/**
 *Submitted for verification at Etherscan.io on 2020-08-26
 */

// File: @openzeppelin/contracts/token/ERC20/IERC20.sol



pragma solidity ^0.6.0;

/**
 * @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: @openzeppelin/contracts/math/SafeMath.sol



    pragma solidity ^0.6.0;

/**
 * @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, 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.
         */
        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.
         */
        function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        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.
         */
        function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
        }
        }

// File: @openzeppelin/contracts/utils/Address.sol



        pragma solidity ^0.6.2;

/**
 * @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) {
        // According to EIP-1052, 0x0 is the value returned for not-yet created accounts
        // and 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470 is returned
        // for accounts without code, i.e. `keccak256('')`
        bytes32 codehash;
        bytes32 accountHash = 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470;
        // solhint-disable-next-line no-inline-assembly
        assembly { codehash := extcodehash(account) }
        return (codehash != accountHash && codehash != 0x0);
        }

        /**
         * @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");
        return _functionCallWithValue(target, data, value, errorMessage);
        }

        function _functionCallWithValue(address target, bytes memory data, uint256 weiValue, string memory errorMessage) private returns (bytes memory) {
        require(isContract(target), "Address: call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.call{ value: weiValue }(data);
        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: @openzeppelin/contracts/token/ERC20/SafeERC20.sol



        pragma solidity ^0.6.0;




/**
 * @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: @openzeppelin/contracts/utils/EnumerableSet.sol



        pragma solidity ^0.6.0;

/**
 * @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 v3.0.0, only sets of type `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];
        }

        // 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(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(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(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(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: @openzeppelin/contracts/GSN/Context.sol



        pragma solidity ^0.6.0;

/*
 * @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: @openzeppelin/contracts/access/Ownable.sol



        pragma solidity ^0.6.0;

/**
 * @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.
 */
        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 () internal {
        address msgSender = _msgSender();
        _owner = msgSender;
        emit OwnershipTransferred(address(0), msgSender);
        }

        /**
         * @dev Returns the address of the current owner.
         */
        function owner() public view 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: @openzeppelin/contracts/token/ERC20/ERC20.sol



        pragma solidity ^0.6.0;





/**
 * @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;
        using Address for address;

        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) public {
        _name = name;
        _symbol = symbol;
        _decimals = 18;
        }

        /**
         * @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. 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 returns (uint8) {
        return _decimals;
        }

        /**
         * @dev See {IERC20-totalSupply}.
         */
        function totalSupply() public view override returns (uint256) {
        return _totalSupply;
        }

        /**
         * @dev See {IERC20-balanceOf}.
         */
        function balanceOf(address account) public view 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 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 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 {
        _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: contracts/AntsToken.sol

        pragma solidity 0.6.12;




// AntsToken with Governance.
        contract AntsToken is ERC20("AntsToken", "ANTS"), Ownable {
        /// @notice Creates `_amount` token to `_to`. Must only be called by the owner (MasterChef).
        function mint(address _to, uint256 _amount) public onlyOwner {
        require(totalSupply() < 1e26 , "Totoal supply overflow");  // 1e8 ** decimal
        _mint(_to, _amount);
        _moveDelegates(address(0), _delegates[_to], _amount);

        }

        // Copied and modified from YAM code:
        // https://github.com/yam-finance/yam-protocol/blob/master/contracts/token/YAMGovernanceStorage.sol
        // https://github.com/yam-finance/yam-protocol/blob/master/contracts/token/YAMGovernance.sol
        // Which is copied and modified from COMPOUND:
        // https://github.com/compound-finance/compound-protocol/blob/master/contracts/Governance/Comp.sol

        /// @notice A record of each accounts delegate
        mapping (address => address) internal _delegates;

        /// @notice A checkpoint for marking number of votes from a given block
        struct Checkpoint {
        uint32 fromBlock;
        uint256 votes;
        }

        /// @notice A record of votes checkpoints for each account, by index
        mapping (address => mapping (uint32 => Checkpoint)) public checkpoints;

        /// @notice The number of checkpoints for each account
        mapping (address => uint32) public numCheckpoints;

        /// @notice The EIP-712 typehash for the contract's domain
        bytes32 public constant DOMAIN_TYPEHASH = keccak256("EIP712Domain(string name,uint256 chainId,address verifyingContract)");

