pragma solidity ^0.4.21;

    /**
    * @title ERC20Basic
    * @dev Simpler version of ERC20 interface
    * @dev see https://github.com/ethereum/EIPs/issues/179
    */
    contract ERC20Basic {
        uint256 public totalSupply;
        function balanceOf(address who) public constant returns (uint256);
        function transfer(address to, uint256 value) public returns (bool);
        event Transfer(address indexed from, address indexed to, uint256 value);
    }

    /**
    * @title ERC20 interface
    * @dev see https://github.com/ethereum/EIPs/issues/20
    */
    contract ERC20 is ERC20Basic {
        function allowance(address owner, address spender) constant returns (uint256);
        function transferFrom(address from, address to, uint256 value) returns (bool);
        function approve(address spender, uint256 value) returns (bool);
        event Approval(address indexed owner, address indexed spender, uint256 value);
    }

    /**
    * @title SafeMath
    * @dev Math operations with safety checks that throw on error
    */
    library SafeMath {
    
        function mul(uint256 a, uint256 b) internal constant returns (uint256) {
            uint256 c = a * b;
            assert(a == 0 || c / a == b);
            return c;
        }

        function div(uint256 a, uint256 b) internal constant 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 constant returns (uint256) {
            assert(b <= a);
            return a - b;
        }

        function add(uint256 a, uint256 b) internal constant returns (uint256) {
            uint256 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;

        /**
        * @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) {
            balances[msg.sender] = balances[msg.sender].sub(_value);
            balances[_to] = balances[_to].add(_value);
            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 constant returns (uint256 balance) {
            return balances[_owner];
        }

    }

    /**
     * @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)) 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 amout of tokens to be transfered
        */
        function transferFrom(address _from, address _to, uint256 _value) returns (bool) {
            var _allowance = allowed[_from][msg.sender];

            // Check is not needed because sub(_allowance, _value) will already throw if this condition is not met
            // require (_value <= _allowance);

            balances[_to] = balances[_to].add(_value);
            balances[_from] = balances[_from].sub(_value);
            allowed[_from][msg.sender] = _allowance.sub(_value);
            Transfer(_from, _to, _value);
            return true;
        }

        /**
        * @dev Aprove the passed address to spend the specified amount of tokens on behalf of msg.sender.
        * @param _spender The address which will spend the funds.
        * @param _value The amount of tokens to be spent.
        */
        function approve(address _spender, uint256 _value) returns (bool) {

            // To change the approve amount you first have to reduce the addresses`
            //  allowance to zero by calling `approve(_spender, 0)` if it is not
            //  already 0 to mitigate the race condition described here:
            //  https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
            require((_value == 0) || (allowed[msg.sender][_spender] == 0));
    
            allowed[msg.sender][_spender] = _value;
            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 specifing the amount of tokens still available for the spender.
        */
        function allowance(address _owner, address _spender) constant returns (uint256 remaining) {
            return allowed[_owner][_spender];
        }

    }

    /**
    * @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;

        /**
        * @dev The Ownable constructor sets the original `owner` of the contract to the sender
        * account.
        */
        function Ownable() {
            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) onlyOwner {
            require(newOwner != address(0));      
            owner = newOwner;
        }

    }   

    /**
    * @title Burnable Token
    * @dev Token that can be irreversibly burned (destroyed).
    */
    contract BurnableToken is StandardToken {

        /**
        * @dev Burns a specific amount of tokens.
        * @param _value The amount of token to be burned.
        */
        function burn(uint _value) public {
            require(_value > 0);
            address burner = msg.sender;
            balances[burner] = balances[burner].sub(_value);
            totalSupply = totalSupply.sub(_value);
            Burn(burner, _value);
        }

        event Burn(address indexed burner, uint indexed value);

    }

    contract WhiteWallToken is BurnableToken, Ownable {
    
        string public constant name = "WhiteWall Token";
   
        string public constant symbol = "WHW";
    
        uint32 public constant decimals = 18;

        uint256 public INITIAL_SUPPLY = 4000000 * 1 ether;
  
        uint public constant start = 1523836800;
  
        uint public constant period = 0;

        function transfer(address _to, uint256 _value) public returns (bool) {
            if (now < start + period * 1 days){
                require(msg.sender == owner);
                balances[msg.sender] = balances[msg.sender].sub(_value);
                balances[_to] = balances[_to].add(_value);
                Transfer(msg.sender, _to, _value);
                return true;
            }else{
                balances[msg.sender] = balances[msg.sender].sub(_value);
                balances[_to] = balances[_to].add(_value);
                Transfer(msg.sender, _to, _value);
                return true; 
            }
        }
    
        function WhiteWallToken() {
            totalSupply = INITIAL_SUPPLY;
            balances[msg.sender] = INITIAL_SUPPLY;
        }
    
    }