// File: contracts/FlyzStaking.sol



// SPDX-License-Identifier: AGPL-3.0-or-later
pragma solidity 0.7.5;

import './interfaces/IFlyzStaking.sol';
import './interfaces/IsFlyzERC20.sol';

import './types/ERC20.sol';
import './types/Ownable.sol';

import './libraries/SafeMath.sol';
import './libraries/SafeERC20.sol';

interface IWarmup {
    function retrieve(address staker_, uint256 amount_) external;
}

interface IDistributor {
    function distribute() external returns (bool);
}

contract FlyzStaking is Ownable, IFlyzStaking {
    using SafeMath for uint256;
    using SafeERC20 for IERC20;

    address public immutable FLYZ;
    address public immutable sFLYZ;

    struct Epoch {
        uint256 length; // in seconds
        uint256 number;
        uint256 endTime; // unix epoch time in seconds
        uint256 distribute;
    }
    Epoch public epoch;

    address public distributor;

    address public locker;
    uint256 public totalBonus;

    address public warmupContract;
    uint256 public warmupPeriod;

    constructor(
        address _FLYZ,
        address _sFLYZ,
        uint256 _epochLength,
        uint256 _firstEpochNumber,
        uint256 _firstEpochTime
    ) {
        require(_FLYZ != address(0));
        FLYZ = _FLYZ;
        require(_sFLYZ != address(0));
        sFLYZ = _sFLYZ;

        epoch = Epoch({
            length: _epochLength,
            number: _firstEpochNumber,
            endTime: _firstEpochTime,
            distribute: 0
        });
    }

    struct Claim {
        uint256 deposit;
        uint256 gons;
        uint256 expiry;
        bool lock; // prevents malicious delays
    }
    mapping(address => Claim) public warmupInfo;

    /**
        @notice stake FLYZ to enter warmup
        @param _amount uint
        @return bool
     */
    function stake(uint256 _amount, address _recipient)
        external
        override
        returns (bool)
    {
        rebase();

        IERC20(FLYZ).safeTransferFrom(msg.sender, address(this), _amount);

        Claim memory info = warmupInfo[_recipient];
        require(!info.lock, 'Deposits for account are locked');

        warmupInfo[_recipient] = Claim({
            deposit: info.deposit.add(_amount),
            gons: info.gons.add(IsFlyzERC20(sFLYZ).gonsForBalance(_amount)),
            expiry: epoch.number.add(warmupPeriod),
            lock: false
        });

        IERC20(sFLYZ).safeTransfer(warmupContract, _amount);
        return true;
    }

    /**
        @notice retrieve sFLYZ from warmup
        @param _recipient address
     */
    function claim(address _recipient) external override {
        Claim memory info = warmupInfo[_recipient];
        if (epoch.number >= info.expiry && info.expiry != 0) {
            delete warmupInfo[_recipient];
            IWarmup(warmupContract).retrieve(
                _recipient,
                IsFlyzERC20(sFLYZ).balanceForGons(info.gons)
            );
        }
    }

    /**
        @notice forfeit sFLYZ in warmup and retrieve FLYZ
     */
    function forfeit() external {
        Claim memory info = warmupInfo[msg.sender];
        delete warmupInfo[msg.sender];

        IWarmup(warmupContract).retrieve(
            address(this),
            IsFlyzERC20(sFLYZ).balanceForGons(info.gons)
        );
        IERC20(FLYZ).safeTransfer(msg.sender, info.deposit);
    }

    /**
        @notice prevent new deposits to address (protection from malicious activity)
     */
    function toggleDepositLock() external {
        warmupInfo[msg.sender].lock = !warmupInfo[msg.sender].lock;
    }

    /**
        @notice redeem sFLYZ for FLYZ
        @param _amount uint
        @param _trigger bool
     */
    function unstake(uint256 _amount, bool _trigger) external {
        if (_trigger) {
            rebase();
        }
        IERC20(sFLYZ).safeTransferFrom(msg.sender, address(this), _amount);
        IERC20(FLYZ).safeTransfer(msg.sender, _amount);
    }

    /**
        @notice returns the sFLYZ index, which tracks rebase growth
        @return uint
     */
    function index() public view returns (uint256) {
        return IsFlyzERC20(sFLYZ).index();
    }

