// File: contracts/examples/erc20-transfer/FxERC20RootTunnel.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import { ERC20 } from "../../lib/ERC20.sol";
import { Create2 } from "../../lib/Create2.sol";
import { FxBaseRootTunnel } from "../../tunnel/FxBaseRootTunnel.sol";
import {SafeERC20,IERC20} from "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";

/**
 * @title FxERC20RootTunnel
 */
contract FxERC20RootTunnel is FxBaseRootTunnel, Create2 {
    using SafeERC20 for IERC20;
    // maybe DEPOSIT and MAP_TOKEN can be reduced to bytes4
    bytes32 public constant DEPOSIT = keccak256("DEPOSIT");
    bytes32 public constant MAP_TOKEN = keccak256("MAP_TOKEN");

    event TokenMappedERC20(address indexed rootToken, address indexed childToken);
    event FxWithdrawERC20(address indexed rootToken, address indexed childToken, address indexed userAddress, uint256 amount);
    event FxDepositERC20(address indexed rootToken, address indexed depositor, address indexed userAddress, uint256 amount);

    mapping(address => address) public rootToChildTokens;
    bytes32 public childTokenTemplateCodeHash;

    constructor(address _checkpointManager, address _fxRoot, address _fxERC20Token) FxBaseRootTunnel(_checkpointManager, _fxRoot) {
        // compute child token template code hash
        childTokenTemplateCodeHash = keccak256(minimalProxyCreationCode(_fxERC20Token));
    }

    /**
     * @notice Map a token to enable its movement via the PoS Portal, callable only by mappers
     * @param rootToken address of token on root chain
     */
    function mapToken(address rootToken) public {
        // check if token is already mapped
        require(rootToChildTokens[rootToken] == address(0x0), "FxERC20RootTunnel: ALREADY_MAPPED");

        // name, symbol and decimals
        ERC20 rootTokenContract = ERC20(rootToken);
        string memory name = rootTokenContract.name();
        string memory symbol = rootTokenContract.symbol();
        uint8 decimals = rootTokenContract.decimals();

        // MAP_TOKEN, encode(rootToken, name, symbol, decimals)
        bytes memory message = abi.encode(MAP_TOKEN, abi.encode(rootToken, name, symbol, decimals));
        _sendMessageToChild(message);

        // compute child token address before deployment using create2
        bytes32 salt = keccak256(abi.encodePacked(rootToken));
        address childToken = computedCreate2Address(salt, childTokenTemplateCodeHash, fxChildTunnel);

        // add into mapped tokens
        rootToChildTokens[rootToken] = childToken;
        emit TokenMappedERC20(rootToken, childToken);
    }

    function deposit(address rootToken, address user, uint256 amount, bytes memory data) public {
        // map token if not mapped
        if (rootToChildTokens[rootToken] == address(0x0)) {
            mapToken(rootToken);
        }

        // transfer from depositor to this contract
        IERC20(rootToken).safeTransferFrom(
            msg.sender,    // depositor
            address(this), // manager contract
            amount
        );

        // DEPOSIT, encode(rootToken, depositor, user, amount, extra data)
        bytes memory message = abi.encode(DEPOSIT, abi.encode(rootToken, msg.sender, user, amount, data));
        _sendMessageToChild(message);
        emit FxDepositERC20(rootToken, msg.sender, user, amount);
    }

    // exit processor
    function _processMessageFromChild(bytes memory data) internal override {
        (address rootToken, address childToken, address to, uint256 amount) = abi.decode(data, (address, address, address, uint256));
        // validate mapping for root to child
        require(rootToChildTokens[rootToken] == childToken, "FxERC20RootTunnel: INVALID_MAPPING_ON_EXIT");

        // transfer from tokens to
        IERC20(rootToken).safeTransfer(
            to,
            amount
        );
        emit FxWithdrawERC20(rootToken, childToken, to, amount);
    }
}

// File: contracts/lib/ERC20.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import { IERC20 } from './IERC20.sol';
import { SafeMath } from './SafeMath.sol';

/**
 * @dev Implementation of the {IERC20} interface.
 *
 * This implementation is agnostic to the way tokens are created. This means
 * that a supply mechanism has to be added in a derived contract using {_mint}.
 * For a generic mechanism see {ERC20PresetMinterPauser}.
 *
 * TIP: For a detailed writeup see our guide
 * https://forum.zeppelin.solutions/t/how-to-implement-erc20-supply-mechanisms/226[How
 * to implement supply mechanisms].
 *
 * We have followed general OpenZeppelin guidelines: functions revert instead
 * of returning `false` on failure. This behavior is nonetheless conventional
 * and does not conflict with the expectations of ERC20 applications.
 *
 * Additionally, an {Approval} event is emitted on calls to {transferFrom}.
 * This allows applications to reconstruct the allowance for all accounts just
 * by listening to said events. Other implementations of the EIP may not emit
 * these events, as it isn't required by the specification.
 *
 * Finally, the non-standard {decreaseAllowance} and {increaseAllowance}
 * functions have been added to mitigate the well-known issues around setting
 * allowances. See {IERC20-approve}.
 */
contract ERC20 is IERC20 {
    using SafeMath for uint256;

    mapping (address => uint256) private _balances;

