// SPDX-License-Identifier: MIT

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;
    }
}

/**
 * @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);
}

/**
 * @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;
}

/**
 * @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;
}

/**
 * @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);
}

/**
 * @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;
    }
}

/**
 * @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);
    }

    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);
            }
        }
    }
}

/**
 * @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);
}

/**
 * @dev Implementation of the {IERC777} 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}.
 *
 * Support for ERC20 is included in this contract, as specified by the EIP: both
 * the ERC777 and ERC20 interfaces can be safely used when interacting with it.
 * Both {IERC777-Sent} and {IERC20-Transfer} events are emitted on token
 * movements.
 *
 * Additionally, the {IERC777-granularity} value is hard-coded to `1`, meaning that there
 * are no special restrictions in the amount of tokens that created, moved, or
 * destroyed. This makes integration with ERC20 applications seamless.
 */
contract ERC777 is Context, IERC777, IERC20 {
    using SafeMath for uint256;
    using Address for address;

    IERC1820Registry constant internal _ERC1820_REGISTRY = IERC1820Registry(0x1820a4B7618BdE71Dce8cdc73aAB6C95905faD24);

    mapping(address => uint256) private _balances;

    uint256 private _totalSupply;

    string private _name;
    string private _symbol;

    // 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;

    // 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;

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

    /**
     * @dev `defaultOperators` may be an empty array.
     */
    constructor(
        string memory name_,
        string memory symbol_,
        address[] memory defaultOperators_
    ) public {
        _name = name_;
        _symbol = symbol_;

        _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));
    }

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

    /**
     * @dev See {IERC777-symbol}.
     */
    function symbol() public view 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 returns (uint8) {
        return 18;
    }

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

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

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

    /**
     * @dev See {IERC777-send}.
     *
     * Also emits a {IERC20-Transfer} event for ERC20 compatibility.
     */
    function send(address recipient, uint256 amount, bytes memory data) public override  {
        _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 override returns (bool) {
        require(recipient != address(0), "ERC777: transfer to the zero address");

        address from = _msgSender();

        _callTokensToSend(from, from, recipient, amount, "", "");

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

        _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 override  {
        _burn(_msgSender(), amount, data, "");
    }

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

    /**
     * @dev See {IERC777-authorizeOperator}.
     */
    function authorizeOperator(address operator) public 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 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 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 override
    {
        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 override {
        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 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 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 override 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();

        _callTokensToSend(spender, holder, recipient, amount, "", "");

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

        _callTokensReceived(spender, holder, recipient, amount, "", "", false);

        return true;
    }

    /**
     * @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
    {
        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);

        _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();

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

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

        // 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
    )
        private
    {
        _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 { }
}

/**
 * @dev Contract module which allows children to implement an emergency stop
 * mechanism that can be triggered by an authorized account.
 *
 * This module is used through inheritance. It will make available the
 * modifiers `whenNotPaused` and `whenPaused`, which can be applied to
 * the functions of your contract. Note that they will not be pausable by
 * simply including this module, only once the modifiers are put in place.
 */
abstract contract Pausable is Context {
    /**
     * @dev Emitted when the pause is triggered by `account`.
     */
    event Paused(address account);

    /**
     * @dev Emitted when the pause is lifted by `account`.
     */
    event Unpaused(address account);

    bool private _paused;

    /**
     * @dev Initializes the contract in unpaused state.
     */
    constructor () internal {
        _paused = false;
    }

    /**
     * @dev Returns true if the contract is paused, and false otherwise.
     */
    function paused() public view returns (bool) {
        return _paused;
    }

    /**
     * @dev Modifier to make a function callable only when the contract is not paused.
     *
     * Requirements:
     *
     * - The contract must not be paused.
     */
    modifier whenNotPaused() {
        require(!_paused, "Pausable: paused");
        _;
    }

    /**
     * @dev Modifier to make a function callable only when the contract is paused.
     *
     * Requirements:
     *
     * - The contract must be paused.
     */
    modifier whenPaused() {
        require(_paused, "Pausable: not paused");
        _;
    }

