XNeutroToken.sol

// File: src/tokens/interfaces/IXNeutroTokenUsage.sol


pragma solidity =0.7.6;

interface IXNeutroTokenUsage {
    function allocate(
        address userAddress,
        uint256 amount,
        bytes calldata data
    ) external;

    function deallocate(
        address userAddress,
        uint256 amount,
        bytes calldata data
    ) external;
}

// File: https://github.com/OpenZeppelin/openzeppelin-contracts/blob/solc-0.7/contracts/utils/ReentrancyGuard.sol



pragma solidity ^0.7.0;

/**
 * @dev Contract module that helps prevent reentrant calls to a function.
 *
 * Inheriting from `ReentrancyGuard` will make the {nonReentrant} modifier
 * available, which can be applied to functions to make sure there are no nested
 * (reentrant) calls to them.
 *
 * Note that because there is a single `nonReentrant` guard, functions marked as
 * `nonReentrant` may not call one another. This can be worked around by making
 * those functions `private`, and then adding `external` `nonReentrant` entry
 * points to them.
 *
 * TIP: If you would like to learn more about reentrancy and alternative ways
 * to protect against it, check out our blog post
 * https://blog.openzeppelin.com/reentrancy-after-istanbul/[Reentrancy After Istanbul].
 */
abstract contract ReentrancyGuard {
    // Booleans are more expensive than uint256 or any type that takes up a full
    // word because each write operation emits an extra SLOAD to first read the
    // slot's contents, replace the bits taken up by the boolean, and then write
    // back. This is the compiler's defense against contract upgrades and
    // pointer aliasing, and it cannot be disabled.

    // The values being non-zero value makes deployment a bit more expensive,
    // but in exchange the refund on every call to nonReentrant will be lower in
    // amount. Since refunds are capped to a percentage of the total
    // transaction's gas, it is best to keep them low in cases like this one, to
    // increase the likelihood of the full refund coming into effect.
    uint256 private constant _NOT_ENTERED = 1;
    uint256 private constant _ENTERED = 2;

    uint256 private _status;

    constructor () {
        _status = _NOT_ENTERED;
    }

    /**
     * @dev Prevents a contract from calling itself, directly or indirectly.
     * Calling a `nonReentrant` function from another `nonReentrant`
     * function is not supported. It is possible to prevent this from happening
     * by making the `nonReentrant` function external, and make it call a
     * `private` function that does the actual work.
     */
    modifier nonReentrant() {
        // On the first call to nonReentrant, _notEntered will be true
        require(_status != _ENTERED, "ReentrancyGuard: reentrant call");

        // Any calls to nonReentrant after this point will fail
        _status = _ENTERED;

        _;

        // By storing the original value once again, a refund is triggered (see
        // https://eips.ethereum.org/EIPS/eip-2200)
        _status = _NOT_ENTERED;
    }
}

// File: https://github.com/OpenZeppelin/openzeppelin-contracts/blob/solc-0.7/contracts/utils/EnumerableSet.sol



pragma solidity ^0.7.0;

/**
 * @dev Library for managing
 * https://en.wikipedia.org/wiki/Set_(abstract_data_type)[sets] of primitive
 * types.
 *
 * Sets have the following properties:
 *
 * - Elements are added, removed, and checked for existence in constant time
 * (O(1)).
 * - Elements are enumerated in O(n). No guarantees are made on the ordering.
 *
 * ```
 * contract Example {
 *     // Add the library methods
 *     using EnumerableSet for EnumerableSet.AddressSet;
 *
 *     // Declare a set state variable
 *     EnumerableSet.AddressSet private mySet;
 * }
 * ```
 *
 * As of v3.3.0, sets of type `bytes32` (`Bytes32Set`), `address` (`AddressSet`)
 * and `uint256` (`UintSet`) are supported.
 */
library EnumerableSet {
    // To implement this library for multiple types with as little code
    // repetition as possible, we write it in terms of a generic Set type with
    // bytes32 values.
    // The Set implementation uses private functions, and user-facing
    // implementations (such as AddressSet) are just wrappers around the
    // underlying Set.
    // This means that we can only create new EnumerableSets for types that fit
    // in bytes32.

    struct Set {
        // Storage of set values
        bytes32[] _values;

        // Position of the value in the `values` array, plus 1 because index 0
        // means a value is not in the set.
        mapping (bytes32 => uint256) _indexes;
    }

    /**
     * @dev Add a value to a set. O(1).
     *
     * Returns true if the value was added to the set, that is if it was not
     * already present.
     */
    function _add(Set storage set, bytes32 value) private returns (bool) {
        if (!_contains(set, value)) {
            set._values.push(value);
            // The value is stored at length-1, but we add 1 to all indexes
            // and use 0 as a sentinel value
            set._indexes[value] = set._values.length;
            return true;
        } else {
            return false;
        }
    }

    /**
     * @dev Removes a value from a set. O(1).
     *
     * Returns true if the value was removed from the set, that is if it was
     * present.
     */
    function _remove(Set storage set, bytes32 value) private returns (bool) {
        // We read and store the value's index to prevent multiple reads from the same storage slot
        uint256 valueIndex = set._indexes[value];

        if (valueIndex != 0) { // Equivalent to contains(set, value)
            // To delete an element from the _values array in O(1), we swap the element to delete with the last one in
            // the array, and then remove the last element (sometimes called as 'swap and pop').
            // This modifies the order of the array, as noted in {at}.

            uint256 toDeleteIndex = valueIndex - 1;
            uint256 lastIndex = set._values.length - 1;

            // When the value to delete is the last one, the swap operation is unnecessary. However, since this occurs
            // so rarely, we still do the swap anyway to avoid the gas cost of adding an 'if' statement.

            bytes32 lastvalue = set._values[lastIndex];

            // Move the last value to the index where the value to delete is
            set._values[toDeleteIndex] = lastvalue;
            // Update the index for the moved value
            set._indexes[lastvalue] = toDeleteIndex + 1; // All indexes are 1-based

