// SPDX-FileCopyrightText: 2025 Lido <info@lido.fi>
// SPDX-License-Identifier: GPL-3.0

// See contracts/COMPILERS.md
pragma solidity 0.4.24;

import {AragonApp} from "@aragon/os/contracts/apps/AragonApp.sol";
import {SafeMath} from "@aragon/os/contracts/lib/math/SafeMath.sol";
import {UnstructuredStorage} from "@aragon/os/contracts/common/UnstructuredStorage.sol";

import {Math256} from "contracts/common/lib/Math256.sol";
import {MinFirstAllocationStrategy} from "contracts/common/lib/MinFirstAllocationStrategy.sol";
import {ILidoLocator} from "contracts/common/interfaces/ILidoLocator.sol";

import {SigningKeys} from "../lib/SigningKeys.sol";
import {Packed64x4} from "../lib/Packed64x4.sol";
import {Versioned} from "../utils/Versioned.sol";

interface IStETH {
    function sharesOf(address _account) external view returns (uint256);
    function transferShares(address _recipient, uint256 _sharesAmount) external returns (uint256);
    function approve(address _spender, uint256 _amount) external returns (bool);
}

/// @title Node Operator registry
/// @notice Node Operator registry manages signing keys and other node operator data.
/// @dev Must implement the full version of IStakingModule interface, not only the one declared locally.
///      It's also responsible for distributing rewards to node operators.
/// NOTE: the code below assumes moderate amount of node operators, i.e. up to `MAX_NODE_OPERATORS_COUNT`.
contract NodeOperatorsRegistry is AragonApp, Versioned {
    using SafeMath for uint256;
    using UnstructuredStorage for bytes32;
    using SigningKeys for bytes32;
    using Packed64x4 for Packed64x4.Packed;

    //
    // EVENTS
    //
    event NodeOperatorAdded(uint256 nodeOperatorId, string name, address rewardAddress, uint64 stakingLimit);
    event NodeOperatorActiveSet(uint256 indexed nodeOperatorId, bool active);
    event NodeOperatorNameSet(uint256 indexed nodeOperatorId, string name);
    event NodeOperatorRewardAddressSet(uint256 indexed nodeOperatorId, address rewardAddress);
    event NodeOperatorTotalKeysTrimmed(uint256 indexed nodeOperatorId, uint64 totalKeysTrimmed);
    event KeysOpIndexSet(uint256 keysOpIndex);
    event StakingModuleTypeSet(bytes32 moduleType);
    event RewardsDistributed(address indexed rewardAddress, uint256 sharesAmount);
    event RewardDistributionStateChanged(RewardDistributionState state);
    event LocatorContractSet(address locatorAddress);
    event VettedSigningKeysCountChanged(uint256 indexed nodeOperatorId, uint256 approvedValidatorsCount);
    event DepositedSigningKeysCountChanged(uint256 indexed nodeOperatorId, uint256 depositedValidatorsCount);
    event ExitedSigningKeysCountChanged(uint256 indexed nodeOperatorId, uint256 exitedValidatorsCount);
    event TotalSigningKeysCountChanged(uint256 indexed nodeOperatorId, uint256 totalValidatorsCount);

    event NonceChanged(uint256 nonce);
    event TargetValidatorsCountChanged(uint256 indexed nodeOperatorId, uint256 targetValidatorsCount, uint256 targetLimitMode);

    event ValidatorExitStatusUpdated(
        uint256 indexed nodeOperatorId,
        bytes publicKey,
        uint256 eligibleToExitInSec,
        uint256 proofSlotTimestamp
    );
    event ValidatorExitTriggered(
        uint256 indexed nodeOperatorId,
        bytes publicKey,
        uint256 withdrawalRequestPaidFee,
        uint256 exitType
    );
    event ExitDeadlineThresholdChanged(uint256 threshold, uint256 reportingWindow);

    // Enum to represent the state of the reward distribution process
    enum RewardDistributionState {
        TransferredToModule,      // New reward portion minted and transferred to the module
        ReadyForDistribution,     // Operators' statistics updated, reward ready for distribution
        Distributed               // Reward distributed among operators
    }

    //
    // ACL
    //
    // bytes32 public constant MANAGE_SIGNING_KEYS = keccak256("MANAGE_SIGNING_KEYS");
    bytes32 public constant MANAGE_SIGNING_KEYS = 0x75abc64490e17b40ea1e66691c3eb493647b24430b358bd87ec3e5127f1621ee;
    // bytes32 public constant SET_NODE_OPERATOR_LIMIT_ROLE = keccak256("SET_NODE_OPERATOR_LIMIT_ROLE");
    bytes32 public constant SET_NODE_OPERATOR_LIMIT_ROLE = 0x07b39e0faf2521001ae4e58cb9ffd3840a63e205d288dc9c93c3774f0d794754;
    // bytes32 public constant MANAGE_NODE_OPERATOR_ROLE = keccak256("MANAGE_NODE_OPERATOR_ROLE");
    bytes32 public constant MANAGE_NODE_OPERATOR_ROLE = 0x78523850fdd761612f46e844cf5a16bda6b3151d6ae961fd7e8e7b92bfbca7f8;
    // bytes32 public constant STAKING_ROUTER_ROLE = keccak256("STAKING_ROUTER_ROLE");
    bytes32 public constant STAKING_ROUTER_ROLE = 0xbb75b874360e0bfd87f964eadd8276d8efb7c942134fc329b513032d0803e0c6;