    /**
     * @dev Triggers stopped state.
     *
     * Requirements:
     *
     * - The contract must not be paused.
     */
    function _pause() internal virtual whenNotPaused {
        _paused = true;
        emit Paused(_msgSender());
    }

    /**
     * @dev Returns to normal state.
     *
     * Requirements:
     *
     * - The contract must be paused.
     */
    function _unpause() internal virtual whenPaused {
        _paused = false;
        emit Unpaused(_msgSender());
    }
}

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

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

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

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

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

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

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

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

            bytes32 lastvalue = set._values[lastIndex];

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

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

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

            return true;
        } else {
            return false;
        }
    }

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

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

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

    // Bytes32Set

    struct Bytes32Set {
        Set _inner;
    }

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

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

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

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

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

    // AddressSet

    struct AddressSet {
        Set _inner;
    }

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

/**
 * @dev Contract module that allows children to implement role-based access
 * control mechanisms.
 *
 * Roles are referred to by their `bytes32` identifier. These should be exposed
 * in the external API and be unique. The best way to achieve this is by
 * using `public constant` hash digests:
 *
 * ```
 * bytes32 public constant MY_ROLE = keccak256("MY_ROLE");
 * ```
 *
 * Roles can be used to represent a set of permissions. To restrict access to a
 * function call, use {hasRole}:
 *
 * ```
 * function foo() public {
 *     require(hasRole(MY_ROLE, msg.sender));
 *     ...
 * }
 * ```
 *
 * Roles can be granted and revoked dynamically via the {grantRole} and
 * {revokeRole} functions. Each role has an associated admin role, and only
 * accounts that have a role's admin role can call {grantRole} and {revokeRole}.
 *
 * By default, the admin role for all roles is `DEFAULT_ADMIN_ROLE`, which means
 * that only accounts with this role will be able to grant or revoke other
 * roles. More complex role relationships can be created by using
 * {_setRoleAdmin}.
 *
 * WARNING: The `DEFAULT_ADMIN_ROLE` is also its own admin: it has permission to
 * grant and revoke this role. Extra precautions should be taken to secure
 * accounts that have been granted it.
 */
abstract contract AccessControl is Context {
    using EnumerableSet for EnumerableSet.AddressSet;
    using Address for address;

    struct RoleData {
        EnumerableSet.AddressSet members;
        bytes32 adminRole;
    }

    mapping (bytes32 => RoleData) private _roles;

    bytes32 public constant DEFAULT_ADMIN_ROLE = 0x00;

    /**
     * @dev Emitted when `newAdminRole` is set as ``role``'s admin role, replacing `previousAdminRole`
     *
     * `DEFAULT_ADMIN_ROLE` is the starting admin for all roles, despite
     * {RoleAdminChanged} not being emitted signaling this.
     *
     * _Available since v3.1._
     */
    event RoleAdminChanged(bytes32 indexed role, bytes32 indexed previousAdminRole, bytes32 indexed newAdminRole);

    /**
     * @dev Emitted when `account` is granted `role`.
     *
     * `sender` is the account that originated the contract call, an admin role
     * bearer except when using {_setupRole}.
     */
    event RoleGranted(bytes32 indexed role, address indexed account, address indexed sender);

    /**
     * @dev Emitted when `account` is revoked `role`.
     *
     * `sender` is the account that originated the contract call:
     *   - if using `revokeRole`, it is the admin role bearer
     *   - if using `renounceRole`, it is the role bearer (i.e. `account`)
     */
    event RoleRevoked(bytes32 indexed role, address indexed account, address indexed sender);

    /**
     * @dev Returns `true` if `account` has been granted `role`.
     */
    function hasRole(bytes32 role, address account) public view returns (bool) {
        return _roles[role].members.contains(account);
    }

    /**
     * @dev Returns the number of accounts that have `role`. Can be used
     * together with {getRoleMember} to enumerate all bearers of a role.
     */
    function getRoleMemberCount(bytes32 role) public view returns (uint256) {
        return _roles[role].members.length();
    }

