Contract Address Details

// SPDX-License-Identifier: GPL-3.0-only

pragma solidity 0.8.9;

import "../interfaces/ISigsVerifier.sol";
import "../interfaces/IPeggedToken.sol";
import "../libraries/PbPegged.sol";
import "../safeguard/Pauser.sol";
import "../safeguard/VolumeControl.sol";
import "../safeguard/DelayedTransfer.sol";

/**
 * @title The bridge contract to mint and burn pegged tokens
 * @dev Work together with OriginalTokenVault deployed at remote chains.
 */
contract PeggedTokenBridge is Pauser, VolumeControl, DelayedTransfer {
    ISigsVerifier public immutable sigsVerifier;

    mapping(bytes32 => bool) public records;

    mapping(address => uint256) public minBurn;
    mapping(address => uint256) public maxBurn;

    event Mint(
        bytes32 mintId,
        address token,
        address account,
        uint256 amount,
        // ref_chain_id defines the reference chain ID, taking values of:
        // 1. The common case: the chain ID on which the remote corresponding deposit or burn happened;
        // 2. Refund for wrong burn: this chain ID on which the burn happened
        uint64 refChainId,
        // ref_id defines a unique reference ID, taking values of:
        // 1. The common case of deposit/burn-mint: the deposit or burn ID on the remote chain;
        // 2. Refund for wrong burn: the burn ID on this chain
        bytes32 refId,
        address depositor
    );
    event Burn(bytes32 burnId, address token, address account, uint256 amount, address withdrawAccount);
    event MinBurnUpdated(address token, uint256 amount);
    event MaxBurnUpdated(address token, uint256 amount);

    constructor(ISigsVerifier _sigsVerifier) {
        sigsVerifier = _sigsVerifier;
    }

    /**
     * @notice Mint tokens triggered by deposit at a remote chain's OriginalTokenVault.
     * @param _request The serialized Mint protobuf.
     * @param _sigs The list of signatures sorted by signing addresses in ascending order. A relay must be signed-off by
     * +2/3 of the sigsVerifier's current signing power to be delivered.
     * @param _signers The sorted list of signers.
     * @param _powers The signing powers of the signers.
     */
    function mint(
        bytes calldata _request,
        bytes[] calldata _sigs,
        address[] calldata _signers,
        uint256[] calldata _powers
    ) external whenNotPaused {
        bytes32 domain = keccak256(abi.encodePacked(block.chainid, address(this), "Mint"));
        sigsVerifier.verifySigs(abi.encodePacked(domain, _request), _sigs, _signers, _powers);
        PbPegged.Mint memory request = PbPegged.decMint(_request);
        bytes32 mintId = keccak256(
            // len = 20 + 20 + 32 + 20 + 8 + 32 = 132
            abi.encodePacked(
                request.account,
                request.token,
                request.amount,
                request.depositor,
                request.refChainId,
                request.refId
            )
        );
        require(records[mintId] == false, "record exists");
        records[mintId] = true;
        _updateVolume(request.token, request.amount);
        uint256 delayThreshold = delayThresholds[request.token];
        if (delayThreshold > 0 && request.amount > delayThreshold) {
            _addDelayedTransfer(mintId, request.account, request.token, request.amount);
        } else {
            IPeggedToken(request.token).mint(request.account, request.amount);
        }
        emit Mint(
            mintId,
            request.token,
            request.account,
            request.amount,
            request.refChainId,
            request.refId,
            request.depositor
        );
    }

    /**
     * @notice Burn pegged tokens to trigger a cross-chain withdrawal of the original tokens at a remote chain's
     * OriginalTokenVault.
     * NOTE: This function DOES NOT SUPPORT fee-on-transfer / rebasing tokens.
     * @param _token The pegged token address.
     * @param _amount The amount to burn.
     * @param _withdrawAccount The account to receive the original tokens withdrawn on the remote chain.
     * @param _nonce A number to guarantee unique depositId. Can be timestamp in practice.
     */
    function burn(
        address _token,
        uint256 _amount,
        address _withdrawAccount,
        uint64 _nonce
    ) external whenNotPaused {
        require(_amount > minBurn[_token], "amount too small");
        require(maxBurn[_token] == 0 || _amount <= maxBurn[_token], "amount too large");
        bytes32 burnId = keccak256(
            // len = 20 + 20 + 32 + 20 + 8 + 8 = 108
            abi.encodePacked(msg.sender, _token, _amount, _withdrawAccount, _nonce, uint64(block.chainid))
        );
        require(records[burnId] == false, "record exists");
        records[burnId] = true;
        IPeggedToken(_token).burn(msg.sender, _amount);
        emit Burn(burnId, _token, msg.sender, _amount, _withdrawAccount);
    }