    //
    // CONSTANTS
    //
    uint256 public constant MAX_NODE_OPERATORS_COUNT = 200;
    uint256 public constant MAX_NODE_OPERATOR_NAME_LENGTH = 255;
    uint256 public constant MAX_STUCK_PENALTY_DELAY = 365 days;

    uint256 internal constant UINT64_MAX = 0xFFFFFFFFFFFFFFFF;

    // SigningKeysStats
    /// @dev Operator's max validator keys count approved for deposit by the DAO
    uint8 internal constant TOTAL_VETTED_KEYS_COUNT_OFFSET = 0;
    /// @dev Number of keys in the EXITED state of this operator for all time
    uint8 internal constant TOTAL_EXITED_KEYS_COUNT_OFFSET = 1;
    /// @dev Total number of keys of this operator for all time
    uint8 internal constant TOTAL_KEYS_COUNT_OFFSET = 2;
    /// @dev Number of keys of this operator which were in DEPOSITED state for all time
    uint8 internal constant TOTAL_DEPOSITED_KEYS_COUNT_OFFSET = 3;

    // TargetValidatorsStats
    /// @dev Target limit mode, allows limiting target active validators count for operator (0 = disabled, 1 = soft mode, 2 = boosted mode)
    uint8 internal constant TARGET_LIMIT_MODE_OFFSET = 0;
    /// @dev relative target active validators limit for operator, set by DAO
    /// @notice used to check how many keys should go to exit, 0 - means all deposited keys would be exited
    uint8 internal constant TARGET_VALIDATORS_COUNT_OFFSET = 1;
    /// @dev actual operators's number of keys which could be deposited
    uint8 internal constant MAX_VALIDATORS_COUNT_OFFSET = 2;

    // Summary SigningKeysStats
    uint8 internal constant SUMMARY_MAX_VALIDATORS_COUNT_OFFSET = 0;
    /// @dev Number of keys of all operators which were in the EXITED state for all time
    uint8 internal constant SUMMARY_EXITED_KEYS_COUNT_OFFSET = 1;
    /// @dev [deprecated] Total number of keys of all operators for all time
    uint8 internal constant SUMMARY_TOTAL_KEYS_COUNT_OFFSET = 2;
    /// @dev Number of keys of all operators which were in the DEPOSITED state for all time
    uint8 internal constant SUMMARY_DEPOSITED_KEYS_COUNT_OFFSET = 3;

    //
    // UNSTRUCTURED STORAGE POSITIONS
    //
    // bytes32 internal constant SIGNING_KEYS_MAPPING_NAME = keccak256("lido.NodeOperatorsRegistry.signingKeysMappingName");
    bytes32 internal constant SIGNING_KEYS_MAPPING_NAME = 0xeb2b7ad4d8ce5610cfb46470f03b14c197c2b751077c70209c5d0139f7c79ee9;

    // bytes32 internal constant LIDO_LOCATOR_POSITION = keccak256("lido.NodeOperatorsRegistry.lidoLocator");
    bytes32 internal constant LIDO_LOCATOR_POSITION = 0xfb2059fd4b64256b64068a0f57046c6d40b9f0e592ba8bcfdf5b941910d03537;

    /// @dev Total number of operators
    // bytes32 internal constant TOTAL_OPERATORS_COUNT_POSITION = keccak256("lido.NodeOperatorsRegistry.totalOperatorsCount");
    bytes32 internal constant TOTAL_OPERATORS_COUNT_POSITION =
        0xe2a589ae0816b289a9d29b7c085f8eba4b5525accca9fa8ff4dba3f5a41287e8;

    /// @dev Cached number of active operators
    // bytes32 internal constant ACTIVE_OPERATORS_COUNT_POSITION = keccak256("lido.NodeOperatorsRegistry.activeOperatorsCount");
    bytes32 internal constant ACTIVE_OPERATORS_COUNT_POSITION =
        0x6f5220989faafdc182d508d697678366f4e831f5f56166ad69bfc253fc548fb1;

    /// @dev link to the index of operations with keys
    // bytes32 internal constant KEYS_OP_INDEX_POSITION = keccak256("lido.NodeOperatorsRegistry.keysOpIndex");
    bytes32 internal constant KEYS_OP_INDEX_POSITION = 0xcd91478ac3f2620f0776eacb9c24123a214bcb23c32ae7d28278aa846c8c380e;

    /// @dev module type
    // bytes32 internal constant TYPE_POSITION = keccak256("lido.NodeOperatorsRegistry.type");
    bytes32 internal constant TYPE_POSITION = 0xbacf4236659a602d72c631ba0b0d67ec320aaf523f3ae3590d7faee4f42351d0;