    /**
        @notice trigger rebase if epoch over
     */
    function rebase() public {
        if (epoch.endTime <= block.timestamp) {
            IsFlyzERC20(sFLYZ).rebase(epoch.distribute, epoch.number);

            epoch.endTime = epoch.endTime.add(epoch.length);
            epoch.number++;

            if (distributor != address(0)) {
                IDistributor(distributor).distribute();
            }

            uint256 balance = contractBalance();
            uint256 staked = IsFlyzERC20(sFLYZ).circulatingSupply();

            if (balance <= staked) {
                epoch.distribute = 0;
            } else {
                epoch.distribute = balance.sub(staked);
            }
        }
    }

    /**
        @notice returns contract FLYZ holdings, including bonuses provided
        @return uint
     */
    function contractBalance() public view returns (uint256) {
        return IERC20(FLYZ).balanceOf(address(this)).add(totalBonus);
    }

    /**
        @notice provide bonus to locked staking contract
        @param _amount uint
     */
    function giveLockBonus(uint256 _amount) external {
        require(msg.sender == locker);
        totalBonus = totalBonus.add(_amount);
        IERC20(sFLYZ).safeTransfer(locker, _amount);
    }

    /**
        @notice reclaim bonus from locked staking contract
        @param _amount uint
     */
    function returnLockBonus(uint256 _amount) external {
        require(msg.sender == locker);
        totalBonus = totalBonus.sub(_amount);
        IERC20(sFLYZ).safeTransferFrom(locker, address(this), _amount);
    }

    enum CONTRACTS {
        DISTRIBUTOR,
        WARMUP,
        LOCKER
    }

    /**
        @notice sets the contract address for LP staking
        @param _contract address
     */
    function setContract(CONTRACTS _contract, address _address)
        external
        onlyOwner
    {
        if (_contract == CONTRACTS.DISTRIBUTOR) {
            // 0
            distributor = _address;
        } else if (_contract == CONTRACTS.WARMUP) {
            // 1
            require(
                warmupContract == address(0),
                'Warmup cannot be set more than once'
            );
            warmupContract = _address;
        } else if (_contract == CONTRACTS.LOCKER) {
            // 2
            require(
                locker == address(0),
                'Locker cannot be set more than once'
            );
            locker = _address;
        }
    }

    /**
     * @notice set warmup period for new stakers
     * @param _warmupPeriod uint
     */
    function setWarmup(uint256 _warmupPeriod) external onlyOwner {
        warmupPeriod = _warmupPeriod;
    }
}

// File: contracts/interfaces/IFlyzStaking.sol



// SPDX-License-Identifier: AGPL-3.0-or-later
pragma solidity 0.7.5;

interface IFlyzStaking {
    function stake(uint256 _amount, address _recipient) external returns (bool);

    function claim(address _recipient) external;
}

// File: contracts/interfaces/IsFlyzERC20.sol



// SPDX-License-Identifier: AGPL-3.0-or-later
pragma solidity >=0.7.5;

import './IERC20.sol';

interface IsFlyzERC20 is IERC20 {
    function rebase(uint256 flyzProfit_, uint256 epoch_)
        external
        returns (uint256);

    function circulatingSupply() external view returns (uint256);

    function gonsForBalance(uint256 amount) external view returns (uint256);

    function balanceForGons(uint256 gons) external view returns (uint256);

    function index() external view returns (uint256);
}

// File: contracts/types/ERC20.sol



// SPDX-License-Identifier: AGPL-3.0-or-later
pragma solidity 0.7.5;

import '../interfaces/IERC20.sol';
import '../libraries/SafeMath.sol';
import '../libraries/Counters.sol';
import '../libraries/Address.sol';

abstract contract ERC20 is IERC20 {
    using SafeMath for uint256;