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

    uint256 private _totalSupply;

    string private _name;
    string private _symbol;
    uint8 private _decimals;

    /**
     * @dev Returns the name of the token.
     */
    function name() public view returns (string memory) {
        return _name;
    }

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

    /**
     * @dev Returns the number of decimals used to get its user representation.
     * For example, if `decimals` equals `2`, a balance of `505` tokens should
     * be displayed to a user as `5,05` (`505 / 10 ** 2`).
     *
     * Tokens usually opt for a value of 18, imitating the relationship between
     * Ether and Wei. This is the value {ERC20} uses, unless {_setupDecimals} is
     * called.
     *
     * NOTE: This information is only used for _display_ purposes: it in
     * no way affects any of the arithmetic of the contract, including
     * {IERC20-balanceOf} and {IERC20-transfer}.
     */
    function decimals() public view returns (uint8) {
        return _decimals;
    }

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

    /**
     * @dev See {IERC20-balanceOf}.
     */
    function balanceOf(address account) public view override returns (uint256) {
        return _balances[account];
    }

    /**
     * @dev See {IERC20-transfer}.
     *
     * Requirements:
     *
     * - `recipient` cannot be the zero address.
     * - the caller must have a balance of at least `amount`.
     */
    function transfer(address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(msg.sender, recipient, amount);
        return true;
    }

    /**
     * @dev See {IERC20-allowance}.
     */
    function allowance(address owner, address spender) public view virtual override returns (uint256) {
        return _allowances[owner][spender];
    }

    /**
     * @dev See {IERC20-approve}.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function approve(address spender, uint256 amount) public virtual override returns (bool) {
        _approve(msg.sender, spender, amount);
        return true;
    }

    /**
     * @dev See {IERC20-transferFrom}.
     *
     * Emits an {Approval} event indicating the updated allowance. This is not
     * required by the EIP. See the note at the beginning of {ERC20}.
     *
     * Requirements:
     *
     * - `sender` and `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     * - the caller must have allowance for ``sender``'s tokens of at least
     * `amount`.
     */
    function transferFrom(address sender, address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(sender, recipient, amount);
        _approve(sender, msg.sender, _allowances[sender][msg.sender].sub(amount, "ERC20: transfer amount exceeds allowance"));
        return true;
    }

    /**
     * @dev Atomically increases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function increaseAllowance(address spender, uint256 addedValue) public virtual returns (bool) {
        _approve(msg.sender, spender, _allowances[msg.sender][spender].add(addedValue));
        return true;
    }

    /**
     * @dev Atomically decreases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     * - `spender` must have allowance for the caller of at least
     * `subtractedValue`.
     */
    function decreaseAllowance(address spender, uint256 subtractedValue) public virtual returns (bool) {
        _approve(msg.sender, spender, _allowances[msg.sender][spender].sub(subtractedValue, "ERC20: decreased allowance below zero"));
        return true;
    }

    /**
     * @dev Moves tokens `amount` from `sender` to `recipient`.
     *
     * This is internal function is equivalent to {transfer}, and can be used to
     * e.g. implement automatic token fees, slashing mechanisms, etc.
     *
     * Emits a {Transfer} event.
     *
     * Requirements:
     *
     * - `sender` cannot be the zero address.
     * - `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     */
    function _transfer(address sender, address recipient, uint256 amount) internal virtual {
        require(sender != address(0), "ERC20: transfer from the zero address");
        require(recipient != address(0), "ERC20: transfer to the zero address");

        _beforeTokenTransfer(sender, recipient, amount);

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

    /** @dev Creates `amount` tokens and assigns them to `account`, increasing
     * the total supply.
     *
     * Emits a {Transfer} event with `from` set to the zero address.
     *
     * Requirements:
     *
     * - `to` cannot be the zero address.
     */
    function _mint(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: mint to the zero address");

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

        _totalSupply = _totalSupply.add(amount);
        _balances[account] = _balances[account].add(amount);
        emit Transfer(address(0), account, amount);
    }

    /**
     * @dev Destroys `amount` tokens from `account`, reducing the
     * total supply.
     *
     * Emits a {Transfer} event with `to` set to the zero address.
     *
     * Requirements:
     *
     * - `account` cannot be the zero address.
     * - `account` must have at least `amount` tokens.
     */
    function _burn(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: burn from the zero address");

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

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

    /**
     * @dev Sets `amount` as the allowance of `spender` over the `owner` s tokens.
     *
     * This internal function is equivalent to `approve`, and can be used to
     * e.g. set automatic allowances for certain subsystems, etc.
     *
     * Emits an {Approval} event.
     *
     * Requirements:
     *
     * - `owner` cannot be the zero address.
     * - `spender` cannot be the zero address.
     */
    function _approve(address owner, address spender, uint256 amount) internal virtual {
        require(owner != address(0), "ERC20: approve from the zero address");
        require(spender != address(0), "ERC20: approve to the zero address");

