Contract Address Details

// File: @openzeppelin/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: @openzeppelin/contracts/token/ERC777/IERC777.sol


pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev Interface of the ERC777Token standard as defined in the EIP.
 *
 * This contract uses the
 * https://eips.ethereum.org/EIPS/eip-1820[ERC1820 registry standard] to let
 * token holders and recipients react to token movements by using setting implementers
 * for the associated interfaces in said registry. See {IERC1820Registry} and
 * {ERC1820Implementer}.
 */
interface IERC777 {
    /**
     * @dev Returns the name of the token.
     */
    function name() external view returns (string memory);

    /**
     * @dev Returns the symbol of the token, usually a shorter version of the
     * name.
     */
    function symbol() external view returns (string memory);

    /**
     * @dev Returns the smallest part of the token that is not divisible. This
     * means all token operations (creation, movement and destruction) must have
     * amounts that are a multiple of this number.
     *
     * For most token contracts, this value will equal 1.
     */
    function granularity() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by an account (`owner`).
     */
    function balanceOf(address owner) external view returns (uint256);

    /**
     * @dev Moves `amount` tokens from the caller's account to `recipient`.
     *
     * If send or receive hooks are registered for the caller and `recipient`,
     * the corresponding functions will be called with `data` and empty
     * `operatorData`. See {IERC777Sender} and {IERC777Recipient}.
     *
     * Emits a {Sent} event.
     *
     * Requirements
     *
     * - the caller must have at least `amount` tokens.
     * - `recipient` cannot be the zero address.
     * - if `recipient` is a contract, it must implement the {IERC777Recipient}
     * interface.
     */
    function send(address recipient, uint256 amount, bytes calldata data) external;

    /**
     * @dev Destroys `amount` tokens from the caller's account, reducing the
     * total supply.
     *
     * If a send hook is registered for the caller, the corresponding function
     * will be called with `data` and empty `operatorData`. See {IERC777Sender}.
     *
     * Emits a {Burned} event.
     *
     * Requirements
     *
     * - the caller must have at least `amount` tokens.
     */
    function burn(uint256 amount, bytes calldata data) external;

    /**
     * @dev Returns true if an account is an operator of `tokenHolder`.
     * Operators can send and burn tokens on behalf of their owners. All
     * accounts are their own operator.
     *
     * See {operatorSend} and {operatorBurn}.
     */
    function isOperatorFor(address operator, address tokenHolder) external view returns (bool);

    /**
     * @dev Make an account an operator of the caller.
     *
     * See {isOperatorFor}.
     *
     * Emits an {AuthorizedOperator} event.
     *
     * Requirements
     *
     * - `operator` cannot be calling address.
     */
    function authorizeOperator(address operator) external;

    /**
     * @dev Revoke an account's operator status for the caller.
     *
     * See {isOperatorFor} and {defaultOperators}.
     *
     * Emits a {RevokedOperator} event.
     *
     * Requirements
     *
     * - `operator` cannot be calling address.
     */
    function revokeOperator(address operator) external;

    /**
     * @dev Returns the list of default operators. These accounts are operators
     * for all token holders, even if {authorizeOperator} was never called on
     * them.
     *
     * This list is immutable, but individual holders may revoke these via
     * {revokeOperator}, in which case {isOperatorFor} will return false.
     */
    function defaultOperators() external view returns (address[] memory);

    /**
     * @dev Moves `amount` tokens from `sender` to `recipient`. The caller must
     * be an operator of `sender`.
     *
     * If send or receive hooks are registered for `sender` and `recipient`,
     * the corresponding functions will be called with `data` and
     * `operatorData`. See {IERC777Sender} and {IERC777Recipient}.
     *
     * Emits a {Sent} event.
     *
     * Requirements
     *
     * - `sender` cannot be the zero address.
     * - `sender` must have at least `amount` tokens.
     * - the caller must be an operator for `sender`.
     * - `recipient` cannot be the zero address.
     * - if `recipient` is a contract, it must implement the {IERC777Recipient}
     * interface.
     */
    function operatorSend(
        address sender,
        address recipient,
        uint256 amount,
        bytes calldata data,
        bytes calldata operatorData
    ) external;