    // TODO comment actual hash value.
    bytes32 private constant ERC20TOKEN_ERC1820_INTERFACE_ID =
        keccak256('ERC20Token');

    mapping(address => uint256) internal _balances;

    mapping(address => mapping(address => uint256)) internal _allowances;

    uint256 internal _totalSupply;

    string internal _name;

    string internal _symbol;

    uint8 internal _decimals;

    constructor(
        string memory name_,
        string memory symbol_,
        uint8 decimals_
    ) {
        _name = name_;
        _symbol = symbol_;
        _decimals = decimals_;
    }

    function name() public view override returns (string memory) {
        return _name;
    }

    function symbol() public view override returns (string memory) {
        return _symbol;
    }

    function decimals() public view override returns (uint8) {
        return _decimals;
    }

    function totalSupply() public view override returns (uint256) {
        return _totalSupply;
    }

    function balanceOf(address account)
        public
        view
        virtual
        override
        returns (uint256)
    {
        return _balances[account];
    }

    function transfer(address recipient, uint256 amount)
        public
        virtual
        override
        returns (bool)
    {
        _transfer(msg.sender, recipient, amount);
        return true;
    }

    function allowance(address owner, address spender)
        public
        view
        virtual
        override
        returns (uint256)
    {
        return _allowances[owner][spender];
    }

    function approve(address spender, uint256 amount)
        public
        virtual
        override
        returns (bool)
    {
        _approve(msg.sender, spender, amount);
        return true;
    }

    function transferFrom(
        address sender,
        address recipient,
        uint256 amount
    ) public virtual override returns (bool) {
        _transfer(sender, recipient, amount);
        _approve(
            sender,
            msg.sender,
            _allowances[sender][msg.sender].sub(
                amount,
                'ERC20: transfer amount exceeds allowance'
            )
        );
        return true;
    }

    function increaseAllowance(address spender, uint256 addedValue)
        public
        virtual
        returns (bool)
    {
        _approve(
            msg.sender,
            spender,
            _allowances[msg.sender][spender].add(addedValue)
        );
        return true;
    }

    function decreaseAllowance(address spender, uint256 subtractedValue)
        public
        virtual
        returns (bool)
    {
        _approve(
            msg.sender,
            spender,
            _allowances[msg.sender][spender].sub(
                subtractedValue,
                'ERC20: decreased allowance below zero'
            )
        );
        return true;
    }

    function _transfer(
        address sender,
        address recipient,
        uint256 amount
    ) internal virtual {
        require(sender != address(0), 'ERC20: transfer from the zero address');
        require(recipient != address(0), 'ERC20: transfer to the zero address');

        _beforeTokenTransfer(sender, recipient, amount);

        _balances[sender] = _balances[sender].sub(
            amount,
            'ERC20: transfer amount exceeds balance'
        );
        _balances[recipient] = _balances[recipient].add(amount);
        emit Transfer(sender, recipient, amount);
    }

    function _mint(address account_, uint256 ammount_) internal virtual {
        require(account_ != address(0), 'ERC20: mint to the zero address');
        _beforeTokenTransfer(address(this), account_, ammount_);
        _totalSupply = _totalSupply.add(ammount_);
        _balances[account_] = _balances[account_].add(ammount_);
        emit Transfer(address(this), account_, ammount_);
    }

    function _burn(address account, uint256 amount) internal virtual {
        require(account != address(0), 'ERC20: burn from the zero address');

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

        _balances[account] = _balances[account].sub(
            amount,
            'ERC20: burn amount exceeds balance'
        );
        _totalSupply = _totalSupply.sub(amount);
        emit Transfer(account, address(0), amount);
    }

    function _approve(
        address owner,
        address spender,
        uint256 amount
    ) internal virtual {
        require(owner != address(0), 'ERC20: approve from the zero address');
        require(spender != address(0), 'ERC20: approve to the zero address');

        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }

    function _beforeTokenTransfer(
        address from_,
        address to_,
        uint256 amount_
    ) internal virtual {}
}

interface IERC2612Permit {
    function permit(
        address owner,
        address spender,
        uint256 amount,
        uint256 deadline,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) external;

    function nonces(address owner) external view returns (uint256);
}

abstract contract ERC20Permit is ERC20, IERC2612Permit {
    using Counters for Counters.Counter;

    mapping(address => Counters.Counter) private _nonces;

    // keccak256("Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)");
    bytes32 public constant PERMIT_TYPEHASH =
        0x6e71edae12b1b97f4d1f60370fef10105fa2faae0126114a169c64845d6126c9;

    bytes32 public DOMAIN_SEPARATOR;

    constructor() {
        uint256 chainID;
        assembly {
            chainID := chainid()
        }

