pragma solidity ^0.4.24;

/**
 * @title Utility contract to allow pausing and unpausing of certain functions
 */
contract Pausable {

    event Pause(uint256 _timestammp);
    event Unpause(uint256 _timestamp);

    bool public paused = false;

    /**
    * @notice Modifier to make a function callable only when the contract is not paused.
    */
    modifier whenNotPaused() {
        require(!paused);
        _;
    }

    /**
    * @notice Modifier to make a function callable only when the contract is paused.
    */
    modifier whenPaused() {
        require(paused);
        _;
    }

   /**
    * @notice called by the owner to pause, triggers stopped state
    */
    function _pause() internal {
        require(!paused);
        paused = true;
        emit Pause(now);
    }

    /**
    * @notice called by the owner to unpause, returns to normal state
    */
    function _unpause() internal {
        require(paused);
        paused = false;
        emit Unpause(now);
    }

}

/**
 * @title ERC20Basic
 * @dev Simpler version of ERC20 interface
 * @dev 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);
}

/**
 * @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;
  }
}

/**
 * @title Basic token
 * @dev Basic version of StandardToken, with no allowances.
 */
contract BasicToken is ERC20Basic {
  using SafeMath for uint256;

  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];
  }

}

/**
 * @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
  );
}

/**
 * @title Standard ERC20 token
 *
 * @dev Implementation of the basic standard token.
 * @dev https://github.com/ethereum/EIPs/issues/20
 * @dev 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(_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];
  }

  /**
   * @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 DetailedERC20 token
 * @dev The decimals are only for visualization purposes.
 * All the operations are done using the smallest and indivisible token unit,
 * just as on Ethereum all the operations are done in wei.
 */
contract DetailedERC20 is ERC20 {
  string public name;
  string public symbol;
  uint8 public decimals;

  constructor(string _name, string _symbol, uint8 _decimals) public {
    name = _name;
    symbol = _symbol;
    decimals = _decimals;
  }
}

/**
 * @title Interface for the ST20 token standard
 */
contract IST20 is StandardToken, DetailedERC20 {

    // off-chain hash
    string public tokenDetails;

    //transfer, transferFrom must respect use respect the result of verifyTransfer
    function verifyTransfer(address _from, address _to, uint256 _amount) public returns (bool success);

    /**
     * @notice mints new tokens and assigns them to the target _investor.
     * Can only be called by the STO attached to the token (Or by the ST owner if there's no STO attached yet)
     */
    function mint(address _investor, uint256 _amount) public returns (bool success);

    /**
     * @notice Burn function used to burn the securityToken
     * @param _value No. of token that get burned
     */
    function burn(uint256 _value) public;

    event Minted(address indexed to, uint256 amount);
    event Burnt(address indexed _burner, 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 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.
   */
  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;
  }
}

/**
 * @title Interface for all security tokens
 */
contract ISecurityToken is IST20, Ownable {

    uint8 public constant PERMISSIONMANAGER_KEY = 1;
    uint8 public constant TRANSFERMANAGER_KEY = 2;
    uint8 public constant STO_KEY = 3;
    uint8 public constant CHECKPOINT_KEY = 4;
    uint256 public granularity;

    // Value of current checkpoint
    uint256 public currentCheckpointId;

    // Total number of non-zero token holders
    uint256 public investorCount;

    // List of token holders
    address[] public investors;

    // Permissions this to a Permission module, which has a key of 1
    // If no Permission return false - note that IModule withPerm will allow ST owner all permissions anyway
    // this allows individual modules to override this logic if needed (to not allow ST owner all permissions)
    function checkPermission(address _delegate, address _module, bytes32 _perm) public view returns(bool);

    /**
     * @notice returns module list for a module type
     * @param _moduleType is which type of module we are trying to remove
     * @param _moduleIndex is the index of the module within the chosen type
     */
    function getModule(uint8 _moduleType, uint _moduleIndex) public view returns (bytes32, address);

