// File: contracts/Refund.sol



//SPDX-License-Identifier: MIT
pragma solidity ^0.8.7;

import "./Services/Blacklist.sol";
import "./Services/Transfers.sol";
import "./Services/Interfaces.sol";

contract Refund is Transfers, BlackList {
    uint public startTimestamp;

    mapping(address => Base) public pTokens;
    address[] public pTokensList;

    struct Base {
        address baseToken;
        uint course;
    }

    mapping(address => mapping(address => uint)) public pTokenAmounts;
    mapping(address => address) public baseTokens;
    address[] public baseTokenList;

    struct Balance {
        uint amount;
        uint out;
    }

    mapping(address => mapping(address => Balance)) public balances;
    mapping(address => uint[]) public checkpoints;
    mapping(address => uint) public totalAmount;

    address public controller;
    address public pETH;
    address public calcPoolPrice;

    constructor(
        uint startTimestamp_,
        address controller_,
        address pETH_,
        address calcPoolPrice_
    ) {
        require(startTimestamp_ != 0, "Refund::Constructor: timestamp is 0");

        require(startTimestamp_ > getBlockTimestamp(), "Refund::Constructor: start timestamp must be more than current timestamp");

        require(
            controller_ != address(0)
            && pETH_ != address(0)
            && calcPoolPrice_ != address(0),
            "Service::Constructor: address is 0"
        );

        controller = controller_;
        pETH = pETH_;
        startTimestamp = startTimestamp_;
        calcPoolPrice = calcPoolPrice_;
    }

    function addRefundPair(address pToken, address baseToken_, uint course_) public onlyOwner returns (bool) {
        require(baseTokens[pToken] == address(0), "pToken has already been added");

        pTokens[pToken] = Base({baseToken: baseToken_, course: course_});
        baseTokens[pToken] = baseToken_;
        pTokensList.push(pToken);
        baseTokenList.push(baseToken_);

        return true;
    }

    function addTokensAndCheckpoint(address baseToken, uint baseTokenAmount) public onlyOwner returns (bool) {
        uint amountIn = doTransferIn(msg.sender, baseToken, baseTokenAmount);

        if (amountIn > 0 ) {
            checkpoints[baseToken].push(amountIn);
        }

        return true;
    }

    function withdraw(address token, uint amount) public onlyOwner returns (bool) {
        doTransferOut(token, msg.sender, amount);

        return true;
    }

    function addUserBalance(address user, address pToken, uint amount) public onlyOwner returns (bool) {
        refundInternal(user, pToken, amount);

        return true;
    }

    function refund(address pToken, uint pTokenAmount) public returns (bool) {
        require(getBlockTimestamp() < startTimestamp, "Refund::refund: you can convert pTokens before start timestamp only");
        require(pTokensIsAllowed(pToken), "Refund::refund: pToken is not allowed");

        uint pTokenAmountIn = doTransferIn(msg.sender, pToken, pTokenAmount);
        refundInternal(msg.sender, pToken, pTokenAmountIn);

        return true;
    }

    function refundInternal(address user, address pToken, uint amount) internal returns (bool) {
        pTokenAmounts[user][pToken] += amount;
        address baseToken = baseTokens[pToken];
        uint baseTokenAmount = calcRefundAmount(pToken, amount);
        balances[user][baseToken].amount += baseTokenAmount;
        totalAmount[baseToken] += baseTokenAmount;

        return true;
    }

    function calcRefundAmount(address pToken, uint amount) public view returns (uint) {
        uint course = pTokens[pToken].course;

        uint pTokenDecimals = ERC20(pToken).decimals();
        uint baseTokenDecimals = ERC20(pTokens[pToken].baseToken).decimals();
        uint factor;

        if (pTokenDecimals >= baseTokenDecimals) {
            factor = 10**(pTokenDecimals - baseTokenDecimals);
            return amount * course / factor / 1e18;
        } else {
            factor = 10**(baseTokenDecimals - pTokenDecimals);
            return amount * course * factor / 1e18;
        }
    }