    /**
     * @dev Destroys `amount` tokens from `account`, reducing the total supply.
     * The caller must be an operator of `account`.
     *
     * If a send hook is registered for `account`, the corresponding function
     * will be called with `data` and `operatorData`. See {IERC777Sender}.
     *
     * Emits a {Burned} event.
     *
     * Requirements
     *
     * - `account` cannot be the zero address.
     * - `account` must have at least `amount` tokens.
     * - the caller must be an operator for `account`.
     */
    function operatorBurn(
        address account,
        uint256 amount,
        bytes calldata data,
        bytes calldata operatorData
    ) external;

    event Sent(
        address indexed operator,
        address indexed from,
        address indexed to,
        uint256 amount,
        bytes data,
        bytes operatorData
    );

    event Minted(address indexed operator, address indexed to, uint256 amount, bytes data, bytes operatorData);

    event Burned(address indexed operator, address indexed from, uint256 amount, bytes data, bytes operatorData);

    event AuthorizedOperator(address indexed operator, address indexed tokenHolder);

    event RevokedOperator(address indexed operator, address indexed tokenHolder);
}

// File: @openzeppelin/contracts/token/ERC777/IERC777Recipient.sol


pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev Interface of the ERC777TokensRecipient standard as defined in the EIP.
 *
 * Accounts can be notified of {IERC777} tokens being sent to them by having a
 * contract implement this interface (contract holders can be their own
 * implementer) and registering it on the
 * https://eips.ethereum.org/EIPS/eip-1820[ERC1820 global registry].
 *
 * See {IERC1820Registry} and {ERC1820Implementer}.
 */
interface IERC777Recipient {
    /**
     * @dev Called by an {IERC777} token contract whenever tokens are being
     * moved or created into a registered account (`to`). The type of operation
     * is conveyed by `from` being the zero address or not.
     *
     * This call occurs _after_ the token contract's state is updated, so
     * {IERC777-balanceOf}, etc., can be used to query the post-operation state.
     *
     * This function may revert to prevent the operation from being executed.
     */
    function tokensReceived(
        address operator,
        address from,
        address to,
        uint256 amount,
        bytes calldata userData,
        bytes calldata operatorData
    ) external;
}

// File: @openzeppelin/contracts/token/ERC777/IERC777Sender.sol


pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev Interface of the ERC777TokensSender standard as defined in the EIP.
 *
 * {IERC777} Token holders can be notified of operations performed on their
 * tokens by having a contract implement this interface (contract holders can be
 *  their own implementer) and registering it on the
 * https://eips.ethereum.org/EIPS/eip-1820[ERC1820 global registry].
 *
 * See {IERC1820Registry} and {ERC1820Implementer}.
 */
interface IERC777Sender {
    /**
     * @dev Called by an {IERC777} token contract whenever a registered holder's
     * (`from`) tokens are about to be moved or destroyed. The type of operation
     * is conveyed by `to` being the zero address or not.
     *
     * This call occurs _before_ the token contract's state is updated, so
     * {IERC777-balanceOf}, etc., can be used to query the pre-operation state.
     *
     * This function may revert to prevent the operation from being executed.
     */
    function tokensToSend(
        address operator,
        address from,
        address to,
        uint256 amount,
        bytes calldata userData,
        bytes calldata operatorData
    ) external;
}

// File: @openzeppelin/contracts/token/ERC20/IERC20.sol


pragma solidity >=0.6.0 <0.8.0;

/**
 * @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 <0.8.0;

/**
 * @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: @openzeppelin/contracts/utils/ReentrancyGuard.sol


pragma solidity >=0.6.0 <0.8.0;

/**
 * @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 () internal {
        _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: @openzeppelin/contracts/utils/Address.sol


pragma solidity >=0.6.2 <0.8.0;

/**
 * @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: @openzeppelin/contracts/introspection/IERC1820Registry.sol


pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev Interface of the global ERC1820 Registry, as defined in the
 * https://eips.ethereum.org/EIPS/eip-1820[EIP]. Accounts may register
 * implementers for interfaces in this registry, as well as query support.
 *
 * Implementers may be shared by multiple accounts, and can also implement more
 * than a single interface for each account. Contracts can implement interfaces
 * for themselves, but externally-owned accounts (EOA) must delegate this to a
 * contract.
 *
 * {IERC165} interfaces can also be queried via the registry.
 *
 * For an in-depth explanation and source code analysis, see the EIP text.
 */
interface IERC1820Registry {
    /**
     * @dev Sets `newManager` as the manager for `account`. A manager of an
     * account is able to set interface implementers for it.
     *
     * By default, each account is its own manager. Passing a value of `0x0` in
     * `newManager` will reset the manager to this initial state.
     *
     * Emits a {ManagerChanged} event.
     *
     * Requirements:
     *
     * - the caller must be the current manager for `account`.
     */
    function setManager(address account, address newManager) external;