            // Delete the slot where the moved value was stored
            set._values.pop();

            // Delete the index for the deleted slot
            delete set._indexes[value];

            return true;
        } else {
            return false;
        }
    }

    /**
     * @dev Returns true if the value is in the set. O(1).
     */
    function _contains(Set storage set, bytes32 value) private view returns (bool) {
        return set._indexes[value] != 0;
    }

    /**
     * @dev Returns the number of values on the set. O(1).
     */
    function _length(Set storage set) private view returns (uint256) {
        return set._values.length;
    }

   /**
    * @dev Returns the value stored at position `index` in the set. O(1).
    *
    * Note that there are no guarantees on the ordering of values inside the
    * array, and it may change when more values are added or removed.
    *
    * Requirements:
    *
    * - `index` must be strictly less than {length}.
    */
    function _at(Set storage set, uint256 index) private view returns (bytes32) {
        require(set._values.length > index, "EnumerableSet: index out of bounds");
        return set._values[index];
    }

    // Bytes32Set

    struct Bytes32Set {
        Set _inner;
    }

    /**
     * @dev Add a value to a set. O(1).
     *
     * Returns true if the value was added to the set, that is if it was not
     * already present.
     */
    function add(Bytes32Set storage set, bytes32 value) internal returns (bool) {
        return _add(set._inner, value);
    }

    /**
     * @dev Removes a value from a set. O(1).
     *
     * Returns true if the value was removed from the set, that is if it was
     * present.
     */
    function remove(Bytes32Set storage set, bytes32 value) internal returns (bool) {
        return _remove(set._inner, value);
    }

    /**
     * @dev Returns true if the value is in the set. O(1).
     */
    function contains(Bytes32Set storage set, bytes32 value) internal view returns (bool) {
        return _contains(set._inner, value);
    }

    /**
     * @dev Returns the number of values in the set. O(1).
     */
    function length(Bytes32Set storage set) internal view returns (uint256) {
        return _length(set._inner);
    }

   /**
    * @dev Returns the value stored at position `index` in the set. O(1).
    *
    * Note that there are no guarantees on the ordering of values inside the
    * array, and it may change when more values are added or removed.
    *
    * Requirements:
    *
    * - `index` must be strictly less than {length}.
    */
    function at(Bytes32Set storage set, uint256 index) internal view returns (bytes32) {
        return _at(set._inner, index);
    }

    // AddressSet

    struct AddressSet {
        Set _inner;
    }

    /**
     * @dev Add a value to a set. O(1).
     *
     * Returns true if the value was added to the set, that is if it was not
     * already present.
     */
    function add(AddressSet storage set, address value) internal returns (bool) {
        return _add(set._inner, bytes32(uint256(uint160(value))));
    }

    /**
     * @dev Removes a value from a set. O(1).
     *
     * Returns true if the value was removed from the set, that is if it was
     * present.
     */
    function remove(AddressSet storage set, address value) internal returns (bool) {
        return _remove(set._inner, bytes32(uint256(uint160(value))));
    }

    /**
     * @dev Returns true if the value is in the set. O(1).
     */
    function contains(AddressSet storage set, address value) internal view returns (bool) {
        return _contains(set._inner, bytes32(uint256(uint160(value))));
    }

    /**
     * @dev Returns the number of values in the set. O(1).
     */
    function length(AddressSet storage set) internal view returns (uint256) {
        return _length(set._inner);
    }

   /**
    * @dev Returns the value stored at position `index` in the set. O(1).
    *
    * Note that there are no guarantees on the ordering of values inside the
    * array, and it may change when more values are added or removed.
    *
    * Requirements:
    *
    * - `index` must be strictly less than {length}.
    */
    function at(AddressSet storage set, uint256 index) internal view returns (address) {
        return address(uint160(uint256(_at(set._inner, index))));
    }


    // UintSet

    struct UintSet {
        Set _inner;
    }

    /**
     * @dev Add a value to a set. O(1).
     *
     * Returns true if the value was added to the set, that is if it was not
     * already present.
     */
    function add(UintSet storage set, uint256 value) internal returns (bool) {
        return _add(set._inner, bytes32(value));
    }

    /**
     * @dev Removes a value from a set. O(1).
     *
     * Returns true if the value was removed from the set, that is if it was
     * present.
     */
    function remove(UintSet storage set, uint256 value) internal returns (bool) {
        return _remove(set._inner, bytes32(value));
    }

    /**
     * @dev Returns true if the value is in the set. O(1).
     */
    function contains(UintSet storage set, uint256 value) internal view returns (bool) {
        return _contains(set._inner, bytes32(value));
    }

    /**
     * @dev Returns the number of values on the set. O(1).
     */
    function length(UintSet storage set) internal view returns (uint256) {
        return _length(set._inner);
    }

   /**
    * @dev Returns the value stored at position `index` in the set. O(1).
    *
    * Note that there are no guarantees on the ordering of values inside the
    * array, and it may change when more values are added or removed.
    *
    * Requirements:
    *
    * - `index` must be strictly less than {length}.
    */
    function at(UintSet storage set, uint256 index) internal view returns (uint256) {
        return uint256(_at(set._inner, index));
    }
}

// File: https://github.com/OpenZeppelin/openzeppelin-contracts/blob/solc-0.7/contracts/utils/Address.sol



pragma solidity ^0.7.0;

/**
 * @dev Collection of functions related to the address type
 */
library Address {
    /**
     * @dev Returns true if `account` is a contract.
     *
     * [IMPORTANT]
     * ====
     * It is unsafe to assume that an address for which this function returns
     * false is an externally-owned account (EOA) and not a contract.
     *
     * Among others, `isContract` will return false for the following
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies on extcodesize, which returns 0 for contracts in
        // construction, since the code is only stored at the end of the
        // constructor execution.

        uint256 size;
        // solhint-disable-next-line no-inline-assembly
        assembly { size := extcodesize(account) }
        return size > 0;
    }

