pragma solidity ^0.4.13;

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;
  }
}

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.
   */
  function Ownable() 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;
  }

}

contract Certifiable is Ownable {
    Certifier public certifier;
    event CertifierChanged(address indexed newCertifier);

    constructor(address _certifier) public {
        certifier = Certifier(_certifier);
    }

    function updateCertifier(address _address) public onlyOwner returns (bool success) {
        require(_address != address(0));
        emit CertifierChanged(_address);
        certifier = Certifier(_address);
        return true;
    }
}

contract KYCToken is Certifiable {
    mapping(address => bool) public kycPending;
    mapping(address => bool) public managers;

    event ManagerAdded(address indexed newManager);
    event ManagerRemoved(address indexed removedManager);

    modifier onlyManager() {
        require(managers[msg.sender] == true);
        _;
    }

    modifier isKnownCustomer(address _address) {
        require(!kycPending[_address] || certifier.certified(_address));
        if (kycPending[_address]) {
            kycPending[_address] = false;
        }
        _;
    }

    constructor(address _certifier) public Certifiable(_certifier)
    {

    }

    function addManager(address _address) external onlyOwner {
        managers[_address] = true;
        emit ManagerAdded(_address);
    }

    function removeManager(address _address) external onlyOwner {
        managers[_address] = false;
        emit ManagerRemoved(_address);
    }

}

contract Certifier {
    event Confirmed(address indexed who);
    event Revoked(address indexed who);
    function certified(address) public constant returns (bool);
    function get(address, string) public constant returns (bytes32);
    function getAddress(address, string) public constant returns (address);
    function getUint(address, string) public constant returns (uint);
}

contract Crowdsale {
  using SafeMath for uint256;

  // The token being sold
  ERC20 public token;

  // Address where funds are collected
  address public wallet;

  // How many token units a buyer gets per wei
  uint256 public rate;

  // Amount of wei raised
  uint256 public weiRaised;

  /**
   * Event for token purchase logging
   * @param purchaser who paid for the tokens
   * @param beneficiary who got the tokens
   * @param value weis paid for purchase
   * @param amount amount of tokens purchased
   */
  event TokenPurchase(address indexed purchaser, address indexed beneficiary, uint256 value, uint256 amount);

  /**
   * @param _rate Number of token units a buyer gets per wei
   * @param _wallet Address where collected funds will be forwarded to
   * @param _token Address of the token being sold
   */
  function Crowdsale(uint256 _rate, address _wallet, ERC20 _token) public {
    require(_rate > 0);
    require(_wallet != address(0));
    require(_token != address(0));

    rate = _rate;
    wallet = _wallet;
    token = _token;
  }

  // -----------------------------------------
  // Crowdsale external interface
  // -----------------------------------------

  /**
   * @dev fallback function ***DO NOT OVERRIDE***
   */
  function () external payable {
    buyTokens(msg.sender);
  }

  /**
   * @dev low level token purchase ***DO NOT OVERRIDE***
   * @param _beneficiary Address performing the token purchase
   */
  function buyTokens(address _beneficiary) public payable {

    uint256 weiAmount = msg.value;
    _preValidatePurchase(_beneficiary, weiAmount);

    // calculate token amount to be created
    uint256 tokens = _getTokenAmount(weiAmount);

    // update state
    weiRaised = weiRaised.add(weiAmount);

    _processPurchase(_beneficiary, tokens);
    emit TokenPurchase(
      msg.sender,
      _beneficiary,
      weiAmount,
      tokens
    );

    _updatePurchasingState(_beneficiary, weiAmount);

    _forwardFunds();
    _postValidatePurchase(_beneficiary, weiAmount);
  }

  // -----------------------------------------
  // Internal interface (extensible)
  // -----------------------------------------

  /**
   * @dev Validation of an incoming purchase. Use require statements to revert state when conditions are not met. Use super to concatenate validations.
   * @param _beneficiary Address performing the token purchase
   * @param _weiAmount Value in wei involved in the purchase
   */
  function _preValidatePurchase(address _beneficiary, uint256 _weiAmount) internal {
    require(_beneficiary != address(0));
    require(_weiAmount != 0);
  }

  /**
   * @dev Validation of an executed purchase. Observe state and use revert statements to undo rollback when valid conditions are not met.
   * @param _beneficiary Address performing the token purchase
   * @param _weiAmount Value in wei involved in the purchase
   */
  function _postValidatePurchase(address _beneficiary, uint256 _weiAmount) internal {
    // optional override
  }

  /**
   * @dev Source of tokens. Override this method to modify the way in which the crowdsale ultimately gets and sends its tokens.
   * @param _beneficiary Address performing the token purchase
   * @param _tokenAmount Number of tokens to be emitted
   */
  function _deliverTokens(address _beneficiary, uint256 _tokenAmount) internal {
    token.transfer(_beneficiary, _tokenAmount);
  }