    /**
     * @dev Returns the manager for `account`.
     *
     * See {setManager}.
     */
    function getManager(address account) external view returns (address);

    /**
     * @dev Sets the `implementer` contract as ``account``'s implementer for
     * `interfaceHash`.
     *
     * `account` being the zero address is an alias for the caller's address.
     * The zero address can also be used in `implementer` to remove an old one.
     *
     * See {interfaceHash} to learn how these are created.
     *
     * Emits an {InterfaceImplementerSet} event.
     *
     * Requirements:
     *
     * - the caller must be the current manager for `account`.
     * - `interfaceHash` must not be an {IERC165} interface id (i.e. it must not
     * end in 28 zeroes).
     * - `implementer` must implement {IERC1820Implementer} and return true when
     * queried for support, unless `implementer` is the caller. See
     * {IERC1820Implementer-canImplementInterfaceForAddress}.
     */
    function setInterfaceImplementer(address account, bytes32 _interfaceHash, address implementer) external;

    /**
     * @dev Returns the implementer of `interfaceHash` for `account`. If no such
     * implementer is registered, returns the zero address.
     *
     * If `interfaceHash` is an {IERC165} interface id (i.e. it ends with 28
     * zeroes), `account` will be queried for support of it.
     *
     * `account` being the zero address is an alias for the caller's address.
     */
    function getInterfaceImplementer(address account, bytes32 _interfaceHash) external view returns (address);

    /**
     * @dev Returns the interface hash for an `interfaceName`, as defined in the
     * corresponding
     * https://eips.ethereum.org/EIPS/eip-1820#interface-name[section of the EIP].
     */
    function interfaceHash(string calldata interfaceName) external pure returns (bytes32);

    /**
     *  @notice Updates the cache with whether the contract implements an ERC165 interface or not.
     *  @param account Address of the contract for which to update the cache.
     *  @param interfaceId ERC165 interface for which to update the cache.
     */
    function updateERC165Cache(address account, bytes4 interfaceId) external;

    /**
     *  @notice Checks whether a contract implements an ERC165 interface or not.
     *  If the result is not cached a direct lookup on the contract address is performed.
     *  If the result is not cached or the cached value is out-of-date, the cache MUST be updated manually by calling
     *  {updateERC165Cache} with the contract address.
     *  @param account Address of the contract to check.
     *  @param interfaceId ERC165 interface to check.
     *  @return True if `account` implements `interfaceId`, false otherwise.
     */
    function implementsERC165Interface(address account, bytes4 interfaceId) external view returns (bool);

    /**
     *  @notice Checks whether a contract implements an ERC165 interface or not without using nor updating the cache.
     *  @param account Address of the contract to check.
     *  @param interfaceId ERC165 interface to check.
     *  @return True if `account` implements `interfaceId`, false otherwise.
     */
    function implementsERC165InterfaceNoCache(address account, bytes4 interfaceId) external view returns (bool);

    event InterfaceImplementerSet(address indexed account, bytes32 indexed interfaceHash, address indexed implementer);

    event ManagerChanged(address indexed account, address indexed newManager);
}

// File: cfil/cfil.sol

pragma solidity >=0.6.2 <0.8.0;










contract CFil is Context, IERC777, IERC20, ReentrancyGuard, IERC777Recipient {
  
  //////////////////// using
  using SafeMath for uint256;
  using Address for address;

  //////////////////// const
  IERC1820Registry constant internal _ERC1820_REGISTRY = IERC1820Registry(0x1820a4B7618BdE71Dce8cdc73aAB6C95905faD24);
  
  // We inline the result of the following hashes because Solidity doesn't resolve them at compile time.
  // See https://github.com/ethereum/solidity/issues/4024.

