// File: contracts/staking/StakedProbablyNothing.sol



// SPDX-License-Identifier: MIT
//                                                      *****+=:.  .=*****+-.      -#@@#-.   .+*****=:.     .****+:   :*****+=:.   -***:  -+**=   =***.
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//    .:-:.         ....:::.....                        ..     ...     ..:::..       ...      ..    ...   ...    ..    ....     .::.....    ..
//
/// @title Probably Nothing Staking Rewards
/// @author 0xEwok and audie.eth
/// @notice Auto-compounding staking rewards for PRBLY.

pragma solidity ^0.8.9;

import "@openzeppelin/contracts/utils/Context.sol";
import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Burnable.sol";
import "@openzeppelin/contracts/token/ERC20/IERC20.sol";

contract StakedProbablyNothing is Ownable, ERC20Burnable {
   event AddStake(address indexed _addr, uint _baseTokenValue, uint _stakedTokenValue);
   event RemoveStake(address indexed _addr, uint _baseTokenValue, uint _stakedTokenValue);
   event FundRewards(address indexed _addr, uint _numEpochs, uint _secondsPerEpoch, uint _rewardsPerEpoch);

    // token address to be staked
    address private tokenAddress;
    // amount of token staked
    uint256 private poolDeposits;
    // token rewards to be vested per epoch
    uint256 private rewardsPerEpoch;
    // tracker variable to track amount funded
    uint256 private cumulativeFundedRewards;

    // cumulative rewards withdrawn
    uint256 private poolWithdrawals;
    uint private rewardsPeriodStartTime;
    uint private rewardsPeriodEndTime;
    uint private rewardsFundedEpochs;
    // vesting interval length
    uint private rewardsEpochLength = 86400;

    constructor(
        string memory name_,
        string memory symbol_,
        address tokenAddress_
    ) ERC20(name_, symbol_) {
        tokenAddress = tokenAddress_;
    }

    /** @notice Mints staked token. Also referred to as "staking token".
     */
    function _mint(address account, uint256 amount) internal override (ERC20) {
        super._mint(account, amount);
    }

    /** @notice Setup and fund the staking rewards period
     *  @param rewardsPerEpoch_ the base token rewards per epoch
     *  @param numEpochs_ the number of epochs to fund
     *  @param secondsPerEpoch_ the number of seconds per epoch
     */
    function fundStakingRewards(uint numEpochs_, uint secondsPerEpoch_, uint256 rewardsPerEpoch_) public onlyOwner {
        // validate input parameters
        require(secondsPerEpoch_ > 0, "Sanity check: minimum epoch length is 1 second");
        require(secondsPerEpoch_ < 86401, "Sanity check: can only set epoch length up to 1 day");
        require(numEpochs_ * secondsPerEpoch_ < 15552000, "Sanity check: can only setup 180 days of rewards at a time");

        // update tracking variables before transfer
        // must be done if at least one withdrawal or vested rewards > 0, so just do every time
        // ok to do if only deposits, or if nothing happened yet
        // check invariants: can only be called when another staking period is not active
        require(block.timestamp > rewardsPeriodEndTime, "Invariant check: Can only update rewards after prior rewards period ends");
        require(block.timestamp > rewardsPeriodStartTime, "Re-entry check: Cannot update rewards before rewards period starts");

        poolDeposits = getStakingPoolSize();
        poolWithdrawals = 0;

        // transfer token in
        uint rewardsTotal = rewardsPerEpoch_ * numEpochs_;
        require(
            IERC20(tokenAddress).transferFrom(msg.sender, address(this), rewardsTotal),
            "Failed transferring tokens from sender"
        );

        // set tracking variables for this vesting rewards period
        rewardsEpochLength = secondsPerEpoch_;
        rewardsPerEpoch = rewardsPerEpoch_;
        rewardsFundedEpochs = numEpochs_;
        rewardsPeriodStartTime = block.timestamp;
        rewardsPeriodEndTime = block.timestamp + numEpochs_ * rewardsEpochLength;
        require(vestedRewards() == 0, "Invariant failed: vested rewards should be 0. None should have vested yet.");

        // read-only variable to track cumulative rewards
        cumulativeFundedRewards = cumulativeFundedRewards + rewardsTotal;

        emit FundRewards(msg.sender, numEpochs_, secondsPerEpoch_, rewardsPerEpoch_);
    }

    /** @notice The length of a vesting period in seconds
     */
    function getRewardsEpochLength() public view returns (uint256) {
        return rewardsEpochLength;
    }

    /** @notice The start time for this reward period
     */
    function getRewardsPeriodStartTime() public view returns (uint256) {
        return rewardsPeriodStartTime;
    }

    /** @notice The end time for this reward period
     */
    function getRewardsPeriodEndTime() public view returns (uint256) {
        return rewardsPeriodEndTime;
    }

    /** @notice Base token rewards per epoch, shared equally across staking token holders
     */
    function getRewardsPerEpoch() public view returns (uint256) {
        return rewardsPerEpoch;
    }

    /** @notice The number of epochs with funded rewards
     */
    function getRewardsFundedEpochs() public view returns (uint256) {
        return rewardsFundedEpochs;
    }