    /**
     * @notice returns module list for a module name - will return first match
     * @param _moduleType is which type of module we are trying to remove
     * @param _name is the name of the module within the chosen type
     */
    function getModuleByName(uint8 _moduleType, bytes32 _name) public view returns (bytes32, address);

    /**
     * @notice Queries totalSupply as of a defined checkpoint
     * @param _checkpointId Checkpoint ID to query as of
     */
    function totalSupplyAt(uint256 _checkpointId) public view returns(uint256);

    /**
     * @notice Queries balances as of a defined checkpoint
     * @param _investor Investor to query balance for
     * @param _checkpointId Checkpoint ID to query as of
     */
    function balanceOfAt(address _investor, uint256 _checkpointId) public view returns(uint256);

    /**
     * @notice Creates a checkpoint that can be used to query historical balances / totalSuppy
     */
    function createCheckpoint() public returns(uint256);

    /**
     * @notice gets length of investors array
     * NB - this length may differ from investorCount if list has not been pruned of zero balance investors
     * @return length
     */
    function getInvestorsLength() public view returns(uint256);

}

/**
 * @title Interface that any module factory contract should implement
 */
contract IModuleFactory is Ownable {

    ERC20 public polyToken;
    uint256 public setupCost;
    uint256 public usageCost;
    uint256 public monthlySubscriptionCost;

    event LogChangeFactorySetupFee(uint256 _oldSetupcost, uint256 _newSetupCost, address _moduleFactory);
    event LogChangeFactoryUsageFee(uint256 _oldUsageCost, uint256 _newUsageCost, address _moduleFactory);
    event LogChangeFactorySubscriptionFee(uint256 _oldSubscriptionCost, uint256 _newMonthlySubscriptionCost, address _moduleFactory);
    event LogGenerateModuleFromFactory(address _module, bytes32 indexed _moduleName, address indexed _moduleFactory, address _creator, uint256 _timestamp);

    /**
     * @notice Constructor
     * @param _polyAddress Address of the polytoken
     */
    constructor (address _polyAddress, uint256 _setupCost, uint256 _usageCost, uint256 _subscriptionCost) public {
      polyToken = ERC20(_polyAddress);
      setupCost = _setupCost;
      usageCost = _usageCost;
      monthlySubscriptionCost = _subscriptionCost;
    }

    //Should create an instance of the Module, or throw
    function deploy(bytes _data) external returns(address);

    /**
     * @notice Type of the Module factory
     */
    function getType() public view returns(uint8);

    /**
     * @notice Get the name of the Module
     */
    function getName() public view returns(bytes32);

    /**
     * @notice Get the description of the Module
     */
    function getDescription() public view returns(string);

    /**
     * @notice Get the title of the Module
     */
    function getTitle() public view returns(string);

    /**
     * @notice Get the Instructions that helped to used the module
     */
    function getInstructions() public view returns (string);

    /**
     * @notice Get the tags related to the module factory
     */
    function getTags() public view returns (bytes32[]);

    //Pull function sig from _data
    function getSig(bytes _data) internal pure returns (bytes4 sig) {
        uint len = _data.length < 4 ? _data.length : 4;
        for (uint i = 0; i < len; i++) {
            sig = bytes4(uint(sig) + uint(_data[i]) * (2 ** (8 * (len - 1 - i))));
        }
    }

    /**
     * @notice used to change the fee of the setup cost
     * @param _newSetupCost new setup cost
     */
    function changeFactorySetupFee(uint256 _newSetupCost) public onlyOwner {
        emit LogChangeFactorySetupFee(setupCost, _newSetupCost, address(this));
        setupCost = _newSetupCost;
    }

    /**
     * @notice used to change the fee of the usage cost
     * @param _newUsageCost new usage cost
     */
    function changeFactoryUsageFee(uint256 _newUsageCost) public onlyOwner {
        emit LogChangeFactoryUsageFee(usageCost, _newUsageCost, address(this));
        usageCost = _newUsageCost;
    }

