contract DividendToken is IERC20, CanReclaimToken {

    string public name;                //The Token's name: e.g. DigixDAO Tokens
    uint8 public decimals;             //Number of decimals of the smallest unit
    string public symbol;              //An identifier: e.g. REP

    /// @dev `Checkpoint` is the structure that attaches a block number to a
    ///  given value, the block number attached is the one that last changed the
    ///  value
    struct  Checkpoint {

        // `fromBlock` is the block number that the value was generated from
        uint128 fromBlock;

        // `value` is the amount of tokens at a specific block number
        uint128 value;
    }

    // `parentToken` is the Token address that was cloned to produce this token;
    //  it will be 0x0 for a token that was not cloned
    DividendToken public parentToken;

    // `parentSnapShotBlock` is the block number from the Parent Token that was
    //  used to determine the initial distribution of the Clone Token
    uint public parentSnapShotBlock;

    // `creationBlock` is the block number that the Clone Token was created
    uint public creationBlock;

    // `balances` is the map that tracks the balance of each address, in this
    //  contract when the balance changes the block number that the change
    //  occurred is also included in the map
    mapping (address => Checkpoint[]) balances;

    // `allowed` tracks any extra transfer rights as in all ERC20 tokens
    mapping (address => mapping (address => uint256)) allowed;

    // Tracks the history of the `totalSupply` of the token
    Checkpoint[] totalSupplyHistory;


    ////////////////
    // Constructor
    ////////////////

    /// @param _parentToken Address of the parent token, set to 0x0 if it is a
    ///  new token
    /// @param _parentSnapShotBlock Block of the parent token that will
    ///  determine the initial distribution of the clone token, set to 0 if it
    ///  is a new token
    constructor (address _parentToken, uint _parentSnapShotBlock) public {
        name = "Holddapp Dividend Token";
        symbol = "HDT";
        decimals = 6;
        parentToken = DividendToken(_parentToken);
        parentSnapShotBlock = _parentSnapShotBlock == 0 ? block.number : _parentSnapShotBlock;
        creationBlock = block.number;

        //initial emission
        uint _amount = 380000 * (10 ** uint256(decimals));
        updateValueAtNow(totalSupplyHistory, _amount);
        updateValueAtNow(balances[msg.sender], _amount);
        emit Transfer(address(0), msg.sender, _amount);
    }

    /// @notice The fallback function
    function () external {}


    ///////////////////
    // ERC20 Methods
    ///////////////////

    /// @notice Send `_amount` tokens to `_to` from `msg.sender`
    /// @param _to The address of the recipient
    /// @param _amount The amount of tokens to be transferred
    /// @return Whether the transfer was successful or not
    function transfer(address _to, uint256 _amount) external returns (bool success) {
        doTransfer(msg.sender, _to, _amount);
        return true;
    }

    /// @notice Send `_amount` tokens to `_to` from `_from` on the condition it
    ///  is approved by `_from`
    /// @param _from The address holding the tokens being transferred
    /// @param _to The address of the recipient
    /// @param _amount The amount of tokens to be transferred
    /// @return True if the transfer was successful
    function transferFrom(address _from, address _to, uint256 _amount) external returns (bool success) {
        // The standard ERC 20 transferFrom functionality
        require(allowed[_from][msg.sender] >= _amount);
        allowed[_from][msg.sender] -= _amount;
        doTransfer(_from, _to, _amount);
        return true;
    }

    /// @dev This is the actual transfer function in the token contract, it can
    ///  only be called by other functions in this contract.
    /// @param _from The address holding the tokens being transferred
    /// @param _to The address of the recipient
    /// @param _amount The amount of tokens to be transferred
    /// @return True if the transfer was successful
    function doTransfer(address _from, address _to, uint _amount) internal {

        if (_amount == 0) {
            emit Transfer(_from, _to, _amount);    // Follow the spec to louch the event when transfer 0
            return;
        }

        require(parentSnapShotBlock < block.number);

        // Do not allow transfer to 0x0 or the token contract itself
        require((_to != address(0)) && (_to != address(this)));

        // If the amount being transfered is more than the balance of the
        //  account the transfer throws
        uint previousBalanceFrom = balanceOfAt(_from, block.number);

        require(previousBalanceFrom >= _amount);

        // First update the balance array with the new value for the address
        //  sending the tokens
        updateValueAtNow(balances[_from], previousBalanceFrom - _amount);

        // Then update the balance array with the new value for the address
        //  receiving the tokens
        uint previousBalanceTo = balanceOfAt(_to, block.number);
        require(previousBalanceTo + _amount >= previousBalanceTo); // Check for overflow
        updateValueAtNow(balances[_to], previousBalanceTo + _amount);

        // An event to make the transfer easy to find on the blockchain
        emit Transfer(_from, _to, _amount);

    }

    /// @param _owner The address that's balance is being requested
    /// @return The balance of `_owner` at the current block
    function balanceOf(address _owner) public view returns (uint256 balance) {
        return balanceOfAt(_owner, block.number);
    }

    /// @notice `msg.sender` approves `_spender` to spend `_amount` tokens on
    ///  its behalf. This is a modified version of the ERC20 approve function
    ///  to be a little bit safer
    /// @param _spender The address of the account able to transfer the tokens
    /// @param _amount The amount of tokens to be approved for transfer
    /// @return True if the approval was successful
    function approve(address _spender, uint256 _amount) public returns (bool success) {
        // 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((_amount == 0) || (allowed[msg.sender][_spender] == 0));

        allowed[msg.sender][_spender] = _amount;
        emit Approval(msg.sender, _spender, _amount);
        return true;
    }