    function claimToken(address pToken) public returns (bool) {
        require(getBlockTimestamp() > startTimestamp, "Refund::claimToken: bad timing for the request");
        require(!isBlackListed[msg.sender], "Refund::claimToken: user in black list");

        uint amount = calcClaimAmount(msg.sender, pToken);

        address baseToken = baseTokens[pToken];
        balances[msg.sender][baseToken].out += amount;

        doTransferOut(baseToken, msg.sender, amount);

        return true;
    }

    function calcClaimAmount(address user, address pToken) public view returns (uint) {
        address baseToken = baseTokens[pToken];
        uint amount = balances[user][baseToken].amount;

        if (amount == 0 || amount == balances[user][baseToken].out || getBlockTimestamp() <= startTimestamp ) {
            return 0;
        }

        uint claimAmount;

        for (uint i = 0; i < checkpoints[baseToken].length; i++) {
            claimAmount += amount * checkpoints[baseToken][i] / totalAmount[baseToken];
        }

        if (claimAmount > amount) {
            return amount - balances[user][baseToken].out;
        } else {
            return claimAmount - balances[user][baseToken].out;
        }
    }

    function getCheckpointsLength(address baseToken_) public view returns (uint) {
        return checkpoints[baseToken_].length;
    }

    function getPTokenList() public view returns (address[] memory) {
        return pTokensList;
    }

    function getPTokenListLength() public view returns (uint) {
        return pTokensList.length;
    }

    function getBaseTokenList() public view returns (address[] memory) {
        return baseTokenList;
    }

    function getBaseTokenListLength() public view returns (uint) {
        return baseTokenList.length;
    }

    function getAllTotalAmount() public view returns (uint) {
        uint allAmount;
        uint price;
        address baseToken;

        for(uint i = 0; i < baseTokenList.length; i++ ) {
            baseToken = baseTokenList[i];
            price = pTokensList[i] == pETH ? CalcPoolPrice(calcPoolPrice).getPoolPriceInUSD(pETH) : CalcPoolPrice(calcPoolPrice).getPoolPriceInUSD(baseToken);
            allAmount += price * totalAmount[baseToken] / 1e18 / (10 ** ERC20(baseToken).decimals());
        }

        return allAmount;
    }

    function getUserUsdAmount(address user) public view returns (uint) {
        uint userTotalAmount;
        uint price;
        address baseToken;

        for(uint i = 0; i < baseTokenList.length; i++ ) {
            baseToken = baseTokenList[i];

            price = pTokensList[i] == pETH ? CalcPoolPrice(calcPoolPrice).getPoolPriceInUSD(pETH) : CalcPoolPrice(calcPoolPrice).getPoolPriceInUSD(baseToken);
            userTotalAmount += price * balances[user][baseToken].amount / 1e18 / (10 ** ERC20(baseToken).decimals());
        }

        return userTotalAmount;
    }

    function pTokensIsAllowed(address pToken_) public view returns (bool) {
        for (uint i = 0; i < pTokensList.length; i++ ) {
            if (pTokensList[i] == pToken_) {
                return true;
            }
        }

        return false;
    }

    function getAvailableLiquidity() public view returns (uint) {
        uint availableLiquidity;
        uint price;
        address baseToken;

        for(uint i = 0; i < baseTokenList.length; i++ ) {
            baseToken = baseTokenList[i];
            price = ControllerInterface(controller).getOracle().getPriceInUSD(baseToken);
            availableLiquidity += price * ERC20(baseToken).balanceOf(address(this)) / 1e18  / (10 ** ERC20(baseToken).decimals());
        }

        return availableLiquidity;
    }

    function getBlockTimestamp() public view virtual returns (uint) {
        return block.timestamp;
    }
}

// File: contracts/Services/Blacklist.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.7;

import "openzeppelin-solidity/contracts/access/Ownable.sol";

contract BlackList is Ownable {
    mapping (address => bool) public isBlackListed;

    event AddedBlackList(address _user);

    event RemovedBlackList(address _user);

    function addBlackList(address _evilUser) public onlyOwner {
        isBlackListed[_evilUser] = true;

        emit AddedBlackList(_evilUser);
    }

    function removeBlackList(address _clearedUser) public onlyOwner {
        isBlackListed[_clearedUser] = false;

        emit RemovedBlackList(_clearedUser);
    }

    function getBlackListStatus(address _maker) external view returns (bool) {
        return isBlackListed[_maker];
    }
}