    /**
     * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
     * `recipient`, forwarding all available gas and reverting on errors.
     *
     * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
     * of certain opcodes, possibly making contracts go over the 2300 gas limit
     * imposed by `transfer`, making them unable to receive funds via
     * `transfer`. {sendValue} removes this limitation.
     *
     * https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
     *
     * IMPORTANT: because control is transferred to `recipient`, care must be
     * taken to not create reentrancy vulnerabilities. Consider using
     * {ReentrancyGuard} or the
     * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
     */
    function sendValue(address payable recipient, uint256 amount) internal {
        require(address(this).balance >= amount, "Address: insufficient balance");

        // solhint-disable-next-line avoid-low-level-calls, avoid-call-value
        (bool success, ) = recipient.call{ value: amount }("");
        require(success, "Address: unable to send value, recipient may have reverted");
    }

    /**
     * @dev Performs a Solidity function call using a low level `call`. A
     * plain`call` is an unsafe replacement for a function call: use this
     * function instead.
     *
     * If `target` reverts with a revert reason, it is bubbled up by this
     * function (like regular Solidity function calls).
     *
     * Returns the raw returned data. To convert to the expected return value,
     * use https://solidity.readthedocs.io/en/latest/units-and-global-variables.html?highlight=abi.decode#abi-encoding-and-decoding-functions[`abi.decode`].
     *
     * Requirements:
     *
     * - `target` must be a contract.
     * - calling `target` with `data` must not revert.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data) internal returns (bytes memory) {
      return functionCall(target, data, "Address: low-level call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`], but with
     * `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
        return functionCallWithValue(target, data, 0, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but also transferring `value` wei to `target`.
     *
     * Requirements:
     *
     * - the calling contract must have an ETH balance of at least `value`.
     * - the called Solidity function must be `payable`.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(address target, bytes memory data, uint256 value) internal returns (bytes memory) {
        return functionCallWithValue(target, data, value, "Address: low-level call with value failed");
    }

    /**
     * @dev Same as {xref-Address-functionCallWithValue-address-bytes-uint256-}[`functionCallWithValue`], but
     * with `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(address target, bytes memory data, uint256 value, string memory errorMessage) internal returns (bytes memory) {
        require(address(this).balance >= value, "Address: insufficient balance for call");
        require(isContract(target), "Address: call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.call{ value: value }(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(address target, bytes memory data) internal view returns (bytes memory) {
        return functionStaticCall(target, data, "Address: low-level static call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(address target, bytes memory data, string memory errorMessage) internal view returns (bytes memory) {
        require(isContract(target), "Address: static call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.staticcall(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(address target, bytes memory data) internal returns (bytes memory) {
        return functionDelegateCall(target, data, "Address: low-level delegate call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
        require(isContract(target), "Address: delegate call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.delegatecall(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    function _verifyCallResult(bool success, bytes memory returndata, string memory errorMessage) private pure returns(bytes memory) {
        if (success) {
            return returndata;
        } else {
            // Look for revert reason and bubble it up if present
            if (returndata.length > 0) {
                // The easiest way to bubble the revert reason is using memory via assembly

                // solhint-disable-next-line no-inline-assembly
                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }
}

// File: https://github.com/OpenZeppelin/openzeppelin-contracts/blob/solc-0.7/contracts/math/SafeMath.sol



pragma solidity ^0.7.0;

/**
 * @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, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryAdd(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        uint256 c = a + b;
        if (c < a) return (false, 0);
        return (true, c);
    }

    /**
     * @dev Returns the substraction of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function trySub(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b > a) return (false, 0);
        return (true, a - b);
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryMul(uint256 a, uint256 b) internal pure returns (bool, 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 (true, 0);
        uint256 c = a * b;
        if (c / a != b) return (false, 0);
        return (true, c);
    }

    /**
     * @dev Returns the division of two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryDiv(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b == 0) return (false, 0);
        return (true, a / b);
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryMod(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b == 0) return (false, 0);
        return (true, a % b);
    }

    /**
     * @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) {
        require(b <= a, "SafeMath: subtraction overflow");
        return a - b;
    }

    /**
     * @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) {
        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, reverting 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) {
        require(b > 0, "SafeMath: division by zero");
        return a / b;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting 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) {
        require(b > 0, "SafeMath: modulo by zero");
        return a % b;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {trySub}.
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        return a - b;
    }

    /**
     * @dev Returns the integer division of two unsigned integers, reverting with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryDiv}.
     *
     * 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, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        return a / b;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting with custom message when dividing by zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryMod}.
     *
     * 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, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        return a % b;
    }
}

// File: https://github.com/OpenZeppelin/openzeppelin-contracts/blob/solc-0.7/contracts/token/ERC20/IERC20.sol



pragma solidity ^0.7.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
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);
}

// File: src/tokens/interfaces/tokens/IXNeutroToken.sol


pragma solidity =0.7.6;

// import "@openzeppelin/contracts/token/ERC20/IERC20.sol";


interface IXNeutroToken is IERC20 {
    function usageAllocations(address userAddress, address usageAddress)
        external
        view
        returns (uint256 allocation);

    function allocateFromUsage(address userAddress, uint256 amount) external;

    function convertTo(uint256 amount, address to) external;

    function deallocateFromUsage(address userAddress, uint256 amount) external;

    function isTransferWhitelisted(address account)
        external
        view
        returns (bool);
}

// File: src/tokens/interfaces/tokens/INeutroTokenV2.sol


pragma solidity =0.7.6;

// import "@openzeppelin/contracts/token/ERC20/IERC20.sol";


interface INeutroTokenV2 is IERC20 {
    function lastEmissionTime() external view returns (uint256);

    function claimMasterRewards(uint256 amount)
        external
        returns (uint256 effectiveAmount);

    function masterEmissionRate() external view returns (uint256);

    function burn(uint256 amount) external;
}

// File: https://github.com/OpenZeppelin/openzeppelin-contracts/blob/solc-0.7/contracts/token/ERC20/SafeERC20.sol



pragma solidity ^0.7.0;




