownership/Ownable.sol

pragma solidity ^0.4.24;


/**
 * @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 OwnershipRenounced(address indexed previousOwner);
  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 relinquish control of the contract.
   * @notice Renouncing to ownership will leave the contract without an owner.
   * It will not be possible to call the functions with the `onlyOwner`
   * modifier anymore.
   */
  function renounceOwnership() public onlyOwner {
    emit OwnershipRenounced(owner);
    owner = address(0);
  }

  /**
   * @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 {
    _transferOwnership(_newOwner);
  }

  /**
   * @dev Transfers control of the contract to a newOwner.
   * @param _newOwner The address to transfer ownership to.
   */
  function _transferOwnership(address _newOwner) internal {
    require(_newOwner != address(0));
    emit OwnershipTransferred(owner, _newOwner);
    owner = _newOwner;
  }
}

// File: zeppelin-solidity/contracts/token/ERC20/ERC20Basic.sol

pragma solidity ^0.4.24;


/**
 * @title ERC20Basic
 * @dev Simpler version of ERC20 interface
 * See https://github.com/ethereum/EIPs/issues/179
 */
contract ERC20Basic {
  function totalSupply() public view returns (uint256);
  function balanceOf(address _who) public view returns (uint256);
  function transfer(address _to, uint256 _value) public returns (bool);
  event Transfer(address indexed from, address indexed to, uint256 value);
}

// File: zeppelin-solidity/contracts/math/SafeMath.sol

pragma solidity ^0.4.24;


/**
 * @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) {
    // 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;
    }

    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;
  }
}

// File: zeppelin-solidity/contracts/token/ERC20/BasicToken.sol

pragma solidity ^0.4.24;




/**
 * @title Basic token
 * @dev Basic version of StandardToken, with no allowances.
 */
contract BasicToken is ERC20Basic {
  using SafeMath for uint256;

  mapping(address => uint256) internal balances;

  uint256 internal 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(_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 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];
  }

}

// File: zeppelin-solidity/contracts/token/ERC20/ERC20.sol

pragma solidity ^0.4.24;



/**
 * @title ERC20 interface
 * @dev see https://github.com/ethereum/EIPs/issues/20
 */
contract ERC20 is ERC20Basic {
  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
  );
}

// File: zeppelin-solidity/contracts/token/ERC20/StandardToken.sol

pragma solidity ^0.4.24;




/**
 * @title Standard ERC20 token
 *
 * @dev Implementation of the basic standard token.
 * https://github.com/ethereum/EIPs/issues/20
 * Based on code by FirstBlood: https://github.com/Firstbloodio/token/blob/master/smart_contract/FirstBloodToken.sol
 */
contract StandardToken is ERC20, BasicToken {

  mapping (address => mapping (address => uint256)) internal allowed;


  /**
   * @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(_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 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];
  }

  /**
   * @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
    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
    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;
  }

}

// File: zeppelin-solidity/contracts/token/ERC20/BurnableToken.sol

pragma solidity ^0.4.24;



/**
 * @title Burnable Token
 * @dev Token that can be irreversibly burned (destroyed).
 */
contract BurnableToken is BasicToken {

  event Burn(address indexed burner, uint256 value);

  /**
   * @dev Burns a specific amount of tokens.
   * @param _value The amount of token to be burned.
   */
  function burn(uint256 _value) public {
    _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);
    totalSupply_ = totalSupply_.sub(_value);
    emit Burn(_who, _value);
    emit Transfer(_who, address(0), _value);
  }
}

// File: contracts/DrkToken.sol

pragma solidity ^0.4.24;