    // bytes32 internal constant REWARD_DISTRIBUTION_STATE = keccak256("lido.NodeOperatorsRegistry.rewardDistributionState");
    bytes32 internal constant REWARD_DISTRIBUTION_STATE = 0x4ddbb0dcdc5f7692e494c15a7fca1f9eb65f31da0b5ce1c3381f6a1a1fd579b6;

    // bytes32 internal constant EXIT_DELAY_STATS = keccak256("lido.NodeOperatorsRegistry.exitDelayStats");
    bytes32 internal constant EXIT_DELAY_STATS = 0x9fe52a88cbf7bfbe5e42abc45469ad27b2231a10bcbcd0a227c7ca0835cecbd8;
    /// @dev Exit delay stats offsets in Packed64x4:
    /// @dev The delay threshold in seconds after which a validator exit is considered late
    uint8 internal constant EXIT_DELAY_THRESHOLD_OFFSET = 0;
    /// @dev Timestamp before which validators reported as late will not result in penalties for their Node Operators.
    uint8 internal constant EXIT_PENALTY_CUTOFF_TIMESTAMP_OFFSET = 1;


    //
    // DATA TYPES
    //

    /// @dev Node Operator parameters and internal state
    struct NodeOperator {
        /// @dev Flag indicating if the operator can participate in further staking and reward distribution
        bool active;
        /// @dev Ethereum address on Execution Layer which receives stETH rewards for this operator
        address rewardAddress;
        /// @dev Human-readable name
        string name;
        /// @dev The below variables store the signing keys info of the node operator.
        ///     signingKeysStats - contains packed variables: uint64 exitedSigningKeysCount, uint64 depositedSigningKeysCount,
        ///                        uint64 vettedSigningKeysCount, uint64 totalSigningKeysCount
        ///
        ///     These variables can take values in the following ranges:
        ///
        ///                0             <=  exitedSigningKeysCount   <= depositedSigningKeysCount
        ///     exitedSigningKeysCount   <= depositedSigningKeysCount <=  vettedSigningKeysCount
        ///    depositedSigningKeysCount <=   vettedSigningKeysCount  <=   totalSigningKeysCount
        ///    depositedSigningKeysCount <=   totalSigningKeysCount   <=        UINT64_MAX
        ///
        /// Additionally, the exitedSigningKeysCount and depositedSigningKeysCount values are monotonically increasing:
        /// :                              :         :         :         :
        /// [....exitedSigningKeysCount....]-------->:         :         :
        /// [....depositedSigningKeysCount :.........]-------->:         :
        /// [....vettedSigningKeysCount....:.........:<--------]-------->:
        /// [....totalSigningKeysCount.....:.........:<--------:---------]------->
        /// :                              :         :         :         :
        Packed64x4.Packed signingKeysStats;
        Packed64x4.Packed stuckPenaltyStats;
        Packed64x4.Packed targetValidatorsStats;
    }

    struct NodeOperatorSummary {
        Packed64x4.Packed summarySigningKeysStats;
    }

    //
    // STORAGE VARIABLES
    //

    /// @dev Mapping of all node operators. Mapping is used to be able to extend the struct.
    mapping(uint256 => NodeOperator) internal _nodeOperators;
    NodeOperatorSummary internal _nodeOperatorSummary;

    /// @dev Mapping of Node Operator exit delay keys
    mapping(bytes32 => bool) internal _validatorProcessedLateKeys;

    //
    // METHODS
    //
    function initialize(
        address _locator,
        bytes32 _type,
        uint256 _exitDeadlineThresholdInSeconds
    ) public onlyInit {
        // Initializations for v1 --> v2
        _initialize_v2(_locator, _type);

        // Initializations for v2 --> v3
        _initialize_v3();

        // Initializations for v3 --> v4
        _initialize_v4(_exitDeadlineThresholdInSeconds);

        initialized();
    }

    function _initialize_v2(address _locator, bytes32 _type) internal {
        _onlyNonZeroAddress(_locator);
        LIDO_LOCATOR_POSITION.setStorageAddress(_locator);
        TYPE_POSITION.setStorageBytes32(_type);

        _setContractVersion(2);

        emit LocatorContractSet(_locator);
        emit StakingModuleTypeSet(_type);
    }

    function _initialize_v3() internal {
        _setContractVersion(3);
        _updateRewardDistributionState(RewardDistributionState.Distributed);
    }

    function _initialize_v4(uint256 _exitDeadlineThresholdInSeconds) internal {
        _setContractVersion(4);
        /// @dev The reportingWindowThreshold is set to 0 because it is not required during cold start.
        ///      This parameter is only relevant when changing _exitDeadlineThresholdInSeconds in future upgrades.
        _setExitDeadlineThreshold(_exitDeadlineThresholdInSeconds, 0);
    }

    /// @notice A function to finalize upgrade to v2 (from v1). Removed and no longer used.
    /// For more details see https://github.com/lidofinance/lido-improvement-proposals/blob/develop/LIPS/lip-10.md
    /// See historical usage in commit: https://github.com/lidofinance/core/blob/c19480aa3366b26aa6eac17f85a6efae8b9f4f72/contracts/0.4.24/nos/NodeOperatorsRegistry.sol#L230
    /// function finalizeUpgrade_v2(address _locator, bytes32 _type, uint256 _stuckPenaltyDelay) external