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

    function _setupMetaData(string memory name_, string memory symbol_, uint8 decimals_) internal virtual {
        _name = name_;
        _symbol = symbol_;
        _decimals = decimals_;
    }

    /**
     * @dev Hook that is called before any transfer of tokens. This includes
     * minting and burning.
     *
     * Calling conditions:
     *
     * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
     * will be to transferred to `to`.
     * - when `from` is zero, `amount` tokens will be minted for `to`.
     * - when `to` is zero, `amount` of ``from``'s tokens will be burned.
     * - `from` and `to` are never both zero.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _beforeTokenTransfer(address from, address to, uint256 amount) internal virtual { }
}
// File: contracts/lib/Create2.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;


// Create2 adds common methods for minimal proxy with create2
abstract contract Create2 {
    // creates clone using minimal proxy
    function createClone(bytes32 _salt, address _target) internal returns (address _result) {
        bytes20 _targetBytes = bytes20(_target);

        assembly {
            let clone := mload(0x40)
            mstore(clone, 0x3d602d80600a3d3981f3363d3d373d3d3d363d73000000000000000000000000)
            mstore(add(clone, 0x14), _targetBytes)
            mstore(add(clone, 0x28), 0x5af43d82803e903d91602b57fd5bf30000000000000000000000000000000000)
            _result := create2(0, clone, 0x37, _salt)
        }

        require(_result != address(0), "Create2: Failed on minimal deploy");
    }

    // get minimal proxy creation code
    function minimalProxyCreationCode(address logic) internal pure returns (bytes memory) {
        bytes10 creation = 0x3d602d80600a3d3981f3;
        bytes10 prefix = 0x363d3d373d3d3d363d73;
        bytes20 targetBytes = bytes20(logic);
        bytes15 suffix = 0x5af43d82803e903d91602b57fd5bf3;
        return abi.encodePacked(creation, prefix, targetBytes, suffix);
    }

    // get computed create2 address
    function computedCreate2Address(bytes32 salt, bytes32 bytecodeHash, address deployer) public pure returns (address) {
        bytes32 _data = keccak256(
            abi.encodePacked(bytes1(0xff), deployer, salt, bytecodeHash)
        );
        return address(uint160(uint256(_data)));
    }
}

// File: contracts/tunnel/FxBaseRootTunnel.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;


import {RLPReader} from "../lib/RLPReader.sol";
import {MerklePatriciaProof} from "../lib/MerklePatriciaProof.sol";
import {Merkle} from "../lib/Merkle.sol";


interface IFxStateSender {
    function sendMessageToChild(address _receiver, bytes calldata _data) external;
}

contract ICheckpointManager {
    struct HeaderBlock {
        bytes32 root;
        uint256 start;
        uint256 end;
        uint256 createdAt;
        address proposer;
    }

    /**
     * @notice mapping of checkpoint header numbers to block details
     * @dev These checkpoints are submited by plasma contracts
     */
    mapping(uint256 => HeaderBlock) public headerBlocks;
}

abstract contract FxBaseRootTunnel {
    using RLPReader for bytes;
    using RLPReader for RLPReader.RLPItem;
    using Merkle for bytes32;

    // keccak256(MessageSent(bytes))
    bytes32 public constant SEND_MESSAGE_EVENT_SIG = 0x8c5261668696ce22758910d05bab8f186d6eb247ceac2af2e82c7dc17669b036;

    // state sender contract
    IFxStateSender public fxRoot;
    // root chain manager
    ICheckpointManager public checkpointManager;
    // child tunnel contract which receives and sends messages 
    address public fxChildTunnel;

    // storage to avoid duplicate exits
    mapping(bytes32 => bool) public processedExits;

    constructor(address _checkpointManager, address _fxRoot) {
        checkpointManager = ICheckpointManager(_checkpointManager);
        fxRoot = IFxStateSender(_fxRoot);
    }

    // set fxChildTunnel if not set already
    function setFxChildTunnel(address _fxChildTunnel) public {
        require(fxChildTunnel == address(0x0), "FxBaseRootTunnel: CHILD_TUNNEL_ALREADY_SET");
        fxChildTunnel = _fxChildTunnel;
    }

    /**
     * @notice Send bytes message to Child Tunnel
     * @param message bytes message that will be sent to Child Tunnel
     * some message examples -
     *   abi.encode(tokenId);
     *   abi.encode(tokenId, tokenMetadata);
     *   abi.encode(messageType, messageData);
     */
    function _sendMessageToChild(bytes memory message) internal {
        fxRoot.sendMessageToChild(fxChildTunnel, message);
    }

    function _validateAndExtractMessage(bytes memory inputData) internal returns (bytes memory) {
        RLPReader.RLPItem[] memory inputDataRLPList = inputData
            .toRlpItem()
            .toList();