    function executeDelayedTransfer(bytes32 id) external whenNotPaused {
        delayedTransfer memory transfer = _executeDelayedTransfer(id);
        IPeggedToken(transfer.token).mint(transfer.receiver, transfer.amount);
    }

    function setMinBurn(address[] calldata _tokens, uint256[] calldata _amounts) external onlyGovernor {
        require(_tokens.length == _amounts.length, "length mismatch");
        for (uint256 i = 0; i < _tokens.length; i++) {
            minBurn[_tokens[i]] = _amounts[i];
            emit MinBurnUpdated(_tokens[i], _amounts[i]);
        }
    }

    function setMaxBurn(address[] calldata _tokens, uint256[] calldata _amounts) external onlyGovernor {
        require(_tokens.length == _amounts.length, "length mismatch");
        for (uint256 i = 0; i < _tokens.length; i++) {
            maxBurn[_tokens[i]] = _amounts[i];
            emit MaxBurnUpdated(_tokens[i], _amounts[i]);
        }
    }
}
        

// SPDX-License-Identifier: GPL-3.0-only

pragma solidity >=0.8.0;

interface IPeggedToken {
    function mint(address _to, uint256 _amount) external;

    function burn(address _from, uint256 _amount) external;
}
          

// SPDX-License-Identifier: GPL-3.0-only

pragma solidity >=0.8.0;

interface ISigsVerifier {
    /**
     * @notice Verifies that a message is signed by a quorum among the signers.
     * @param _msg signed message
     * @param _sigs list of signatures sorted by signer addresses in ascending order
     * @param _signers sorted list of current signers
     * @param _powers powers of current signers
     */
    function verifySigs(
        bytes memory _msg,
        bytes[] calldata _sigs,
        address[] calldata _signers,
        uint256[] calldata _powers
    ) external view;
}
          

// SPDX-License-Identifier: GPL-3.0-only

pragma solidity 0.8.9;

// runtime proto sol library
library Pb {
    enum WireType {
        Varint,
        Fixed64,
        LengthDelim,
        StartGroup,
        EndGroup,
        Fixed32
    }

    struct Buffer {
        uint256 idx; // the start index of next read. when idx=b.length, we're done
        bytes b; // hold serialized proto msg, readonly
    }

    // create a new in-memory Buffer object from raw msg bytes
    function fromBytes(bytes memory raw) internal pure returns (Buffer memory buf) {
        buf.b = raw;
        buf.idx = 0;
    }

    // whether there are unread bytes
    function hasMore(Buffer memory buf) internal pure returns (bool) {
        return buf.idx < buf.b.length;
    }

    // decode current field number and wiretype
    function decKey(Buffer memory buf) internal pure returns (uint256 tag, WireType wiretype) {
        uint256 v = decVarint(buf);
        tag = v / 8;
        wiretype = WireType(v & 7);
    }

    // count tag occurrences, return an array due to no memory map support
    // have to create array for (maxtag+1) size. cnts[tag] = occurrences
    // should keep buf.idx unchanged because this is only a count function
    function cntTags(Buffer memory buf, uint256 maxtag) internal pure returns (uint256[] memory cnts) {
        uint256 originalIdx = buf.idx;
        cnts = new uint256[](maxtag + 1); // protobuf's tags are from 1 rather than 0
        uint256 tag;
        WireType wire;
        while (hasMore(buf)) {
            (tag, wire) = decKey(buf);
            cnts[tag] += 1;
            skipValue(buf, wire);
        }
        buf.idx = originalIdx;
    }

    // read varint from current buf idx, move buf.idx to next read, return the int value
    function decVarint(Buffer memory buf) internal pure returns (uint256 v) {
        bytes10 tmp; // proto int is at most 10 bytes (7 bits can be used per byte)
        bytes memory bb = buf.b; // get buf.b mem addr to use in assembly
        v = buf.idx; // use v to save one additional uint variable
        assembly {
            tmp := mload(add(add(bb, 32), v)) // load 10 bytes from buf.b[buf.idx] to tmp
        }
        uint256 b; // store current byte content
        v = 0; // reset to 0 for return value
        for (uint256 i = 0; i < 10; i++) {
            assembly {
                b := byte(i, tmp) // don't use tmp[i] because it does bound check and costs extra
            }
            v |= (b & 0x7F) << (i * 7);
            if (b & 0x80 == 0) {
                buf.idx += i + 1;
                return v;
            }
        }
        revert(); // i=10, invalid varint stream
    }

