// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v5.6.0) (token/ERC20/extensions/ERC4626.sol)

pragma solidity ^0.8.24;

import {IERC20} from "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import {IERC20Metadata} from "@openzeppelin/contracts/token/ERC20/extensions/IERC20Metadata.sol";
import {ERC20Upgradeable} from "../ERC20Upgradeable.sol";
import {SafeERC20} from "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";
import {IERC4626} from "@openzeppelin/contracts/interfaces/IERC4626.sol";
import {LowLevelCall} from "@openzeppelin/contracts/utils/LowLevelCall.sol";
import {Memory} from "@openzeppelin/contracts/utils/Memory.sol";
import {Math} from "@openzeppelin/contracts/utils/math/Math.sol";
import {Initializable} from "@openzeppelin/contracts/proxy/utils/Initializable.sol";

/**
 * @dev Implementation of the ERC-4626 "Tokenized Vault Standard" as defined in
 * https://eips.ethereum.org/EIPS/eip-4626[ERC-4626].
 *
 * This extension allows the minting and burning of "shares" (represented using the ERC-20 inheritance) in exchange for
 * underlying "assets" through standardized {deposit}, {mint}, {redeem} and {burn} workflows. This contract extends
 * the ERC-20 standard. Any additional extensions included along it would affect the "shares" token represented by this
 * contract and not the "assets" token which is an independent contract.
 *
 * [CAUTION]
 * ====
 * In empty (or nearly empty) ERC-4626 vaults, deposits are at high risk of being stolen through frontrunning
 * with a "donation" to the vault that inflates the price of a share. This is variously known as a donation or inflation
 * attack and is essentially a problem of slippage. Vault deployers can protect against this attack by making an initial
 * deposit of a non-trivial amount of the asset, such that price manipulation becomes infeasible. Withdrawals may
 * similarly be affected by slippage. Users can protect against this attack as well as unexpected slippage in general by
 * verifying the amount received is as expected, using a wrapper that performs these checks such as
 * https://github.com/fei-protocol/ERC4626#erc4626router-and-base[ERC4626Router].
 *
 * Since v4.9, this implementation introduces configurable virtual assets and shares to help developers mitigate that risk.
 * The `_decimalsOffset()` corresponds to an offset in the decimal representation between the underlying asset's decimals
 * and the vault decimals. This offset also determines the rate of virtual shares to virtual assets in the vault, which
 * itself determines the initial exchange rate. While not fully preventing the attack, analysis shows that the default
 * offset (0) makes it non-profitable even if an attacker is able to capture value from multiple user deposits, as a result
 * of the value being captured by the virtual shares (out of the attacker's donation) matching the attacker's expected gains.
 * With a larger offset, the attack becomes orders of magnitude more expensive than it is profitable. More details about the
 * underlying math can be found xref:ROOT:erc4626.adoc#inflation-attack[here].
 *
 * The drawback of this approach is that the virtual shares do capture (a very small) part of the value being accrued
 * to the vault. Also, if the vault experiences losses, the users try to exit the vault, the virtual shares and assets
 * will cause the first user to exit to experience reduced losses in detriment to the last users that will experience
 * bigger losses. Developers willing to revert back to the pre-v4.9 behavior just need to override the
 * `_convertToShares` and `_convertToAssets` functions.
 *
 * To learn more, check out our xref:ROOT:erc4626.adoc[ERC-4626 guide].
 * ====
 *
 * [NOTE]
 * ====
 * When overriding this contract, some elements must be considered:
 *
 * * When overriding the behavior of the deposit or withdraw mechanisms, it is recommended to override the internal
 * functions. Overriding {_deposit} automatically affects both {deposit} and {mint}. Similarly, overriding {_withdraw}
 * automatically affects both {withdraw} and {redeem}. Overall it is not recommended to override the public facing
 * functions since that could lead to inconsistent behaviors between the {deposit} and {mint} or between {withdraw} and
 * {redeem}, which is documented to have led to loss of funds.
 *
 * * Overrides to the deposit or withdraw mechanism must be reflected in the preview functions as well.
 *
 * * {maxWithdraw} depends on {maxRedeem}. Therefore, overriding {maxRedeem} only is enough. On the other hand,
 * overriding {maxWithdraw} only would have no effect on {maxRedeem}, and could create an inconsistency between the two
 * functions.
 *
 * * If {previewRedeem} is overridden to revert, {maxWithdraw} must be overridden as necessary to ensure it
 * always return successfully.
 * ====
 */
abstract contract ERC4626Upgradeable is Initializable, ERC20Upgradeable, IERC4626 {
    using Math for uint256;

    /// @custom:storage-location erc7201:openzeppelin.storage.ERC4626
    struct ERC4626Storage {
        IERC20 _asset;
        uint8 _underlyingDecimals;
    }