/**
 * @title SafeERC20
 * @dev Wrappers around ERC20 operations that throw on failure (when the token
 * contract returns false). Tokens that return no value (and instead revert or
 * throw on failure) are also supported, non-reverting calls are assumed to be
 * successful.
 * To use this library you can add a `using SafeERC20 for IERC20;` statement to your contract,
 * which allows you to call the safe operations as `token.safeTransfer(...)`, etc.
 */
library SafeERC20 {
    using SafeMath for uint256;
    using Address for address;

    function safeTransfer(IERC20 token, address to, uint256 value) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transfer.selector, to, value));
    }

    function safeTransferFrom(IERC20 token, address from, address to, uint256 value) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transferFrom.selector, from, to, value));
    }

    /**
     * @dev Deprecated. This function has issues similar to the ones found in
     * {IERC20-approve}, and its usage is discouraged.
     *
     * Whenever possible, use {safeIncreaseAllowance} and
     * {safeDecreaseAllowance} instead.
     */
    function safeApprove(IERC20 token, address spender, uint256 value) internal {
        // safeApprove should only be called when setting an initial allowance,
        // or when resetting it to zero. To increase and decrease it, use
        // 'safeIncreaseAllowance' and 'safeDecreaseAllowance'
        // solhint-disable-next-line max-line-length
        require((value == 0) || (token.allowance(address(this), spender) == 0),
            "SafeERC20: approve from non-zero to non-zero allowance"
        );
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, value));
    }

    function safeIncreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).add(value);
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    function safeDecreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).sub(value, "SafeERC20: decreased allowance below zero");
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    /**
     * @dev Imitates a Solidity high-level call (i.e. a regular function call to a contract), relaxing the requirement
     * on the return value: the return value is optional (but if data is returned, it must not be false).
     * @param token The token targeted by the call.
     * @param data The call data (encoded using abi.encode or one of its variants).
     */
    function _callOptionalReturn(IERC20 token, bytes memory data) private {
        // We need to perform a low level call here, to bypass Solidity's return data size checking mechanism, since
        // we're implementing it ourselves. We use {Address.functionCall} to perform this call, which verifies that
        // the target address contains contract code and also asserts for success in the low-level call.

        bytes memory returndata = address(token).functionCall(data, "SafeERC20: low-level call failed");
        if (returndata.length > 0) { // Return data is optional
            // solhint-disable-next-line max-line-length
            require(abi.decode(returndata, (bool)), "SafeERC20: ERC20 operation did not succeed");
        }
    }
}

// File: https://github.com/OpenZeppelin/openzeppelin-contracts/blob/solc-0.7/contracts/utils/Context.sol



pragma solidity >=0.6.0 <0.8.0;

/*
 * @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.
 */
abstract contract Context {
    function _msgSender() internal view virtual returns (address payable) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes memory) {
        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
        return msg.data;
    }
}

// File: https://github.com/OpenZeppelin/openzeppelin-contracts/blob/solc-0.7/contracts/token/ERC20/ERC20.sol



pragma solidity ^0.7.0;




/**
 * @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 {ERC20PresetMinterPauser}.
 *
 * 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;

    string private _name;
    string private _symbol;
    uint8 private _decimals;

    /**
     * @dev Sets the values for {name} and {symbol}, initializes {decimals} with
     * a default value of 18.
     *
     * To select a different value for {decimals}, use {_setupDecimals}.
     *
     * All three of these values are immutable: they can only be set once during
     * construction.
     */
    constructor (string memory name_, string memory symbol_) {
        _name = name_;
        _symbol = symbol_;
        _decimals = 18;
    }

    /**
     * @dev Returns the name of the token.
     */
    function name() public view virtual returns (string memory) {
        return _name;
    }

    /**
     * @dev Returns the symbol of the token, usually a shorter version of the
     * name.
     */
    function symbol() public view virtual 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. This is the value {ERC20} uses, unless {_setupDecimals} is
     * called.
     *
     * NOTE: 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 virtual returns (uint8) {
        return _decimals;
    }

    /**
     * @dev See {IERC20-totalSupply}.
     */
    function totalSupply() public view virtual override returns (uint256) {
        return _totalSupply;
    }

    /**
     * @dev See {IERC20-balanceOf}.
     */
    function balanceOf(address account) public view virtual override 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 virtual override returns (bool) {
        _transfer(_msgSender(), recipient, amount);
        return true;
    }

    /**
     * @dev See {IERC20-allowance}.
     */
    function allowance(address owner, address spender) public view virtual override returns (uint256) {
        return _allowances[owner][spender];
    }

    /**
     * @dev See {IERC20-approve}.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function approve(address spender, uint256 amount) public virtual override 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 virtual override 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 virtual 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 virtual 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 virtual {
        require(sender != address(0), "ERC20: transfer from the zero address");
        require(recipient != address(0), "ERC20: transfer to the zero address");

        _beforeTokenTransfer(sender, recipient, amount);

        _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 virtual {
        require(account != address(0), "ERC20: mint to the zero address");

        _beforeTokenTransfer(address(0), account, amount);

        _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 virtual {
        require(account != address(0), "ERC20: burn from the zero address");

        _beforeTokenTransfer(account, address(0), amount);

        _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 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 virtual {
        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 Sets {decimals} to a value other than the default one of 18.
     *
     * WARNING: This function should only be called from the constructor. Most
     * applications that interact with token contracts will not expect
     * {decimals} to ever change, and may work incorrectly if it does.
     */
    function _setupDecimals(uint8 decimals_) internal virtual {
        _decimals = decimals_;
    }

    /**
     * @dev Hook that is called before any transfer of tokens. This includes
     * minting and burning.
     *
     * Calling conditions:
     *
     * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
     * will be to transferred to `to`.
     * - when `from` is zero, `amount` tokens will be minted for `to`.
     * - when `to` is zero, `amount` of ``from``'s tokens will be burned.
     * - `from` and `to` are never both zero.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _beforeTokenTransfer(address from, address to, uint256 amount) internal virtual { }
}