// File: contracts/Services/Transfers.sol



//SPDX-License-Identifier: MIT
pragma solidity ^0.8.7;

import "./ERC20.sol";

contract Transfers {
    function doTransferIn(address from, address token, uint amount) internal returns (uint) {
        uint balanceBefore = ERC20(token).balanceOf(address(this));
        ERC20(token).transferFrom(from, address(this), amount);

        bool success;
        assembly {
            switch returndatasize()
            case 0 {                       // This is a non-standard ERC-20
                success := not(0)          // set success to true
            }
            case 32 {                      // This is a compliant ERC-20
                returndatacopy(0, 0, 32)
                success := mload(0)        // Set `success = returndata` of external call
            }
            default {                      // This is an excessively non-compliant ERC-20, revert.
                revert(0, 0)
            }
        }
        require(success, "TOKEN_TRANSFER_IN_FAILED");

        // Calculate the amount that was *actually* transferred
        uint balanceAfter = ERC20(token).balanceOf(address(this));
        require(balanceAfter >= balanceBefore, "TOKEN_TRANSFER_IN_OVERFLOW");
        return balanceAfter - balanceBefore;   // underflow already checked above, just subtract
    }

    function doTransferOut(address token, address to, uint amount) internal {
        ERC20(token).transfer(to, amount);

        bool success;
        assembly {
            switch returndatasize()
            case 0 {                      // This is a non-standard ERC-20
                success := not(0)          // set success to true
            }
            case 32 {                     // This is a complaint ERC-20
                returndatacopy(0, 0, 32)
                success := mload(0)        // Set `success = returndata` of external call
            }
            default {                     // This is an excessively non-compliant ERC-20, revert.
                revert(0, 0)
            }
        }
        require(success, "TOKEN_TRANSFER_OUT_FAILED");
    }
}

// File: contracts/Services/Interfaces.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.7;

interface RegistryInterface {
    function pETH() external view returns (address);
}

interface FactoryInterface {
    function registry() external view returns (address);
}

interface PTokenInterface {
    function exchangeRateStored() external view returns (uint);
    function borrowBalanceStored(address account) external view returns (uint);
    function underlying() external view returns (address);
}

interface CalcPoolPrice {
    function getPoolPriceInUSD(address asset) external view returns (uint);
}

interface PriceOracle {
    function getUnderlyingPrice(address pToken) external view returns (uint);
    function getPriceInUSD(address underlying) external view returns (uint);
}

interface ControllerInterface {
    function getOracle() external view returns (PriceOracle);
    function getAssetsIn(address account) external view returns (address[] memory);
    function factory() external view returns (address);
}

interface AggregatorInterface {
    function latestAnswer() external view returns (int256);
}

interface ConvertInterface {
    function getPTokenInAmount(address user) external view returns (uint);
    function pTokenFrom() external view returns (address);
}

// File: openzeppelin-solidity/contracts/access/Ownable.sol



// SPDX-License-Identifier: MIT

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() {
        _setOwner(_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 {
        _setOwner(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");
        _setOwner(newOwner);
    }

    function _setOwner(address newOwner) private {
        address oldOwner = _owner;
        _owner = newOwner;
        emit OwnershipTransferred(oldOwner, newOwner);
    }
}

// File: openzeppelin-solidity/contracts/utils/Context.sol



// SPDX-License-Identifier: MIT

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;
    }
}

// File: contracts/Services/ERC20.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.7;

import "openzeppelin-solidity/contracts/token/ERC20/ERC20.sol";

contract ERC20Token is ERC20 {
    constructor(
        uint256 initialSupply,
        string memory name,
        string memory symbol
    ) ERC20(name, symbol) {
        _mint(msg.sender, initialSupply);
    }

    function mint(uint256 amount) external {
        _mint(msg.sender, amount);
    }
}

contract ERC20TokenDec6 is ERC20 {
    constructor(
        uint256 initialSupply,
        string memory name,
        string memory symbol
    ) ERC20(name, symbol) {
        _mint(msg.sender, initialSupply);
    }

    function mint(uint256 amount) external {
        _mint(msg.sender, amount);
    }

    function decimals() public view virtual override returns (uint8) {
        return 6;
    }
}

