// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;

import {Ownable, Ownable2Step} from "@openzeppelin/contracts/access/Ownable2Step.sol";
import {ERC20} from "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import {IERC20} from "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import {ERC4626} from "@openzeppelin/contracts/token/ERC20/extensions/ERC4626.sol";
import {Math} from "@openzeppelin/contracts/utils/math/Math.sol";

/// @title SigmaVault
/// @author sigmacode.io (Sanicura d.o.o.)
/// @notice Fee-free ERC-4626 tokenized vault over a single ERC-20 asset, with a configurable deposit cap.
/// @dev Yield accrues by increasing the vault's asset balance (e.g. a strategy or treasury "donates" profits),
///      which raises the share price for all holders pro rata.
///
///      Inflation ("donation") attack mitigation: OpenZeppelin's virtual shares/assets with a
///      {DECIMALS_OFFSET} of 6. Shares have `asset.decimals() + 6` decimals, so an attacker who front-runs
///      the first deposit and donates `X` assets would have to lose roughly `X * 1e6`-fold more value than
///      they could steal. Rounding always favours the vault (ERC-4626 spec).
///
///      Deposit cap: {maxDeposit} / {maxMint} return the remaining headroom, so standard ERC-4626 integrators
///      and routers see the limit before calling. Exceeding it reverts with OZ's `ERC4626ExceededMaxDeposit`
///      / `ERC4626ExceededMaxMint`. Withdrawals are never restricted by the cap.
///
///      Not supported: fee-on-transfer and rebasing assets.
contract SigmaVault is ERC4626, Ownable2Step {
    /// @notice Extra decimals of shares relative to the asset (virtual-shares offset).
    uint8 public constant DECIMALS_OFFSET = 6;

    /// @notice Maximum total assets the vault accepts through deposits/mints.
    uint256 public depositCap;

    /// @notice Emitted when the deposit cap changes.
    event DepositCapUpdated(uint256 oldCap, uint256 newCap);

    /// @param asset_ Underlying ERC-20.
    /// @param name_ Share token name.
    /// @param symbol_ Share token symbol.
    /// @param initialOwner Owner allowed to change the cap.
    /// @param depositCap_ Initial deposit cap in asset units.
    constructor(IERC20 asset_, string memory name_, string memory symbol_, address initialOwner, uint256 depositCap_)
        ERC20(name_, symbol_)
        ERC4626(asset_)
        Ownable(initialOwner)
    {
        depositCap = depositCap_;
        emit DepositCapUpdated(0, depositCap_);
    }

    /// @notice Sets a new deposit cap. Lowering it below current assets only blocks new deposits.
    /// @param newCap New cap in asset units.
    function setDepositCap(uint256 newCap) external onlyOwner {
        emit DepositCapUpdated(depositCap, newCap);
        depositCap = newCap;
    }

    /// @notice Remaining assets that can be deposited before hitting the cap.
    function maxDeposit(address) public view override returns (uint256) {
        uint256 assets = totalAssets();
        return assets >= depositCap ? 0 : depositCap - assets;
    }

    /// @notice Remaining shares that can be minted before hitting the cap.
    function maxMint(address receiver) public view override returns (uint256) {
        return _convertToShares(maxDeposit(receiver), Math.Rounding.Floor);
    }

    /// @dev Virtual shares offset for inflation-attack resistance.
    function _decimalsOffset() internal pure override returns (uint8) {
        return DECIMALS_OFFSET;
    }
}