    /// @notice A function to finalize upgrade to v3 (from v2). Removed and no longer used.
    /// See historical usage in commit: https://github.com/lidofinance/core/blob/c19480aa3366b26aa6eac17f85a6efae8b9f4f72/contracts/0.4.24/nos/NodeOperatorsRegistry.sol#L298
    /// function finalizeUpgrade_v3() external

    /// @notice Finalizes upgrade to version 4 by initializing new exit-related parameters.
    /// @param _exitDeadlineThresholdInSeconds Exit deadline threshold in seconds for validator exits.
    function finalizeUpgrade_v4(uint256 _exitDeadlineThresholdInSeconds) external {
        require(hasInitialized(), "CONTRACT_NOT_INITIALIZED");
        _checkContractVersion(3);

        // Set allowance to 0 since the stuck keys logic has been removed and burning shares is no longer needed
        IStETH(getLocator().lido()).approve(getLocator().burner(), 0);
        _initialize_v4(_exitDeadlineThresholdInSeconds);
    }

    /// @notice Add node operator named `name` with reward address `rewardAddress` and staking limit = 0 validators
    /// @param _name Human-readable name
    /// @param _rewardAddress Ethereum 1 address which receives stETH rewards for this operator
    /// @return id a unique key of the added operator
    function addNodeOperator(string _name, address _rewardAddress) external returns (uint256 id) {
        _onlyValidNodeOperatorName(_name);
        _onlyValidRewardAddress(_rewardAddress);
        _auth(MANAGE_NODE_OPERATOR_ROLE);

        id = getNodeOperatorsCount();
        require(id < MAX_NODE_OPERATORS_COUNT, "MAX_OPERATORS_COUNT_EXCEEDED");

        TOTAL_OPERATORS_COUNT_POSITION.setStorageUint256(id + 1);

        NodeOperator storage operator = _nodeOperators[id];

        uint256 activeOperatorsCount = getActiveNodeOperatorsCount();
        ACTIVE_OPERATORS_COUNT_POSITION.setStorageUint256(activeOperatorsCount + 1);

        operator.active = true;
        operator.name = _name;
        operator.rewardAddress = _rewardAddress;

        emit NodeOperatorAdded(id, _name, _rewardAddress, 0);
    }

    /// @notice Activates deactivated node operator with given id
    /// @param _nodeOperatorId Node operator id to activate
    function activateNodeOperator(uint256 _nodeOperatorId) external {
        _onlyExistedNodeOperator(_nodeOperatorId);
        _auth(MANAGE_NODE_OPERATOR_ROLE);

        _onlyCorrectNodeOperatorState(!getNodeOperatorIsActive(_nodeOperatorId));

        ACTIVE_OPERATORS_COUNT_POSITION.setStorageUint256(getActiveNodeOperatorsCount() + 1);

        _nodeOperators[_nodeOperatorId].active = true;

        emit NodeOperatorActiveSet(_nodeOperatorId, true);
        _increaseValidatorsKeysNonce();
    }

    /// @notice Deactivates active node operator with given id
    /// @param _nodeOperatorId Node operator id to deactivate
    function deactivateNodeOperator(uint256 _nodeOperatorId) external {
        _onlyExistedNodeOperator(_nodeOperatorId);
        _auth(MANAGE_NODE_OPERATOR_ROLE);

        _onlyCorrectNodeOperatorState(getNodeOperatorIsActive(_nodeOperatorId));

        uint256 activeOperatorsCount = getActiveNodeOperatorsCount();
        ACTIVE_OPERATORS_COUNT_POSITION.setStorageUint256(activeOperatorsCount.sub(1));

        _nodeOperators[_nodeOperatorId].active = false;

        emit NodeOperatorActiveSet(_nodeOperatorId, false);

        Packed64x4.Packed memory signingKeysStats = _loadOperatorSigningKeysStats(_nodeOperatorId);
        uint256 vettedSigningKeysCount = signingKeysStats.get(TOTAL_VETTED_KEYS_COUNT_OFFSET);
        uint256 depositedSigningKeysCount = signingKeysStats.get(TOTAL_DEPOSITED_KEYS_COUNT_OFFSET);

        // reset vetted keys count to the deposited validators count
        if (vettedSigningKeysCount > depositedSigningKeysCount) {
            signingKeysStats.set(TOTAL_VETTED_KEYS_COUNT_OFFSET, depositedSigningKeysCount);
            _saveOperatorSigningKeysStats(_nodeOperatorId, signingKeysStats);

            emit VettedSigningKeysCountChanged(_nodeOperatorId, depositedSigningKeysCount);

            _updateSummaryMaxValidatorsCount(_nodeOperatorId);
        }
        _increaseValidatorsKeysNonce();
    }

    /// @notice Change human-readable name of the node operator with given id
    /// @param _nodeOperatorId Node operator id to set name for
    /// @param _name New human-readable name of the node operator
    function setNodeOperatorName(uint256 _nodeOperatorId, string _name) external {
        _onlyValidNodeOperatorName(_name);
        _onlyExistedNodeOperator(_nodeOperatorId);
        _auth(MANAGE_NODE_OPERATOR_ROLE);