    /**
     * @notice used to change the fee of the subscription cost
     * @param _newSubscriptionCost new subscription cost
     */
    function changeFactorySubscriptionFee(uint256 _newSubscriptionCost) public onlyOwner {
        emit LogChangeFactorySubscriptionFee(monthlySubscriptionCost, _newSubscriptionCost, address(this));
        monthlySubscriptionCost = _newSubscriptionCost;
        
    }

}

/**
 * @title Interface that any module contract should implement
 */
contract IModule {

    address public factory;

    address public securityToken;

    bytes32 public constant FEE_ADMIN = "FEE_ADMIN";

    ERC20 public polyToken;

    /**
     * @notice Constructor
     * @param _securityToken Address of the security token
     * @param _polyAddress Address of the polytoken
     */
    constructor (address _securityToken, address _polyAddress) public {
        securityToken = _securityToken;
        factory = msg.sender;
        polyToken = ERC20(_polyAddress);
    }

    /**
     * @notice This function returns the signature of configure function
     */
    function getInitFunction() public pure returns (bytes4);

    //Allows owner, factory or permissioned delegate
    modifier withPerm(bytes32 _perm) {
        bool isOwner = msg.sender == ISecurityToken(securityToken).owner();
        bool isFactory = msg.sender == factory;
        require(isOwner||isFactory||ISecurityToken(securityToken).checkPermission(msg.sender, address(this), _perm), "Permission check failed");
        _;
    }

    modifier onlyOwner {
        require(msg.sender == ISecurityToken(securityToken).owner(), "Sender is not owner");
        _;
    }

    modifier onlyFactory {
        require(msg.sender == factory, "Sender is not factory");
        _;
    }

    modifier onlyFactoryOwner {
        require(msg.sender == IModuleFactory(factory).owner(), "Sender is not factory owner");
        _;
    }

    /**
     * @notice Return the permissions flag that are associated with Module
     */
    function getPermissions() public view returns(bytes32[]);

    /**
     * @notice used to withdraw the fee by the factory owner
     */
    function takeFee(uint256 _amount) public withPerm(FEE_ADMIN) returns(bool) {
        require(polyToken.transferFrom(address(this), IModuleFactory(factory).owner(), _amount), "Unable to take fee");
        return true;
    }
}

/**
 * @title Interface to be implemented by all Transfer Manager modules
 */
contract ITransferManager is IModule, Pausable {

    //If verifyTransfer returns:
    //  FORCE_VALID, the transaction will always be valid, regardless of other TM results
    //  INVALID, then the transfer should not be allowed regardless of other TM results
    //  VALID, then the transfer is valid for this TM
    //  NA, then the result from this TM is ignored
    enum Result {INVALID, NA, VALID, FORCE_VALID}

    function verifyTransfer(address _from, address _to, uint256 _amount, bool _isTransfer) public returns(Result);

    function unpause() onlyOwner public {
        super._unpause();
    }

    function pause() onlyOwner public {
        super._pause();
    }
}

/////////////////////
// Module permissions
/////////////////////
//                                        Owner       WHITELIST      FLAGS
// changeIssuanceAddress                    X                          X
// changeAllowAllTransfers                  X                          X
// changeAllowAllWhitelistTransfers         X                          X
// changeAllowAllWhitelistIssuances         X                          X
// modifyWhitelist                          X             X
// modifyWhitelistMulti                     X             X

/**
 * @title Transfer Manager module for core transfer validation functionality
 */
contract GeneralTransferManager is ITransferManager {

    using SafeMath for uint256;

    //Address from which issuances come
    address public issuanceAddress = address(0);

    //Address which can sign whitelist changes
    address public signingAddress = address(0);

    bytes32 public constant WHITELIST = "WHITELIST";
    bytes32 public constant FLAGS = "FLAGS";

    //from and to timestamps that an investor can send / receive tokens respectively
    struct TimeRestriction {
        uint256 fromTime;
        uint256 toTime;
        uint256 expiryTime;
        bool canBuyFromSTO;
    }