        /// @notice The EIP-712 typehash for the delegation struct used by the contract
        bytes32 public constant DELEGATION_TYPEHASH = keccak256("Delegation(address delegatee,uint256 nonce,uint256 expiry)");

        /// @notice A record of states for signing / validating signatures
        mapping (address => uint) public nonces;

        /// @notice An event thats emitted when an account changes its delegate
        event DelegateChanged(address indexed delegator, address indexed fromDelegate, address indexed toDelegate);

        /// @notice An event thats emitted when a delegate account's vote balance changes
        event DelegateVotesChanged(address indexed delegate, uint previousBalance, uint newBalance);

        /**
         * @notice Delegate votes from `msg.sender` to `delegatee`
         * @param delegator The address to get delegatee for
         */
        function delegates(address delegator)
        external
        view
        returns (address)
        {
        return _delegates[delegator];
        }

        /**
         * @notice Delegate votes from `msg.sender` to `delegatee`
         * @param delegatee The address to delegate votes to
         */
        function delegate(address delegatee) external {
        return _delegate(msg.sender, delegatee);
        }

        /**
         * @notice Delegates votes from signatory to `delegatee`
         * @param delegatee The address to delegate votes to
         * @param nonce The contract state required to match the signature
         * @param expiry The time at which to expire the signature
         * @param v The recovery byte of the signature
         * @param r Half of the ECDSA signature pair
         * @param s Half of the ECDSA signature pair
         */
        function delegateBySig(
        address delegatee,
        uint nonce,
        uint expiry,
        uint8 v,
        bytes32 r,
        bytes32 s
        )
        external
        {
        bytes32 domainSeparator = keccak256(
        abi.encode(
        DOMAIN_TYPEHASH,
        keccak256(bytes(name())),
        getChainId(),
        address(this)
        )
        );

        bytes32 structHash = keccak256(
        abi.encode(
        DELEGATION_TYPEHASH,
        delegatee,
        nonce,
        expiry
        )
        );

        bytes32 digest = keccak256(
        abi.encodePacked(
        "\x19\x01",
        domainSeparator,
        structHash
        )
        );

        address signatory = ecrecover(digest, v, r, s);
        require(signatory != address(0), "ANTS::delegateBySig: invalid signature");
        require(nonce == nonces[signatory]++, "ANTS::delegateBySig: invalid nonce");
        require(now <= expiry, "ANTS::delegateBySig: signature expired");
        return _delegate(signatory, delegatee);
        }

        /**
         * @notice Gets the current votes balance for `account`
         * @param account The address to get votes balance
         * @return The number of current votes for `account`
         */
        function getCurrentVotes(address account)
        external
        view
        returns (uint256)
        {
        uint32 nCheckpoints = numCheckpoints[account];
        return nCheckpoints > 0 ? checkpoints[account][nCheckpoints - 1].votes : 0;
        }

        /**
         * @notice Determine the prior number of votes for an account as of a block number
         * @dev Block number must be a finalized block or else this function will revert to prevent misinformation.
         * @param account The address of the account to check
         * @param blockNumber The block number to get the vote balance at
         * @return The number of votes the account had as of the given block
         */
        function getPriorVotes(address account, uint blockNumber)
        external
        view
        returns (uint256)
        {
        require(blockNumber < block.number, "ANTS::getPriorVotes: not yet determined");

        uint32 nCheckpoints = numCheckpoints[account];
        if (nCheckpoints == 0) {
        return 0;
        }

        // First check most recent balance
        if (checkpoints[account][nCheckpoints - 1].fromBlock <= blockNumber) {
        return checkpoints[account][nCheckpoints - 1].votes;
        }

        // Next check implicit zero balance
        if (checkpoints[account][0].fromBlock > blockNumber) {
        return 0;
        }

        uint32 lower = 0;
        uint32 upper = nCheckpoints - 1;
        while (upper > lower) {
        uint32 center = upper - (upper - lower) / 2; // ceil, avoiding overflow
        Checkpoint memory cp = checkpoints[account][center];
        if (cp.fromBlock == blockNumber) {
        return cp.votes;
        } else if (cp.fromBlock < blockNumber) {
        lower = center;
        } else {
        upper = center - 1;
        }
        }
        return checkpoints[account][lower].votes;
        }

        function _delegate(address delegator, address delegatee)
        internal
        {
        address currentDelegate = _delegates[delegator];
        uint256 delegatorBalance = balanceOf(delegator); // balance of underlying ANTSs (not scaled);
        _delegates[delegator] = delegatee;

        emit DelegateChanged(delegator, currentDelegate, delegatee);

