in this contract // SPDX-License-Identifier: MIT
pragma solidity 0.8.19;

import {Ownable2Step} from "openzeppelin-contracts/contracts/access/Ownable2Step.sol";
import {ERC4626} from "solmate/mixins/ERC4626.sol";
import {ERC20} from "solmate/tokens/ERC20.sol";
import {FixedPointMathLib} from "solmate/utils/FixedPointMathLib.sol";
import {SafeTransferLib} from "solmate/utils/SafeTransferLib.sol";
import {Errors} from "./libraries/Errors.sol";
import {IPirexEth} from "./interfaces/IPirexEth.sol";

/**
 * @title AutoPxEth
 * @notice Autocompounding vault for (staked) pxETH, adapted from pxCVX vault system
 * @dev This contract enables autocompounding for pxETH assets and includes various fee mechanisms.
 * @author redactedcartel.finance
 */
contract AutoPxEth is Ownable2Step, ERC4626 {
    /**
     * @dev Library: SafeTransferLib - Provides safe transfer functions for ERC20 tokens.
     */
    using SafeTransferLib for ERC20;

    /**
     * @dev Library: FixedPointMathLib - Provides fixed-point arithmetic for uint256.
     */
    using FixedPointMathLib for uint256;

    // Constants

    /**
     * @dev Maximum withdrawal penalty percentage.
     */
    uint256 private constant MAX_WITHDRAWAL_PENALTY = 50_000;
    

    /**
     * @dev Maximum platform fee percentage.
     */
    uint256 private constant MAX_PLATFORM_FEE = 200_000;

    /**
     * @dev Fee denominator for precise fee calculations.
     */
    uint256 private constant FEE_DENOMINATOR = 1_000_000;

    /**
     * @dev Duration of the rewards period.
     */
    uint256 private constant REWARDS_DURATION = 7 days;

    // State variables for tracking rewards and actively staked assets

    /**
     * @notice Reference to the PirexEth contract.
     */
    IPirexEth public pirexEth;
    
    /**
     * @notice Timestamp when the current rewards period will end.
     */
    uint256 public periodFinish;
    
    /**
     * @notice Rate at which rewards are distributed per second.
     */
    uint256 public rewardRate;
    
    /**
     * @notice Timestamp of the last update to the reward variables.
     */
    uint256 public lastUpdateTime;
    
    /**
     * @notice Accumulated reward per token stored.
     */
    uint256 public rewardPerTokenStored;
    
    /**
     * @notice Last calculated reward per token paid to stakers.
     */
    uint256 public rewardPerTokenPaid;
    
    /**
     * @notice Total rewards available for distribution.
     */
    uint256 public rewards;
    
    /**
     * @notice Total assets actively staked in the vault.
     */
    uint256 public totalStaked;

    // State variables related to fees
    /**
     * @notice Withdrawal penalty percentage.
     */
    uint256 public withdrawalPenalty = 30_000;
    
    /**
     * @notice Platform fee percentage.
     */
    uint256 public platformFee = 100_000;
    
    /**
     * @notice Address of the platform that receives fees.
     */
    address public platform;

    // Events

    /**
     * @notice Emitted when rewards are harvested and staked.
     * @dev This event is emitted when a user triggers the harvest function.
     * @param caller address indexed Address that triggered the harvest.
     * @param value  uint256         Amount of rewards harvested.
     */
    event Harvest(address indexed caller, uint256 value);

    /**
     * @notice Emitted when the withdrawal penalty is updated.
     * @dev This event is emitted when the withdrawal penalty is modified.
     * @param penalty uint256 New withdrawal penalty percentage.
     */
    event WithdrawalPenaltyUpdated(uint256 penalty);

    /**
     * @notice Emitted when the platform fee is updated.
     * @dev This event is emitted when the platform fee is modified.
     * @param fee uint256 New platform fee percentage.
     */
    event PlatformFeeUpdated(uint256 fee);
    
    /**
     * @notice Emitted when the platform address is updated.
     * @dev This event is emitted when the platform address is modified.
     * @param _platform address New platform address.
     */
    event PlatformUpdated(address _platform);

    /**
     * @notice Emitted when new rewards are added to the vault.
     * @dev This event is emitted when new rewards are added to the vault.
     * @param reward uint256 Amount of rewards added.
     */
    event RewardAdded(uint256 reward);

    /**
     * @notice Emitted when the PirexEth contract address is set.
     * @dev This event is emitted when the PirexEth contract address is set.
     * @param _pirexEth address New PirexEth contract address.
     */
    event SetPirexEth(address _pirexEth);

    // Modifiers
    /**
     * @dev Update reward states modifier
     * @param updateEarned bool Whether to update earned amount so far
     */
    modifier updateReward(bool updateEarned) {
        rewardPerTokenStored = rewardPerToken();
        lastUpdateTime = lastTimeRewardApplicable();

        if (updateEarned) {
            rewards = earned();
            rewardPerTokenPaid = rewardPerTokenStored;
        }
        _;
    }