/*
 * DrkToken is a standard ERC20 token with some additional functionalities:
 * - Transfers are only enabled after contract owner enables it (after the ICO)
 * - Contract sets 40% of the total supply as allowance for ICO contract
 *
 * Note: Token Offering == Initial Coin Offering(ICO)
 */

contract DrkToken is StandardToken, BurnableToken, Ownable {
	string public constant symbol = "DRK";
	string public constant name = "DIRK";
	uint8 public constant decimals = 18;
	uint256 public constant INITIAL_SUPPLY = 5000000000 * (10 ** uint256(decimals));
	uint256 public constant TOKEN_OFFERING_ALLOWANCE = 5000000000 * (10 ** uint256(decimals));
	uint256 public constant ADMIN_ALLOWANCE = INITIAL_SUPPLY - TOKEN_OFFERING_ALLOWANCE;

	// Address of token admin
	address public adminAddr;
	// Address of token offering
	address public tokenOfferingAddr;
	// Enable transfers after conclusion of token offering
	bool public transferEnabled = true;

	/**
	 * Check if transfer is allowed
	 *
	 * Permissions:
	 *														Owner	Admin	OfferingContract	Others
	 * transfer (before transferEnabled is true)			x		x			x				x
	 * transferFrom (before transferEnabled is true)		x		o			o				x
	 * transfer/transferFrom(after transferEnabled is true)	o		x			x				o
	 */
	modifier onlyWhenTransferAllowed() {
		require(transferEnabled || msg.sender == adminAddr || msg.sender == tokenOfferingAddr);
		_;
	}

	/**
	 * Check if token offering address is set or not
	 */
	modifier onlyTokenOfferingAddrNotSet() {
		require(tokenOfferingAddr == address(0x0));
		_;
	}

	/**
	* Check if address is a valid destination to transfer tokens to
	* - must not be zero address
	* - must not be the token address
	* - must not be the owner's address
	* - must not be the admin's address
	* - must not be the token offering contract address
	*/
	modifier validDestination(address to) {
		require(to != address(0x0));
		require(to != address(this));
		require(to != owner);
		require(to != address(adminAddr));
		require(to != address(tokenOfferingAddr));
		_;
	}	

	/**
	* Token contract constructor
	*
	* @param admin Address of admin account
	*/
	constructor(address admin) public {
		totalSupply_ = INITIAL_SUPPLY;

		// Mint tokens
		balances[msg.sender] = totalSupply_;
		emit Transfer(address(0x0), msg.sender, totalSupply_);

		// Approve allowance for admin account
		adminAddr = admin;
		approve(adminAddr, ADMIN_ALLOWANCE);
	}

	/**
	* Set token offering to approve allowance for offering contract to distribute tokens
	*
	* @param offeringAddr Address of token offering contract
	* @param amountForSale Amount of tokens for sale, set 0 to max out
	*/
	function setTokenOffering(address offeringAddr, uint256 amountForSale) external onlyOwner onlyTokenOfferingAddrNotSet {
		require(!transferEnabled);

		uint256 amount = (amountForSale == 0) ? TOKEN_OFFERING_ALLOWANCE : amountForSale;
		require(amount <= TOKEN_OFFERING_ALLOWANCE);

		approve(offeringAddr, amount);
		tokenOfferingAddr = offeringAddr;
	}

	/**
	* Enable transfers
	*/
	function enableTransfer() external onlyOwner {
		transferEnabled = true;

		// End the offering
		approve(tokenOfferingAddr, 0);
	}

	/**
	* Transfer from sender to another account
	*
	* @param to Destination address
	* @param value Amount of drktokens to send
	*/
	function transfer(address to, uint256 value) public onlyWhenTransferAllowed validDestination(to) returns (bool) {
		return super.transfer(to, value);
	}

	/**
	* Transfer from `from` account to `to` account using allowance in `from` account to the sender
	*
	* @param from Origin address
	* @param to Destination address
	* @param value Amount of drktokens to send
	*/
	function transferFrom(address from, address to, uint256 value) public onlyWhenTransferAllowed validDestination(to) returns (bool) {
		return super.transferFrom(from, to, value);
	}

	/**
	* Burn token, only owner is allowed to do this
	*
	* @param value Amount of tokens to burn
	*/
	function burn(uint256 value) public {
		require(transferEnabled || msg.sender == owner);
		super.burn(value);
	}
}