    // read length delimited field and return bytes
    function decBytes(Buffer memory buf) internal pure returns (bytes memory b) {
        uint256 len = decVarint(buf);
        uint256 end = buf.idx + len;
        require(end <= buf.b.length); // avoid overflow
        b = new bytes(len);
        bytes memory bufB = buf.b; // get buf.b mem addr to use in assembly
        uint256 bStart;
        uint256 bufBStart = buf.idx;
        assembly {
            bStart := add(b, 32)
            bufBStart := add(add(bufB, 32), bufBStart)
        }
        for (uint256 i = 0; i < len; i += 32) {
            assembly {
                mstore(add(bStart, i), mload(add(bufBStart, i)))
            }
        }
        buf.idx = end;
    }

    // return packed ints
    function decPacked(Buffer memory buf) internal pure returns (uint256[] memory t) {
        uint256 len = decVarint(buf);
        uint256 end = buf.idx + len;
        require(end <= buf.b.length); // avoid overflow
        // array in memory must be init w/ known length
        // so we have to create a tmp array w/ max possible len first
        uint256[] memory tmp = new uint256[](len);
        uint256 i = 0; // count how many ints are there
        while (buf.idx < end) {
            tmp[i] = decVarint(buf);
            i++;
        }
        t = new uint256[](i); // init t with correct length
        for (uint256 j = 0; j < i; j++) {
            t[j] = tmp[j];
        }
        return t;
    }

    // move idx pass current value field, to beginning of next tag or msg end
    function skipValue(Buffer memory buf, WireType wire) internal pure {
        if (wire == WireType.Varint) {
            decVarint(buf);
        } else if (wire == WireType.LengthDelim) {
            uint256 len = decVarint(buf);
            buf.idx += len; // skip len bytes value data
            require(buf.idx <= buf.b.length); // avoid overflow
        } else {
            revert();
        } // unsupported wiretype
    }

    // type conversion help utils
    function _bool(uint256 x) internal pure returns (bool v) {
        return x != 0;
    }

    function _uint256(bytes memory b) internal pure returns (uint256 v) {
        require(b.length <= 32); // b's length must be smaller than or equal to 32
        assembly {
            v := mload(add(b, 32))
        } // load all 32bytes to v
        v = v >> (8 * (32 - b.length)); // only first b.length is valid
    }

    function _address(bytes memory b) internal pure returns (address v) {
        v = _addressPayable(b);
    }

    function _addressPayable(bytes memory b) internal pure returns (address payable v) {
        require(b.length == 20);
        //load 32bytes then shift right 12 bytes
        assembly {
            v := div(mload(add(b, 32)), 0x1000000000000000000000000)
        }
    }

    function _bytes32(bytes memory b) internal pure returns (bytes32 v) {
        require(b.length == 32);
        assembly {
            v := mload(add(b, 32))
        }
    }

    // uint[] to uint8[]
    function uint8s(uint256[] memory arr) internal pure returns (uint8[] memory t) {
        t = new uint8[](arr.length);
        for (uint256 i = 0; i < t.length; i++) {
            t[i] = uint8(arr[i]);
        }
    }

    function uint32s(uint256[] memory arr) internal pure returns (uint32[] memory t) {
        t = new uint32[](arr.length);
        for (uint256 i = 0; i < t.length; i++) {
            t[i] = uint32(arr[i]);
        }
    }

    function uint64s(uint256[] memory arr) internal pure returns (uint64[] memory t) {
        t = new uint64[](arr.length);
        for (uint256 i = 0; i < t.length; i++) {
            t[i] = uint64(arr[i]);
        }
    }

    function bools(uint256[] memory arr) internal pure returns (bool[] memory t) {
        t = new bool[](arr.length);
        for (uint256 i = 0; i < t.length; i++) {
            t[i] = arr[i] != 0;
        }
    }
}
          

// SPDX-License-Identifier: GPL-3.0-only

// Code generated by protoc-gen-sol. DO NOT EDIT.
// source: contracts/libraries/proto/pegged.proto
pragma solidity 0.8.9;
import "./Pb.sol";

library PbPegged {
    using Pb for Pb.Buffer; // so we can call Pb funcs on Buffer obj

    struct Mint {
        address token; // tag: 1
        address account; // tag: 2
        uint256 amount; // tag: 3
        address depositor; // tag: 4
        uint64 refChainId; // tag: 5
        bytes32 refId; // tag: 6
    } // end struct Mint

    function decMint(bytes memory raw) internal pure returns (Mint memory m) {
        Pb.Buffer memory buf = Pb.fromBytes(raw);