    /**
     * @dev Returns one of the accounts that have `role`. `index` must be a
     * value between 0 and {getRoleMemberCount}, non-inclusive.
     *
     * Role bearers are not sorted in any particular way, and their ordering may
     * change at any point.
     *
     * WARNING: When using {getRoleMember} and {getRoleMemberCount}, make sure
     * you perform all queries on the same block. See the following
     * https://forum.openzeppelin.com/t/iterating-over-elements-on-enumerableset-in-openzeppelin-contracts/2296[forum post]
     * for more information.
     */
    function getRoleMember(bytes32 role, uint256 index) public view returns (address) {
        return _roles[role].members.at(index);
    }

    /**
     * @dev Returns the admin role that controls `role`. See {grantRole} and
     * {revokeRole}.
     *
     * To change a role's admin, use {_setRoleAdmin}.
     */
    function getRoleAdmin(bytes32 role) public view returns (bytes32) {
        return _roles[role].adminRole;
    }

    /**
     * @dev Grants `role` to `account`.
     *
     * If `account` had not been already granted `role`, emits a {RoleGranted}
     * event.
     *
     * Requirements:
     *
     * - the caller must have ``role``'s admin role.
     */
    function grantRole(bytes32 role, address account) public virtual {
        require(hasRole(_roles[role].adminRole, _msgSender()), "AccessControl: sender must be an admin to grant");

        _grantRole(role, account);
    }

    /**
     * @dev Revokes `role` from `account`.
     *
     * If `account` had been granted `role`, emits a {RoleRevoked} event.
     *
     * Requirements:
     *
     * - the caller must have ``role``'s admin role.
     */
    function revokeRole(bytes32 role, address account) public virtual {
        require(hasRole(_roles[role].adminRole, _msgSender()), "AccessControl: sender must be an admin to revoke");

        _revokeRole(role, account);
    }

    /**
     * @dev Revokes `role` from the calling account.
     *
     * Roles are often managed via {grantRole} and {revokeRole}: this function's
     * purpose is to provide a mechanism for accounts to lose their privileges
     * if they are compromised (such as when a trusted device is misplaced).
     *
     * If the calling account had been granted `role`, emits a {RoleRevoked}
     * event.
     *
     * Requirements:
     *
     * - the caller must be `account`.
     */
    function renounceRole(bytes32 role, address account) public virtual {
        require(account == _msgSender(), "AccessControl: can only renounce roles for self");

        _revokeRole(role, account);
    }

    /**
     * @dev Grants `role` to `account`.
     *
     * If `account` had not been already granted `role`, emits a {RoleGranted}
     * event. Note that unlike {grantRole}, this function doesn't perform any
     * checks on the calling account.
     *
     * [WARNING]
     * ====
     * This function should only be called from the constructor when setting
     * up the initial roles for the system.
     *
     * Using this function in any other way is effectively circumventing the admin
     * system imposed by {AccessControl}.
     * ====
     */
    function _setupRole(bytes32 role, address account) internal virtual {
        _grantRole(role, account);
    }

    /**
     * @dev Sets `adminRole` as ``role``'s admin role.
     *
     * Emits a {RoleAdminChanged} event.
     */
    function _setRoleAdmin(bytes32 role, bytes32 adminRole) internal virtual {
        emit RoleAdminChanged(role, _roles[role].adminRole, adminRole);
        _roles[role].adminRole = adminRole;
    }

    function _grantRole(bytes32 role, address account) private {
        if (_roles[role].members.add(account)) {
            emit RoleGranted(role, account, _msgSender());
        }
    }

    function _revokeRole(bytes32 role, address account) private {
        if (_roles[role].members.remove(account)) {
            emit RoleRevoked(role, account, _msgSender());
        }
    }
}

