pragma solidity ^0.5.2;

/**
 * @dev Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     * - Subtraction cannot overflow.
     *
     * _Available since v2.4.0._
     */
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;

        return c;
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return div(a, b, "SafeMath: division by zero");
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     *
     * _Available since v2.4.0._
     */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        // Solidity only automatically asserts when dividing by 0
        require(b > 0, errorMessage);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return mod(a, b, "SafeMath: modulo by zero");
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts with custom message when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     *
     * _Available since v2.4.0._
     */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}

/*
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with GSN meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
contract Context {
    // Empty internal constructor, to prevent people from mistakenly deploying
    // an instance of this contract, which should be used via inheritance.
    constructor () internal { }
    // solhint-disable-previous-line no-empty-blocks

    function _msgSender() internal view returns (address payable) {
        return msg.sender;
    }

    function _msgData() internal view returns (bytes memory) {
        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
        return msg.data;
    }
}

/**
 * @dev Interface of the ERC20 standard as defined in the EIP. Does not include
 * the optional functions; to access them see {ERC20Detailed}.
 */
interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Moves `amount` tokens from the caller's account to `recipient`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: 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
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `sender` to `recipient` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);
}

/**
 * @dev Implementation of the {IERC20} interface.
 *
 * This implementation is agnostic to the way tokens are created. This means
 * that a supply mechanism has to be added in a derived contract using {_mint}.
 * For a generic mechanism see {ERC20Mintable}.
 *
 * TIP: For a detailed writeup see our guide
 * https://forum.zeppelin.solutions/t/how-to-implement-erc20-supply-mechanisms/226[How
 * to implement supply mechanisms].
 *
 * We have followed general OpenZeppelin guidelines: functions revert instead
 * of returning `false` on failure. This behavior is nonetheless conventional
 * and does not conflict with the expectations of ERC20 applications.
 *
 * Additionally, an {Approval} event is emitted on calls to {transferFrom}.
 * This allows applications to reconstruct the allowance for all accounts just
 * by listening to said events. Other implementations of the EIP may not emit
 * these events, as it isn't required by the specification.
 *
 * Finally, the non-standard {decreaseAllowance} and {increaseAllowance}
 * functions have been added to mitigate the well-known issues around setting
 * allowances. See {IERC20-approve}.
 */
contract ERC20 is Context, IERC20 {
    using SafeMath for uint256;

    mapping (address => uint256) private _balances;

    mapping (address => mapping (address => uint256)) private _allowances;

    uint256 private _totalSupply;

    /**
     * @dev See {IERC20-totalSupply}.
     */
    function totalSupply() public view returns (uint256) {
        return _totalSupply;
    }

    /**
     * @dev See {IERC20-balanceOf}.
     */
    function balanceOf(address account) public view returns (uint256) {
        return _balances[account];
    }

    /**
     * @dev See {IERC20-transfer}.
     *
     * Requirements:
     *
     * - `recipient` cannot be the zero address.
     * - the caller must have a balance of at least `amount`.
     */
    function transfer(address recipient, uint256 amount) public returns (bool) {
        _transfer(_msgSender(), recipient, amount);
        return true;
    }

    /**
     * @dev See {IERC20-allowance}.
     */
    function allowance(address owner, address spender) public view returns (uint256) {
        return _allowances[owner][spender];
    }

    /**
     * @dev See {IERC20-approve}.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function approve(address spender, uint256 amount) public returns (bool) {
        _approve(_msgSender(), spender, amount);
        return true;
    }

    /**
     * @dev See {IERC20-transferFrom}.
     *
     * Emits an {Approval} event indicating the updated allowance. This is not
     * required by the EIP. See the note at the beginning of {ERC20};
     *
     * Requirements:
     * - `sender` and `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     * - the caller must have allowance for `sender`'s tokens of at least
     * `amount`.
     */
    function transferFrom(address sender, address recipient, uint256 amount) public returns (bool) {
        _transfer(sender, recipient, amount);
        _approve(sender, _msgSender(), _allowances[sender][_msgSender()].sub(amount, "ERC20: transfer amount exceeds allowance"));
        return true;
    }