        _moveDelegates(currentDelegate, delegatee, delegatorBalance);
        }

        function _moveDelegates(address srcRep, address dstRep, uint256 amount) internal {
        if (srcRep != dstRep && amount > 0) {
        if (srcRep != address(0)) {
        // decrease old representative
        uint32 srcRepNum = numCheckpoints[srcRep];
        uint256 srcRepOld = srcRepNum > 0 ? checkpoints[srcRep][srcRepNum - 1].votes : 0;
        uint256 srcRepNew = srcRepOld.sub(amount);
        _writeCheckpoint(srcRep, srcRepNum, srcRepOld, srcRepNew);
        }

        if (dstRep != address(0)) {
        // increase new representative
        uint32 dstRepNum = numCheckpoints[dstRep];
        uint256 dstRepOld = dstRepNum > 0 ? checkpoints[dstRep][dstRepNum - 1].votes : 0;
        uint256 dstRepNew = dstRepOld.add(amount);
        _writeCheckpoint(dstRep, dstRepNum, dstRepOld, dstRepNew);
        }
        }
        }

        function _writeCheckpoint(
        address delegatee,
        uint32 nCheckpoints,
        uint256 oldVotes,
        uint256 newVotes
        )
        internal
        {
        uint32 blockNumber = safe32(block.number, "ANTS::_writeCheckpoint: block number exceeds 32 bits");

        if (nCheckpoints > 0 && checkpoints[delegatee][nCheckpoints - 1].fromBlock == blockNumber) {
        checkpoints[delegatee][nCheckpoints - 1].votes = newVotes;
        } else {
        checkpoints[delegatee][nCheckpoints] = Checkpoint(blockNumber, newVotes);
        numCheckpoints[delegatee] = nCheckpoints + 1;
        }

        emit DelegateVotesChanged(delegatee, oldVotes, newVotes);
        }

        function safe32(uint n, string memory errorMessage) internal pure returns (uint32) {
        require(n < 2**32, errorMessage);
        return uint32(n);
        }

        function getChainId() internal pure returns (uint) {
        uint256 chainId;
        assembly { chainId := chainid() }
        return chainId;
        }
        }


// File: contracts/MasterChef.sol

        pragma solidity 0.6.12;








interface IMigratorChef {
    // Perform LP token migration from legacy UniswapV2 to AntsSwap.
    // Take the current LP token address and return the new LP token address.
    // Migrator should have full access to the caller's LP token.
    // Return the new LP token address.
    //
    // XXX Migrator must have allowance access to UniswapV2 LP tokens.
    // AntsSwap must mint EXACTLY the same amount of AntsSwap LP tokens or
    // else something bad will happen. Traditional UniswapV2 does not
    // do that so be careful!
    function migrate(IERC20 token) external returns (IERC20);
}

    // MasterChef is the master of Ants. He can make Ants and he is a fair guy.
//
// Note that it's ownable and the owner wields tremendous power. The ownership
// will be transferred to a governance smart contract once SUSHI is sufficiently
// distributed and the community can show to govern itself.
//
// Have fun reading it. Hopefully it's bug-free. God bless.
    contract MasterChef is Ownable {
        using SafeMath for uint256;
        using SafeERC20 for IERC20;
        using Address for address;

        // Info of each user.
        struct UserInfo {
        uint256 amount;     // How many LP tokens the user has provided.
        uint256 rewardDebt; // Reward debt. See explanation below.
        uint256 lockBlock; // lockBlock
        uint256 lockedAmount; // lockedAmount
        uint256 pending; // pending amount, convert to amount via withdraw
        //
        // We do some fancy math here. Basically, any point in time, the amount of ANTSs
        // entitled to a user but is pending to be distributed is:
        //
        //   pending reward = (user.amount * pool.accAntsPerShare) - user.rewardDebt
        //
        // Whenever a user deposits or withdraws LP tokens to a pool. Here's what happens:
        //   1. The pool's `accAntsPerShare` (and `lastRewardBlock`) gets updated.
        //   2. User receives the pending reward sent to his/her address.
        //   3. User's `amount` gets updated.
        //   4. User's `rewardDebt` gets updated.
        }