/**
 * @dev ERC777 token with pausable token transfers, minting and burning.
 *
 * Useful for scenarios such as preventing trades until the end of an evaluation
 * period, or having an emergency switch for freezing all token transfers in the
 * event of a large bug.
 *
 * _Available since v3.1._
 */
abstract contract ERC777MintablePausableBlocklistable is Context, AccessControl, ERC777, Pausable {
    bytes32 public constant MINTER_ROLE = keccak256("MINTER_ROLE");
    bytes32 public constant PAUSER_ROLE = keccak256("PAUSER_ROLE");
    bytes32 public constant BLOCK_ROLE = keccak256("BLOCK_ROLE");

    bool public _mintingFinished = false;

    mapping(address => bool) _blocklist;
    
    event Blocked(address account);
    event Unblocked(address account);
    event MintFinished();

    /**
     * @dev Grants `DEFAULT_ADMIN_ROLE`, `MINTER_ROLE`, and `PAUSER_ROLE` to the account that
     * deploys the contract.
     */
    constructor(        
        string memory name,
        string memory symbol,
        address[] memory defaultOperators
    ) 
        public ERC777(name, symbol, defaultOperators) 
    {
        _setupRole(DEFAULT_ADMIN_ROLE, _msgSender());

        _setupRole(MINTER_ROLE, _msgSender());
        _setupRole(PAUSER_ROLE, _msgSender());
        _setupRole(BLOCK_ROLE, _msgSender());
    }

    /**
     * @dev Pauses all token transfers.
     *
     * See {Pausable-_pause}.
     *
     * Requirements:
     *
     * - the caller must have the `PAUSER_ROLE`.
     */
    function pause() public virtual {
        require(hasRole(PAUSER_ROLE, _msgSender()), "ERC777MintablePausableBlacklistable: must have pauser role to pause");
        _pause();
    }

    /**
     * @dev Unpauses all token transfers.
     *
     * See {Pausable-_unpause}.
     *
     * Requirements:
     *
     * - the caller must have the `PAUSER_ROLE`.
     */
    function unpause() public virtual {
        require(hasRole(PAUSER_ROLE, _msgSender()), "ERC777MintablePausableBlocklistable: must have pauser role to unpause");
        _unpause();
    }

    /**
     * @dev Block account
     *
     * Requirements:
     *
     * - the caller must have the `BLOCK_ROLE`.
     */
    function blockAccount(address account) public virtual {
        require(hasRole(BLOCK_ROLE, _msgSender()), "ERC777MintablePausableBlocklistable: must have block role to block");
        _blocklist[account] = true;
        emit Blocked(account);
    }
    
    /**
     * @dev Unblock account
     *
     * Requirements:
     *
     * - the caller must have the `BLOCK_ROLE`.
     */    
    function unblockAccount(address account) public virtual {
        require(hasRole(BLOCK_ROLE, _msgSender()), "ERC777MintablePausableBlocklistable: must have block role to unblock");
        _blocklist[account] = false;
        emit Unblocked(account);
    }

   /**
    * @return true if the user is blocked
    */
    function isBlockListed(address account) public view returns (bool) {
        return _blocklist[account];
    }

    /**
     * @dev See {ERC777-_mint}.
     *
     * Requirements:
     *
     * - the caller must have the {MinterRole}.
     */
    function mint(
        address account,
        uint256 amount,
        bytes memory userData,
        bytes memory operatorData
    ) public virtual {
        require(hasRole(MINTER_ROLE, _msgSender()), "ERC777MintablePausableBlocklistable: must have minter role to mint");
        require(!_mintingFinished, "ERC777MintablePausableBlocklistable: mint finished");
        
        _mint(account, amount, userData, operatorData);
    }

   /**
    * @return true if the minting is finished
    */
    function isFinishedMinting() public view returns (bool) {
        return _mintingFinished;
    }

    /**
    * @dev Function to stop minting new tokens.
    * @return True if the operation was successful.
    */
    function finishMinting() public returns (bool) {
        require(hasRole(MINTER_ROLE, _msgSender()), "ERC777MintablePausableBlocklistable: must have minter role to finish minting");
        _mintingFinished = true;

        emit MintFinished();
        return true;
    }

    /**
     * @dev See {ERC777-_beforeTokenTransfer}.
     *
     * Requirements:
     *
     * - the contract must not be paused.
     */
    function _beforeTokenTransfer(
        address operator, 
        address from, 
        address to, 
        uint256 amount
    )

        internal virtual override
    {
        super._beforeTokenTransfer(operator, from, to, amount);

        require(!paused(), "ERC20MintablePausableBlocklistable: token transfer while paused");
        require(!isBlockListed(operator), "ERC20MintablePausableBlocklistable: account is blocked");
        require(!isBlockListed(from), "ERC20MintablePausableBlocklistable: account is blocked");
        require(!isBlockListed(to), "ERC20MintablePausableBlocklistable: account is blocked");
    }