        // checking if exit has already been processed
        // unique exit is identified using hash of (blockNumber, branchMask, receiptLogIndex)
        bytes32 exitHash = keccak256(
            abi.encodePacked(
                inputDataRLPList[2].toUint(), // blockNumber
                // first 2 nibbles are dropped while generating nibble array
                // this allows branch masks that are valid but bypass exitHash check (changing first 2 nibbles only)
                // so converting to nibble array and then hashing it
                MerklePatriciaProof._getNibbleArray(inputDataRLPList[8].toBytes()), // branchMask
                inputDataRLPList[9].toUint() // receiptLogIndex
            )
        );
        require(
            processedExits[exitHash] == false,
            "FxRootTunnel: EXIT_ALREADY_PROCESSED"
        );
        processedExits[exitHash] = true;

        RLPReader.RLPItem[] memory receiptRLPList = inputDataRLPList[6]
            .toBytes()
            .toRlpItem()
            .toList();
        RLPReader.RLPItem memory logRLP = receiptRLPList[3]
            .toList()[
                inputDataRLPList[9].toUint() // receiptLogIndex
            ];

        RLPReader.RLPItem[] memory logRLPList = logRLP.toList();
        
        // check child tunnel
        require(fxChildTunnel == RLPReader.toAddress(logRLPList[0]), "FxRootTunnel: INVALID_FX_CHILD_TUNNEL");

        // verify receipt inclusion
        require(
            MerklePatriciaProof.verify(
                inputDataRLPList[6].toBytes(), // receipt
                inputDataRLPList[8].toBytes(), // branchMask
                inputDataRLPList[7].toBytes(), // receiptProof
                bytes32(inputDataRLPList[5].toUint()) // receiptRoot
            ),
            "FxRootTunnel: INVALID_RECEIPT_PROOF"
        );

        // verify checkpoint inclusion
        _checkBlockMembershipInCheckpoint(
            inputDataRLPList[2].toUint(), // blockNumber
            inputDataRLPList[3].toUint(), // blockTime
            bytes32(inputDataRLPList[4].toUint()), // txRoot
            bytes32(inputDataRLPList[5].toUint()), // receiptRoot
            inputDataRLPList[0].toUint(), // headerNumber
            inputDataRLPList[1].toBytes() // blockProof
        );

        RLPReader.RLPItem[] memory logTopicRLPList = logRLPList[1].toList(); // topics

        require(
            bytes32(logTopicRLPList[0].toUint()) == SEND_MESSAGE_EVENT_SIG, // topic0 is event sig
            "FxRootTunnel: INVALID_SIGNATURE"
        );

        // received message data
        bytes memory receivedData = logRLPList[2].toBytes();
        (bytes memory message) = abi.decode(receivedData, (bytes)); // event decodes params again, so decoding bytes to get message
        return message;
    }

    function _checkBlockMembershipInCheckpoint(
        uint256 blockNumber,
        uint256 blockTime,
        bytes32 txRoot,
        bytes32 receiptRoot,
        uint256 headerNumber,
        bytes memory blockProof
    ) private view returns (uint256) {
        (
            bytes32 headerRoot,
            uint256 startBlock,
            ,
            uint256 createdAt,

        ) = checkpointManager.headerBlocks(headerNumber);

        require(
            keccak256(
                abi.encodePacked(blockNumber, blockTime, txRoot, receiptRoot)
            )
                .checkMembership(
                blockNumber-startBlock,
                headerRoot,
                blockProof
            ),
            "FxRootTunnel: INVALID_HEADER"
        );
        return createdAt;
    }

    /**
     * @notice receive message from  L2 to L1, validated by proof
     * @dev This function verifies if the transaction actually happened on child chain
     *
     * @param inputData RLP encoded data of the reference tx containing following list of fields
     *  0 - headerNumber - Checkpoint header block number containing the reference tx
     *  1 - blockProof - Proof that the block header (in the child chain) is a leaf in the submitted merkle root
     *  2 - blockNumber - Block number containing the reference tx on child chain
     *  3 - blockTime - Reference tx block time
     *  4 - txRoot - Transactions root of block
     *  5 - receiptRoot - Receipts root of block
     *  6 - receipt - Receipt of the reference transaction
     *  7 - receiptProof - Merkle proof of the reference receipt
     *  8 - branchMask - 32 bits denoting the path of receipt in merkle tree
     *  9 - receiptLogIndex - Log Index to read from the receipt
     */
    function receiveMessage(bytes memory inputData) public virtual {
        bytes memory message = _validateAndExtractMessage(inputData);
        _processMessageFromChild(message);
    }

    /**
     * @notice Process message received from Child Tunnel
     * @dev function needs to be implemented to handle message as per requirement
     * This is called by onStateReceive function.
     * Since it is called via a system call, any event will not be emitted during its execution.
     * @param message bytes message that was sent from Child Tunnel
     */
    function _processMessageFromChild(bytes memory message) virtual internal;
}
// File: @openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "../IERC20.sol";
import "../../../utils/Address.sol";