  // keccak256("ERC777TokensSender")
  bytes32 constant private _TOKENS_SENDER_INTERFACE_HASH =
    0x29ddb589b1fb5fc7cf394961c1adf5f8c6454761adf795e67fe149f658abe895;

  // keccak256("ERC777TokensRecipient")
  bytes32 constant private _TOKENS_RECIPIENT_INTERFACE_HASH =
    0xb281fc8c12954d22544db45de3159a39272895b169a852b314f9cc762e44c53b;

  IERC777 CRFI;

  uint256 constant calcDecimals = 1e18;
  
  //////////////////// for admin
  address public superAdmin;
  mapping(address => uint256) public admins;

  // only effect erc20 interface.
  // when erc777mode equal 0, the erc777 feature is disabled;
  // when erc777mode equal 1, the erc777 feature is enabled by whitelist.
  // when erc777 mode equal 2, the erc777 feature is disabled by blacklist.
  // when erc777 mode equal 3, the erc777 feature is enabled;
  // in whitelist or black list mode, whether "from" or "to" address in list, the feature would be effected.
  enum Erc777ModeType {disabled, whitelist, blacklist, enabled}
  Erc777ModeType public erc777Mode;
  mapping(address=>bool) public blacklist;
  mapping(address=>bool) public whitelist;
  
  //////////////////// for coin
  mapping(address => uint256) private _balances;

  uint256 private _totalSupply;

  string private _name;
  string private _symbol;

  // ERC20-allowances
  mapping (address => mapping (address => uint256)) private _allowances;

  mapping(address=>bool) private _freezeAddress;

  //////////////////// for operator  
  // This isn't ever read from - it's only used to respond to the defaultOperators query.
  address[] private _defaultOperatorsArray;

  // Immutable, but accounts may revoke them (tracked in __revokedDefaultOperators).
  mapping(address => bool) private _defaultOperators;

  // For each account, a mapping of its operators and revoked default operators.
  mapping(address => mapping(address => bool)) private _operators;
  mapping(address => mapping(address => bool)) private _revokedDefaultOperators;

  //////////////////// for burn
  uint256 public burnCFilRateCRFI;
  uint256 public burnCFilFee;

  //////////////////// constructor
  /**
   * @dev `defaultOperators` may be an empty array.
   */
  constructor(address[] memory defaultOperators_,
              address CRFIAddr
              )
      {
        require(CRFIAddr.isContract(), "CRFIAddr error");
        CRFI = IERC777(CRFIAddr);
        _name = "CFIL";
        _symbol = "CFIL";

        _defaultOperatorsArray = defaultOperators_;
        for (uint256 i = 0; i < _defaultOperatorsArray.length; i++) {
          _defaultOperators[_defaultOperatorsArray[i]] = true;
        }

        // register interfaces
        _ERC1820_REGISTRY.setInterfaceImplementer(address(this), keccak256("ERC777Token"), address(this));
        _ERC1820_REGISTRY.setInterfaceImplementer(address(this), keccak256("ERC20Token"), address(this));

        superAdmin = msg.sender;

        // init mode
        ChangeMode(Erc777ModeType.disabled);
        burnCFilRateCRFI = calcDecimals / 100;

        _ERC1820_REGISTRY.setInterfaceImplementer(address(this), _TOKENS_RECIPIENT_INTERFACE_HASH, address(this));
      }

  //////////////////// modifier
  modifier IsAdmin() {
    require(msg.sender == superAdmin || admins[msg.sender] == 1, "only admin");
    _;
  }

  modifier IsSuperAdmin() {
    require(superAdmin == msg.sender, "only super admin");
    _;
  }

  modifier CheckFreeze(address addr){
    require(_freezeAddress[addr] == false, "account is freeze");
    _;
  }

  //////////////////// super admin func
  function AddAdmin(address adminAddr)
    public
    IsSuperAdmin(){
    require(admins[adminAddr] == 0, "already add this admin");
    admins[adminAddr] = 1;
  }

  function DelAdmin(address adminAddr)
    public
    IsSuperAdmin(){
    require(admins[adminAddr] == 1, "this addr is not admin");
    admins[adminAddr] = 0;
  }

  function ChangeSuperAdmin(address suAdminAddr)
    public
    IsSuperAdmin(){
    require(suAdminAddr != address(0x0), "empty new super admin");

    superAdmin = suAdminAddr;
  }

  //////////////////// for admin func
  function ChangeBurnCFilRateCRFI(uint256 rate)
    public
    IsAdmin(){