    /** @notice The total base tokens deposited for this reward period
     */
    function getPoolDeposits() public view returns (uint256) {
        return poolDeposits;
    }

    /** @notice The total base tokens withdrawn for this reward period
     */
    function getRewardsPeriodPoolWithdrawalsTotal() public view returns (uint256) {
        return poolWithdrawals;
    }

    /** @notice The total funded rewards for this reward period
     */
    function totalRewards() public view returns (uint256) {
        return rewardsPerEpoch * rewardsFundedEpochs;
    }

    /** @notice The number of elapsed epochs that have vested for this reward period
     */
    function getElapsedEpochs() public view returns (uint256) {
        if (rewardsPeriodStartTime == 0) {
            return 0;
        }
        if (block.timestamp >= rewardsPeriodEndTime) {
            return rewardsFundedEpochs;
        }
        return (block.timestamp - rewardsPeriodStartTime) / rewardsEpochLength;
    }

    /** @notice The remaining number of epochs that will vest for this reward period
     */
    function getRemainingEpochs() public view returns (uint256) {
        return rewardsFundedEpochs - getElapsedEpochs();
    }

    /** @notice The amount of rewards that have vested for this reward period
     */
    function vestedRewards() public view returns (uint256) {
        if (rewardsPeriodStartTime == 0 || block.timestamp < rewardsPeriodStartTime) {
            return 0;
        }

        uint elapsedEpochs = (block.timestamp - rewardsPeriodStartTime) / rewardsEpochLength;
        if (elapsedEpochs >= rewardsFundedEpochs) {
            return totalRewards();
        }

        return elapsedEpochs * rewardsPerEpoch;
    }

    /** @notice The next vest time
     */
    function nextVestTime() public view returns (uint256) {
        if (rewardsPeriodStartTime == 0 || block.timestamp < rewardsPeriodStartTime) {
            return 0;
        }

        uint elapsedEpochs = (block.timestamp - rewardsPeriodStartTime) / rewardsEpochLength;
        if (elapsedEpochs >= rewardsFundedEpochs) {
            return rewardsPeriodStartTime + rewardsFundedEpochs * rewardsEpochLength;
        }

        return rewardsPeriodStartTime + (elapsedEpochs + 1) * rewardsEpochLength;
    }

    /** @notice The number of seconds until the next vest time
     */
    function secondsUntilNextVest() public view returns (uint256) {
        return nextVestTime() - block.timestamp;
    }

    /** @notice Whether rewards are actively vesting
     */
    function isVestingRewardsNow() public view returns (bool) {
        return block.timestamp >= rewardsPeriodStartTime && block.timestamp < rewardsPeriodEndTime;
    }

    /** @notice The size of the staking pool, including deposits and vested rewards
     */
    function getStakingPoolSize() public view returns (uint256) {
        return poolDeposits + vestedRewards() - poolWithdrawals;
    }

    /** @notice Convert base token to staking token based on current conversion ratio
     *  @param amount The amount of based token
     */
    function toStakedToken(uint256 amount) public view returns (uint256) {
        uint256 totalStakedToken = totalSupply();

        // first staker has claim to entire pool, even if some of it has vested already
        if (totalStakedToken == 0) {
            return amount;
        }

        uint256 totalBaseToken = getStakingPoolSize();

        // ammount * staking/base
        return amount * totalStakedToken / totalBaseToken;
    }

    /** @notice Convert staking token to base token based on current conversion ratio
     *  @param amount The amount of staking token
     */
    function toBaseToken(uint256 amount) public view returns (uint256) {
        uint256 totalStakedToken = totalSupply();

        if (totalStakedToken == 0) {
            return amount;
        }

        uint256 totalBaseToken = getStakingPoolSize();

        // ammount * base/staking
        return amount * totalBaseToken / totalStakedToken;
    }

    /** @notice Stake base token and received staked token.
     */
    function addStake(uint256 baseTokenAmount) external {
        // take base token token in
        require(
            IERC20(tokenAddress).transferFrom(msg.sender, address(this), baseTokenAmount),
            "Failed transferring token from sender"
        );

        // conversion relies on supply of staked token and amount of base token staked, so must do math first
        uint256 stakedTokenAmount = toStakedToken(baseTokenAmount);

        // give back staked token
        _mint(msg.sender, stakedTokenAmount);
        poolDeposits += baseTokenAmount;

        emit AddStake(msg.sender, baseTokenAmount, stakedTokenAmount);
    }

    /** @notice Remove staking token and withdraw base token.
     */
    function removeStake(uint256 stakedTokenAmount) external {
        // take staking token in
        require(
            stakedTokenAmount <= balanceOf(msg.sender), "Cannot remove stake for more tokens than owned"
        );

        // give back their stake
        uint256 baseTokenAmount = toBaseToken(stakedTokenAmount);
        require(baseTokenAmount <= getStakingPoolSize(), "Converted token amount is greater than staked + rewards. Something went wrong.");
        require(
            IERC20(tokenAddress).transfer(msg.sender, baseTokenAmount),
            "Insufficient token reward in staking contract. Unexpected."
        );