/**
 * @title SafeERC20
 * @dev Wrappers around ERC20 operations that throw on failure (when the token
 * contract returns false). Tokens that return no value (and instead revert or
 * throw on failure) are also supported, non-reverting calls are assumed to be
 * successful.
 * To use this library you can add a `using SafeERC20 for IERC20;` statement to your contract,
 * which allows you to call the safe operations as `token.safeTransfer(...)`, etc.
 */
library SafeERC20 {
    using Address for address;

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

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

    /**
     * @dev Deprecated. This function has issues similar to the ones found in
     * {IERC20-approve}, and its usage is discouraged.
     *
     * Whenever possible, use {safeIncreaseAllowance} and
     * {safeDecreaseAllowance} instead.
     */
    function safeApprove(
        IERC20 token,
        address spender,
        uint256 value
    ) internal {
        // safeApprove should only be called when setting an initial allowance,
        // or when resetting it to zero. To increase and decrease it, use
        // 'safeIncreaseAllowance' and 'safeDecreaseAllowance'
        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) + value;
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    function safeDecreaseAllowance(
        IERC20 token,
        address spender,
        uint256 value
    ) internal {
        unchecked {
            uint256 oldAllowance = token.allowance(address(this), spender);
            require(oldAllowance >= value, "SafeERC20: decreased allowance below zero");
            uint256 newAllowance = oldAllowance - value;
            _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
        }
    }

    /**
     * @dev Imitates a Solidity high-level call (i.e. a regular function call to a contract), relaxing the requirement
     * on the return value: the return value is optional (but if data is returned, it must not be false).
     * @param token The token targeted by the call.
     * @param data The call data (encoded using abi.encode or one of its variants).
     */
    function _callOptionalReturn(IERC20 token, bytes memory data) private {
        // We need to perform a low level call here, to bypass Solidity's return data size checking mechanism, since
        // we're implementing it ourselves. We use {Address.functionCall} to perform this call, which verifies that
        // the target address contains contract code and also asserts for success in the low-level call.

        bytes memory returndata = address(token).functionCall(data, "SafeERC20: low-level call failed");
        if (returndata.length > 0) {
            // Return data is optional
            require(abi.decode(returndata, (bool)), "SafeERC20: ERC20 operation did not succeed");
        }
    }
}

// File: contracts/lib/IERC20.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

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

    /**
     * @dev Moves `amount` tokens from the caller's account to `recipient`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `sender` to `recipient` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);
}
// File: contracts/lib/SafeMath.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

/**
 * @dev Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     *
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;

        return c;
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     *
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
        if (a == 0) {
            return 0;
        }

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

        return c;
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return div(a, b, "SafeMath: division by zero");
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return mod(a, b, "SafeMath: modulo by zero");
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts with custom message when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}
// File: contracts/lib/RLPReader.sol



/*
* @author Hamdi Allam hamdi.allam97@gmail.com
* Please reach out with any questions or concerns
*/
pragma solidity ^0.8.0;

library RLPReader {
    uint8 constant STRING_SHORT_START = 0x80;
    uint8 constant STRING_LONG_START  = 0xb8;
    uint8 constant LIST_SHORT_START   = 0xc0;
    uint8 constant LIST_LONG_START    = 0xf8;
    uint8 constant WORD_SIZE = 32;

    struct RLPItem {
        uint len;
        uint memPtr;
    }

    struct Iterator {
        RLPItem item;   // Item that's being iterated over.
        uint nextPtr;   // Position of the next item in the list.
    }

    /*
    * @dev Returns the next element in the iteration. Reverts if it has not next element.
    * @param self The iterator.
    * @return The next element in the iteration.
    */
    function next(Iterator memory self) internal pure returns (RLPItem memory) {
        require(hasNext(self));

        uint ptr = self.nextPtr;
        uint itemLength = _itemLength(ptr);
        self.nextPtr = ptr + itemLength;

        return RLPItem(itemLength, ptr);
    }

    /*
    * @dev Returns true if the iteration has more elements.
    * @param self The iterator.
    * @return true if the iteration has more elements.
    */
    function hasNext(Iterator memory self) internal pure returns (bool) {
        RLPItem memory item = self.item;
        return self.nextPtr < item.memPtr + item.len;
    }

    /*
    * @param item RLP encoded bytes
    */
    function toRlpItem(bytes memory item) internal pure returns (RLPItem memory) {
        uint memPtr;
        assembly {
            memPtr := add(item, 0x20)
        }

        return RLPItem(item.length, memPtr);
    }

    /*
    * @dev Create an iterator. Reverts if item is not a list.
    * @param self The RLP item.
    * @return An 'Iterator' over the item.
    */
    function iterator(RLPItem memory self) internal pure returns (Iterator memory) {
        require(isList(self));

        uint ptr = self.memPtr + _payloadOffset(self.memPtr);
        return Iterator(self, ptr);
    }