// File: https://github.com/OpenZeppelin/openzeppelin-contracts/blob/solc-0.7/contracts/access/Ownable.sol



pragma solidity ^0.7.0;

/**
 * @dev Contract module which provides a basic access control mechanism, where
 * there is an account (an owner) that can be granted exclusive access to
 * specific functions.
 *
 * By default, the owner account will be the one that deploys the contract. This
 * can later be changed with {transferOwnership}.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be applied to your functions to restrict their use to
 * the owner.
 */
abstract contract Ownable is Context {
    address private _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor () {
        address msgSender = _msgSender();
        _owner = msgSender;
        emit OwnershipTransferred(address(0), msgSender);
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view virtual returns (address) {
        return _owner;
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(owner() == _msgSender(), "Ownable: caller is not the owner");
        _;
    }

    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions anymore. Can only be called by the current owner.
     *
     * NOTE: Renouncing ownership will leave the contract without an owner,
     * thereby removing any functionality that is only available to the owner.
     */
    function renounceOwnership() public virtual onlyOwner {
        emit OwnershipTransferred(_owner, address(0));
        _owner = address(0);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Can only be called by the current owner.
     */
    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}

// File: src/tokens/XNeutroToken.sol


pragma solidity =0.7.6;

// import "@openzeppelin/contracts/access/Ownable.sol";
// import "@openzeppelin/contracts/math/SafeMath.sol";
// import "@openzeppelin/contracts/token/ERC20/SafeERC20.sol";
// import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
// import "@openzeppelin/contracts/utils/ReentrancyGuard.sol";
// import "@openzeppelin/contracts/utils/EnumerableSet.sol";











/*
 * xNEUTRO is Neutroswap's escrowed governance token obtainable by converting NEUTRO to it
 * It's non-transferable, except from/to whitelisted addresses
 * It can be converted back to NEUTRO through a vesting process
 * This contract is made to receive xNEUTRO deposits from users in order to allocate them to Usages (plugins) contracts
 */
contract XNeutroToken is Ownable, ReentrancyGuard, ERC20("Neutro escrowed token", "xNEUTRO"), IXNeutroToken {
  using Address for address;
  using SafeMath for uint256;
  using EnumerableSet for EnumerableSet.AddressSet;
  using SafeERC20 for INeutroTokenV2;

  struct XNeutroBalance {
    uint256 allocatedAmount; // Amount of xNEUTRO allocated to a Usage
    uint256 redeemingAmount; // Total amount of xNEUTRO currently being redeemed
  }

  struct RedeemInfo {
    uint256 neutroAmount; // NEUTRO amount to receive when vesting has ended
    uint256 xNeutroAmount; // xNEUTRO amount to redeem
    uint256 endTime;
    IXNeutroTokenUsage dividendsAddress;
    uint256 dividendsAllocation; // Share of redeeming xNEUTRO to allocate to the Dividends Usage contract
  }

  INeutroTokenV2 public immutable neutroToken; // NEUTRO token to convert to/from
  IXNeutroTokenUsage public dividendsAddress; // Neutroswap dividends contract

  EnumerableSet.AddressSet private _transferWhitelist; // addresses allowed to send/receive xNEUTRO

  mapping(address => mapping(address => uint256)) public usageApprovals; // Usage approvals to allocate xNEUTRO
  mapping(address => mapping(address => uint256)) public override usageAllocations; // Active xNEUTRO allocations to usages

  uint256 public constant MAX_DEALLOCATION_FEE = 200; // 2%
  mapping(address => uint256) public usagesDeallocationFee; // Fee paid when deallocating xNEUTRO

  uint256 public constant MAX_FIXED_RATIO = 100; // 100%

  // Redeeming min/max settings
  uint256 public minRedeemRatio = 50; // 1:0.5
  uint256 public maxRedeemRatio = 100; // 1:1
  uint256 public minRedeemDuration = 15 days; // 1296000s
  uint256 public maxRedeemDuration = 90 days; // 7776000s
  // Adjusted dividends rewards for redeeming xNEUTRO
  uint256 public redeemDividendsAdjustment = 50; // 50%

  mapping(address => XNeutroBalance) public XNeutroBalances; // User's xNEUTRO balances
  mapping(address => RedeemInfo[]) public userRedeems; // User's redeeming instances


  constructor(INeutroTokenV2 neutroToken_) {
    neutroToken = neutroToken_;
    _transferWhitelist.add(address(this));
  }

  /********************************************/
  /****************** EVENTS ******************/
  /********************************************/

  event ApproveUsage(address indexed userAddress, address indexed usageAddress, uint256 amount);
  event Convert(address indexed from, address to, uint256 amount);
  event UpdateRedeemSettings(uint256 minRedeemRatio, uint256 maxRedeemRatio, uint256 minRedeemDuration, uint256 maxRedeemDuration, uint256 redeemDividendsAdjustment);
  event UpdateDividendsAddress(address previousDividendsAddress, address newDividendsAddress);
  event UpdateDeallocationFee(address indexed usageAddress, uint256 fee);
  event SetTransferWhitelist(address account, bool add);
  event Redeem(address indexed userAddress, uint256 xNeutroAmount, uint256 neutroAmount, uint256 duration);
  event FinalizeRedeem(address indexed userAddress, uint256 xNeutroAmount, uint256 neutroAmount);
  event CancelRedeem(address indexed userAddress, uint256 xNeutroAmount);
  event UpdateRedeemDividendsAddress(address indexed userAddress, uint256 redeemIndex, address previousDividendsAddress, address newDividendsAddress);
  event Allocate(address indexed userAddress, address indexed usageAddress, uint256 amount);
  event Deallocate(address indexed userAddress, address indexed usageAddress, uint256 amount, uint256 fee);

  /***********************************************/
  /****************** MODIFIERS ******************/
  /***********************************************/