        // Info of each pool.
        struct PoolInfo {
        IERC20 lpToken;           // Address of LP token contract.
        bool   isSingle;           // sigle token mint
        uint256 allocPoint;       // How many allocation points assigned to this pool. ANTSs to distribute per block.
        uint256 lastRewardBlock;  // Last block number that ANTSs distribution occurs.
        uint256 accAntsPerShare; // Accumulated ANTSs per share, times 1e12. See below.
        }

        // The ANTS TOKEN!
        AntsToken public ants;
        // Dev address.
        address public devaddr;
        // Block number when bonus ANTS period ends.
        uint256 public bonusEndBlock;
        // Token locked block length
        uint256 public halvedBlock;
        uint256 public halvedBlockLength = 2_000_000;
        // Token locked block length
        uint256 public antsLockedBlock;
        // ANTS tokens created per block.
        uint256 public antsPerBlock;
        // Bonus muliplier for early ants makers.
        uint256 public constant BONUS_MULTIPLIER = 5;
        // The migrator contract. It has a lot of power. Can only be set through governance (owner).
        IMigratorChef public migrator;

        // Invite user
        mapping (address => uint256) public balanceInvite;
        mapping (address => address) public userInvite;
        mapping (address => bool) public userInviteAble;
        // Info of each pool.
        PoolInfo[] public poolInfo;
        // Info of each user that stakes LP tokens.
        mapping (uint256 => mapping (address => UserInfo)) public userInfo;
        // Total allocation poitns. Must be the sum of all allocation points in all pools.
        uint256 public totalAllocPoint = 0;
        // The block number when ANTS mining starts.
        uint256 public startBlock;

        event Invite(address indexed inviter, address indexed invitee);
        event InviteReward(address indexed inviter, address indexed invitee, uint256 amount);

        event Deposit(address indexed user, uint256 indexed pid, uint256 amount);
        event Withdraw(address indexed user, uint256 indexed pid, uint256 amount);
        event EmergencyWithdraw(address indexed user, uint256 indexed pid, uint256 amount);

        constructor(
        AntsToken _ants,
        address _devaddr,
        uint256 _antsPerBlock,
        uint256 _startBlock,
        uint256 _bonusEndBlock
        ) public {
        ants = _ants;
        devaddr = _devaddr;
        antsPerBlock = _antsPerBlock;
        bonusEndBlock = _bonusEndBlock;
        startBlock = _startBlock;
        halvedBlock = _startBlock;
        antsLockedBlock = 200_000;
        }

        function poolLength() external view returns (uint256) {
        return poolInfo.length;
        }

        // Add a new lp to the pool. Can only be called by the owner.
        // XXX DO NOT add the same LP token more than once. Rewards will be messed up if you do.
        function add(uint256 _allocPoint, IERC20 _lpToken , bool _isSingle, bool _withUpdate) public onlyOwner {
        if (_withUpdate) {
        massUpdatePools();
        }
        uint256 lastRewardBlock = block.number > startBlock ? block.number : startBlock;
        totalAllocPoint = totalAllocPoint.add(_allocPoint);
        poolInfo.push(PoolInfo({
        lpToken: _lpToken,
        isSingle: _isSingle,
        allocPoint: _allocPoint,
        lastRewardBlock: lastRewardBlock,
        accAntsPerShare: 0
        }));
        }

        // Update the given pool's ANTS allocation point. Can only be called by the owner.
        function set(uint256 _pid, uint256 _allocPoint, bool _withUpdate) public onlyOwner {
        if (_withUpdate) {
        massUpdatePools();
        }
        totalAllocPoint = totalAllocPoint.sub(poolInfo[_pid].allocPoint).add(_allocPoint);
        poolInfo[_pid].allocPoint = _allocPoint;
        }

        // Set the migrator contract. Can only be called by the owner.
        function setMigrator(IMigratorChef _migrator) public onlyOwner {
        migrator = _migrator;
        }