        _requireNotSameValue(keccak256(bytes(_nodeOperators[_nodeOperatorId].name)) != keccak256(bytes(_name)));
        _nodeOperators[_nodeOperatorId].name = _name;
        emit NodeOperatorNameSet(_nodeOperatorId, _name);
    }

    /// @notice Change reward address of the node operator with given id
    /// @param _nodeOperatorId Node operator id to set reward address for
    /// @param _rewardAddress Execution layer Ethereum address to set as reward address
    function setNodeOperatorRewardAddress(uint256 _nodeOperatorId, address _rewardAddress) external {
        _onlyValidRewardAddress(_rewardAddress);
        _onlyExistedNodeOperator(_nodeOperatorId);
        _auth(MANAGE_NODE_OPERATOR_ROLE);

        _requireNotSameValue(_nodeOperators[_nodeOperatorId].rewardAddress != _rewardAddress);
        _nodeOperators[_nodeOperatorId].rewardAddress = _rewardAddress;
        emit NodeOperatorRewardAddressSet(_nodeOperatorId, _rewardAddress);
    }

    /// @notice Set the maximum number of validators to stake for the node operator with given id
    /// @dev Current implementation preserves invariant: depositedSigningKeysCount <= vettedSigningKeysCount <= totalSigningKeysCount.
    ///     If _vettedSigningKeysCount out of range [depositedSigningKeysCount, totalSigningKeysCount], the new vettedSigningKeysCount
    ///     value will be set to the nearest range border.
    /// @param _nodeOperatorId Node operator id to set staking limit for
    /// @param _vettedSigningKeysCount New staking limit of the node operator
    function setNodeOperatorStakingLimit(uint256 _nodeOperatorId, uint64 _vettedSigningKeysCount) external {
        _onlyExistedNodeOperator(_nodeOperatorId);
        _authP(SET_NODE_OPERATOR_LIMIT_ROLE, arr(uint256(_nodeOperatorId), uint256(_vettedSigningKeysCount)));
        _onlyCorrectNodeOperatorState(getNodeOperatorIsActive(_nodeOperatorId));

        _updateVettedSigningKeysCount(_nodeOperatorId, _vettedSigningKeysCount, true /* _allowIncrease */);
        _increaseValidatorsKeysNonce();
    }

    /// @notice Called by StakingRouter to decrease the number of vetted keys for node operator with given id
    /// @param _nodeOperatorIds bytes packed array of the node operators id
    /// @param _vettedSigningKeysCounts bytes packed array of the new number of vetted keys for the node operators
    function decreaseVettedSigningKeysCount(
        bytes _nodeOperatorIds,
        bytes _vettedSigningKeysCounts
    ) external {
        _auth(STAKING_ROUTER_ROLE);
        uint256 nodeOperatorsCount = _checkReportPayload(_nodeOperatorIds.length, _vettedSigningKeysCounts.length);
        uint256 totalNodeOperatorsCount = getNodeOperatorsCount();

        uint256 nodeOperatorId;
        uint256 vettedKeysCount;
        uint256 _nodeOperatorIdsOffset;
        uint256 _vettedKeysCountsOffset;

        /// @dev calldata layout:
        /// | func sig (4 bytes) | ABI-enc data |
        ///
        /// ABI-enc data:
        ///
        /// |    32 bytes    |     32 bytes      |  32 bytes  | ... |  32 bytes  | ...... |
        /// | ids len offset | counts len offset |  ids len   | ids | counts len | counts |
        assembly {
            _nodeOperatorIdsOffset := add(calldataload(4), 36) // arg1 calldata offset + 4 (signature len) + 32 (length slot)
            _vettedKeysCountsOffset := add(calldataload(36), 36) // arg2 calldata offset + 4 (signature len) + 32 (length slot))
        }
        for (uint256 i; i < nodeOperatorsCount;) {
            /// @solidity memory-safe-assembly
            assembly {
                nodeOperatorId := shr(192, calldataload(add(_nodeOperatorIdsOffset, mul(i, 8))))
                vettedKeysCount := shr(128, calldataload(add(_vettedKeysCountsOffset, mul(i, 16))))
                i := add(i, 1)
            }
            _requireValidRange(nodeOperatorId < totalNodeOperatorsCount);
            _updateVettedSigningKeysCount(nodeOperatorId, vettedKeysCount, false /* only decrease */);
        }
        _increaseValidatorsKeysNonce();
    }

    function _updateVettedSigningKeysCount(
        uint256 _nodeOperatorId,
        uint256 _vettedSigningKeysCount,
        bool _allowIncrease
    ) internal {
        Packed64x4.Packed memory signingKeysStats = _loadOperatorSigningKeysStats(_nodeOperatorId);
        uint256 vettedSigningKeysCountBefore = signingKeysStats.get(TOTAL_VETTED_KEYS_COUNT_OFFSET);
        uint256 depositedSigningKeysCount = signingKeysStats.get(TOTAL_DEPOSITED_KEYS_COUNT_OFFSET);
        uint256 totalSigningKeysCount = signingKeysStats.get(TOTAL_KEYS_COUNT_OFFSET);