  /*
   * @dev Check if a redeem entry exists
   */
  modifier validateRedeem(address userAddress, uint256 redeemIndex) {
    require(redeemIndex < userRedeems[userAddress].length, "validateRedeem: redeem entry does not exist");
    _;
  }

  /**************************************************/
  /****************** PUBLIC VIEWS ******************/
  /**************************************************/

  /*
   * @dev Returns user's xNEUTRO balances
   */
  function getXNeutroBalance(address userAddress) external view returns (uint256 allocatedAmount, uint256 redeemingAmount) {
    XNeutroBalance storage balance = XNeutroBalances[userAddress];
    return (balance.allocatedAmount, balance.redeemingAmount);
  }

  /*
   * @dev returns redeemable NEUTRO for "amount" of xNEUTRO vested for "duration" seconds
   */
  function getNeutroByVestingDuration(uint256 amount, uint256 duration) public view returns (uint256) {
    if(duration < minRedeemDuration) {
      return 0;
    }

    // capped to maxRedeemDuration
    if (duration > maxRedeemDuration) {
      return amount.mul(maxRedeemRatio).div(100);
    }

    uint256 ratio = minRedeemRatio.add(
      (duration.sub(minRedeemDuration)).mul(maxRedeemRatio.sub(minRedeemRatio))
      .div(maxRedeemDuration.sub(minRedeemDuration))
    );

    return amount.mul(ratio).div(100);
  }

  /**
   * @dev returns quantity of "userAddress" pending redeems
   */
  function getUserRedeemsLength(address userAddress) external view returns (uint256) {
    return userRedeems[userAddress].length;
  }

  /**
   * @dev returns "userAddress" info for a pending redeem identified by "redeemIndex"
   */
  function getUserRedeem(address userAddress, uint256 redeemIndex) external view validateRedeem(userAddress, redeemIndex) returns (uint256 neutroAmount, uint256 xNeutroAmount, uint256 endTime, address dividendsContract, uint256 dividendsAllocation) {
    RedeemInfo storage _redeem = userRedeems[userAddress][redeemIndex];
    return (_redeem.neutroAmount, _redeem.xNeutroAmount, _redeem.endTime, address(_redeem.dividendsAddress), _redeem.dividendsAllocation);
  }

  /**
   * @dev returns approved xNeutro to allocate from "userAddress" to "usageAddress"
   */
  function getUsageApproval(address userAddress, address usageAddress) external view returns (uint256) {
    return usageApprovals[userAddress][usageAddress];
  }

  /**
   * @dev returns allocated xNeutro from "userAddress" to "usageAddress"
   */
  function getUsageAllocation(address userAddress, address usageAddress) external view returns (uint256) {
    return usageAllocations[userAddress][usageAddress];
  }

  /**
   * @dev returns length of transferWhitelist array
   */
  function transferWhitelistLength() external view returns (uint256) {
    return _transferWhitelist.length();
  }

  /**
   * @dev returns transferWhitelist array item's address for "index"
   */
  function transferWhitelist(uint256 index) external view returns (address) {
    return _transferWhitelist.at(index);
  }

  /**
   * @dev returns if "account" is allowed to send/receive xNEUTRO
   */
  function isTransferWhitelisted(address account) external override view returns (bool) {
    return _transferWhitelist.contains(account);
  }

  /*******************************************************/
  /****************** OWNABLE FUNCTIONS ******************/
  /*******************************************************/

  /**
   * @dev Updates all redeem ratios and durations
   *
   * Must only be called by owner
   */
  function updateRedeemSettings(uint256 minRedeemRatio_, uint256 maxRedeemRatio_, uint256 minRedeemDuration_, uint256 maxRedeemDuration_, uint256 redeemDividendsAdjustment_) external onlyOwner {
    require(minRedeemRatio_ <= maxRedeemRatio_, "updateRedeemSettings: wrong ratio values");
    require(minRedeemDuration_ < maxRedeemDuration_, "updateRedeemSettings: wrong duration values");
    // should never exceed 100%
    require(maxRedeemRatio_ <= MAX_FIXED_RATIO && redeemDividendsAdjustment_ <= MAX_FIXED_RATIO, "updateRedeemSettings: wrong ratio values");

    minRedeemRatio = minRedeemRatio_;
    maxRedeemRatio = maxRedeemRatio_;
    minRedeemDuration = minRedeemDuration_;
    maxRedeemDuration = maxRedeemDuration_;
    redeemDividendsAdjustment = redeemDividendsAdjustment_;

    emit UpdateRedeemSettings(minRedeemRatio_, maxRedeemRatio_, minRedeemDuration_, maxRedeemDuration_, redeemDividendsAdjustment_);
  }

  /**
   * @dev Updates dividends contract address
   *
   * Must only be called by owner
   */
  function updateDividendsAddress(IXNeutroTokenUsage dividendsAddress_) external onlyOwner {
    // if set to 0, also set divs earnings while redeeming to 0
    if(address(dividendsAddress_) == address(0)) {
      redeemDividendsAdjustment = 0;
    }

    emit UpdateDividendsAddress(address(dividendsAddress), address(dividendsAddress_));
    dividendsAddress = dividendsAddress_;
  }

  /**
   * @dev Updates fee paid by users when deallocating from "usageAddress"
   */
  function updateDeallocationFee(address usageAddress, uint256 fee) external onlyOwner {
    require(fee <= MAX_DEALLOCATION_FEE, "updateDeallocationFee: too high");

    usagesDeallocationFee[usageAddress] = fee;
    emit UpdateDeallocationFee(usageAddress, fee);
  }

  /**
   * @dev Adds or removes addresses from the transferWhitelist
   */
  function updateTransferWhitelist(address account, bool add) external onlyOwner {
    require(account != address(this), "updateTransferWhitelist: Cannot remove xNeutro from whitelist");

    if(add) _transferWhitelist.add(account);
    else _transferWhitelist.remove(account);

    emit SetTransferWhitelist(account, add);
  }

  /*****************************************************************/
  /******************  EXTERNAL PUBLIC FUNCTIONS  ******************/
  /*****************************************************************/