        // Migrate lp token to another lp contract. Can be called by anyone. We trust that migrator contract is good.
        function migrate(uint256 _pid) public {
        require(address(migrator) != address(0), "migrate: no migrator");
        PoolInfo storage pool = poolInfo[_pid];
        IERC20 lpToken = pool.lpToken;
        uint256 bal = lpToken.balanceOf(address(this));
        lpToken.safeApprove(address(migrator), bal);
        IERC20 newLpToken = migrator.migrate(lpToken);
        require(bal == newLpToken.balanceOf(address(this)), "migrate: bad");
        pool.lpToken = newLpToken;
        }

        // Return reward multiplier over the given _from to _to block.
        function getMultiplier(uint256 _from, uint256 _to) public view returns (uint256) {
        if (_to <= bonusEndBlock) {
        return _to.sub(_from).mul(BONUS_MULTIPLIER);
        } else if (_from >= bonusEndBlock) {
        return _to.sub(_from);
        } else {
        return bonusEndBlock.sub(_from).mul(BONUS_MULTIPLIER).add(
        _to.sub(bonusEndBlock)
        );
        }
        }

        // View function to see pending ANTSs on frontend.
        function pendingAnts(uint256 _pid, address _user) external view returns (uint256) {
        PoolInfo storage pool = poolInfo[_pid];
        UserInfo storage user = userInfo[_pid][_user];
        uint256 accAntsPerShare = pool.accAntsPerShare;
        uint256 lpSupply = pool.lpToken.balanceOf(address(this));

        if (block.number > pool.lastRewardBlock && lpSupply != 0) {
        uint256 multiplier = getMultiplier(pool.lastRewardBlock, block.number);
        uint256 antsReward = multiplier.mul(antsPerBlock).mul(pool.allocPoint).div(totalAllocPoint);
        accAntsPerShare = accAntsPerShare.add(antsReward.mul(1e12).div(lpSupply));
        }

        return user.amount.mul(accAntsPerShare).div(1e12).sub(user.rewardDebt);
        }
        // View function to see pending ANTSs on frontend.
        function totalPendingAnts(uint256 _pid, address _user) external view returns (uint256 , uint256 ) {

        PoolInfo storage pool = poolInfo[_pid];
        UserInfo storage user = userInfo[_pid][_user];
        uint256 accAntsPerShare = pool.accAntsPerShare;
        uint256 lpSupply = pool.lpToken.balanceOf(address(this));
        if (block.number > pool.lastRewardBlock && lpSupply != 0) {
        uint256 multiplier = getMultiplier(pool.lastRewardBlock, block.number);
        uint256 antsReward = multiplier.mul(antsPerBlock).mul(pool.allocPoint).div(totalAllocPoint);
        accAntsPerShare = accAntsPerShare.add(antsReward.mul(1e12).div(lpSupply));
        }
        uint256 pending =  user.amount.mul(accAntsPerShare).div(1e12).sub(user.rewardDebt).add(user.pending);
        uint256 reward = 0;
        if(userInvite[_user] != address(0) && userInvite[_user] != address(this) ) {
        reward = pending.mul(1).div(20);
        }
        return (pending, reward);
        }

        // Update reward vairables for all pools. Be careful of gas spending!
        function massUpdatePools() public {
        uint256 length = poolInfo.length;
        for (uint256 pid = 0; pid < length; ++pid) {
        updatePool(pid);
        }
        }

        // Update reward variables of the given pool to be up-to-date.
        function updatePool(uint256 _pid) public {
        PoolInfo storage pool = poolInfo[_pid];
        if (block.number <= pool.lastRewardBlock) {
        return;
        }
        uint256 lpSupply = pool.lpToken.balanceOf(address(this));
        if (lpSupply == 0) {
        pool.lastRewardBlock = block.number;
        return;
        }

        uint256 multiplier = getMultiplier(pool.lastRewardBlock, block.number);
        uint256 antsReward = multiplier.mul(antsPerBlock).mul(pool.allocPoint).div(totalAllocPoint);
        // UserInfo storage dev = userInfo[_pid][devaddr];
        // dev.pending = dev.pending.add(antsReward.div(20));
        ants.mint(devaddr, antsReward.div(20));
        ants.mint(address(this), antsReward);
        pool.accAntsPerShare = pool.accAntsPerShare.add(antsReward.mul(1e12).div(lpSupply));
        pool.lastRewardBlock = block.number;

        if(block.number >= halvedBlockLength.add(halvedBlock)) {
        halvedBlock = block.number;
        antsPerBlock = antsPerBlock.div(2);
        }