    /**
     * @dev Atomically increases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function increaseAllowance(address spender, uint256 addedValue) public returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].add(addedValue));
        return true;
    }

    /**
     * @dev Atomically decreases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     * - `spender` must have allowance for the caller of at least
     * `subtractedValue`.
     */
    function decreaseAllowance(address spender, uint256 subtractedValue) public returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].sub(subtractedValue, "ERC20: decreased allowance below zero"));
        return true;
    }

    /**
     * @dev Moves tokens `amount` from `sender` to `recipient`.
     *
     * This is internal function is equivalent to {transfer}, and can be used to
     * e.g. implement automatic token fees, slashing mechanisms, etc.
     *
     * Emits a {Transfer} event.
     *
     * Requirements:
     *
     * - `sender` cannot be the zero address.
     * - `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     */
    function _transfer(address sender, address recipient, uint256 amount) internal {
        require(sender != address(0), "ERC20: transfer from the zero address");
        require(recipient != address(0), "ERC20: transfer to the zero address");

        _balances[sender] = _balances[sender].sub(amount, "ERC20: transfer amount exceeds balance");
        _balances[recipient] = _balances[recipient].add(amount);
        emit Transfer(sender, recipient, amount);
    }

    /** @dev Creates `amount` tokens and assigns them to `account`, increasing
     * the total supply.
     *
     * Emits a {Transfer} event with `from` set to the zero address.
     *
     * Requirements
     *
     * - `to` cannot be the zero address.
     */
    function _mint(address account, uint256 amount) internal {
        require(account != address(0), "ERC20: mint to the zero address");

        _totalSupply = _totalSupply.add(amount);
        _balances[account] = _balances[account].add(amount);
        emit Transfer(address(0), account, amount);
    }

    /**
     * @dev Destroys `amount` tokens from `account`, reducing the
     * total supply.
     *
     * Emits a {Transfer} event with `to` set to the zero address.
     *
     * Requirements
     *
     * - `account` cannot be the zero address.
     * - `account` must have at least `amount` tokens.
     */
    function _burn(address account, uint256 amount) internal {
        require(account != address(0), "ERC20: burn from the zero address");

        _balances[account] = _balances[account].sub(amount, "ERC20: burn amount exceeds balance");
        _totalSupply = _totalSupply.sub(amount);
        emit Transfer(account, address(0), amount);
    }

    /**
     * @dev Sets `amount` as the allowance of `spender` over the `owner`s tokens.
     *
     * This is internal function is equivalent to `approve`, and can be used to
     * e.g. set automatic allowances for certain subsystems, etc.
     *
     * Emits an {Approval} event.
     *
     * Requirements:
     *
     * - `owner` cannot be the zero address.
     * - `spender` cannot be the zero address.
     */
    function _approve(address owner, address spender, uint256 amount) internal {
        require(owner != address(0), "ERC20: approve from the zero address");
        require(spender != address(0), "ERC20: approve to the zero address");

        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }

    /**
     * @dev Destroys `amount` tokens from `account`.`amount` is then deducted
     * from the caller's allowance.
     *
     * See {_burn} and {_approve}.
     */
    function _burnFrom(address account, uint256 amount) internal {
        _burn(account, amount);
        _approve(account, _msgSender(), _allowances[account][_msgSender()].sub(amount, "ERC20: burn amount exceeds allowance"));
    }
}

/**
 * @title SafeMathUint
 * @dev Math operations with safety checks that revert on error
 */
library SafeMathUint {
  function toInt256Safe(uint256 a) internal pure returns (int256) {
    int256 b = int256(a);
    require(b >= 0);
    return b;
  }
}