    burnCFilRateCRFI = rate;
  }

  function ChangeBurnCFilFee(uint256 fee)
    public
    IsAdmin(){

    burnCFilFee = fee;
  }
  
  function AddBlackList(address[] memory addrs)
    public
    IsAdmin(){

    for(uint256 i = 0; i < addrs.length; i++){
      address addr = addrs[i];
      if(blacklist[addr]){
        continue;
      }
      blacklist[addr] = true;
    }
  }

  function DelBlackList(address[] memory addrs)
    public
    IsAdmin(){

    for(uint256 i = 0; i < addrs.length; i++){
      address addr = addrs[i];
      if(!blacklist[addr]){
        continue;
      }
      blacklist[addr] = false;
    }
  }

  function AddWhiteList(address[] memory addrs)
    public
    IsAdmin(){

    for(uint256 i = 0; i < addrs.length; i++){
      address addr = addrs[i];
      if(whitelist[addr]){
        continue;
      }
      whitelist[addr] = true;
    }
  }

  function DelWhiteList(address[] memory addrs)
    public
    IsAdmin(){

    for(uint256 i = 0; i < addrs.length; i++){
      address addr = addrs[i];
      if(!whitelist[addr] ){
        continue;
      }
      whitelist[addr] = false;
    }
  }

  function ChangeMode(Erc777ModeType mode)
    public
    IsAdmin(){

    erc777Mode = mode;
  }

  function FreezeAddr(address[] memory addrs)
    public
    IsAdmin(){
    for(uint256 i = 0; i < addrs.length; i++){
      address addr = addrs[i];
      if(_freezeAddress[addr] == true){
        continue;
      }
      _freezeAddress[addr] = true;
    }
  }

  function UnfreezeAddr(address[] memory addrs)
    public
    IsAdmin(){
    for(uint256 i = 0; i < addrs.length; i++){
      address addr = addrs[i];
      if(_freezeAddress[addr] == false){
        continue;
      }
      _freezeAddress[addr] = false;
    }
  }

  //////////////////// event
  event BurnedCRFICFil(address indexed account,
                       uint256 amount,
                       bytes data);



  //////////////////// interface implement
  
  /**
   * @dev See {IERC777-name}.
   */
  function name() public view virtual override returns (string memory) {
    return _name;
  }

  /**
   * @dev See {IERC777-symbol}.
   */
  function symbol() public view virtual override returns (string memory) {
    return _symbol;
  }

  /**
   * @dev See {ERC20-decimals}.
   *
   * Always returns 18, as per the
   * [ERC777 EIP](https://eips.ethereum.org/EIPS/eip-777#backward-compatibility).
   */
  function decimals() public pure virtual returns (uint8) {
    return 18;
  }

  /**
   * @dev See {IERC777-granularity}.
   *
   * This implementation always returns `1`.
   */
  function granularity() public view virtual override returns (uint256) {
    return 1;
  }

  /**
   * @dev See {IERC777-totalSupply}.
   */
  function totalSupply() public view virtual override(IERC20, IERC777) returns (uint256) {
    return _totalSupply;
  }

  /**
   * @dev Returns the amount of tokens owned by an account (`tokenHolder`).
   */
  function balanceOf(address tokenHolder) public view virtual override(IERC20, IERC777) returns (uint256) {
    return _balances[tokenHolder];
  }

  function tokensReceived(
        address operator,
        address from,
        address to,
        uint256 amount,
        bytes calldata userData,
        bytes calldata operatorData)
    public
    override
    nonReentrant(){

    require(msg.sender == address(CRFI), "only receive CRFI");
    require(burnCFilRateCRFI > 0, "burn cfil rate CRFI is zero, should use burn directly");

    uint256 burnCFil = _calcBurnCFil(amount);
    require(balanceOf(from) >= burnCFil, "not enough cfil");

    _burn(from, burnCFil, userData, operatorData);
    CRFI.burn(amount, userData);

    // for ensure call this method;
    _emitBurn(from, burnCFil, userData);
  }

  /**
   * @dev See {IERC777-send}.
   *
   * Also emits a {IERC20-Transfer} event for ERC20 compatibility.
   */
  function send(address recipient, uint256 amount, bytes memory data) public virtual override  CheckFreeze(_msgSender()){
    _send(_msgSender(), recipient, amount, data, "", true);
  }

