OwnableUpgradeable.sol

// SPDX-License-Identifier: MIT
pragma solidity 0.8.16;

import {IOwnableUpgradeable} from "./IOwnableUpgradeable.sol";
import {Initializable} from "@openzeppelin/contracts-upgradeable/proxy/utils/Initializable.sol";

/// @title Ownable
/// @author Rohan Kulkarni / Iain Nash
/// @notice Modified from OpenZeppelin Contracts v4.7.3 (access/OwnableUpgradeable.sol)
/// - Uses custom errors declared in IOwnable
/// - Adds optional two-step ownership transfer (`safeTransferOwnership` + `acceptOwnership`)
abstract contract OwnableUpgradeable is IOwnableUpgradeable, Initializable {
    ///                                                          ///
    ///                            STORAGE                       ///
    ///                                                          ///

    /// @dev The address of the owner
    address internal _owner;

    /// @dev The address of the pending owner
    address internal _pendingOwner;

    /// @dev Modifier to check if the address argument is the zero/burn address
    modifier notZeroAddress(address check) {
        if (check == address(0)) {
            revert OWNER_CANNOT_BE_ZERO_ADDRESS();
        }
        _;
    }

    ///                                                          ///
    ///                           MODIFIERS                      ///
    ///                                                          ///

    /// @dev Ensures the caller is the owner
    modifier onlyOwner() {
        if (msg.sender != _owner) {
            revert ONLY_OWNER();
        }
        _;
    }

    /// @dev Ensures the caller is the pending owner
    modifier onlyPendingOwner() {
        if (msg.sender != _pendingOwner) {
            revert ONLY_PENDING_OWNER();
        }
        _;
    }

    ///                                                          ///
    ///                           FUNCTIONS                      ///
    ///                                                          ///

    /// @dev Initializes contract ownership
    /// @param _initialOwner The initial owner address
    function __Ownable_init(address _initialOwner)
        internal
        notZeroAddress(_initialOwner)
        onlyInitializing
    {
        _owner = _initialOwner;

        emit OwnerUpdated(address(0), _initialOwner);
    }

    /// @notice The address of the owner
    function owner() public view virtual returns (address) {
        return _owner;
    }

    /// @notice The address of the pending owner
    function pendingOwner() public view returns (address) {
        return _pendingOwner;
    }

    /// @notice Forces an ownership transfer from the last owner
    /// @param _newOwner The new owner address
    function transferOwnership(address _newOwner)
        public
        notZeroAddress(_newOwner)
        onlyOwner
    {
        _transferOwnership(_newOwner);
    }

    /// @notice Forces an ownership transfer from any sender
    /// @param _newOwner New owner to transfer contract to
    /// @dev Ensure is called only from trusted internal code, no access control checks.
    function _transferOwnership(address _newOwner) internal {
        emit OwnerUpdated(_owner, _newOwner);

        _owner = _newOwner;

        if (_pendingOwner != address(0)) {
            delete _pendingOwner;
        }
    }

    /// @notice Initiates a two-step ownership transfer
    /// @param _newOwner The new owner address
    function safeTransferOwnership(address _newOwner)
        public
        notZeroAddress(_newOwner)
        onlyOwner
    {
        _pendingOwner = _newOwner;

        emit OwnerPending(_owner, _newOwner);
    }

    /// @notice Resign ownership of contract
    /// @dev only callably by the owner, dangerous call.
    function resignOwnership() public onlyOwner {
        _transferOwnership(address(0));
    }

    /// @notice Accepts an ownership transfer
    function acceptOwnership() public onlyPendingOwner {
        emit OwnerUpdated(_owner, msg.sender);

        _owner = _pendingOwner;

        delete _pendingOwner;
    }

    /// @notice Cancels a pending ownership transfer
    function cancelOwnershipTransfer() public onlyOwner {
        emit OwnerCanceled(_owner, _pendingOwner);

        delete _pendingOwner;
    }
}