  /**
   * @dev Executed when a purchase has been validated and is ready to be executed. Not necessarily emits/sends tokens.
   * @param _beneficiary Address receiving the tokens
   * @param _tokenAmount Number of tokens to be purchased
   */
  function _processPurchase(address _beneficiary, uint256 _tokenAmount) internal {
    _deliverTokens(_beneficiary, _tokenAmount);
  }

  /**
   * @dev Override for extensions that require an internal state to check for validity (current user contributions, etc.)
   * @param _beneficiary Address receiving the tokens
   * @param _weiAmount Value in wei involved in the purchase
   */
  function _updatePurchasingState(address _beneficiary, uint256 _weiAmount) internal {
    // optional override
  }

  /**
   * @dev Override to extend the way in which ether is converted to tokens.
   * @param _weiAmount Value in wei to be converted into tokens
   * @return Number of tokens that can be purchased with the specified _weiAmount
   */
  function _getTokenAmount(uint256 _weiAmount) internal view returns (uint256) {
    return _weiAmount.mul(rate);
  }

  /**
   * @dev Determines how ETH is stored/forwarded on purchases.
   */
  function _forwardFunds() internal {
    wallet.transfer(msg.value);
  }
}

contract TimedCrowdsale is Crowdsale {
  using SafeMath for uint256;

  uint256 public openingTime;
  uint256 public closingTime;

  /**
   * @dev Reverts if not in crowdsale time range.
   */
  modifier onlyWhileOpen {
    // solium-disable-next-line security/no-block-members
    require(block.timestamp >= openingTime && block.timestamp <= closingTime);
    _;
  }

  /**
   * @dev Constructor, takes crowdsale opening and closing times.
   * @param _openingTime Crowdsale opening time
   * @param _closingTime Crowdsale closing time
   */
  function TimedCrowdsale(uint256 _openingTime, uint256 _closingTime) public {
    // solium-disable-next-line security/no-block-members
    require(_openingTime >= block.timestamp);
    require(_closingTime >= _openingTime);

    openingTime = _openingTime;
    closingTime = _closingTime;
  }

  /**
   * @dev Checks whether the period in which the crowdsale is open has already elapsed.
   * @return Whether crowdsale period has elapsed
   */
  function hasClosed() public view returns (bool) {
    // solium-disable-next-line security/no-block-members
    return block.timestamp > closingTime;
  }

  /**
   * @dev Extend parent behavior requiring to be within contributing period
   * @param _beneficiary Token purchaser
   * @param _weiAmount Amount of wei contributed
   */
  function _preValidatePurchase(address _beneficiary, uint256 _weiAmount) internal onlyWhileOpen {
    super._preValidatePurchase(_beneficiary, _weiAmount);
  }

}

contract AllowanceCrowdsale is Crowdsale {
  using SafeMath for uint256;

  address public tokenWallet;

  /**
   * @dev Constructor, takes token wallet address. 
   * @param _tokenWallet Address holding the tokens, which has approved allowance to the crowdsale
   */
  function AllowanceCrowdsale(address _tokenWallet) public {
    require(_tokenWallet != address(0));
    tokenWallet = _tokenWallet;
  }

  /**
   * @dev Checks the amount of tokens left in the allowance.
   * @return Amount of tokens left in the allowance
   */
  function remainingTokens() public view returns (uint256) {
    return token.allowance(tokenWallet, this);
  }

  /**
   * @dev Overrides parent behavior by transferring tokens from wallet.
   * @param _beneficiary Token purchaser
   * @param _tokenAmount Amount of tokens purchased
   */
  function _deliverTokens(address _beneficiary, uint256 _tokenAmount) internal {
    token.transferFrom(tokenWallet, _beneficiary, _tokenAmount);
  }
}

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);
}

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);
}

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);
}

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];
  }

}

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;
  }

}

contract ERC827Token is ERC827, StandardToken {

  /**
   * @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);

    // solium-disable-next-line security/no-call-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);

    // solium-disable-next-line security/no-call-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);

    // solium-disable-next-line security/no-call-value
    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);

    // solium-disable-next-line security/no-call-value
    require(_spender.call.value(msg.value)(_data));

    return true;
  }

}

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);
  }
}

contract EDUToken is BurnableToken, KYCToken, ERC827Token {
    using SafeMath for uint256;

    string public constant name = "EDU Token";
    string public constant symbol = "EDU";
    uint8 public constant decimals = 18;

    uint256 public constant INITIAL_SUPPLY = 48000000 * (10 ** uint256(decimals));

    constructor(address _certifier) public KYCToken(_certifier) {
        totalSupply_ = INITIAL_SUPPLY;
        balances[msg.sender] = INITIAL_SUPPLY;
        emit Transfer(0x0, msg.sender, INITIAL_SUPPLY);
    }

    function transfer(address _to, uint256 _value) public isKnownCustomer(msg.sender) returns (bool) {
        return super.transfer(_to, _value);
    }

    function transferFrom(address _from, address _to, uint256 _value) public isKnownCustomer(_from) returns (bool) {
        return super.transferFrom(_from, _to, _value);
    }

    function approve(address _spender, uint256 _value) public isKnownCustomer(_spender) returns (bool) {
        return super.approve(_spender, _value);
    }

    function increaseApproval(address _spender, uint _addedValue) public isKnownCustomer(_spender) returns (bool success) {
        return super.increaseApproval(_spender, _addedValue);
    }

    function decreaseApproval(address _spender, uint _subtractedValue) public isKnownCustomer(_spender) returns (bool success) {
        return super.decreaseApproval(_spender, _subtractedValue);
    }

    function delayedTransferFrom(address _tokenWallet, address _to, uint256 _value) public onlyManager returns (bool) {
        transferFrom(_tokenWallet, _to, _value);
        kycPending[_to] = true;
    }