  /**
   * @dev See {IERC20-transfer}.
   *
   * Unlike `send`, `recipient` is _not_ required to implement the {IERC777Recipient}
   * interface if it is a contract.
   *
   * Also emits a {Sent} event.
   */
  function transfer(address recipient, uint256 amount)
    public
    virtual
    override
    CheckFreeze(_msgSender())
    returns (bool) {
    require(recipient != address(0), "ERC777: transfer to the zero address");

    address from = _msgSender();

    bool erc777Enable = _enableERC777(from, recipient);

    if(erc777Enable){
      _callTokensToSend(from, from, recipient, amount, "", "");
    }

    _move(from, from, recipient, amount, "", "", erc777Enable);

    if(erc777Enable){
      _callTokensReceived(from, from, recipient, amount, "", "", false);
    }

    return true;
  }

  /**
   * @dev See {IERC777-burn}.
   *
   * Also emits a {IERC20-Transfer} event for ERC20 compatibility.
   */
  function burn(uint256 amount, bytes memory data) public virtual override  CheckFreeze(_msgSender()){
    _burn(_msgSender(), amount, data, "");
    if(burnCFilRateCRFI == 0){
      _emitBurn(_msgSender(), amount, data);
    }
  }

  /**
   * @dev See {IERC777-isOperatorFor}.
   */
  function isOperatorFor(address operator, address tokenHolder) public view virtual override returns (bool) {
    return operator == tokenHolder ||
      (_defaultOperators[operator] && !_revokedDefaultOperators[tokenHolder][operator]) ||
      _operators[tokenHolder][operator];
  }

  /**
   * @dev See {IERC777-authorizeOperator}.
   */
  function authorizeOperator(address operator) public virtual override  {
    require(_msgSender() != operator, "ERC777: authorizing self as operator");

    if (_defaultOperators[operator]) {
      delete _revokedDefaultOperators[_msgSender()][operator];
    } else {
      _operators[_msgSender()][operator] = true;
    }

    emit AuthorizedOperator(operator, _msgSender());
  }

  /**
   * @dev See {IERC777-revokeOperator}.
   */
  function revokeOperator(address operator) public virtual override  {
    require(operator != _msgSender(), "ERC777: revoking self as operator");

    if (_defaultOperators[operator]) {
      _revokedDefaultOperators[_msgSender()][operator] = true;
    } else {
      delete _operators[_msgSender()][operator];
    }

    emit RevokedOperator(operator, _msgSender());
  }

  /**
   * @dev See {IERC777-defaultOperators}.
   */
  function defaultOperators() public view virtual override returns (address[] memory) {
    return _defaultOperatorsArray;
  }

  /**
   * @dev See {IERC777-operatorSend}.
   *
   * Emits {Sent} and {IERC20-Transfer} events.
   */
  function operatorSend(
                        address sender,
                        address recipient,
                        uint256 amount,
                        bytes memory data,
                        bytes memory operatorData
                        )
    public
    virtual
    override
    CheckFreeze(sender)
  {
    require(isOperatorFor(_msgSender(), sender), "ERC777: caller is not an operator for holder");
    _send(sender, recipient, amount, data, operatorData, true);
  }

  /**
   * @dev See {IERC777-operatorBurn}.
   *
   * Emits {Burned} and {IERC20-Transfer} events.
   */
  function operatorBurn(address account, uint256 amount, bytes memory data, bytes memory operatorData) public virtual override CheckFreeze(account){
    require(isOperatorFor(_msgSender(), account), "ERC777: caller is not an operator for holder");
    _burn(account, amount, data, operatorData);
  }

  /**
   * @dev See {IERC20-allowance}.
   *
   * Note that operator and allowance concepts are orthogonal: operators may
   * not have allowance, and accounts with allowance may not be operators
   * themselves.
   */
  function allowance(address holder, address spender) public view virtual override returns (uint256) {
    return _allowances[holder][spender];
  }

  /**
   * @dev See {IERC20-approve}.
   *
   * Note that accounts cannot have allowance issued by their operators.
   */
  function approve(address spender, uint256 value) public virtual override returns (bool) {
    address holder = _msgSender();
    _approve(holder, spender, value);
    return true;
  }