    /*
    * @param item RLP encoded bytes
    */
    function rlpLen(RLPItem memory item) internal pure returns (uint) {
        return item.len;
    }

    /*
    * @param item RLP encoded bytes
    */
    function payloadLen(RLPItem memory item) internal pure returns (uint) {
        return item.len - _payloadOffset(item.memPtr);
    }

    /*
    * @param item RLP encoded list in bytes
    */
    function toList(RLPItem memory item) internal pure returns (RLPItem[] memory) {
        require(isList(item));

        uint items = numItems(item);
        RLPItem[] memory result = new RLPItem[](items);

        uint memPtr = item.memPtr + _payloadOffset(item.memPtr);
        uint dataLen;
        for (uint i = 0; i < items; i++) {
            dataLen = _itemLength(memPtr);
            result[i] = RLPItem(dataLen, memPtr); 
            memPtr = memPtr + dataLen;
        }

        return result;
    }

    // @return indicator whether encoded payload is a list. negate this function call for isData.
    function isList(RLPItem memory item) internal pure returns (bool) {
        if (item.len == 0) return false;

        uint8 byte0;
        uint memPtr = item.memPtr;
        assembly {
            byte0 := byte(0, mload(memPtr))
        }

        if (byte0 < LIST_SHORT_START)
            return false;
        return true;
    }

    /*
     * @dev A cheaper version of keccak256(toRlpBytes(item)) that avoids copying memory.
     * @return keccak256 hash of RLP encoded bytes.
     */
    function rlpBytesKeccak256(RLPItem memory item) internal pure returns (bytes32) {
        uint256 ptr = item.memPtr;
        uint256 len = item.len;
        bytes32 result;
        assembly {
            result := keccak256(ptr, len)
        }
        return result;
    }

    function payloadLocation(RLPItem memory item) internal pure returns (uint, uint) {
        uint offset = _payloadOffset(item.memPtr);
        uint memPtr = item.memPtr + offset;
        uint len = item.len - offset; // data length
        return (memPtr, len);
    }

    /*
     * @dev A cheaper version of keccak256(toBytes(item)) that avoids copying memory.
     * @return keccak256 hash of the item payload.
     */
    function payloadKeccak256(RLPItem memory item) internal pure returns (bytes32) {
        (uint memPtr, uint len) = payloadLocation(item);
        bytes32 result;
        assembly {
            result := keccak256(memPtr, len)
        }
        return result;
    }

    /** RLPItem conversions into data types **/

    // @returns raw rlp encoding in bytes
    function toRlpBytes(RLPItem memory item) internal pure returns (bytes memory) {
        bytes memory result = new bytes(item.len);
        if (result.length == 0) return result;
        
        uint ptr;
        assembly {
            ptr := add(0x20, result)
        }

        copy(item.memPtr, ptr, item.len);
        return result;
    }

    // any non-zero byte is considered true
    function toBoolean(RLPItem memory item) internal pure returns (bool) {
        require(item.len == 1);
        uint result;
        uint memPtr = item.memPtr;
        assembly {
            result := byte(0, mload(memPtr))
        }

        return result == 0 ? false : true;
    }

    function toAddress(RLPItem memory item) internal pure returns (address) {
        // 1 byte for the length prefix
        require(item.len == 21);

        return address(uint160(toUint(item)));
    }

    function toUint(RLPItem memory item) internal pure returns (uint) {
        require(item.len > 0 && item.len <= 33);

        uint offset = _payloadOffset(item.memPtr);
        uint len = item.len - offset;

        uint result;
        uint memPtr = item.memPtr + offset;
        assembly {
            result := mload(memPtr)

            // shfit to the correct location if neccesary
            if lt(len, 32) {
                result := div(result, exp(256, sub(32, len)))
            }
        }

        return result;
    }

    // enforces 32 byte length
    function toUintStrict(RLPItem memory item) internal pure returns (uint) {
        // one byte prefix
        require(item.len == 33);

        uint result;
        uint memPtr = item.memPtr + 1;
        assembly {
            result := mload(memPtr)
        }

        return result;
    }

    function toBytes(RLPItem memory item) internal pure returns (bytes memory) {
        require(item.len > 0);

        uint offset = _payloadOffset(item.memPtr);
        uint len = item.len - offset; // data length
        bytes memory result = new bytes(len);

        uint destPtr;
        assembly {
            destPtr := add(0x20, result)
        }

        copy(item.memPtr + offset, destPtr, len);
        return result;
    }

    /*
    * Private Helpers
    */

    // @return number of payload items inside an encoded list.
    function numItems(RLPItem memory item) private pure returns (uint) {
        if (item.len == 0) return 0;

        uint count = 0;
        uint currPtr = item.memPtr + _payloadOffset(item.memPtr);
        uint endPtr = item.memPtr + item.len;
        while (currPtr < endPtr) {
           currPtr = currPtr + _itemLength(currPtr); // skip over an item
           count++;
        }