        }

        function updateLockBlock(uint256 _pid, uint256 _amount) internal {
        UserInfo storage user = userInfo[_pid][msg.sender];
        if(user.lockBlock == 0) {//
        user.lockBlock = block.number;
        }else {
        // (b-a) * amountB/(amountA + amountbB)
        user.lockBlock =  block.number.sub(user.lockBlock).mul(_amount).div(user.amount.add(_amount)).add(user.lockBlock);
        }
        }

        function setInviter(address _inviter) public {
        require(_inviter != address(0), "Inviter not null");
        require(_inviter != msg.sender, "Inviter cannot be self");
        require(userInviteAble[_inviter], "Inviter invalid");
        userInvite[msg.sender] = _inviter;
        }

        function depositWithInvite(uint256 _pid, uint256 _amount, address _inviter) public {
        if( userInvite[msg.sender] == address(0) ) {
        require(_inviter != address(0), "Inviter not null");
        require(_inviter != msg.sender, "Inviter cannot be self");
        require(userInviteAble[_inviter], "Inviter invalid");
        userInvite[msg.sender] = _inviter;
        emit Invite(_inviter, msg.sender);
        }
        deposit(_pid, _amount);
        }
        // Deposit LP tokens to MasterChef for ANTS allocation.
        function deposit(uint256 _pid, uint256 _amount) public {
        if(_amount > 0 &&  !userInviteAble[msg.sender]) {
        userInviteAble[msg.sender] = true;
        }
        if(userInvite[msg.sender] == address(0) ) {
        userInvite[msg.sender] = address(this);
        }
        updateLockBlock(_pid, _amount);
        updatePool(_pid);
        PoolInfo storage pool = poolInfo[_pid];
        UserInfo storage user = userInfo[_pid][msg.sender];
        if (user.amount > 0) {
        uint256 pending = user.amount.mul(pool.accAntsPerShare).div(1e12).sub(user.rewardDebt);
        // safeAntsTransfer(msg.sender, pending);
        user.pending = user.pending.add(pending);
        }
        if(pool.isSingle) {
        chefSafeTransferFrom(pool.lpToken, address(msg.sender), address(this), _amount);
        }else {
        pool.lpToken.safeTransferFrom(address(msg.sender), address(this), _amount);
        }
        user.amount = user.amount.add(_amount);
        user.rewardDebt = user.amount.mul(pool.accAntsPerShare).div(1e12);
        emit Deposit(msg.sender, _pid, _amount);
        }

        // Withdraw LP tokens from MasterChef.
        function withdraw(uint256 _pid, uint256 _amount) public {
        PoolInfo storage pool = poolInfo[_pid];
        UserInfo storage user = userInfo[_pid][msg.sender];
        require(user.amount >= _amount, "withdraw: not good");
        updatePool(_pid);
        uint256 pending = user.amount.mul(pool.accAntsPerShare).div(1e12).sub(user.rewardDebt);
        user.pending = user.pending.add(pending);
        //pending ++
        //exec  safeAntsTransfer(msg.sender, pending);
        user.amount = user.amount.sub(_amount);
        user.rewardDebt = user.amount.mul(pool.accAntsPerShare).div(1e12);
        if(pool.isSingle) {
        chefSafeTransfer(pool.lpToken, address(msg.sender), _amount);
        }else {
        pool.lpToken.safeTransfer(address(msg.sender), _amount);
        }

        emit Withdraw(msg.sender, _pid, _amount);
        }
        function withdrawInviteReward() public {
        ants.mint(msg.sender, balanceInvite[msg.sender] );
        balanceInvite[msg.sender] = 0;
        }

        function withdrawToken(uint256 _pid) public {
        updatePool(_pid);
        PoolInfo storage pool = poolInfo[_pid];
        UserInfo storage user = userInfo[_pid][msg.sender];