}

/**
 * @title VraToken
 */
contract VraToken is ERC777MintablePausableBlocklistable {

    /**
     * @dev Constructor that gives msg.sender all of existing tokens.
     */
    constructor () public ERC777MintablePausableBlocklistable("VERA", "VRA", new address[](0)) {
        _mint(msg.sender, 10356466694667075153057994000, "", "");
    }  
}

/* ERC1820 Pseudo-introspection Registry Contract
 * This standard defines a universal registry smart contract where any address (contract or regular account) can
 * register which interface it supports and which smart contract is responsible for its implementation.
 *
 * Written in 2019 by Jordi Baylina and Jacques Dafflon
 *
 * To the extent possible under law, the author(s) have dedicated all copyright and related and neighboring rights to
 * this software to the public domain worldwide. This software is distributed without any warranty.
 *
 * You should have received a copy of the CC0 Public Domain Dedication along with this software. If not, see
 * <http://creativecommons.org/publicdomain/zero/1.0/>.
 *
 *    ███████╗██████╗  ██████╗ ██╗ █████╗ ██████╗  ██████╗
 *    ██╔════╝██╔══██╗██╔════╝███║██╔══██╗╚════██╗██╔═████╗
 *    █████╗  ██████╔╝██║     ╚██║╚█████╔╝ █████╔╝██║██╔██║
 *    ██╔══╝  ██╔══██╗██║      ██║██╔══██╗██╔═══╝ ████╔╝██║
 *    ███████╗██║  ██║╚██████╗ ██║╚█████╔╝███████╗╚██████╔╝
 *    ╚══════╝╚═╝  ╚═╝ ╚═════╝ ╚═╝ ╚════╝ ╚══════╝ ╚═════╝
 *
 *    ██████╗ ███████╗ ██████╗ ██╗███████╗████████╗██████╗ ██╗   ██╗
 *    ██╔══██╗██╔════╝██╔════╝ ██║██╔════╝╚══██╔══╝██╔══██╗╚██╗ ██╔╝
 *    ██████╔╝█████╗  ██║  ███╗██║███████╗   ██║   ██████╔╝ ╚████╔╝
 *    ██╔══██╗██╔══╝  ██║   ██║██║╚════██║   ██║   ██╔══██╗  ╚██╔╝
 *    ██║  ██║███████╗╚██████╔╝██║███████║   ██║   ██║  ██║   ██║
 *    ╚═╝  ╚═╝╚══════╝ ╚═════╝ ╚═╝╚══════╝   ╚═╝   ╚═╝  ╚═╝   ╚═╝
 *
 */
pragma solidity 0.5.3;
// IV is value needed to have a vanity address starting with '0x1820'.
// IV: 53759

/// @dev The interface a contract MUST implement if it is the implementer of
/// some (other) interface for any address other than itself.
interface ERC1820ImplementerInterface {
    /// @notice Indicates whether the contract implements the interface 'interfaceHash' for the address 'addr' or not.
    /// @param interfaceHash keccak256 hash of the name of the interface
    /// @param addr Address for which the contract will implement the interface
    /// @return ERC1820_ACCEPT_MAGIC only if the contract implements 'interfaceHash' for the address 'addr'.
    function canImplementInterfaceForAddress(bytes32 interfaceHash, address addr) external view returns(bytes32);
}