  /**
   * @dev See {IERC20-transferFrom}.
   *
   * Note that operator and allowance concepts are orthogonal: operators cannot
   * call `transferFrom` (unless they have allowance), and accounts with
   * allowance cannot call `operatorSend` (unless they are operators).
   *
   * Emits {Sent}, {IERC20-Transfer} and {IERC20-Approval} events.
   */
  function transferFrom(address holder, address recipient, uint256 amount) public virtual override CheckFreeze(holder) returns (bool) {
    require(recipient != address(0), "ERC777: transfer to the zero address");
    require(holder != address(0), "ERC777: transfer from the zero address");

    address spender = _msgSender();

    bool erc777Enable = _enableERC777(holder, recipient);

    if(erc777Enable){
      _callTokensToSend(spender, holder, recipient, amount, "", "");
    }

    _move(spender, holder, recipient, amount, "", "", erc777Enable);
    _approve(holder, spender, _allowances[holder][spender].sub(amount, "ERC777: transfer amount exceeds allowance"));

    if(erc777Enable){
      _callTokensReceived(spender, holder, recipient, amount, "", "", false);
    }

    return true;
  }

  function mint(address account,
                uint256 amount,
                bytes memory userData)
    public
    IsAdmin(){
    _mint(account, amount, userData, "");
  }
  
  /**
   * @dev Creates `amount` tokens and assigns them to `account`, increasing
   * the total supply.
   *
   * If a send hook is registered for `account`, the corresponding function
   * will be called with `operator`, `data` and `operatorData`.
   *
   * See {IERC777Sender} and {IERC777Recipient}.
   *
   * Emits {Minted} and {IERC20-Transfer} events.
   *
   * Requirements
   *
   * - `account` cannot be the zero address.
   * - if `account` is a contract, it must implement the {IERC777Recipient}
   * interface.
   */
  function _mint(
                 address account,
                 uint256 amount,
                 bytes memory userData,
                 bytes memory operatorData
                 )
    internal
    virtual
  {
    require(account != address(0), "ERC777: mint to the zero address");

    address operator = _msgSender();

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

    // Update state variables
    _totalSupply = _totalSupply.add(amount);
    _balances[account] = _balances[account].add(amount);

    _callTokensReceived(operator, address(0), account, amount, userData, operatorData, true);

    emit Minted(operator, account, amount, userData, operatorData);
    emit Transfer(address(0), account, amount);
  }

  /**
   * @dev Send tokens
   * @param from address token holder address
   * @param to address recipient address
   * @param amount uint256 amount of tokens to transfer
   * @param userData bytes extra information provided by the token holder (if any)
   * @param operatorData bytes extra information provided by the operator (if any)
   * @param requireReceptionAck if true, contract recipients are required to implement ERC777TokensRecipient
   */
  function _send(
                 address from,
                 address to,
                 uint256 amount,
                 bytes memory userData,
                 bytes memory operatorData,
                 bool requireReceptionAck
                 )
    internal
    virtual
  {
    require(from != address(0), "ERC777: send from the zero address");
    require(to != address(0), "ERC777: send to the zero address");

    address operator = _msgSender();

    _callTokensToSend(operator, from, to, amount, userData, operatorData);

    _move(operator, from, to, amount, userData, operatorData, true);

    _callTokensReceived(operator, from, to, amount, userData, operatorData, requireReceptionAck);
  }

  /**
   * @dev Burn tokens
   * @param from address token holder address
   * @param amount uint256 amount of tokens to burn
   * @param data bytes extra information provided by the token holder
   * @param operatorData bytes extra information provided by the operator (if any)
   */
  function _burn(
                 address from,
                 uint256 amount,
                 bytes memory data,
                 bytes memory operatorData
                 )
    internal
    virtual
  {
    require(from != address(0), "ERC777: burn from the zero address");

    address operator = _msgSender();

    _callTokensToSend(operator, from, address(0), amount, data, operatorData);

    _beforeTokenTransfer(operator, from, address(0), amount);

    // Update state variables
    _balances[from] = _balances[from].sub(amount, "ERC777: burn amount exceeds balance");
    _totalSupply = _totalSupply.sub(amount);

    emit Burned(operator, from, amount, data, operatorData);
    emit Transfer(from, address(0), amount);
  }

  function _move(
                 address operator,
                 address from,
                 address to,
                 uint256 amount,
                 bytes memory userData,
                 bytes memory operatorData,
                 bool erc777Enable
                 )
    private
  {
    if(erc777Enable){
      _beforeTokenTransfer(operator, from, to, amount);
    }