}

contract CappedCrowdsale is Crowdsale {
  using SafeMath for uint256;

  uint256 public cap;

  /**
   * @dev Constructor, takes maximum amount of wei accepted in the crowdsale.
   * @param _cap Max amount of wei to be contributed
   */
  function CappedCrowdsale(uint256 _cap) public {
    require(_cap > 0);
    cap = _cap;
  }

  /**
   * @dev Checks whether the cap has been reached. 
   * @return Whether the cap was reached
   */
  function capReached() public view returns (bool) {
    return weiRaised >= cap;
  }

  /**
   * @dev Extend parent behavior requiring purchase to respect the funding cap.
   * @param _beneficiary Token purchaser
   * @param _weiAmount Amount of wei contributed
   */
  function _preValidatePurchase(address _beneficiary, uint256 _weiAmount) internal {
    super._preValidatePurchase(_beneficiary, _weiAmount);
    require(weiRaised.add(_weiAmount) <= cap);
  }

}

contract EDUCrowdsale is AllowanceCrowdsale, CappedCrowdsale, TimedCrowdsale, Ownable, Certifiable {
    using SafeMath for uint256;

    uint256 constant FIFTY_ETH = 50 * (10 ** 18);
    uint256 constant HUNDRED_AND_FIFTY_ETH = 150 * (10 ** 18);
    uint256 constant TWO_HUNDRED_AND_FIFTY_ETH = 250 * (10 ** 18);
    uint256 constant TEN_ETH = 10 * (10 ** 18);

    EDUToken public token;
    event TokenWalletChanged(address indexed newTokenWallet);
    event WalletChanged(address indexed newWallet);

    constructor(
        address _wallet,
        EDUToken _token,
        address _tokenWallet,
        uint256 _cap,
        uint256 _openingTime,
        uint256 _closingTime,
        address _certifier
    ) public
      Crowdsale(getCurrentRate(), _wallet, _token)
      AllowanceCrowdsale(_tokenWallet)
      CappedCrowdsale(_cap)
      TimedCrowdsale(_openingTime, _closingTime)
      Certifiable(_certifier)
    {
        token = _token;
    }

    function _deliverTokens(address _beneficiary, uint256 _tokenAmount) internal {
        if (certifier.certified(_beneficiary)) {
            token.transferFrom(tokenWallet, _beneficiary, _tokenAmount);
        } else {
            token.delayedTransferFrom(tokenWallet, _beneficiary, _tokenAmount);
        }
    }

    /**
     * @dev Returns the rate of tokens per wei at the present time.
     * Note that, as price _increases_ with time, the rate _decreases_.
     * @return The number of tokens a buyer gets per wei at a given time
     */
    function getCurrentRate() public view returns (uint256) {
        if (block.timestamp < 1528156799) {         // 4th of June 2018 23:59:59 GTC
            return 1050;
        } else if (block.timestamp < 1528718400) {  // 11th of June 2018 12:00:00 GTC
            return 940;
        } else if (block.timestamp < 1529323200) {  // 18th of June 2018 12:00:00 GTC
            return 865;
        } else if (block.timestamp < 1529928000) {  // 25th of June 2018 12:00:00 GTC
            return 790;
        } else {
            return 750;
        }
    }

    /**
     * @dev Overrides parent method taking into account variable rate.
     * @param _weiAmount The value in wei to be converted into tokens
     * @return The number of tokens _weiAmount wei will buy at present time
     */
    function _getTokenAmount(uint256 _weiAmount) internal view returns (uint256)
    {
        uint256 currentRate = getCurrentRate();
        uint256 volumeBonus = _getVolumeBonus(currentRate, _weiAmount);
        return currentRate.mul(_weiAmount).add(volumeBonus);
    }

    function _getVolumeBonus(uint256 _currentRate, uint256 _weiAmount) internal view returns (uint256) {
        if (_weiAmount >= TEN_ETH) {
            return _currentRate.mul(_weiAmount).mul(20).div(100);
        }
        return 0;
    }

    function changeTokenWallet(address _tokenWallet) external onlyOwner {
        require(_tokenWallet != address(0x0));
        tokenWallet = _tokenWallet;
        emit TokenWalletChanged(_tokenWallet);
    }

    function changeWallet(address _wallet) external onlyOwner {
        require(_wallet != address(0x0));
        wallet = _wallet;
        emit WalletChanged(_wallet);
    }

}