        uint256 vettedSigningKeysCountAfter = Math256.min(
            totalSigningKeysCount, Math256.max(_vettedSigningKeysCount, depositedSigningKeysCount)
        );

        if (vettedSigningKeysCountAfter == vettedSigningKeysCountBefore) return;

        require(
            _allowIncrease || vettedSigningKeysCountAfter < vettedSigningKeysCountBefore,
            "VETTED_KEYS_COUNT_INCREASED"
        );

        signingKeysStats.set(TOTAL_VETTED_KEYS_COUNT_OFFSET, vettedSigningKeysCountAfter);
        _saveOperatorSigningKeysStats(_nodeOperatorId, signingKeysStats);

        emit VettedSigningKeysCountChanged(_nodeOperatorId, vettedSigningKeysCountAfter);

        _updateSummaryMaxValidatorsCount(_nodeOperatorId);
    }

    /// @notice Called by StakingRouter to signal that stETH rewards were minted for this module.
    function onRewardsMinted(uint256 /* _totalShares */) external {
        _auth(STAKING_ROUTER_ROLE);
        _updateRewardDistributionState(RewardDistributionState.TransferredToModule);
    }

    function _checkReportPayload(uint256 idsLength, uint256 countsLength) internal pure returns (uint256 count) {
        count = idsLength / 8;
        require(countsLength / 16 == count && idsLength % 8 == 0 && countsLength % 16 == 0, "INVALID_REPORT_DATA");
    }

    /// @notice Called by StakingRouter to update the number of the validators in the EXITED state
    /// for node operator with given id
    ///
    /// @param _nodeOperatorIds bytes packed array of the node operators id
    /// @param _exitedValidatorsCounts bytes packed array of the new number of EXITED validators for the node operators
    function updateExitedValidatorsCount(
        bytes _nodeOperatorIds,
        bytes _exitedValidatorsCounts
    )
        external
    {
        _auth(STAKING_ROUTER_ROLE);
        uint256 nodeOperatorsCount = _checkReportPayload(_nodeOperatorIds.length, _exitedValidatorsCounts.length);
        uint256 totalNodeOperatorsCount = getNodeOperatorsCount();

        uint256 nodeOperatorId;
        uint256 validatorsCount;
        uint256 _nodeOperatorIdsOffset;
        uint256 _exitedValidatorsCountsOffset;

        assembly {
            _nodeOperatorIdsOffset := add(calldataload(4), 36) // arg1 calldata offset + 4 (signature len) + 32 (length slot)
            _exitedValidatorsCountsOffset := add(calldataload(36), 36) // arg2 calldata offset + 4 (signature len) + 32 (length slot))
        }
        for (uint256 i; i < nodeOperatorsCount;) {
            /// @solidity memory-safe-assembly
            assembly {
                nodeOperatorId := shr(192, calldataload(add(_nodeOperatorIdsOffset, mul(i, 8))))
                validatorsCount := shr(128, calldataload(add(_exitedValidatorsCountsOffset, mul(i, 16))))
                i := add(i, 1)
            }
            _requireValidRange(nodeOperatorId < totalNodeOperatorsCount);
            _updateExitedValidatorsCount(nodeOperatorId, validatorsCount, false);
        }
        _increaseValidatorsKeysNonce();
    }

    /// @notice Permissionless method for distributing all accumulated module rewards among node operators
    /// based on the latest accounting report.
    ///
    /// @dev Rewards can be distributed after all necessary data required to distribute rewards among operators
    /// has been delivered, including exited and stuck keys.
    ///
    /// The reward distribution lifecycle:
    ///
    /// 1. TransferredToModule: Rewards are transferred to the module during an oracle main report.
    /// 2. ReadyForDistribution: All necessary data required to distribute rewards among operators has been delivered.
    /// 3. Distributed: Rewards have been successfully distributed.
    ///
    /// The function can only be called when the state is ReadyForDistribution.
    ///
    /// @dev Rewards can be distributed after node operators' statistics are updated until the next reward
    /// is transferred to the module during the next oracle frame.
    function distributeReward() external {
        require(getRewardDistributionState() == RewardDistributionState.ReadyForDistribution, "DISTRIBUTION_NOT_READY");
        _updateRewardDistributionState(RewardDistributionState.Distributed);
        _distributeRewards();
    }

    /// @notice Called by StakingRouter after it finishes updating exited and stuck validators
    /// counts for this module's node operators.
    ///
    /// Guaranteed to be called after an oracle report is applied, regardless of whether any node
    /// operator in this module has actually received any updated counts as a result of the report
    /// but given that the total number of exited validators returned from getStakingModuleSummary
    /// is the same as StakingRouter expects based on the total count received from the oracle.
    function onExitedAndStuckValidatorsCountsUpdated() external {
        _auth(STAKING_ROUTER_ROLE);
        _updateRewardDistributionState(RewardDistributionState.ReadyForDistribution);
    }