    // An address can only send / receive tokens once their corresponding uint256 > block.number
    // (unless allowAllTransfers == true or allowAllWhitelistTransfers == true)
    mapping (address => TimeRestriction) public whitelist;

    //If true, there are no transfer restrictions, for any addresses
    bool public allowAllTransfers = false;
    //If true, time lock is ignored for transfers (address must still be on whitelist)
    bool public allowAllWhitelistTransfers = false;
    //If true, time lock is ignored for issuances (address must still be on whitelist)
    bool public allowAllWhitelistIssuances = true;
    //If true, time lock is ignored for burn transactions
    bool public allowAllBurnTransfers = false;

    // Emit when Issuance address get changed
    event LogChangeIssuanceAddress(address _issuanceAddress);
    // Emit when there is change in the flag variable called allowAllTransfers
    event LogAllowAllTransfers(bool _allowAllTransfers);
    // Emit when there is change in the flag variable called allowAllWhitelistTransfers
    event LogAllowAllWhitelistTransfers(bool _allowAllWhitelistTransfers);
    // Emit when there is change in the flag variable called allowAllWhitelistIssuances
    event LogAllowAllWhitelistIssuances(bool _allowAllWhitelistIssuances);
    // Emit when there is change in the flag variable called allowAllBurnTransfers
    event LogAllowAllBurnTransfers(bool _allowAllBurnTransfers);
    // Emit when there is change in the flag variable called signingAddress
    event LogChangeSigningAddress(address _signingAddress);
    // Emit when investor details get modified related to their whitelisting
    event LogModifyWhitelist(
        address _investor,
        uint256 _dateAdded,
        address _addedBy,
        uint256 _fromTime,
        uint256 _toTime,
        uint256 _expiryTime,
        bool _canBuyFromSTO
    );

    /**
     * @notice Constructor
     * @param _securityToken Address of the security token
     * @param _polyAddress Address of the polytoken
     */
    constructor (address _securityToken, address _polyAddress)
    public
    IModule(_securityToken, _polyAddress)
    {
    }

    /**
     * @notice This function returns the signature of configure function
     */
    function getInitFunction() public pure returns (bytes4) {
        return bytes4(0);
    }

    /**
     * @notice Used to change the Issuance Address
     * @param _issuanceAddress new address for the issuance
     */
    function changeIssuanceAddress(address _issuanceAddress) public withPerm(FLAGS) {
        issuanceAddress = _issuanceAddress;
        emit LogChangeIssuanceAddress(_issuanceAddress);
    }

    /**
     * @notice Used to change the Sigining Address
     * @param _signingAddress new address for the signing
     */
    function changeSigningAddress(address _signingAddress) public withPerm(FLAGS) {
        signingAddress = _signingAddress;
        emit LogChangeSigningAddress(_signingAddress);
    }

    /**
     * @notice Used to change the flag
            true - It refers there are no transfer restrictions, for any addresses
            false - It refers transfers are restricted for all addresses.
     * @param _allowAllTransfers flag value
     */
    function changeAllowAllTransfers(bool _allowAllTransfers) public withPerm(FLAGS) {
        allowAllTransfers = _allowAllTransfers;
        emit LogAllowAllTransfers(_allowAllTransfers);
    }

    /**
     * @notice Used to change the flag
            true - It refers that time lock is ignored for transfers (address must still be on whitelist)
            false - It refers transfers are restricted for all addresses.
     * @param _allowAllWhitelistTransfers flag value
     */
    function changeAllowAllWhitelistTransfers(bool _allowAllWhitelistTransfers) public withPerm(FLAGS) {
        allowAllWhitelistTransfers = _allowAllWhitelistTransfers;
        emit LogAllowAllWhitelistTransfers(_allowAllWhitelistTransfers);
    }