    /**
     * @dev Contract constructor
     * @param _asset address Asset contract address
     * @param _platform address Platform address
     */
    constructor(
        address _asset,
        address _platform
    ) ERC4626(ERC20(_asset), "Autocompounding Pirex Ether", "apxETH") {
        if (_platform == address(0)) revert Errors.ZeroAddress();

        platform = _platform;
    }

    /*//////////////////////////////////////////////////////////////
                        RESTRICTED FUNCTIONS
    //////////////////////////////////////////////////////////////*/

    /**
     * @notice Set the PirexEth contract address
     * @dev Function access restricted to only owner
     * @param _pirexEth address PirexEth contract address
     */
    function setPirexEth(address _pirexEth) external onlyOwner {
        if (_pirexEth == address(0)) revert Errors.ZeroAddress();

        emit SetPirexEth(_pirexEth);

        pirexEth = IPirexEth(_pirexEth);
    }

    /**
     * @notice Set the withdrawal penalty
     * @dev Function access restricted to only owner
     * @param penalty uint256 Withdrawal penalty
     */
    function setWithdrawalPenalty(uint256 penalty) external onlyOwner {
        if (penalty > MAX_WITHDRAWAL_PENALTY) revert Errors.ExceedsMax();

        withdrawalPenalty = penalty;

        emit WithdrawalPenaltyUpdated(penalty);
    }

    /**
     * @notice Set the platform fee
     * @dev Function access restricted to only owner
     * @param fee uint256 Platform fee
     */
    function setPlatformFee(uint256 fee) external onlyOwner {
        if (fee > MAX_PLATFORM_FEE) revert Errors.ExceedsMax();

        platformFee = fee;

        emit PlatformFeeUpdated(fee);
    }

    /**
     * @notice Set the platform
     * @dev Function access restricted to only owner
     * @param _platform address Platform
     */
    function setPlatform(address _platform) external onlyOwner {
        if (_platform == address(0)) revert Errors.ZeroAddress();

        platform = _platform;

        emit PlatformUpdated(_platform);
    }

    /**
     * @notice Notify and sync the newly added rewards to be streamed over time
     * @dev Rewards are streamed following the duration set in REWARDS_DURATION
     */
    function notifyRewardAmount() external updateReward(false) {
        if (msg.sender != address(pirexEth)) revert Errors.NotPirexEth();

        // Rewards transferred directly to this contract are not added to totalStaked
        // To get the rewards w/o relying on a potentially incorrect passed in arg,
        // we can use the difference between the asset balance and totalStaked.
        // Additionally, to avoid re-distributing rewards, deduct the output of `earned`
        uint256 rewardBalance = asset.balanceOf(address(this)) -
            totalStaked -
            earned();

        rewardRate = rewardBalance / REWARDS_DURATION;

        if (rewardRate == 0) revert Errors.NoRewards();

        lastUpdateTime = block.timestamp;
        periodFinish = block.timestamp + REWARDS_DURATION;

        emit RewardAdded(rewardBalance);
    }

    /*//////////////////////////////////////////////////////////////
                                VIEWS
    //////////////////////////////////////////////////////////////*/

    /**
     * @inheritdoc ERC4626
     * @notice Get the amount of available pxETH in the contract
     * @dev Rewards are streamed for the duration set in REWARDS_DURATION
     */
    function totalAssets() public view override returns (uint256) {
        // Based on the current totalStaked and available rewards
        uint256 _totalStaked = totalStaked;
        uint256 _rewards = ((_totalStaked *
            (rewardPerToken() - rewardPerTokenPaid)) / 1e18) + rewards;

        // Deduct the exact reward amount staked (after fees are deducted when calling `harvest`)
        return
            _totalStaked +
            (
                _rewards == 0
                    ? 0
                    : (_rewards - ((_rewards * platformFee) / FEE_DENOMINATOR))
            );
    }

    /**
     * @notice Returns the last effective timestamp of the current reward period
     * @return uint256 Timestamp
     */
    function lastTimeRewardApplicable() public view returns (uint256) {
        return block.timestamp < periodFinish ? block.timestamp : periodFinish;
    }

    /**
     * @notice Returns the amount of rewards per staked token/asset
     * @return uint256 Rewards amount
     */
    function rewardPerToken() public view returns (uint256) {
        if (totalStaked == 0) {
            return rewardPerTokenStored;
        }

        return
            rewardPerTokenStored +
            ((((lastTimeRewardApplicable() - lastUpdateTime) * rewardRate) *
                1e18) / totalStaked);
    }

    /**
     * @notice Returns the earned rewards amount so far
     * @return uint256 Rewards amount
     */
    function earned() public view returns (uint256) {
        return
            ((totalStaked * (rewardPerToken() - rewardPerTokenPaid)) / 1e18) +
            rewards;
    }

    /**
     * @notice Return the amount of assets per 1 (1e18) share
     * @return uint256 Assets
     */
    function assetsPerShare() external view returns (uint256) {
        return previewRedeem(1e18);
    }