/**
 * @title SafeMathInt
 * @dev Math operations with safety checks that revert on error
 * @dev SafeMath adapted for int256
 * Based on code of  https://github.com/RequestNetwork/requestNetwork/blob/master/packages/requestNetworkSmartContracts/contracts/base/math/SafeMathInt.sol
 */
library SafeMathInt {
  function mul(int256 a, int256 b) internal pure returns (int256) {
    // Prevent overflow when multiplying INT256_MIN with -1
    // https://github.com/RequestNetwork/requestNetwork/issues/43
    require(!(a == - 2**255 && b == -1) && !(b == - 2**255 && a == -1));

    int256 c = a * b;
    require((b == 0) || (c / b == a));
    return c;
  }

  function div(int256 a, int256 b) internal pure returns (int256) {
    // Prevent overflow when dividing INT256_MIN by -1
    // https://github.com/RequestNetwork/requestNetwork/issues/43
    require(!(a == - 2**255 && b == -1) && (b > 0));

    return a / b;
  }

  function sub(int256 a, int256 b) internal pure returns (int256) {
    require((b >= 0 && a - b <= a) || (b < 0 && a - b > a));

    return a - b;
  }

  function add(int256 a, int256 b) internal pure returns (int256) {
    int256 c = a + b;
    require((b >= 0 && c >= a) || (b < 0 && c < a));
    return c;
  }

  function toUint256Safe(int256 a) internal pure returns (uint256) {
    require(a >= 0);
    return uint256(a);
  }
}

interface IFundsDistributionToken {

	/**
	 * @dev Returns the total amount of funds a given address is able to withdraw currently.
	 * @param owner Address of FundsDistributionToken holder
	 * @return A uint256 representing the available funds for a given account
	 */
	function withdrawableFundsOf(address owner) external view returns (uint256);

	/**
	 * @dev Withdraws all available funds for a FundsDistributionToken holder.
	 */
	function withdrawFunds() external;

	/**
	 * @dev This event emits when new funds are distributed
	 * @param by the address of the sender who distributed funds
	 * @param fundsDistributed the amount of funds received for distribution
	 */
	event FundsDistributed(address indexed by, uint256 fundsDistributed);

	/**
	 * @dev This event emits when distributed funds are withdrawn by a token holder.
	 * @param by the address of the receiver of funds
	 * @param fundsWithdrawn the amount of funds that were withdrawn
	 */
	event FundsWithdrawn(address indexed by, uint256 fundsWithdrawn);
}

/**
 * @dev Optional functions from the ERC20 standard.
 */
contract ERC20Detailed is IERC20 {
    string private _name;
    string private _symbol;
    uint8 private _decimals;

    /**
     * @dev Sets the values for `name`, `symbol`, and `decimals`. All three of
     * these values are immutable: they can only be set once during
     * construction.
     */
    constructor (string memory name, string memory symbol, uint8 decimals) public {
        _name = name;
        _symbol = symbol;
        _decimals = decimals;
    }

    /**
     * @dev Returns the name of the token.
     */
    function name() public view returns (string memory) {
        return _name;
    }

    /**
     * @dev Returns the symbol of the token, usually a shorter version of the
     * name.
     */
    function symbol() public view returns (string memory) {
        return _symbol;
    }

    /**
     * @dev Returns the number of decimals used to get its user representation.
     * For example, if `decimals` equals `2`, a balance of `505` tokens should
     * be displayed to a user as `5,05` (`505 / 10 ** 2`).
     *
     * Tokens usually opt for a value of 18, imitating the relationship between
     * Ether and Wei.
     *
     * > Note that this information is only used for _display_ purposes: it in
     * no way affects any of the arithmetic of the contract, including
     * `IERC20.balanceOf` and `IERC20.transfer`.
     */
    function decimals() public view returns (uint8) {
        return _decimals;
    }
}