        // burn their staked token
        burn(stakedTokenAmount);
        poolWithdrawals += baseTokenAmount;

        emit RemoveStake(msg.sender, baseTokenAmount, stakedTokenAmount);
    }

    /** @notice The cumulative amount of rewards that have been funded.
     */
    function getCumulativeFundedRewards() public view returns (uint256) {
        return cumulativeFundedRewards;
    }

    /** @notice The cumulative amount of rewards that have vested.
     */
    function getCumulativeVestedRewards() public view returns (uint256) {
        return cumulativeFundedRewards + vestedRewards() - totalRewards();
    }
}

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



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

pragma solidity ^0.8.0;

/**
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
abstract contract Context {
    function _msgSender() internal view virtual returns (address) {
        return msg.sender;
    }

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

// File: @openzeppelin/contracts/access/Ownable.sol



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

pragma solidity ^0.8.0;

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

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

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

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

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

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

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

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

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

// File: @openzeppelin/contracts/token/ERC20/extensions/ERC20Burnable.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.5.0) (token/ERC20/extensions/ERC20Burnable.sol)

pragma solidity ^0.8.0;

import "../ERC20.sol";
import "../../../utils/Context.sol";

/**
 * @dev Extension of {ERC20} that allows token holders to destroy both their own
 * tokens and those that they have an allowance for, in a way that can be
 * recognized off-chain (via event analysis).
 */
abstract contract ERC20Burnable is Context, ERC20 {
    /**
     * @dev Destroys `amount` tokens from the caller.
     *
     * See {ERC20-_burn}.
     */
    function burn(uint256 amount) public virtual {
        _burn(_msgSender(), amount);
    }

    /**
     * @dev Destroys `amount` tokens from `account`, deducting from the caller's
     * allowance.
     *
     * See {ERC20-_burn} and {ERC20-allowance}.
     *
     * Requirements:
     *
     * - the caller must have allowance for ``accounts``'s tokens of at least
     * `amount`.
     */
    function burnFrom(address account, uint256 amount) public virtual {
        _spendAllowance(account, _msgSender(), amount);
        _burn(account, amount);
    }
}

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



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.6.0) (token/ERC20/IERC20.sol)

pragma solidity ^0.8.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

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

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

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



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.6.0) (token/ERC20/ERC20.sol)

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:
     *
     * - `to` cannot be the zero address.
     * - the caller must have a balance of at least `amount`.
     */
    function transfer(address to, uint256 amount) public virtual override returns (bool) {
        address owner = _msgSender();
        _transfer(owner, to, 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}.
     *
     * NOTE: If `amount` is the maximum `uint256`, the allowance is not updated on
     * `transferFrom`. This is semantically equivalent to an infinite approval.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function approve(address spender, uint256 amount) public virtual override returns (bool) {
        address owner = _msgSender();
        _approve(owner, 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}.
     *
     * NOTE: Does not update the allowance if the current allowance
     * is the maximum `uint256`.
     *
     * Requirements:
     *
     * - `from` and `to` cannot be the zero address.
     * - `from` must have a balance of at least `amount`.
     * - the caller must have allowance for ``from``'s tokens of at least
     * `amount`.
     */
    function transferFrom(
        address from,
        address to,
        uint256 amount
    ) public virtual override returns (bool) {
        address spender = _msgSender();
        _spendAllowance(from, spender, amount);
        _transfer(from, to, 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) {
        address owner = _msgSender();
        _approve(owner, spender, allowance(owner, 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) {
        address owner = _msgSender();
        uint256 currentAllowance = allowance(owner, spender);
        require(currentAllowance >= subtractedValue, "ERC20: decreased allowance below zero");
        unchecked {
            _approve(owner, 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:
     *
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     * - `from` must have a balance of at least `amount`.
     */
    function _transfer(
        address from,
        address to,
        uint256 amount
    ) internal virtual {
        require(from != address(0), "ERC20: transfer from the zero address");
        require(to != address(0), "ERC20: transfer to the zero address");

        _beforeTokenTransfer(from, to, amount);

        uint256 fromBalance = _balances[from];
        require(fromBalance >= amount, "ERC20: transfer amount exceeds balance");
        unchecked {
            _balances[from] = fromBalance - amount;
        }
        _balances[to] += amount;

        emit Transfer(from, to, amount);

        _afterTokenTransfer(from, to, 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 Updates `owner` s allowance for `spender` based on spent `amount`.
     *
     * Does not update the allowance amount in case of infinite allowance.
     * Revert if not enough allowance is available.
     *
     * Might emit an {Approval} event.
     */
    function _spendAllowance(
        address owner,
        address spender,
        uint256 amount
    ) internal virtual {
        uint256 currentAllowance = allowance(owner, spender);
        if (currentAllowance != type(uint256).max) {
            require(currentAllowance >= amount, "ERC20: insufficient allowance");
            unchecked {
                _approve(owner, spender, currentAllowance - 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/contracts/token/ERC20/extensions/IERC20Metadata.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (token/ERC20/extensions/IERC20Metadata.sol)

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);
}