    /*//////////////////////////////////////////////////////////////
                            INTERNAL FUNCTIONS
    //////////////////////////////////////////////////////////////*/

    /**
     * @dev Internal method to keep track of the total amount of staked token/asset on deposit/mint
     */
    function _stake(uint256 amount) internal updateReward(true) {
        totalStaked += amount;
    }

    /**
     * @dev Internal method to keep track of the total amount of staked token/asset on withdrawal/redeem
     */
    function _withdraw(uint256 amount) internal updateReward(true) {
        totalStaked -= amount;
    }

    /*//////////////////////////////////////////////////////////////
                            ERC4626 OVERRIDES
    //////////////////////////////////////////////////////////////*/

    /**
     * @inheritdoc ERC4626
     * @dev Deduct the specified amount of assets from totalStaked to prepare for transfer to the user
     * @param assets uint256 Assets
     */
    function beforeWithdraw(uint256 assets, uint256) internal override {
        // Perform harvest to make sure that totalStaked is always equal or larger than assets to be withdrawn
        if (assets > totalStaked) harvest();

        _withdraw(assets);
    }

    /**
     * @inheritdoc ERC4626
     * @dev Include the new assets in totalStaked so that rewards can be properly distributed
     * @param assets uint256 Assets
     */
    function afterDeposit(uint256 assets, uint256) internal override {
        _stake(assets);
    }

    /**
     * @inheritdoc ERC4626
     * @dev Preview the amount of assets a user would receive from redeeming shares
     */
    function previewRedeem(
        uint256 shares
    ) public view override returns (uint256) {
        // Calculate assets based on a user's % ownership of vault shares
        uint256 assets = convertToAssets(shares);

        uint256 _totalSupply = totalSupply;

        // Calculate a penalty - zero if user is the last to withdraw.
        uint256 penalty = (_totalSupply == 0 || _totalSupply - shares == 0)
            ? 0
            : assets.mulDivUp(withdrawalPenalty, FEE_DENOMINATOR); // Round up the penalty in favour of the protocol.

        // Redeemable amount is the post-penalty amount
        return assets - penalty;
    }

    /**
     * @inheritdoc ERC4626
     * @notice Preview the amount of shares a user would need to redeem the specified asset amount
     * @dev This modified version takes into consideration the withdrawal fee
     */
    function previewWithdraw(
        uint256 assets
    ) public view override returns (uint256) {
        // Calculate shares based on the specified assets' proportion of the pool
        uint256 shares = convertToShares(assets);

        // Save 1 SLOAD
        uint256 _totalSupply = totalSupply;

        // Factor in additional shares to fulfill withdrawal if user is not the last to withdraw
        return
            (_totalSupply == 0 || _totalSupply - shares == 0)
                ? shares
                : (shares * FEE_DENOMINATOR) /
                    (FEE_DENOMINATOR - withdrawalPenalty);
    }

    /*//////////////////////////////////////////////////////////////
                            MUTATIVE FUNCTIONS
    //////////////////////////////////////////////////////////////*/

    /**
     * @notice Harvest and stake available rewards after distributing fees to the platform
     * @dev This function claims and stakes the available rewards, deducting a fee for the platform.
     */
    function harvest() public updateReward(true) {
        uint256 _rewards = rewards;

        if (_rewards != 0) {
            rewards = 0;

            // Fee for platform
            uint256 feeAmount = (_rewards * platformFee) / FEE_DENOMINATOR;

            // Deduct fee from reward balance
            _rewards -= feeAmount;

            // Claimed rewards should be in pxETH
            asset.safeTransfer(platform, feeAmount);

            // Stake rewards sans fee
            _stake(_rewards);

            emit Harvest(msg.sender, _rewards);
        }
    }

    /**
     * @notice Override transfer logic to trigger direct `initiateRedemption`.
     * @dev This function overrides the standard transfer logic to initiate redemption when transferring to the PirexEth contract.
     * @param to     address Transfer destination
     * @param amount uint256 Amount
     * @return       bool
     */
    function transfer(
        address to,
        uint256 amount
    ) public override returns (bool) {
        super.transfer(to, amount);

        if (to == address(pirexEth)) {
            pirexEth.initiateRedemption(amount, msg.sender, false);
        }

        return true;
    }

    /**
     * @notice Override transferFrom logic to trigger direct `initiateRedemption`.
     * @dev This function overrides the standard transferFrom logic to initiate redemption when transferring from the PirexEth contract.
     * @param from   Address of the transfer origin.
     * @param to     Address of the transfer destination.
     * @param amount Amount of tokens to transfer.
     * @return       A boolean indicating the success of the transfer.
     */
    function transferFrom(
        address from,
        address to,
        uint256 amount
    ) public override returns (bool) {
        super.transferFrom(from, to, amount);

        if (to == address(pirexEth)) {
            pirexEth.initiateRedemption(amount, from, false);
        }

        return true;
    }
} review and explain  tell me which parts of the contract are most critical for its operation? For example, are there any specific functions or mechanisms that are central to the contract's functionality?