  /**
   * @dev Approves "usage" address to get allocations up to "amount" of xNEUTRO from msg.sender
   */
  function approveUsage(IXNeutroTokenUsage usage, uint256 amount) external nonReentrant {
    require(address(usage) != address(0), "approveUsage: approve to the zero address");

    usageApprovals[msg.sender][address(usage)] = amount;
    emit ApproveUsage(msg.sender, address(usage), amount);
  }

  /**
   * @dev Convert caller's "amount" of NEUTRO to xNEUTRO
   */
  function convert(uint256 amount) external nonReentrant {
    _convert(amount, msg.sender);
  }

  /**
   * @dev Convert caller's "amount" of NEUTRO to xNEUTRO to "to" address
   */
  function convertTo(uint256 amount, address to) external override nonReentrant {
    require(address(msg.sender).isContract(), "convertTo: not allowed");
    _convert(amount, to);
  }

  /**
   * @dev Initiates redeem process (xNEUTRO to NEUTRO)
   *
   * Handles dividends' compensation allocation during the vesting process if needed
   */
  function redeem(uint256 xNeutroAmount, uint256 duration) external nonReentrant {
    require(xNeutroAmount > 0, "redeem: xNeutroAmount cannot be null");
    require(duration >= minRedeemDuration, "redeem: duration too low");

    _transfer(msg.sender, address(this), xNeutroAmount);
    XNeutroBalance storage balance = XNeutroBalances[msg.sender];

    // get corresponding NEUTRO amount
    uint256 neutroAmount = getNeutroByVestingDuration(xNeutroAmount, duration);
    emit Redeem(msg.sender, xNeutroAmount, neutroAmount, duration);

    // if redeeming is not immediate, go through vesting process
    if(duration > 0) {
      // add to SBT total
      balance.redeemingAmount = balance.redeemingAmount.add(xNeutroAmount);

      // handle dividends during the vesting process
      uint256 dividendsAllocation = xNeutroAmount.mul(redeemDividendsAdjustment).div(100);
      // only if compensation is active
      if(dividendsAllocation > 0) {
        // allocate to dividends
        dividendsAddress.allocate(msg.sender, dividendsAllocation, new bytes(0));
      }

      // add redeeming entry
      userRedeems[msg.sender].push(RedeemInfo(neutroAmount, xNeutroAmount, _currentBlockTimestamp().add(duration), dividendsAddress, dividendsAllocation));
    } else {
      // immediately redeem for NEUTRO
      _finalizeRedeem(msg.sender, xNeutroAmount, neutroAmount);
    }
  }

  /**
   * @dev Finalizes redeem process when vesting duration has been reached
   *
   * Can only be called by the redeem entry owner
   */
  function finalizeRedeem(uint256 redeemIndex) external nonReentrant validateRedeem(msg.sender, redeemIndex) {
    XNeutroBalance storage balance = XNeutroBalances[msg.sender];
    RedeemInfo storage _redeem = userRedeems[msg.sender][redeemIndex];
    require(_currentBlockTimestamp() >= _redeem.endTime, "finalizeRedeem: vesting duration has not ended yet");

    // remove from SBT total
    balance.redeemingAmount = balance.redeemingAmount.sub(_redeem.xNeutroAmount);
    _finalizeRedeem(msg.sender, _redeem.xNeutroAmount, _redeem.neutroAmount);

    // handle dividends compensation if any was active
    if(_redeem.dividendsAllocation > 0) {
      // deallocate from dividends
      IXNeutroTokenUsage(_redeem.dividendsAddress).deallocate(msg.sender, _redeem.dividendsAllocation, new bytes(0));
    }

    // remove redeem entry
    _deleteRedeemEntry(redeemIndex);
  }

  /**
   * @dev Updates dividends address for an existing active redeeming process
   *
   * Can only be called by the involved user
   * Should only be used if dividends contract was to be migrated
   */
  function updateRedeemDividendsAddress(uint256 redeemIndex) external nonReentrant validateRedeem(msg.sender, redeemIndex) {
    RedeemInfo storage _redeem = userRedeems[msg.sender][redeemIndex];

    // only if the active dividends contract is not the same anymore
    if(dividendsAddress != _redeem.dividendsAddress && address(dividendsAddress) != address(0)) {
      if(_redeem.dividendsAllocation > 0) {
        // deallocate from old dividends contract
        _redeem.dividendsAddress.deallocate(msg.sender, _redeem.dividendsAllocation, new bytes(0));
        // allocate to new used dividends contract
        dividendsAddress.allocate(msg.sender, _redeem.dividendsAllocation, new bytes(0));
      }

      emit UpdateRedeemDividendsAddress(msg.sender, redeemIndex, address(_redeem.dividendsAddress), address(dividendsAddress));
      _redeem.dividendsAddress = dividendsAddress;
    }
  }

  /**
   * @dev Cancels an ongoing redeem entry
   *
   * Can only be called by its owner
   */
  function cancelRedeem(uint256 redeemIndex) external nonReentrant validateRedeem(msg.sender, redeemIndex) {
    XNeutroBalance storage balance = XNeutroBalances[msg.sender];
    RedeemInfo storage _redeem = userRedeems[msg.sender][redeemIndex];

    // make redeeming xNEUTRO available again
    balance.redeemingAmount = balance.redeemingAmount.sub(_redeem.xNeutroAmount);
    _transfer(address(this), msg.sender, _redeem.xNeutroAmount);

    // handle dividends compensation if any was active
    if(_redeem.dividendsAllocation > 0) {
      // deallocate from dividends
      IXNeutroTokenUsage(_redeem.dividendsAddress).deallocate(msg.sender, _redeem.dividendsAllocation, new bytes(0));
    }

    emit CancelRedeem(msg.sender, _redeem.xNeutroAmount);