    /**
     * @notice Used to change the flag
            true - It refers that time lock is ignored for issuances (address must still be on whitelist)
            false - It refers transfers are restricted for all addresses.
     * @param _allowAllWhitelistIssuances flag value
     */
    function changeAllowAllWhitelistIssuances(bool _allowAllWhitelistIssuances) public withPerm(FLAGS) {
        allowAllWhitelistIssuances = _allowAllWhitelistIssuances;
        emit LogAllowAllWhitelistIssuances(_allowAllWhitelistIssuances);
    }

    /**
     * @notice Used to change the flag
            true - It allow to burn the tokens
            false - It deactivate the burning mechanism.
     * @param _allowAllBurnTransfers flag value
     */
    function changeAllowAllBurnTransfers(bool _allowAllBurnTransfers) public withPerm(FLAGS) {
        allowAllBurnTransfers = _allowAllBurnTransfers;
        emit LogAllowAllBurnTransfers(_allowAllBurnTransfers);
    }

    /**
    * @notice default implementation of verifyTransfer used by SecurityToken
    * If the transfer request comes from the STO, it only checks that the investor is in the whitelist
    * If the transfer request comes from a token holder, it checks that:
    * a) Both are on the whitelist
    * b) Seller's sale lockup period is over
    * c) Buyer's purchase lockup is over
    */
    function verifyTransfer(address _from, address _to, uint256 /*_amount*/, bool /* _isTransfer */) public returns(Result) {
        if (!paused) {
            if (allowAllTransfers) {
                //All transfers allowed, regardless of whitelist
                return Result.VALID;
            }
            if (allowAllBurnTransfers && (_to == address(0))) {
                return Result.VALID;
            }
            if (allowAllWhitelistTransfers) {
                //Anyone on the whitelist can transfer, regardless of block number
                return (onWhitelist(_to) && onWhitelist(_from)) ? Result.VALID : Result.NA;
            }
            if (allowAllWhitelistIssuances && _from == issuanceAddress) {
                if (!whitelist[_to].canBuyFromSTO && isSTOAttached()) {
                    return Result.NA;
                }
                return onWhitelist(_to) ? Result.VALID : Result.NA;
            }
            //Anyone on the whitelist can transfer provided the blocknumber is large enough
            return ((onWhitelist(_from) && whitelist[_from].fromTime <= now) &&
                (onWhitelist(_to) && whitelist[_to].toTime <= now)) ? Result.VALID : Result.NA;
        }
        return Result.NA;
    }

    /**
    * @notice adds or removes addresses from the whitelist.
    * @param _investor is the address to whitelist
    * @param _fromTime is the moment when the sale lockup period ends and the investor can freely sell his tokens
    * @param _toTime is the moment when the purchase lockup period ends and the investor can freely purchase tokens from others
    * @param _expiryTime is the moment till investors KYC will be validated. After that investor need to do re-KYC
    * @param _canBuyFromSTO is used to know whether the investor is restricted investor or not.
    */
    function modifyWhitelist(address _investor, uint256 _fromTime, uint256 _toTime, uint256 _expiryTime, bool _canBuyFromSTO) public withPerm(WHITELIST) {
        //Passing a _time == 0 into this function, is equivalent to removing the _investor from the whitelist
        whitelist[_investor] = TimeRestriction(_fromTime, _toTime, _expiryTime, _canBuyFromSTO);
        emit LogModifyWhitelist(_investor, now, msg.sender, _fromTime, _toTime, _expiryTime, _canBuyFromSTO);
    }