    // keccak256(abi.encode(uint256(keccak256("openzeppelin.storage.ERC4626")) - 1)) & ~bytes32(uint256(0xff))
    bytes32 private constant ERC4626StorageLocation = 0x0773e532dfede91f04b12a73d3d2acd361424f41f76b4fb79f090161e36b4e00;

    function _getERC4626Storage() private pure returns (ERC4626Storage storage $) {
        assembly {
            $.slot := ERC4626StorageLocation
        }
    }

    /**
     * @dev Attempted to deposit more assets than the max amount for `receiver`.
     */
    error ERC4626ExceededMaxDeposit(address receiver, uint256 assets, uint256 max);

    /**
     * @dev Attempted to mint more shares than the max amount for `receiver`.
     */
    error ERC4626ExceededMaxMint(address receiver, uint256 shares, uint256 max);

    /**
     * @dev Attempted to withdraw more assets than the max amount for `owner`.
     */
    error ERC4626ExceededMaxWithdraw(address owner, uint256 assets, uint256 max);

    /**
     * @dev Attempted to redeem more shares than the max amount for `owner`.
     */
    error ERC4626ExceededMaxRedeem(address owner, uint256 shares, uint256 max);

    /**
     * @dev Set the underlying asset contract. This must be an ERC20-compatible contract (ERC-20 or ERC-777).
     */
    function __ERC4626_init(IERC20 asset_) internal onlyInitializing {
        __ERC4626_init_unchained(asset_);
    }

    function __ERC4626_init_unchained(IERC20 asset_) internal onlyInitializing {
        ERC4626Storage storage $ = _getERC4626Storage();
        (bool success, uint8 assetDecimals) = _tryGetAssetDecimals(asset_);
        $._underlyingDecimals = success ? assetDecimals : 18;
        $._asset = asset_;
    }

    /**
     * @dev Attempts to fetch the asset decimals. A return value of false indicates that the attempt failed in some way.
     */
    function _tryGetAssetDecimals(IERC20 asset_) private view returns (bool ok, uint8 assetDecimals) {
        Memory.Pointer ptr = Memory.getFreeMemoryPointer();
        (bool success, bytes32 returnedDecimals, ) = LowLevelCall.staticcallReturn64Bytes(
            address(asset_),
            abi.encodeCall(IERC20Metadata.decimals, ())
        );
        Memory.unsafeSetFreeMemoryPointer(ptr);

        return
            (success && LowLevelCall.returnDataSize() >= 32 && uint256(returnedDecimals) <= type(uint8).max)
                ? (true, uint8(uint256(returnedDecimals)))
                : (false, 0);
    }

    /**
     * @dev Decimals are computed by adding the decimal offset on top of the underlying asset's decimals. This
     * "original" value is cached during construction of the vault contract. If this read operation fails (e.g., the
     * asset has not been created yet), a default of 18 is used to represent the underlying asset's decimals.
     *
     * See {IERC20Metadata-decimals}.
     */
    function decimals() public view virtual override(IERC20Metadata, ERC20Upgradeable) returns (uint8) {
        ERC4626Storage storage $ = _getERC4626Storage();
        return $._underlyingDecimals + _decimalsOffset();
    }

    /// @inheritdoc IERC4626
    function asset() public view virtual returns (address) {
        ERC4626Storage storage $ = _getERC4626Storage();
        return address($._asset);
    }

    /// @inheritdoc IERC4626
    function totalAssets() public view virtual returns (uint256) {
        return IERC20(asset()).balanceOf(address(this));
    }

    /// @inheritdoc IERC4626
    function convertToShares(uint256 assets) public view virtual returns (uint256) {
        return _convertToShares(assets, Math.Rounding.Floor);
    }

    /// @inheritdoc IERC4626
    function convertToAssets(uint256 shares) public view virtual returns (uint256) {
        return _convertToAssets(shares, Math.Rounding.Floor);
    }

    /// @inheritdoc IERC4626
    function maxDeposit(address) public view virtual returns (uint256) {
        return type(uint256).max;
    }

    /// @inheritdoc IERC4626
    function maxMint(address) public view virtual returns (uint256) {
        return type(uint256).max;
    }

    /// @inheritdoc IERC4626
    function maxWithdraw(address owner) public view virtual returns (uint256) {
        return previewRedeem(maxRedeem(owner));
    }

    /// @inheritdoc IERC4626
    function maxRedeem(address owner) public view virtual returns (uint256) {
        return balanceOf(owner);
    }

    /// @inheritdoc IERC4626
    function previewDeposit(uint256 assets) public view virtual returns (uint256) {
        return _convertToShares(assets, Math.Rounding.Floor);
    }

    /// @inheritdoc IERC4626
    function previewMint(uint256 shares) public view virtual returns (uint256) {
        return _convertToAssets(shares, Math.Rounding.Ceil);
    }

    /// @inheritdoc IERC4626
    function previewWithdraw(uint256 assets) public view virtual returns (uint256) {
        return _convertToShares(assets, Math.Rounding.Ceil);
    }