    // remove redeem entry
    _deleteRedeemEntry(redeemIndex);
  }


  /**
   * @dev Allocates caller's "amount" of available xNEUTRO to "usageAddress" contract
   *
   * args specific to usage contract must be passed into "usageData"
   */
  function allocate(address usageAddress, uint256 amount, bytes calldata usageData) external nonReentrant {
    _allocate(msg.sender, usageAddress, amount);

    // allocates xNEUTRO to usageContract
    IXNeutroTokenUsage(usageAddress).allocate(msg.sender, amount, usageData);
  }

  /**
   * @dev Allocates "amount" of available xNEUTRO from "userAddress" to caller (ie usage contract)
   *
   * Caller must have an allocation approval for the required xNeutro xNEUTRO from "userAddress"
   */
  function allocateFromUsage(address userAddress, uint256 amount) external override nonReentrant {
    _allocate(userAddress, msg.sender, amount);
  }

  /**
   * @dev Deallocates caller's "amount" of available xNEUTRO from "usageAddress" contract
   *
   * args specific to usage contract must be passed into "usageData"
   */
  function deallocate(address usageAddress, uint256 amount, bytes calldata usageData) external nonReentrant {
    _deallocate(msg.sender, usageAddress, amount);

    // deallocate xNEUTRO into usageContract
    IXNeutroTokenUsage(usageAddress).deallocate(msg.sender, amount, usageData);
  }

  /**
   * @dev Deallocates "amount" of allocated xNEUTRO belonging to "userAddress" from caller (ie usage contract)
   *
   * Caller can only deallocate xNEUTRO from itself
   */
  function deallocateFromUsage(address userAddress, uint256 amount) external override nonReentrant {
    _deallocate(userAddress, msg.sender, amount);
  }

  /********************************************************/
  /****************** INTERNAL FUNCTIONS ******************/
  /********************************************************/

  /**
   * @dev Convert caller's "amount" of NEUTRO into xNEUTRO to "to"
   */
  function _convert(uint256 amount, address to) internal {
    require(amount != 0, "convert: amount cannot be null");

    // mint new xNEUTRO
    _mint(to, amount);

    emit Convert(msg.sender, to, amount);
    neutroToken.safeTransferFrom(msg.sender, address(this), amount);
  }

  /**
   * @dev Finalizes the redeeming process for "userAddress" by transferring him "neutroAmount" and removing "xNeutroAmount" from supply
   *
   * Any vesting check should be ran before calling this
   * NEUTRO excess is automatically burnt
   */
  function _finalizeRedeem(address userAddress, uint256 xNeutroAmount, uint256 neutroAmount) internal {
    uint256 neutroExcess = xNeutroAmount.sub(neutroAmount);

    // sends due NEUTRO tokens
    neutroToken.safeTransfer(userAddress, neutroAmount);

    // burns NEUTRO excess if any
    neutroToken.burn(neutroExcess);
    _burn(address(this), xNeutroAmount);

    emit FinalizeRedeem(userAddress, xNeutroAmount, neutroAmount);
  }

  /**
   * @dev Allocates "userAddress" user's "amount" of available xNEUTRO to "usageAddress" contract
   *
   */
  function _allocate(address userAddress, address usageAddress, uint256 amount) internal {
    require(amount > 0, "allocate: amount cannot be null");

    XNeutroBalance storage balance = XNeutroBalances[userAddress];

    // approval checks if allocation request amount has been approved by userAddress to be allocated to this usageAddress
    uint256 approvedXNeutro = usageApprovals[userAddress][usageAddress];
    require(approvedXNeutro >= amount, "allocate: non authorized amount");

    // remove allocated amount from usage's approved amount
    usageApprovals[userAddress][usageAddress] = approvedXNeutro.sub(amount);

    // update usage's allocatedAmount for userAddress
    usageAllocations[userAddress][usageAddress] = usageAllocations[userAddress][usageAddress].add(amount);

    // adjust user's xNEUTRO balances
    balance.allocatedAmount = balance.allocatedAmount.add(amount);
    _transfer(userAddress, address(this), amount);

    emit Allocate(userAddress, usageAddress, amount);
  }

  /**
   * @dev Deallocates "amount" of available xNEUTRO to "usageAddress" contract
   *
   * args specific to usage contract must be passed into "usageData"
   */
  function _deallocate(address userAddress, address usageAddress, uint256 amount) internal {
    require(amount > 0, "deallocate: amount cannot be null");

    // check if there is enough allocated xNEUTRO to this usage to deallocate
    uint256 allocatedAmount = usageAllocations[userAddress][usageAddress];
    require(allocatedAmount >= amount, "deallocate: non authorized amount");

    // remove deallocated amount from usage's allocation
    usageAllocations[userAddress][usageAddress] = allocatedAmount.sub(amount);

    uint256 deallocationFeeAmount = amount.mul(usagesDeallocationFee[usageAddress]).div(10000);

    // adjust user's xNEUTRO balances
    XNeutroBalance storage balance = XNeutroBalances[userAddress];
    balance.allocatedAmount = balance.allocatedAmount.sub(amount);
    _transfer(address(this), userAddress, amount.sub(deallocationFeeAmount));
    // burn corresponding NEUTRO and XNEUTRO
    neutroToken.burn(deallocationFeeAmount);
    _burn(address(this), deallocationFeeAmount);

    emit Deallocate(userAddress, usageAddress, amount, deallocationFeeAmount);
  }

  function _deleteRedeemEntry(uint256 index) internal {
    userRedeems[msg.sender][index] = userRedeems[msg.sender][userRedeems[msg.sender].length - 1];
    userRedeems[msg.sender].pop();
  }

  /**
   * @dev Hook override to forbid transfers except from whitelisted addresses and minting
   */
  function _beforeTokenTransfer(address from, address to, uint256 /*amount*/) internal view override {
    require(from == address(0) || _transferWhitelist.contains(from) || _transferWhitelist.contains(to), "transfer: not allowed");
  }

  /**
   * @dev Utility function to get the current block timestamp
   */
  function _currentBlockTimestamp() internal view virtual returns (uint256) {
    /* solhint-disable not-rely-on-time */
    return block.timestamp;
  }

}