    /**
    * @notice adds or removes addresses from the whitelist.
    * @param _investors List of the addresses to whitelist
    * @param _fromTimes An array of the moment when the sale lockup period ends and the investor can freely sell his tokens
    * @param _toTimes An array of the moment when the purchase lockup period ends and the investor can freely purchase tokens from others
    * @param _expiryTimes An array of the moment till investors KYC will be validated. After that investor need to do re-KYC
    * @param _canBuyFromSTO An array of boolean values
    */
    function modifyWhitelistMulti(
        address[] _investors,
        uint256[] _fromTimes,
        uint256[] _toTimes,
        uint256[] _expiryTimes,
        bool[] _canBuyFromSTO
    ) public withPerm(WHITELIST) {
        require(_investors.length == _fromTimes.length, "Mismatched input lengths");
        require(_fromTimes.length == _toTimes.length, "Mismatched input lengths");
        require(_toTimes.length == _expiryTimes.length, "Mismatched input lengths");
        require(_canBuyFromSTO.length == _toTimes.length, "Mismatched input length");
        for (uint256 i = 0; i < _investors.length; i++) {
            modifyWhitelist(_investors[i], _fromTimes[i], _toTimes[i], _expiryTimes[i], _canBuyFromSTO[i]);
        }
    }

    /**
    * @notice adds or removes addresses from the whitelist - can be called by anyone with a valid signature
    * @param _investor is the address to whitelist
    * @param _fromTime is the moment when the sale lockup period ends and the investor can freely sell his tokens
    * @param _toTime is the moment when the purchase lockup period ends and the investor can freely purchase tokens from others
    * @param _expiryTime is the moment till investors KYC will be validated. After that investor need to do re-KYC
    * @param _canBuyFromSTO is used to know whether the investor is restricted investor or not.
    * @param _validFrom is the time that this signature is valid from
    * @param _validTo is the time that this signature is valid until
    * @param _v issuer signature
    * @param _r issuer signature
    * @param _s issuer signature
    */
    function modifyWhitelistSigned(
        address _investor,
        uint256 _fromTime,
        uint256 _toTime,
        uint256 _expiryTime,
        bool _canBuyFromSTO,
        uint256 _validFrom,
        uint256 _validTo,
        uint8 _v,
        bytes32 _r,
        bytes32 _s
    ) public {
        require(_validFrom <= now, "ValidFrom is too early");
        require(_validTo >= now, "ValidTo is too late");
        bytes32 hash = keccak256(abi.encodePacked(this, _investor, _fromTime, _toTime, _expiryTime, _canBuyFromSTO, _validFrom, _validTo));
        checkSig(hash, _v, _r, _s);
        //Passing a _time == 0 into this function, is equivalent to removing the _investor from the whitelist
        whitelist[_investor] = TimeRestriction(_fromTime, _toTime, _expiryTime, _canBuyFromSTO);
        emit LogModifyWhitelist(_investor, now, msg.sender, _fromTime, _toTime, _expiryTime, _canBuyFromSTO);
    }

    /**
     * @notice used to verify the signature
     */
    function checkSig(bytes32 _hash, uint8 _v, bytes32 _r, bytes32 _s) internal view {
        //Check that the signature is valid
        //sig should be signing - _investor, _fromTime, _toTime & _expiryTime and be signed by the issuer address
        address signer = ecrecover(keccak256(abi.encodePacked("\x19Ethereum Signed Message:\n32", _hash)), _v, _r, _s);
        require(signer == ISecurityToken(securityToken).owner() || signer == signingAddress, "Incorrect signer");
    }

    /**
     * @notice Return the permissions flag that are associated with general trnasfer manager
     */
    function getPermissions() public view returns(bytes32[]) {
        bytes32[] memory allPermissions = new bytes32[](2);
        allPermissions[0] = WHITELIST;
        allPermissions[1] = FLAGS;
        return allPermissions;
    }

    /**
     * @notice Internal function used to check whether the investor is in the whitelist or not
            & also checks whether the KYC of investor get expired or not
     * @param _investor Address of the investor
     */
    function onWhitelist(address _investor) internal view returns(bool) {
        return (((whitelist[_investor].fromTime != 0) || (whitelist[_investor].toTime != 0)) &&
            (whitelist[_investor].expiryTime >= now));
    }

    /**
     * @notice Internal function use to know whether the STO is attached or not
     */
    function isSTOAttached() internal view returns(bool) {
        address _sto;
        (, _sto) = ISecurityToken(securityToken).getModule(3, 0);
        if (_sto == address(0))
            return false;
        return true;
    }

}