        return count;
    }

    // @return entire rlp item byte length
    function _itemLength(uint memPtr) private pure returns (uint) {
        uint itemLen;
        uint byte0;
        assembly {
            byte0 := byte(0, mload(memPtr))
        }

        if (byte0 < STRING_SHORT_START)
            itemLen = 1;
        
        else if (byte0 < STRING_LONG_START)
            itemLen = byte0 - STRING_SHORT_START + 1;

        else if (byte0 < LIST_SHORT_START) {
            assembly {
                let byteLen := sub(byte0, 0xb7) // # of bytes the actual length is
                memPtr := add(memPtr, 1) // skip over the first byte
                /* 32 byte word size */
                let dataLen := div(mload(memPtr), exp(256, sub(32, byteLen))) // right shifting to get the len
                itemLen := add(dataLen, add(byteLen, 1))
            }
        }

        else if (byte0 < LIST_LONG_START) {
            itemLen = byte0 - LIST_SHORT_START + 1;
        } 

        else {
            assembly {
                let byteLen := sub(byte0, 0xf7)
                memPtr := add(memPtr, 1)

                let dataLen := div(mload(memPtr), exp(256, sub(32, byteLen))) // right shifting to the correct length
                itemLen := add(dataLen, add(byteLen, 1))
            }
        }

        return itemLen;
    }

    // @return number of bytes until the data
    function _payloadOffset(uint memPtr) private pure returns (uint) {
        uint byte0;
        assembly {
            byte0 := byte(0, mload(memPtr))
        }

        if (byte0 < STRING_SHORT_START) 
            return 0;
        else if (byte0 < STRING_LONG_START || (byte0 >= LIST_SHORT_START && byte0 < LIST_LONG_START))
            return 1;
        else if (byte0 < LIST_SHORT_START)  // being explicit
            return byte0 - (STRING_LONG_START - 1) + 1;
        else
            return byte0 - (LIST_LONG_START - 1) + 1;
    }

    /*
    * @param src Pointer to source
    * @param dest Pointer to destination
    * @param len Amount of memory to copy from the source
    */
    function copy(uint src, uint dest, uint len) private pure {
        if (len == 0) return;

        // copy as many word sizes as possible
        for (; len >= WORD_SIZE; len -= WORD_SIZE) {
            assembly {
                mstore(dest, mload(src))
            }

            src += WORD_SIZE;
            dest += WORD_SIZE;
        }

        // left over bytes. Mask is used to remove unwanted bytes from the word
        uint mask = 256 ** (WORD_SIZE - len) - 1;
        assembly {
            let srcpart := and(mload(src), not(mask)) // zero out src
            let destpart := and(mload(dest), mask) // retrieve the bytes
            mstore(dest, or(destpart, srcpart))
        }
    }
}
// File: contracts/lib/MerklePatriciaProof.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import {RLPReader} from "./RLPReader.sol";

library MerklePatriciaProof {
    /*
     * @dev Verifies a merkle patricia proof.
     * @param value The terminating value in the trie.
     * @param encodedPath The path in the trie leading to value.
     * @param rlpParentNodes The rlp encoded stack of nodes.
     * @param root The root hash of the trie.
     * @return The boolean validity of the proof.
     */
    function verify(
        bytes memory value,
        bytes memory encodedPath,
        bytes memory rlpParentNodes,
        bytes32 root
    ) internal pure returns (bool) {
        RLPReader.RLPItem memory item = RLPReader.toRlpItem(rlpParentNodes);
        RLPReader.RLPItem[] memory parentNodes = RLPReader.toList(item);

        bytes memory currentNode;
        RLPReader.RLPItem[] memory currentNodeList;

        bytes32 nodeKey = root;
        uint256 pathPtr = 0;

        bytes memory path = _getNibbleArray(encodedPath);
        if (path.length == 0) {
            return false;
        }

        for (uint256 i = 0; i < parentNodes.length; i++) {
            if (pathPtr > path.length) {
                return false;
            }

            currentNode = RLPReader.toRlpBytes(parentNodes[i]);
            if (nodeKey != keccak256(currentNode)) {
                return false;
            }
            currentNodeList = RLPReader.toList(parentNodes[i]);

            if (currentNodeList.length == 17) {
                if (pathPtr == path.length) {
                    if (
                        keccak256(RLPReader.toBytes(currentNodeList[16])) ==
                        keccak256(value)
                    ) {
                        return true;
                    } else {
                        return false;
                    }
                }

                uint8 nextPathNibble = uint8(path[pathPtr]);
                if (nextPathNibble > 16) {
                    return false;
                }
                nodeKey = bytes32(
                    RLPReader.toUintStrict(currentNodeList[nextPathNibble])
                );
                pathPtr += 1;
            } else if (currentNodeList.length == 2) {
                uint256 traversed = _nibblesToTraverse(
                    RLPReader.toBytes(currentNodeList[0]),
                    path,
                    pathPtr
                );
                if (pathPtr + traversed == path.length) {
                    //leaf node
                    if (
                        keccak256(RLPReader.toBytes(currentNodeList[1])) ==
                        keccak256(value)
                    ) {
                        return true;
                    } else {
                        return false;
                    }
                }