/** 
 * @title FundsDistributionToken
 * @author Johannes Escherich
 * @author Roger-Wu
 * @author Johannes Pfeffer
 * @author Tom Lam
 * @dev A  mintable token that can represent claims on cash flow of arbitrary assets such as dividends, loan repayments, 
 * fee or revenue shares among large numbers of token holders. Anyone can deposit funds, token holders can withdraw 
 * their claims.
 * FundsDistributionToken (FDT) implements the accounting logic. FDT-Extension contracts implement methods for depositing and 
 * withdrawing funds in Ether or according to a token standard such as ERC20, ERC223, ERC777.
 */
contract FundsDistributionToken is IFundsDistributionToken, ERC20Detailed, ERC20 {

	using SafeMath for uint256;
	using SafeMathUint for uint256;
	using SafeMathInt for int256;

	// optimize, see https://github.com/ethereum/EIPs/issues/1726#issuecomment-472352728
	uint256 constant internal pointsMultiplier = 2**128;
	uint256 internal pointsPerShare;

	mapping(address => int256) internal pointsCorrection;
	mapping(address => uint256) internal withdrawnFunds;

	constructor (
		string memory name, 
		string memory symbol
	) 
		public 
		ERC20Detailed(name, symbol, 18) 
	{}

	/** 
	 * prev. distributeDividends
	 * @notice Distributes funds to token holders.
	 * @dev It reverts if the total supply of tokens is 0.
	 * It emits the `FundsDistributed` event if the amount of received ether is greater than 0.
	 * About undistributed funds:
	 *   In each distribution, there is a small amount of funds which does not get distributed,
	 *     which is `(msg.value * pointsMultiplier) % totalSupply()`.
	 *   With a well-chosen `pointsMultiplier`, the amount funds that are not getting distributed
	 *     in a distribution can be less than 1 (base unit).
	 *   We can actually keep track of the undistributed ether in a distribution
	 *     and try to distribute it in the next distribution ....... todo implement  
	 */
	function _distributeFunds(uint256 value) internal {
		require(totalSupply() > 0, "FundsDistributionToken._distributeFunds: SUPPLY_IS_ZERO");

		if (value > 0) {
			pointsPerShare = pointsPerShare.add(
				value.mul(pointsMultiplier) / totalSupply()
			);
			emit FundsDistributed(msg.sender, value);
		}
	}

	/**
	 * prev. withdrawDividend
	 * @notice Prepares funds withdrawal
	 * @dev It emits a `FundsWithdrawn` event if the amount of withdrawn ether is greater than 0.
	 */
	function _prepareWithdraw() internal returns (uint256) {
		uint256 _withdrawableDividend = withdrawableFundsOf(msg.sender);

		withdrawnFunds[msg.sender] = withdrawnFunds[msg.sender].add(_withdrawableDividend);

		emit FundsWithdrawn(msg.sender, _withdrawableDividend);

		return _withdrawableDividend;
	}

	/** 
	 * prev. withdrawableDividendOf
	 * @notice View the amount of funds that an address can withdraw.
	 * @param _owner The address of a token holder.
	 * @return The amount funds that `_owner` can withdraw.
	 */
	function withdrawableFundsOf(address _owner) public view returns(uint256) {
		return accumulativeFundsOf(_owner).sub(withdrawnFunds[_owner]);
	}

	/**
	 * prev. withdrawnDividendOf
	 * @notice View the amount of funds that an address has withdrawn.
	 * @param _owner The address of a token holder.
	 * @return The amount of funds that `_owner` has withdrawn.
	 */
	function withdrawnFundsOf(address _owner) public view returns(uint256) {
		return withdrawnFunds[_owner];
	}

	/**
	 * prev. accumulativeDividendOf
	 * @notice View the amount of funds that an address has earned in total.
	 * @dev accumulativeFundsOf(_owner) = withdrawableFundsOf(_owner) + withdrawnFundsOf(_owner)
	 * = (pointsPerShare * balanceOf(_owner) + pointsCorrection[_owner]) / pointsMultiplier
	 * @param _owner The address of a token holder.
	 * @return The amount of funds that `_owner` has earned in total.
	 */
	function accumulativeFundsOf(address _owner) public view returns(uint256) {
		return pointsPerShare.mul(balanceOf(_owner)).toInt256Safe()
			.add(pointsCorrection[_owner]).toUint256Safe() / pointsMultiplier;
	}