    _balances[from] = _balances[from].sub(amount, "ERC777: transfer amount exceeds balance");
    _balances[to] = _balances[to].add(amount);

    emit Sent(operator, from, to, amount, userData, operatorData);
    emit Transfer(from, to, amount);
  }

  /**
   * @dev See {ERC20-_approve}.
   *
   * Note that accounts cannot have allowance issued by their operators.
   */
  function _approve(address holder, address spender, uint256 value) internal {
    require(holder != address(0), "ERC777: approve from the zero address");
    require(spender != address(0), "ERC777: approve to the zero address");

    _allowances[holder][spender] = value;
    emit Approval(holder, spender, value);
  }

  /**
   * @dev Call from.tokensToSend() if the interface is registered
   * @param operator address operator requesting the transfer
   * @param from address token holder address
   * @param to address recipient address
   * @param amount uint256 amount of tokens to transfer
   * @param userData bytes extra information provided by the token holder (if any)
   * @param operatorData bytes extra information provided by the operator (if any)
   */
  function _callTokensToSend(
                             address operator,
                             address from,
                             address to,
                             uint256 amount,
                             bytes memory userData,
                             bytes memory operatorData
                             )
    private
  {
    address implementer = _ERC1820_REGISTRY.getInterfaceImplementer(from, _TOKENS_SENDER_INTERFACE_HASH);
    if (implementer != address(0)) {
      IERC777Sender(implementer).tokensToSend(operator, from, to, amount, userData, operatorData);
    }
  }

  /**
   * @dev Call to.tokensReceived() if the interface is registered. Reverts if the recipient is a contract but
   * tokensReceived() was not registered for the recipient
   * @param operator address operator requesting the transfer
   * @param from address token holder address
   * @param to address recipient address
   * @param amount uint256 amount of tokens to transfer
   * @param userData bytes extra information provided by the token holder (if any)
   * @param operatorData bytes extra information provided by the operator (if any)
   * @param requireReceptionAck if true, contract recipients are required to implement ERC777TokensRecipient
   */
  function _callTokensReceived(
                               address operator,
                               address from,
                               address to,
                               uint256 amount,
                               bytes memory userData,
                               bytes memory operatorData,
                               bool requireReceptionAck
                               )
    private
  {
    address implementer = _ERC1820_REGISTRY.getInterfaceImplementer(to, _TOKENS_RECIPIENT_INTERFACE_HASH);
    if (implementer != address(0)) {
      IERC777Recipient(implementer).tokensReceived(operator, from, to, amount, userData, operatorData);
    } else if (requireReceptionAck) {
      require(!to.isContract(), "ERC777: token recipient contract has no implementer for ERC777TokensRecipient");
    }
  }

  /**
   * @dev Hook that is called before any token transfer. This includes
   * calls to {send}, {transfer}, {operatorSend}, 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 operator, address from, address to, uint256 amount) internal virtual { }

  
  function _enableERC777(address from, address to)
    internal
    view
    returns(bool){

    if(erc777Mode == Erc777ModeType.disabled){
      return false;
    }

    if(erc777Mode == Erc777ModeType.enabled){
      return true;
    }

    if(erc777Mode == Erc777ModeType.whitelist){
      return whitelist[from] || whitelist[to];
    }

    if(erc777Mode == Erc777ModeType.blacklist){
      return (!blacklist[from]) && (!blacklist[to]);
    }

    return false;
  }

  function _calcBurnCFil(uint256 CRFINum)
    public
    view
    returns(uint256 CFilNum){

    return CRFINum.mul(calcDecimals) / burnCFilRateCRFI;
  }

  function _calcNeedBurnCRFI(uint256 CFilNum)
    public
    view
    returns(uint256 CRFINum){

    return CFilNum.mul(burnCFilRateCRFI) / calcDecimals;
  }

  function _emitBurn(address from, uint256 amount, bytes memory data)
    internal{

    require(amount >= burnCFilFee, "amount <= burnCFilFee");
    require(data.length > 0, "no user data");

    amount = amount.sub(burnCFilFee);

    if(amount > 0){
      emit BurnedCRFICFil(from, amount, data);
    }
  }
}