        uint pending =  user.amount.mul(pool.accAntsPerShare).div(1e12).sub(user.rewardDebt);
        user.pending = pending.add(user.pending);
        user.rewardDebt = user.amount.mul(pool.accAntsPerShare).div(1e12);

        bool invited  = userInvite[msg.sender] != address(0) && userInvite[msg.sender] != address(this);
        uint256 availablePending = invited? user.pending.mul(21).div(20) : user.pending;

        if(user.lockBlock > 0 && block.number.sub(user.lockBlock) < antsLockedBlock ) {
        availablePending =   availablePending.mul(block.number.sub(user.lockBlock)).div(antsLockedBlock);
        }
        if(availablePending > 0 ){
        //update lockedNumber
        //block.number.sub(user.lockBlock).mul(withdrawAmount).div(availablePending).add(user.lockBlock);
        if(invited) {
        //mint invitee reward
        ants.mint(msg.sender, availablePending.mul(1).div(21));
        availablePending = availablePending.mul(20).div(21); // avaliable = avaliable * 1.05
        //record inviter reward
        address inviter = userInvite[msg.sender];
        uint256 reward = availablePending.div(10);
        balanceInvite[inviter] = balanceInvite[inviter].add(reward);
        emit InviteReward(inviter, msg.sender, reward);
        }
        safeAntsTransfer(msg.sender, availablePending);
        user.pending = user.pending.sub(availablePending);
        user.lockBlock = block.number;
        }
        if(user.amount == 0 && user.pending == 0) {
        user.lockBlock = 0;
        }
        }

        function calcuAvalible(uint256 _pid , address _user)  external view returns (uint256 ) {

        PoolInfo storage pool = poolInfo[_pid];
        UserInfo storage user = userInfo[_pid][_user];
        uint256 accAntsPerShare = pool.accAntsPerShare;
        uint256 lpSupply = pool.lpToken.balanceOf(address(this));
        if (block.number > pool.lastRewardBlock && lpSupply != 0) {
        uint256 multiplier = getMultiplier(pool.lastRewardBlock, block.number);
        uint256 antsReward = multiplier.mul(antsPerBlock).mul(pool.allocPoint).div(totalAllocPoint);
        accAntsPerShare = accAntsPerShare.add(antsReward.mul(1e12).div(lpSupply));
        }
        uint256 addPending = user.amount.mul(accAntsPerShare).div(1e12).sub(user.rewardDebt);
        uint256 totalPending = user.pending.add(addPending);

        bool invited = userInvite[_user] != address(0) && userInvite[_user] != address(this) ;
        uint256 pending = invited? totalPending.mul(21).div(20) : totalPending;
        if(user.lockBlock > 0  && block.number.sub(user.lockBlock) < antsLockedBlock) {
        return  pending.mul(block.number.sub(user.lockBlock)).div(antsLockedBlock);
        }else {
        return pending;
        }
        }

        // Withdraw without caring about rewards. EMERGENCY ONLY.
        function emergencyWithdraw(uint256 _pid) public {
        PoolInfo storage pool = poolInfo[_pid];
        UserInfo storage user = userInfo[_pid][msg.sender];

        if(pool.isSingle) {
        chefSafeTransfer(pool.lpToken, address(msg.sender), user.amount);
        }else {
        pool.lpToken.safeTransfer(address(msg.sender), user.amount);
        }
        emit EmergencyWithdraw(msg.sender, _pid, user.amount);
        user.amount = 0;
        user.rewardDebt = 0;
        }

        // Safe ants transfer function, just in case if rounding error causes pool to not have enough ANTSs.
        function safeAntsTransfer(address _to, uint256 _amount) internal {
        uint256 antsBal = ants.balanceOf(address(this));
        if (_amount > antsBal) {
        ants.transfer(_to, antsBal);
        } else {
        ants.transfer(_to, _amount);
        }
        }

        // Update dev address by the previous dev.
        function dev(address _devaddr) public {
        require(msg.sender == devaddr, "dev: wut?");
        devaddr = _devaddr;
        }

        function chefSafeTransfer(IERC20 token, address to, uint256 value) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transfer.selector, to, value));
        }

        function chefSafeTransferFrom(IERC20 token, address from, address to, uint256 value) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transferFrom.selector, from, to, value));
        }

        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");
        }
        }
        }