/// @title ERC1820 Pseudo-introspection Registry Contract
/// @author Jordi Baylina and Jacques Dafflon
/// @notice This contract is the official implementation of the ERC1820 Registry.
/// @notice For more details, see https://eips.ethereum.org/EIPS/eip-1820
contract ERC1820Registry {
    /// @notice ERC165 Invalid ID.
    bytes4 constant internal INVALID_ID = 0xffffffff;
    /// @notice Method ID for the ERC165 supportsInterface method (= `bytes4(keccak256('supportsInterface(bytes4)'))`).
    bytes4 constant internal ERC165ID = 0x01ffc9a7;
    /// @notice Magic value which is returned if a contract implements an interface on behalf of some other address.
    bytes32 constant internal ERC1820_ACCEPT_MAGIC = keccak256(abi.encodePacked("ERC1820_ACCEPT_MAGIC"));

    /// @notice mapping from addresses and interface hashes to their implementers.
    mapping(address => mapping(bytes32 => address)) internal interfaces;
    /// @notice mapping from addresses to their manager.
    mapping(address => address) internal managers;
    /// @notice flag for each address and erc165 interface to indicate if it is cached.
    mapping(address => mapping(bytes4 => bool)) internal erc165Cached;

    /// @notice Indicates a contract is the 'implementer' of 'interfaceHash' for 'addr'.
    event InterfaceImplementerSet(address indexed addr, bytes32 indexed interfaceHash, address indexed implementer);
    /// @notice Indicates 'newManager' is the address of the new manager for 'addr'.
    event ManagerChanged(address indexed addr, address indexed newManager);

    /// @notice Query if an address implements an interface and through which contract.
    /// @param _addr Address being queried for the implementer of an interface.
    /// (If '_addr' is the zero address then 'msg.sender' is assumed.)
    /// @param _interfaceHash Keccak256 hash of the name of the interface as a string.
    /// E.g., 'web3.utils.keccak256("ERC777TokensRecipient")' for the 'ERC777TokensRecipient' interface.
    /// @return The address of the contract which implements the interface '_interfaceHash' for '_addr'
    /// or '0' if '_addr' did not register an implementer for this interface.
    function getInterfaceImplementer(address _addr, bytes32 _interfaceHash) external view returns (address) {
        address addr = _addr == address(0) ? msg.sender : _addr;
        if (isERC165Interface(_interfaceHash)) {
            bytes4 erc165InterfaceHash = bytes4(_interfaceHash);
            return implementsERC165Interface(addr, erc165InterfaceHash) ? addr : address(0);
        }
        return interfaces[addr][_interfaceHash];
    }

    /// @notice Sets the contract which implements a specific interface for an address.
    /// Only the manager defined for that address can set it.
    /// (Each address is the manager for itself until it sets a new manager.)
    /// @param _addr Address for which to set the interface.
    /// (If '_addr' is the zero address then 'msg.sender' is assumed.)
    /// @param _interfaceHash Keccak256 hash of the name of the interface as a string.
    /// E.g., 'web3.utils.keccak256("ERC777TokensRecipient")' for the 'ERC777TokensRecipient' interface.
    /// @param _implementer Contract address implementing '_interfaceHash' for '_addr'.
    function setInterfaceImplementer(address _addr, bytes32 _interfaceHash, address _implementer) external {
        address addr = _addr == address(0) ? msg.sender : _addr;
        require(getManager(addr) == msg.sender, "Not the manager");

        require(!isERC165Interface(_interfaceHash), "Must not be an ERC165 hash");
        if (_implementer != address(0) && _implementer != msg.sender) {
            require(
                ERC1820ImplementerInterface(_implementer)
                    .canImplementInterfaceForAddress(_interfaceHash, addr) == ERC1820_ACCEPT_MAGIC,
                "Does not implement the interface"
            );
        }
        interfaces[addr][_interfaceHash] = _implementer;
        emit InterfaceImplementerSet(addr, _interfaceHash, _implementer);
    }

    /// @notice Sets '_newManager' as manager for '_addr'.
    /// The new manager will be able to call 'setInterfaceImplementer' for '_addr'.
    /// @param _addr Address for which to set the new manager.
    /// @param _newManager Address of the new manager for 'addr'. (Pass '0x0' to reset the manager to '_addr'.)
    function setManager(address _addr, address _newManager) external {
        require(getManager(_addr) == msg.sender, "Not the manager");
        managers[_addr] = _newManager == _addr ? address(0) : _newManager;
        emit ManagerChanged(_addr, _newManager);
    }