    /// @notice Unsafely updates the number of validators in the EXITED/STUCK states for node operator with given id.
    /// @param _nodeOperatorId Id of the node operator
    /// @param _exitedValidatorsCount New number of EXITED validators for the node operator
    function unsafeUpdateValidatorsCount(
        uint256 _nodeOperatorId,
        uint256 _exitedValidatorsCount
    ) external {
        _onlyExistedNodeOperator(_nodeOperatorId);
        _auth(STAKING_ROUTER_ROLE);

        _updateExitedValidatorsCount(_nodeOperatorId, _exitedValidatorsCount, true /* _allowDecrease */ );
        _increaseValidatorsKeysNonce();
    }

    function _updateExitedValidatorsCount(uint256 _nodeOperatorId, uint256 _exitedValidatorsCount, bool _allowDecrease)
        internal
    {
        Packed64x4.Packed memory signingKeysStats = _loadOperatorSigningKeysStats(_nodeOperatorId);
        uint256 oldExitedValidatorsCount = signingKeysStats.get(TOTAL_EXITED_KEYS_COUNT_OFFSET);
        if (_exitedValidatorsCount == oldExitedValidatorsCount) return;
        require(
            _allowDecrease || _exitedValidatorsCount > oldExitedValidatorsCount,
            "EXITED_VALIDATORS_COUNT_DECREASED"
        );

        uint256 depositedValidatorsCount = signingKeysStats.get(TOTAL_DEPOSITED_KEYS_COUNT_OFFSET);

        // sustain invariant exited <= deposited
        _requireValidRange(_exitedValidatorsCount <= depositedValidatorsCount);

        signingKeysStats.set(TOTAL_EXITED_KEYS_COUNT_OFFSET, _exitedValidatorsCount);
        _saveOperatorSigningKeysStats(_nodeOperatorId, signingKeysStats);
        emit ExitedSigningKeysCountChanged(_nodeOperatorId, _exitedValidatorsCount);

        Packed64x4.Packed memory summarySigningKeysStats = _loadSummarySigningKeysStats();
        uint256 exitedValidatorsAbsDiff = Math256.absDiff(_exitedValidatorsCount, oldExitedValidatorsCount);
        if (_exitedValidatorsCount > oldExitedValidatorsCount) {
            summarySigningKeysStats.add(SUMMARY_EXITED_KEYS_COUNT_OFFSET, exitedValidatorsAbsDiff);
        } else {
            summarySigningKeysStats.sub(SUMMARY_EXITED_KEYS_COUNT_OFFSET, exitedValidatorsAbsDiff);
        }
        _saveSummarySigningKeysStats(summarySigningKeysStats);
        _updateSummaryMaxValidatorsCount(_nodeOperatorId);
    }

    /// @notice Updates the limit of the validators that can be used for deposit by DAO
    /// @param _nodeOperatorId Id of the node operator
    /// @param _isTargetLimitActive Flag indicating if the soft target limit is active
    /// @param _targetLimit Target limit of the node operator
    /// @dev DEPRECATED: This function updateTargetValidatorsLimits(uint256, bool, uint256) is deprecated
    /// @dev Use updateTargetValidatorsLimits(uint256, uint256, uint256) instead
    function updateTargetValidatorsLimits(uint256 _nodeOperatorId, bool _isTargetLimitActive, uint256 _targetLimit) public {
        updateTargetValidatorsLimits(_nodeOperatorId, _isTargetLimitActive ? 1 : 0, _targetLimit);
    }

    /// @notice Updates the limit of the validators that can be used for deposit by DAO
    /// @param _nodeOperatorId Id of the node operator
    /// @param _targetLimitMode target limit mode (0 = disabled, 1 = soft mode, 2 = boosted mode)
    /// @param _targetLimit Target limit of the node operator
    function updateTargetValidatorsLimits(uint256 _nodeOperatorId, uint256 _targetLimitMode, uint256 _targetLimit) public {
        _onlyExistedNodeOperator(_nodeOperatorId);
        _auth(STAKING_ROUTER_ROLE);
        _requireValidRange(_targetLimit <= UINT64_MAX);

        Packed64x4.Packed memory operatorTargetStats = _loadOperatorTargetValidatorsStats(_nodeOperatorId);
        operatorTargetStats.set(TARGET_LIMIT_MODE_OFFSET, _targetLimitMode);
        if (_targetLimitMode == 0) {
            _targetLimit = 0;
        }
        operatorTargetStats.set(TARGET_VALIDATORS_COUNT_OFFSET, _targetLimit);
        _saveOperatorTargetValidatorsStats(_nodeOperatorId, operatorTargetStats);

        emit TargetValidatorsCountChanged(_nodeOperatorId, _targetLimit, _targetLimitMode);

        _updateSummaryMaxValidatorsCount(_nodeOperatorId);
        _increaseValidatorsKeysNonce();
    }

    // @dev Recalculate and update the max validator count for operator and summary stats
    function _updateSummaryMaxValidatorsCount(uint256 _nodeOperatorId) internal {
        (uint256 oldMaxSigningKeysCount, uint256 newMaxSigningKeysCount) = _applyNodeOperatorLimits(_nodeOperatorId);

        if (newMaxSigningKeysCount == oldMaxSigningKeysCount) return;