	/**
	 * @dev Internal function that transfer tokens from one address to another.
	 * Update pointsCorrection to keep funds unchanged.
	 * @param from The address to transfer from.
	 * @param to The address to transfer to.
	 * @param value The amount to be transferred.
	 */
	function _transfer(address from, address to, uint256 value) internal {
		super._transfer(from, to, value);

		int256 _magCorrection = pointsPerShare.mul(value).toInt256Safe();
		pointsCorrection[from] = pointsCorrection[from].add(_magCorrection);
		pointsCorrection[to] = pointsCorrection[to].sub(_magCorrection);
	}

	/**
	 * @dev Internal function that mints tokens to an account.
	 * Update pointsCorrection to keep funds unchanged.
	 * @param account The account that will receive the created tokens.
	 * @param value The amount that will be created.
	 */
	function _mint(address account, uint256 value) internal {
		super._mint(account, value);

		pointsCorrection[account] = pointsCorrection[account]
			.sub( (pointsPerShare.mul(value)).toInt256Safe() );
	}

	/** 
	 * @dev Internal function that burns an amount of the token of a given account.
	 * Update pointsCorrection to keep funds unchanged.
	 * @param account The account whose tokens will be burnt.
	 * @param value The amount that will be burnt.
	 */
	function _burn(address account, uint256 value) internal {
		super._burn(account, value);

		pointsCorrection[account] = pointsCorrection[account]
			.add( (pointsPerShare.mul(value)).toInt256Safe() );
	}
}

contract FDT_ERC20Extension_LTD is IFundsDistributionToken, FundsDistributionToken {

	using SafeMathUint for uint256;
	using SafeMathInt for int256;

	// token in which the funds can be sent to the FundsDistributionToken
	IERC20 public fundsToken;
	
	// balance of fundsToken that the FundsDistributionToken currently holds
	uint256 public fundsTokenBalance;
	
	// address that receives initialized token supply
	address private initialOwner;

	modifier onlyFundsToken () {
		require(msg.sender == address(fundsToken), "FDT_ERC20Extension_LTD.onlyFundsToken: UNAUTHORIZED_SENDER");
		_;
	}

	constructor(
		string memory name, 
		string memory symbol,
		IERC20 _fundsToken,
		address _initialOwner
	) 
		public 
		FundsDistributionToken(name, symbol)
	{
		require(address(_fundsToken) != address(0), "FDT_ERC20Extension_LTD: INVALID_FUNDS_TOKEN_ADDRESS");

		fundsToken = _fundsToken;
		initialOwner = _initialOwner;
		
		_mint(initialOwner, 100000000000000000000);
	}

	/**
	 * @notice Withdraws all available funds for a token holder
	 */
	function withdrawFunds() 
		external 
	{
		uint256 withdrawableFunds = _prepareWithdraw();

		require(fundsToken.transfer(msg.sender, withdrawableFunds), "FDT_ERC20Extension_LTD.withdrawFunds: TRANSFER_FAILED");

		_updateFundsTokenBalance();
	}

	/**
	 * @dev Updates the current funds token balance 
	 * and returns the difference of new and previous funds token balances
	 * @return A int256 representing the difference of the new and previous funds token balance
	 */
	function _updateFundsTokenBalance() internal returns (int256) {
		uint256 prevFundsTokenBalance = fundsTokenBalance;

		fundsTokenBalance = fundsToken.balanceOf(address(this));

		return int256(fundsTokenBalance).sub(int256(prevFundsTokenBalance));
	}

	/**
	 * @notice Register a payment of funds in tokens. May be called directly after a deposit is made.
	 * @dev Calls _updateFundsTokenBalance(), whereby the contract computes the delta of the previous and the new 
	 * funds token balance and increments the total received funds (cumulative) by delta by calling _registerFunds()
	 */
	function updateFundsReceived() external {
		int256 newFunds = _updateFundsTokenBalance();

		if (newFunds > 0) {
			_distributeFunds(newFunds.toUint256Safe());
		}
	}
}