        DOMAIN_SEPARATOR = keccak256(
            abi.encode(
                keccak256(
                    'EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)'
                ),
                keccak256(bytes(name())),
                keccak256(bytes('1')), // Version
                chainID,
                address(this)
            )
        );
    }

    function permit(
        address owner,
        address spender,
        uint256 amount,
        uint256 deadline,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) public virtual override {
        require(block.timestamp <= deadline, 'Permit: expired deadline');

        bytes32 hashStruct = keccak256(
            abi.encode(
                PERMIT_TYPEHASH,
                owner,
                spender,
                amount,
                _nonces[owner].current(),
                deadline
            )
        );

        bytes32 _hash = keccak256(
            abi.encodePacked(uint16(0x1901), DOMAIN_SEPARATOR, hashStruct)
        );

        address signer = ecrecover(_hash, v, r, s);
        require(
            signer != address(0) && signer == owner,
            'ZeroSwapPermit: Invalid signature'
        );

        _nonces[owner].increment();
        _approve(owner, spender, amount);
    }

    function nonces(address owner) public view override returns (uint256) {
        return _nonces[owner].current();
    }
}

// File: contracts/types/Ownable.sol



// SPDX-License-Identifier: AGPL-3.0-or-later
pragma solidity 0.7.5;

interface IOwnable {
    function owner() external view returns (address);

    function renounceManagement() external;

    function pushManagement(address newOwner_) external;

    function pullManagement() external;
}

contract Ownable is IOwnable {
    address internal _owner;
    address internal _newOwner;

    event OwnershipPushed(
        address indexed previousOwner,
        address indexed newOwner
    );
    event OwnershipPulled(
        address indexed previousOwner,
        address indexed newOwner
    );

    constructor() {
        _owner = msg.sender;
        emit OwnershipPushed(address(0), _owner);
    }

    function owner() public view override returns (address) {
        return _owner;
    }

    modifier onlyOwner() {
        require(_owner == msg.sender, 'Ownable: caller is not the owner');
        _;
    }

    function renounceManagement() public virtual override onlyOwner {
        emit OwnershipPushed(_owner, address(0));
        _owner = address(0);
    }

    function pushManagement(address newOwner_)
        public
        virtual
        override
        onlyOwner
    {
        require(
            newOwner_ != address(0),
            'Ownable: new owner is the zero address'
        );
        emit OwnershipPushed(_owner, newOwner_);
        _newOwner = newOwner_;
    }

    function pullManagement() public virtual override {
        require(msg.sender == _newOwner, 'Ownable: must be new owner to pull');
        emit OwnershipPulled(_owner, _newOwner);
        _owner = _newOwner;
    }
}

// File: contracts/libraries/SafeMath.sol



// SPDX-License-Identifier: AGPL-3.0-or-later
pragma solidity 0.7.5;

library SafeMath {
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, 'SafeMath: addition overflow');

        return c;
    }

    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return sub(a, b, 'SafeMath: subtraction overflow');
    }

    function sub(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;

        return c;
    }

    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b, 'SafeMath: multiplication overflow');

        return c;
    }

    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return div(a, b, 'SafeMath: division by 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;
    }

    function sqrrt(uint256 a) internal pure returns (uint256 c) {
        if (a > 3) {
            c = a;
            uint256 b = add(div(a, 2), 1);
            while (b < c) {
                c = b;
                b = div(add(div(a, b), b), 2);
            }
        } else if (a != 0) {
            c = 1;
        }
    }
}

// File: contracts/libraries/SafeERC20.sol



// SPDX-License-Identifier: AGPL-3.0-or-later
pragma solidity 0.7.5;

import '../interfaces/IERC20.sol';

import './SafeMath.sol';
import './Counters.sol';
import './Address.sol';

library SafeERC20 {
    using SafeMath for uint256;
    using Address for address;

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

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

    function safeApprove(
        IERC20 token,
        address spender,
        uint256 value
    ) internal {
        require(
            (value == 0) || (token.allowance(address(this), spender) == 0),
            'SafeERC20: approve from non-zero to non-zero allowance'
        );
        _callOptionalReturn(
            token,
            abi.encodeWithSelector(token.approve.selector, spender, value)
        );
    }

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

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

    function _callOptionalReturn(IERC20 token, bytes memory data) private {
        bytes memory returndata = address(token).functionCall(
            data,
            'SafeERC20: low-level call failed'
        );
        if (returndata.length > 0) {
            // Return data is optional
            // solhint-disable-next-line max-line-length
            require(
                abi.decode(returndata, (bool)),
                'SafeERC20: ERC20 operation did not succeed'
            );
        }
    }
}