                //extension node
                if (traversed == 0) {
                    return false;
                }

                pathPtr += traversed;
                nodeKey = bytes32(RLPReader.toUintStrict(currentNodeList[1]));
            } else {
                return false;
            }
        }
    }

    function _nibblesToTraverse(
        bytes memory encodedPartialPath,
        bytes memory path,
        uint256 pathPtr
    ) private pure returns (uint256) {
        uint256 len = 0;
        // encodedPartialPath has elements that are each two hex characters (1 byte), but partialPath
        // and slicedPath have elements that are each one hex character (1 nibble)
        bytes memory partialPath = _getNibbleArray(encodedPartialPath);
        bytes memory slicedPath = new bytes(partialPath.length);

        // pathPtr counts nibbles in path
        // partialPath.length is a number of nibbles
        for (uint256 i = pathPtr; i < pathPtr + partialPath.length; i++) {
            bytes1 pathNibble = path[i];
            slicedPath[i - pathPtr] = pathNibble;
        }

        if (keccak256(partialPath) == keccak256(slicedPath)) {
            len = partialPath.length;
        } else {
            len = 0;
        }
        return len;
    }

    // bytes b must be hp encoded
    function _getNibbleArray(bytes memory b)
        internal
        pure
        returns (bytes memory)
    {
        bytes memory nibbles = "";
        if (b.length > 0) {
            uint8 offset;
            uint8 hpNibble = uint8(_getNthNibbleOfBytes(0, b));
            if (hpNibble == 1 || hpNibble == 3) {
                nibbles = new bytes(b.length * 2 - 1);
                bytes1 oddNibble = _getNthNibbleOfBytes(1, b);
                nibbles[0] = oddNibble;
                offset = 1;
            } else {
                nibbles = new bytes(b.length * 2 - 2);
                offset = 0;
            }

            for (uint256 i = offset; i < nibbles.length; i++) {
                nibbles[i] = _getNthNibbleOfBytes(i - offset + 2, b);
            }
        }
        return nibbles;
    }

    function _getNthNibbleOfBytes(uint256 n, bytes memory str)
        private
        pure
        returns (bytes1)
    {
        return
            bytes1(
                n % 2 == 0 ? uint8(str[n / 2]) / 0x10 : uint8(str[n / 2]) % 0x10
            );
    }
}
// File: contracts/lib/Merkle.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

library Merkle {
    function checkMembership(
        bytes32 leaf,
        uint256 index,
        bytes32 rootHash,
        bytes memory proof
    ) internal pure returns (bool) {
        require(proof.length % 32 == 0, "Invalid proof length");
        uint256 proofHeight = proof.length / 32;
        // Proof of size n means, height of the tree is n+1.
        // In a tree of height n+1, max #leafs possible is 2 ^ n
        require(index < 2 ** proofHeight, "Leaf index is too big");

        bytes32 proofElement;
        bytes32 computedHash = leaf;
        for (uint256 i = 32; i <= proof.length; i += 32) {
            assembly {
                proofElement := mload(add(proof, i))
            }

            if (index % 2 == 0) {
                computedHash = keccak256(
                    abi.encodePacked(computedHash, proofElement)
                );
            } else {
                computedHash = keccak256(
                    abi.encodePacked(proofElement, computedHash)
                );
            }

            index = index / 2;
        }
        return computedHash == rootHash;
    }
}

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

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

    /**
     * @dev Moves `amount` tokens from the caller's account to `recipient`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `sender` to `recipient` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(
        address sender,
        address recipient,
        uint256 amount
    ) external returns (bool);

    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);
}

// File: @openzeppelin/contracts/utils/Address.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

/**
 * @dev Collection of functions related to the address type
 */
library Address {
    /**
     * @dev Returns true if `account` is a contract.
     *
     * [IMPORTANT]
     * ====
     * It is unsafe to assume that an address for which this function returns
     * false is an externally-owned account (EOA) and not a contract.
     *
     * Among others, `isContract` will return false for the following
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies on extcodesize, which returns 0 for contracts in
        // construction, since the code is only stored at the end of the
        // constructor execution.

        uint256 size;
        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");

        (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");

        (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");

        (bool success, bytes memory returndata) = target.staticcall(data);
        return verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(address target, bytes memory data) internal returns (bytes memory) {
        return functionDelegateCall(target, data, "Address: low-level delegate call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(
        address target,
        bytes memory data,
        string memory errorMessage
    ) internal returns (bytes memory) {
        require(isContract(target), "Address: delegate call to non-contract");

        (bool success, bytes memory returndata) = target.delegatecall(data);
        return verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Tool to verifies that a low level call was successful, and revert if it wasn't, either by bubbling the
     * revert reason using the provided one.
     *
     * _Available since v4.3._
     */
    function verifyCallResult(
        bool success,
        bytes memory returndata,
        string memory errorMessage
    ) internal 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

                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }
}