    /// @notice Get the manager of an address.
    /// @param _addr Address for which to return the manager.
    /// @return Address of the manager for a given address.
    function getManager(address _addr) public view returns(address) {
        // By default the manager of an address is the same address
        if (managers[_addr] == address(0)) {
            return _addr;
        } else {
            return managers[_addr];
        }
    }

    /// @notice Compute the keccak256 hash of an interface given its name.
    /// @param _interfaceName Name of the interface.
    /// @return The keccak256 hash of an interface name.
    function interfaceHash(string calldata _interfaceName) external pure returns(bytes32) {
        return keccak256(abi.encodePacked(_interfaceName));
    }

    /* --- ERC165 Related Functions --- */
    /* --- Developed in collaboration with William Entriken. --- */

    /// @notice Updates the cache with whether the contract implements an ERC165 interface or not.
    /// @param _contract Address of the contract for which to update the cache.
    /// @param _interfaceId ERC165 interface for which to update the cache.
    function updateERC165Cache(address _contract, bytes4 _interfaceId) external {
        interfaces[_contract][_interfaceId] = implementsERC165InterfaceNoCache(
            _contract, _interfaceId) ? _contract : address(0);
        erc165Cached[_contract][_interfaceId] = true;
    }

    /// @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 _contract Address of the contract to check.
    /// @param _interfaceId ERC165 interface to check.
    /// @return True if '_contract' implements '_interfaceId', false otherwise.
    function implementsERC165Interface(address _contract, bytes4 _interfaceId) public view returns (bool) {
        if (!erc165Cached[_contract][_interfaceId]) {
            return implementsERC165InterfaceNoCache(_contract, _interfaceId);
        }
        return interfaces[_contract][_interfaceId] == _contract;
    }

    /// @notice Checks whether a contract implements an ERC165 interface or not without using nor updating the cache.
    /// @param _contract Address of the contract to check.
    /// @param _interfaceId ERC165 interface to check.
    /// @return True if '_contract' implements '_interfaceId', false otherwise.
    function implementsERC165InterfaceNoCache(address _contract, bytes4 _interfaceId) public view returns (bool) {
        uint256 success;
        uint256 result;

        (success, result) = noThrowCall(_contract, ERC165ID);
        if (success == 0 || result == 0) {
            return false;
        }

        (success, result) = noThrowCall(_contract, INVALID_ID);
        if (success == 0 || result != 0) {
            return false;
        }

        (success, result) = noThrowCall(_contract, _interfaceId);
        if (success == 1 && result == 1) {
            return true;
        }
        return false;
    }

    /// @notice Checks whether the hash is a ERC165 interface (ending with 28 zeroes) or not.
    /// @param _interfaceHash The hash to check.
    /// @return True if '_interfaceHash' is an ERC165 interface (ending with 28 zeroes), false otherwise.
    function isERC165Interface(bytes32 _interfaceHash) internal pure returns (bool) {
        return _interfaceHash & 0x00000000FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF == 0;
    }

    /// @dev Make a call on a contract without throwing if the function does not exist.
    function noThrowCall(address _contract, bytes4 _interfaceId)
        internal view returns (uint256 success, uint256 result)
    {
        bytes4 erc165ID = ERC165ID;

        assembly {
            let x := mload(0x40)               // Find empty storage location using "free memory pointer"
            mstore(x, erc165ID)                // Place signature at beginning of empty storage
            mstore(add(x, 0x04), _interfaceId) // Place first argument directly next to signature

            success := staticcall(
                30000,                         // 30k gas
                _contract,                     // To addr
                x,                             // Inputs are stored at location x
                0x24,                          // Inputs are 36 (4 + 32) bytes long
                x,                             // Store output over input (saves space)
                0x20                           // Outputs are 32 bytes long
            )

            result := mload(x)                 // Load the result
        }
    }
}