// File: contracts/interfaces/IERC20.sol



// SPDX-License-Identifier: AGPL-3.0-or-later
pragma solidity >=0.5.0;

interface IERC20 {
    event Approval(
        address indexed owner,
        address indexed spender,
        uint256 value
    );
    event Transfer(address indexed from, address indexed to, uint256 value);

    function name() external view returns (string memory);

    function symbol() external view returns (string memory);

    function decimals() external view returns (uint8);

    function totalSupply() external view returns (uint256);

    function balanceOf(address owner) external view returns (uint256);

    function allowance(address owner, address spender)
        external
        view
        returns (uint256);

    function approve(address spender, uint256 value) external returns (bool);

    function transfer(address to, uint256 value) external returns (bool);

    function transferFrom(
        address from,
        address to,
        uint256 value
    ) external returns (bool);
}

interface IERC20Mintable {
    function mint(uint256 amount_) external;

    function mint(address account_, uint256 ammount_) external;
}

// File: contracts/libraries/Counters.sol



// SPDX-License-Identifier: AGPL-3.0-or-later
pragma solidity 0.7.5;

import './SafeMath.sol';

library Counters {
    using SafeMath for uint256;

    struct Counter {
        uint256 _value; // default: 0
    }

    function current(Counter storage counter) internal view returns (uint256) {
        return counter._value;
    }

    function increment(Counter storage counter) internal {
        counter._value += 1;
    }

    function decrement(Counter storage counter) internal {
        counter._value = counter._value.sub(1);
    }
}

// File: contracts/libraries/Address.sol



// SPDX-License-Identifier: AGPL-3.0-or-later
pragma solidity 0.7.5;

library Address {
    function isContract(address account) internal view returns (bool) {
        uint256 size;
        // solhint-disable-next-line no-inline-assembly
        assembly {
            size := extcodesize(account)
        }
        return size > 0;
    }

    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'
        );
    }

    function functionCall(address target, bytes memory data)
        internal
        returns (bytes memory)
    {
        return functionCall(target, data, 'Address: low-level call failed');
    }

    function functionCall(
        address target,
        bytes memory data,
        string memory errorMessage
    ) internal returns (bytes memory) {
        return _functionCallWithValue(target, data, 0, errorMessage);
    }

    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'
            );
    }

    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);
    }

    function _functionCallWithValue(
        address target,
        bytes memory data,
        uint256 weiValue,
        string memory errorMessage
    ) private returns (bytes memory) {
        require(isContract(target), 'Address: call to non-contract');

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.call{value: weiValue}(
            data
        );
        if (success) {
            return returndata;
        } else {
            // Look for revert reason and bubble it up if present
            if (returndata.length > 0) {
                // The easiest way to bubble the revert reason is using memory via assembly

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

    function functionStaticCall(address target, bytes memory data)
        internal
        view
        returns (bytes memory)
    {
        return
            functionStaticCall(
                target,
                data,
                'Address: low-level static call failed'
            );
    }

    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 functionDelegateCall(address target, bytes memory data)
        internal
        returns (bytes memory)
    {
        return
            functionDelegateCall(
                target,
                data,
                'Address: low-level delegate call failed'
            );
    }

    function functionDelegateCall(
        address target,
        bytes memory data,
        string memory errorMessage
    ) internal returns (bytes memory) {
        require(isContract(target), 'Address: delegate call to non-contract');

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

    function _verifyCallResult(
        bool success,
        bytes memory returndata,
        string memory errorMessage
    ) private pure returns (bytes memory) {
        if (success) {
            return returndata;
        } else {
            if (returndata.length > 0) {
                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }

    function addressToString(address _address)
        internal
        pure
        returns (string memory)
    {
        bytes32 _bytes = bytes32(uint256(_address));
        bytes memory HEX = '0123456789abcdef';
        bytes memory _addr = new bytes(42);

        _addr[0] = '0';
        _addr[1] = 'x';

        for (uint256 i = 0; i < 20; i++) {
            _addr[2 + i * 2] = HEX[uint8(_bytes[i + 12] >> 4)];
            _addr[3 + i * 2] = HEX[uint8(_bytes[i + 12] & 0x0f)];
        }

        return string(_addr);
    }
}