    /// @inheritdoc IERC4626
    function previewRedeem(uint256 shares) public view virtual returns (uint256) {
        return _convertToAssets(shares, Math.Rounding.Floor);
    }

    /// @inheritdoc IERC4626
    function deposit(uint256 assets, address receiver) public virtual returns (uint256) {
        uint256 maxAssets = maxDeposit(receiver);
        if (assets > maxAssets) {
            revert ERC4626ExceededMaxDeposit(receiver, assets, maxAssets);
        }

        uint256 shares = previewDeposit(assets);
        _deposit(_msgSender(), receiver, assets, shares);

        return shares;
    }

    /// @inheritdoc IERC4626
    function mint(uint256 shares, address receiver) public virtual returns (uint256) {
        uint256 maxShares = maxMint(receiver);
        if (shares > maxShares) {
            revert ERC4626ExceededMaxMint(receiver, shares, maxShares);
        }

        uint256 assets = previewMint(shares);
        _deposit(_msgSender(), receiver, assets, shares);

        return assets;
    }

    /// @inheritdoc IERC4626
    function withdraw(uint256 assets, address receiver, address owner) public virtual returns (uint256) {
        uint256 maxAssets = maxWithdraw(owner);
        if (assets > maxAssets) {
            revert ERC4626ExceededMaxWithdraw(owner, assets, maxAssets);
        }

        uint256 shares = previewWithdraw(assets);
        _withdraw(_msgSender(), receiver, owner, assets, shares);

        return shares;
    }

    /// @inheritdoc IERC4626
    function redeem(uint256 shares, address receiver, address owner) public virtual returns (uint256) {
        uint256 maxShares = maxRedeem(owner);
        if (shares > maxShares) {
            revert ERC4626ExceededMaxRedeem(owner, shares, maxShares);
        }

        uint256 assets = previewRedeem(shares);
        _withdraw(_msgSender(), receiver, owner, assets, shares);

        return assets;
    }

    /**
     * @dev Internal conversion function (from assets to shares) with support for rounding direction.
     */
    function _convertToShares(uint256 assets, Math.Rounding rounding) internal view virtual returns (uint256) {
        return assets.mulDiv(totalSupply() + 10 ** _decimalsOffset(), totalAssets() + 1, rounding);
    }

    /**
     * @dev Internal conversion function (from shares to assets) with support for rounding direction.
     */
    function _convertToAssets(uint256 shares, Math.Rounding rounding) internal view virtual returns (uint256) {
        return shares.mulDiv(totalAssets() + 1, totalSupply() + 10 ** _decimalsOffset(), rounding);
    }

    /**
     * @dev Deposit/mint common workflow.
     */
    function _deposit(address caller, address receiver, uint256 assets, uint256 shares) internal virtual {
        // If asset() is ERC-777, `transferFrom` can trigger a reentrancy BEFORE the transfer happens through the
        // `tokensToSend` hook. On the other hand, the `tokenReceived` hook, that is triggered after the transfer,
        // calls the vault, which is assumed not malicious.
        //
        // Conclusion: we need to do the transfer before we mint so that any reentrancy would happen before the
        // assets are transferred and before the shares are minted, which is a valid state.
        // slither-disable-next-line reentrancy-no-eth
        _transferIn(caller, assets);
        _mint(receiver, shares);

        emit Deposit(caller, receiver, assets, shares);
    }

    /**
     * @dev Withdraw/redeem common workflow.
     */
    function _withdraw(
        address caller,
        address receiver,
        address owner,
        uint256 assets,
        uint256 shares
    ) internal virtual {
        if (caller != owner) {
            _spendAllowance(owner, caller, shares);
        }

        // If asset() is ERC-777, `transfer` can trigger a reentrancy AFTER the transfer happens through the
        // `tokensReceived` hook. On the other hand, the `tokensToSend` hook, that is triggered before the transfer,
        // calls the vault, which is assumed not malicious.
        //
        // Conclusion: we need to do the transfer after the burn so that any reentrancy would happen after the
        // shares are burned and after the assets are transferred, which is a valid state.
        _burn(owner, shares);
        _transferOut(receiver, assets);

        emit Withdraw(caller, receiver, owner, assets, shares);
    }

    /// @dev Performs a transfer in of underlying assets. The default implementation uses `SafeERC20`. Used by {_deposit}.
    function _transferIn(address from, uint256 assets) internal virtual {
        SafeERC20.safeTransferFrom(IERC20(asset()), from, address(this), assets);
    }

    /// @dev Performs a transfer out of underlying assets. The default implementation uses `SafeERC20`. Used by {_withdraw}.
    function _transferOut(address to, uint256 assets) internal virtual {
        SafeERC20.safeTransfer(IERC20(asset()), to, assets);
    }

    function _decimalsOffset() internal view virtual returns (uint8) {
        return 0;
    }
}