// File: openzeppelin-solidity/contracts/token/ERC20/ERC20.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "./IERC20.sol";
import "./extensions/IERC20Metadata.sol";
import "../../utils/Context.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 Contracts guidelines: functions revert
 * instead 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 Context, IERC20, IERC20Metadata {
    mapping(address => uint256) private _balances;

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

    uint256 private _totalSupply;

    string private _name;
    string private _symbol;

    /**
     * @dev Sets the values for {name} and {symbol}.
     *
     * The default value of {decimals} is 18. To select a different value for
     * {decimals} you should overload it.
     *
     * All two of these values are immutable: they can only be set once during
     * construction.
     */
    constructor(string memory name_, string memory symbol_) {
        _name = name_;
        _symbol = symbol_;
    }

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

    /**
     * @dev Returns the symbol of the token, usually a shorter version of the
     * name.
     */
    function symbol() public view virtual override 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 this function is
     * overridden;
     *
     * 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 virtual override returns (uint8) {
        return 18;
    }

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

    /**
     * @dev See {IERC20-balanceOf}.
     */
    function balanceOf(address account) public view virtual 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(_msgSender(), 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(_msgSender(), 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);

        uint256 currentAllowance = _allowances[sender][_msgSender()];
        require(currentAllowance >= amount, "ERC20: transfer amount exceeds allowance");
        unchecked {
            _approve(sender, _msgSender(), currentAllowance - amount);
        }

        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(_msgSender(), spender, _allowances[_msgSender()][spender] + 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) {
        uint256 currentAllowance = _allowances[_msgSender()][spender];
        require(currentAllowance >= subtractedValue, "ERC20: decreased allowance below zero");
        unchecked {
            _approve(_msgSender(), spender, currentAllowance - subtractedValue);
        }

        return true;
    }

    /**
     * @dev Moves `amount` of tokens from `sender` to `recipient`.
     *
     * This 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);

        uint256 senderBalance = _balances[sender];
        require(senderBalance >= amount, "ERC20: transfer amount exceeds balance");
        unchecked {
            _balances[sender] = senderBalance - amount;
        }
        _balances[recipient] += amount;

        emit Transfer(sender, recipient, amount);

        _afterTokenTransfer(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:
     *
     * - `account` 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 += amount;
        _balances[account] += amount;
        emit Transfer(address(0), account, amount);

        _afterTokenTransfer(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);

        uint256 accountBalance = _balances[account];
        require(accountBalance >= amount, "ERC20: burn amount exceeds balance");
        unchecked {
            _balances[account] = accountBalance - amount;
        }
        _totalSupply -= amount;

        emit Transfer(account, address(0), amount);

        _afterTokenTransfer(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);
    }

    /**
     * @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 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 {}

    /**
     * @dev Hook that is called after any transfer of tokens. This includes
     * minting and burning.
     *
     * Calling conditions:
     *
     * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
     * has been transferred to `to`.
     * - when `from` is zero, `amount` tokens have been minted for `to`.
     * - when `to` is zero, `amount` of ``from``'s tokens have been 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 _afterTokenTransfer(
        address from,
        address to,
        uint256 amount
    ) internal virtual {}
}

// File: openzeppelin-solidity/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-solidity/contracts/token/ERC20/extensions/IERC20Metadata.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "../IERC20.sol";

/**
 * @dev Interface for the optional metadata functions from the ERC20 standard.
 *
 * _Available since v4.1._
 */
interface IERC20Metadata is IERC20 {
    /**
     * @dev Returns the name of the token.
     */
    function name() external view returns (string memory);

    /**
     * @dev Returns the symbol of the token.
     */
    function symbol() external view returns (string memory);

    /**
     * @dev Returns the decimals places of the token.
     */
    function decimals() external view returns (uint8);
}