        uint256 tag;
        Pb.WireType wire;
        while (buf.hasMore()) {
            (tag, wire) = buf.decKey();
            if (false) {}
            // solidity has no switch/case
            else if (tag == 1) {
                m.token = Pb._address(buf.decBytes());
            } else if (tag == 2) {
                m.account = Pb._address(buf.decBytes());
            } else if (tag == 3) {
                m.amount = Pb._uint256(buf.decBytes());
            } else if (tag == 4) {
                m.depositor = Pb._address(buf.decBytes());
            } else if (tag == 5) {
                m.refChainId = uint64(buf.decVarint());
            } else if (tag == 6) {
                m.refId = Pb._bytes32(buf.decBytes());
            } else {
                buf.skipValue(wire);
            } // skip value of unknown tag
        }
    } // end decoder Mint

    struct Withdraw {
        address token; // tag: 1
        address receiver; // tag: 2
        uint256 amount; // tag: 3
        address burnAccount; // tag: 4
        uint64 refChainId; // tag: 5
        bytes32 refId; // tag: 6
    } // end struct Withdraw

    function decWithdraw(bytes memory raw) internal pure returns (Withdraw memory m) {
        Pb.Buffer memory buf = Pb.fromBytes(raw);

        uint256 tag;
        Pb.WireType wire;
        while (buf.hasMore()) {
            (tag, wire) = buf.decKey();
            if (false) {}
            // solidity has no switch/case
            else if (tag == 1) {
                m.token = Pb._address(buf.decBytes());
            } else if (tag == 2) {
                m.receiver = Pb._address(buf.decBytes());
            } else if (tag == 3) {
                m.amount = Pb._uint256(buf.decBytes());
            } else if (tag == 4) {
                m.burnAccount = Pb._address(buf.decBytes());
            } else if (tag == 5) {
                m.refChainId = uint64(buf.decVarint());
            } else if (tag == 6) {
                m.refId = Pb._bytes32(buf.decBytes());
            } else {
                buf.skipValue(wire);
            } // skip value of unknown tag
        }
    } // end decoder Withdraw
}
          

// SPDX-License-Identifier: GPL-3.0-only

pragma solidity 0.8.9;

import "./Governor.sol";

abstract contract DelayedTransfer is Governor {
    struct delayedTransfer {
        address receiver;
        address token;
        uint256 amount;
        uint256 timestamp;
    }
    mapping(bytes32 => delayedTransfer) public delayedTransfers;
    mapping(address => uint256) public delayThresholds;
    uint256 public delayPeriod; // in seconds

    event DelayedTransferAdded(bytes32 id);
    event DelayedTransferExecuted(bytes32 id, address receiver, address token, uint256 amount);

    event DelayPeriodUpdated(uint256 period);
    event DelayThresholdUpdated(address token, uint256 threshold);

    function setDelayThresholds(address[] calldata _tokens, uint256[] calldata _thresholds) external onlyGovernor {
        require(_tokens.length == _thresholds.length, "length mismatch");
        for (uint256 i = 0; i < _tokens.length; i++) {
            delayThresholds[_tokens[i]] = _thresholds[i];
            emit DelayThresholdUpdated(_tokens[i], _thresholds[i]);
        }
    }

    function setDelayPeriod(uint256 _period) external onlyGovernor {
        delayPeriod = _period;
        emit DelayPeriodUpdated(_period);
    }

    function _addDelayedTransfer(
        bytes32 id,
        address receiver,
        address token,
        uint256 amount
    ) internal {
        require(delayedTransfers[id].timestamp == 0, "delayed transfer already exists");
        delayedTransfers[id] = delayedTransfer({
            receiver: receiver,
            token: token,
            amount: amount,
            timestamp: block.timestamp
        });
        emit DelayedTransferAdded(id);
    }

    // caller needs to do the actual token transfer
    function _executeDelayedTransfer(bytes32 id) internal returns (delayedTransfer memory) {
        delayedTransfer memory transfer = delayedTransfers[id];
        require(transfer.timestamp > 0, "delayed transfer not exist");
        require(block.timestamp > transfer.timestamp + delayPeriod, "delayed transfer still locked");
        delete delayedTransfers[id];
        emit DelayedTransferExecuted(id, transfer.receiver, transfer.token, transfer.amount);
        return transfer;
    }
}
          