    /**
     * @dev Increase the amount of tokens that an owner allowed to a spender.
     *
     * approve should be called when allowance[_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 _addedAmount The amount of tokens to increase the allowance by.
     */
    function increaseApproval(address _spender, uint _addedAmount) external returns (bool) {
        require(allowed[msg.sender][_spender] + _addedAmount >= allowed[msg.sender][_spender]); // Check for overflow
        allowed[msg.sender][_spender] = allowed[msg.sender][_spender] + _addedAmount;
        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 allowance[_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 _subtractedAmount The amount of tokens to decrease the allowance by.
     */
    function decreaseApproval(address _spender, uint _subtractedAmount) external returns (bool)
    {
        uint oldValue = allowed[msg.sender][_spender];
        if (_subtractedAmount >= oldValue) {
            allowed[msg.sender][_spender] = 0;
        } else {
            allowed[msg.sender][_spender] = oldValue - _subtractedAmount;
        }
        emit Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
        return true;
    }


    /// @dev This function makes it easy to read the `allowed[]` map
    /// @param _owner The address of the account that owns the token
    /// @param _spender The address of the account able to transfer the tokens
    /// @return Amount of remaining tokens of _owner that _spender is allowed
    ///  to spend
    function allowance(address _owner, address _spender) external view returns (uint256 remaining) {
        return allowed[_owner][_spender];
    }


    /// @dev This function makes it easy to get the total number of tokens
    /// @return The total number of tokens
    function totalSupply() public view returns (uint) {
        return totalSupplyAt(block.number);
    }


    ////////////////
    // Query balance and totalSupply in History
    ////////////////

    /// @dev Queries the balance of `_owner` at a specific `_blockNumber`
    /// @param _owner The address from which the balance will be retrieved
    /// @param _blockNumber The block number when the balance is queried
    /// @return The balance at `_blockNumber`
    function balanceOfAt(address _owner, uint _blockNumber) public view returns (uint) {

        // These next few lines are used when the balance of the token is
        //  requested before a check point was ever created for this token, it
        //  requires that the `parentToken.balanceOfAt` be queried at the
        //  genesis block for that token as this contains initial balance of
        //  this token
        if ((balances[_owner].length == 0)
            || (balances[_owner][0].fromBlock > _blockNumber)) {
            if (address(parentToken) != address(0)) {
                return parentToken.balanceOfAt(_owner, min(_blockNumber, parentSnapShotBlock));
            } else {
                // Has no parent
                return 0;
            }

            // This will return the expected balance during normal situations
        } else {
            return getValueAt(balances[_owner], _blockNumber);
        }
    }

    /// @notice Total amount of tokens at a specific `_blockNumber`.
    /// @param _blockNumber The block number when the totalSupply is queried
    /// @return The total amount of tokens at `_blockNumber`
    function totalSupplyAt(uint _blockNumber) public view returns(uint) {

        // These next few lines are used when the totalSupply of the token is
        //  requested before a check point was ever created for this token, it
        //  requires that the `parentToken.totalSupplyAt` be queried at the
        //  genesis block for this token as that contains totalSupply of this
        //  token at this block number.
        if ((totalSupplyHistory.length == 0)
            || (totalSupplyHistory[0].fromBlock > _blockNumber)) {
            if (address(parentToken) != address(0)) {
                return parentToken.totalSupplyAt(min(_blockNumber, parentSnapShotBlock));
            } else {
                return 0;
            }

            // This will return the expected totalSupply during normal situations
        } else {
            return getValueAt(totalSupplyHistory, _blockNumber);
        }
    }


   

    ////////////////
    // Internal helper functions to query and set a value in a snapshot array
    ////////////////

    /// @dev `getValueAt` retrieves the number of tokens at a given block number
    /// @param checkpoints The history of values being queried
    /// @param _block The block number to retrieve the value at
    /// @return The number of tokens being queried
    function getValueAt(Checkpoint[] storage checkpoints, uint _block) view internal returns (uint) {
        if (checkpoints.length == 0) return 0;

        // Shortcut for the actual value
        if (_block >= checkpoints[checkpoints.length-1].fromBlock)
            return checkpoints[checkpoints.length-1].value;
        if (_block < checkpoints[0].fromBlock) return 0;

        // Binary search of the value in the array
        uint min = 0;
        uint max = checkpoints.length-1;
        while (max > min) {
            uint mid = (max + min + 1)/ 2;
            if (checkpoints[mid].fromBlock<=_block) {
                min = mid;
            } else {
                max = mid-1;
            }
        }
        return checkpoints[min].value;
    }

    /// @dev `updateValueAtNow` used to update the `balances` map and the
    ///  `totalSupplyHistory`
    /// @param checkpoints The history of data being updated
    /// @param _value The new number of tokens
    function updateValueAtNow(Checkpoint[] storage checkpoints, uint _value) internal  {
        if ((checkpoints.length == 0)
            || (checkpoints[checkpoints.length -1].fromBlock < block.number)) {
            Checkpoint storage newCheckPoint = checkpoints[ checkpoints.length++ ];
            newCheckPoint.fromBlock =  uint128(block.number);
            newCheckPoint.value = uint128(_value);
        } else {
            Checkpoint storage oldCheckPoint = checkpoints[checkpoints.length-1];
            oldCheckPoint.value = uint128(_value);
        }
    }


    /// @dev Helper function to return a min betwen the two uints
    function min(uint a, uint b) pure internal returns (uint) {
        return a < b ? a : b;
    }


}
/// @dev The actual token contract, the default owner is the msg.sender
function totalSupply() public view returns (uint) {
        return totalSupplyAt(block.number);
    }
/// @dev This function makes it easy to get the total number of tokens
/// @return The total number of tokens