// SPDX-License-Identifier: GPL-3.0-only

pragma solidity 0.8.9;

import "@openzeppelin/contracts/access/Ownable.sol";

abstract contract Governor is Ownable {
    mapping(address => bool) public governors;

    event GovernorAdded(address account);
    event GovernorRemoved(address account);

    modifier onlyGovernor() {
        require(isGovernor(msg.sender), "Caller is not governor");
        _;
    }

    constructor() {
        _addGovernor(msg.sender);
    }

    function isGovernor(address _account) public view returns (bool) {
        return governors[_account];
    }

    function addGovernor(address _account) public onlyOwner {
        _addGovernor(_account);
    }

    function removeGovernor(address _account) public onlyOwner {
        _removeGovernor(_account);
    }

    function renounceGovernor() public {
        _removeGovernor(msg.sender);
    }

    function _addGovernor(address _account) private {
        require(!isGovernor(_account), "Account is already governor");
        governors[_account] = true;
        emit GovernorAdded(_account);
    }

    function _removeGovernor(address _account) private {
        require(isGovernor(_account), "Account is not governor");
        governors[_account] = false;
        emit GovernorRemoved(_account);
    }
}
          

// SPDX-License-Identifier: GPL-3.0-only

pragma solidity 0.8.9;

import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/security/Pausable.sol";

abstract contract Pauser is Ownable, Pausable {
    mapping(address => bool) public pausers;

    event PauserAdded(address account);
    event PauserRemoved(address account);

    constructor() {
        _addPauser(msg.sender);
    }

    modifier onlyPauser() {
        require(isPauser(msg.sender), "Caller is not pauser");
        _;
    }

    function pause() public onlyPauser {
        _pause();
    }

    function unpause() public onlyPauser {
        _unpause();
    }

    function isPauser(address account) public view returns (bool) {
        return pausers[account];
    }

    function addPauser(address account) public onlyOwner {
        _addPauser(account);
    }

    function removePauser(address account) public onlyOwner {
        _removePauser(account);
    }

    function renouncePauser() public {
        _removePauser(msg.sender);
    }

    function _addPauser(address account) private {
        require(!isPauser(account), "Account is already pauser");
        pausers[account] = true;
        emit PauserAdded(account);
    }

    function _removePauser(address account) private {
        require(isPauser(account), "Account is not pauser");
        pausers[account] = false;
        emit PauserRemoved(account);
    }
}
          

// SPDX-License-Identifier: GPL-3.0-only

pragma solidity 0.8.9;

import "./Governor.sol";

abstract contract VolumeControl is Governor {
    uint256 public epochLength; // seconds
    mapping(address => uint256) public epochVolumes; // key is token
    mapping(address => uint256) public epochVolumeCaps; // key is token
    mapping(address => uint256) public lastOpTimestamps; // key is token

    event EpochLengthUpdated(uint256 length);
    event EpochVolumeUpdated(address token, uint256 cap);

    function setEpochLength(uint256 _length) external onlyGovernor {
        epochLength = _length;
        emit EpochLengthUpdated(_length);
    }

    function setEpochVolumeCaps(address[] calldata _tokens, uint256[] calldata _caps) external onlyGovernor {
        require(_tokens.length == _caps.length, "length mismatch");
        for (uint256 i = 0; i < _tokens.length; i++) {
            epochVolumeCaps[_tokens[i]] = _caps[i];
            emit EpochVolumeUpdated(_tokens[i], _caps[i]);
        }
    }

    function _updateVolume(address _token, uint256 _amount) internal {
        if (epochLength == 0) {
            return;
        }
        uint256 cap = epochVolumeCaps[_token];
        if (cap == 0) {
            return;
        }
        uint256 volume = epochVolumes[_token];
        uint256 timestamp = block.timestamp;
        uint256 epochStartTime = (timestamp / epochLength) * epochLength;
        if (lastOpTimestamps[_token] < epochStartTime) {
            volume = _amount;
        } else {
            volume += _amount;
        }
        require(volume <= cap, "volume exceeds cap");
        epochVolumes[_token] = volume;
        lastOpTimestamps[_token] = timestamp;
    }
}
          

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (access/Ownable.sol)

pragma solidity ^0.8.0;

import "../utils/Context.sol";

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

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

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor() {
        _transferOwnership(_msgSender());
    }

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

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

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

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

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Internal function without access restriction.
     */
    function _transferOwnership(address newOwner) internal virtual {
        address oldOwner = _owner;
        _owner = newOwner;
        emit OwnershipTransferred(oldOwner, newOwner);
    }
}
          

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (security/Pausable.sol)

pragma solidity ^0.8.0;

import "../utils/Context.sol";

/**
 * @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() {
        _paused = false;
    }

    /**
     * @dev Returns true if the contract is paused, and false otherwise.
     */
    function paused() public view virtual 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());
    }
}
          

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (utils/Context.sol)

pragma solidity ^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 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) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes calldata) {
        return msg.data;
    }
}