        Packed64x4.Packed memory summarySigningKeysStats = _loadSummarySigningKeysStats();

        uint256 maxSigningKeysCountAbsDiff = Math256.absDiff(newMaxSigningKeysCount, oldMaxSigningKeysCount);
        if (newMaxSigningKeysCount > oldMaxSigningKeysCount) {
            summarySigningKeysStats.add(SUMMARY_MAX_VALIDATORS_COUNT_OFFSET, maxSigningKeysCountAbsDiff);
        } else {
            summarySigningKeysStats.sub(SUMMARY_MAX_VALIDATORS_COUNT_OFFSET, maxSigningKeysCountAbsDiff);
        }
        _saveSummarySigningKeysStats(summarySigningKeysStats);
    }

    /// @notice Invalidates all unused deposit data for all node operators
    function onWithdrawalCredentialsChanged() external {
        _auth(STAKING_ROUTER_ROLE);
        uint256 operatorsCount = getNodeOperatorsCount();
        if (operatorsCount > 0) {
            _invalidateReadyToDepositKeysRange(0, operatorsCount - 1);
        }
    }

    /// @notice Invalidates all unused validators keys for node operators in the given range
    /// @param _indexFrom the first index (inclusive) of the node operator to invalidate keys for
    /// @param _indexTo the last index (inclusive) of the node operator to invalidate keys for
    function invalidateReadyToDepositKeysRange(uint256 _indexFrom, uint256 _indexTo) external {
        _auth(MANAGE_NODE_OPERATOR_ROLE);
        _invalidateReadyToDepositKeysRange(_indexFrom, _indexTo);
    }

    function _invalidateReadyToDepositKeysRange(uint256 _indexFrom, uint256 _indexTo) internal {
        _requireValidRange(_indexFrom <= _indexTo && _indexTo < getNodeOperatorsCount());

        uint256 trimmedKeysCount;
        uint256 totalTrimmedKeysCount;
        uint256 totalSigningKeysCount;
        uint256 depositedSigningKeysCount;
        Packed64x4.Packed memory signingKeysStats;
        for (uint256 nodeOperatorId = _indexFrom; nodeOperatorId <= _indexTo; ++nodeOperatorId) {
            signingKeysStats = _loadOperatorSigningKeysStats(nodeOperatorId);

            totalSigningKeysCount = signingKeysStats.get(TOTAL_KEYS_COUNT_OFFSET);
            depositedSigningKeysCount = signingKeysStats.get(TOTAL_DEPOSITED_KEYS_COUNT_OFFSET);

            if (totalSigningKeysCount == depositedSigningKeysCount) continue;
            assert(totalSigningKeysCount > depositedSigningKeysCount);

            trimmedKeysCount = totalSigningKeysCount - depositedSigningKeysCount;
            totalTrimmedKeysCount += trimmedKeysCount;

            signingKeysStats.set(TOTAL_KEYS_COUNT_OFFSET, depositedSigningKeysCount);
            signingKeysStats.set(TOTAL_VETTED_KEYS_COUNT_OFFSET, depositedSigningKeysCount);
            _saveOperatorSigningKeysStats(nodeOperatorId, signingKeysStats);

            _updateSummaryMaxValidatorsCount(nodeOperatorId);

            emit TotalSigningKeysCountChanged(nodeOperatorId, depositedSigningKeysCount);
            emit VettedSigningKeysCountChanged(nodeOperatorId, depositedSigningKeysCount);
            emit NodeOperatorTotalKeysTrimmed(nodeOperatorId, uint64(trimmedKeysCount));
        }

        if (totalTrimmedKeysCount > 0) {
            _increaseValidatorsKeysNonce();
        }
    }

    /// @notice Obtains deposit data to be used by StakingRouter to deposit to the Ethereum Deposit
    ///     contract
    /// @param _depositsCount Number of deposits to be done
    /// @return publicKeys Batch of the concatenated public validators keys
    /// @return signatures Batch of the concatenated deposit signatures for returned public keys
    function obtainDepositData(
        uint256 _depositsCount,
        bytes /* _depositCalldata */
    ) external returns (bytes memory publicKeys, bytes memory signatures) {
        _auth(STAKING_ROUTER_ROLE);

        if (_depositsCount == 0) return (new bytes(0), new bytes(0));

        (
            uint256 allocatedKeysCount,
            uint256[] memory nodeOperatorIds,
            uint256[] memory activeKeysCountAfterAllocation
        ) = _getSigningKeysAllocationData(_depositsCount);

        require(allocatedKeysCount == _depositsCount, "INVALID_ALLOCATED_KEYS_COUNT");

        (publicKeys, signatures) = _loadAllocatedSigningKeys(
            allocatedKeysCount,
            nodeOperatorIds,
            activeKeysCountAfterAllocation
        );
        _increaseValidatorsKeysNonce();
    }

    function _getNodeOperator(uint256 _nodeOperatorId)
        internal
        view
        returns (uint256 exitedSigningKeysCount, uint256 depositedSigningKeysCount, uint256 maxSigningKeysCount)
    {
        Packed64x4.Packed memory signingKeysStats = _loadOperatorSigningKeysStats(_nodeOperatorId);
        Packed64x4.Packed memory operatorTargetStats = _loadOperatorTargetValidatorsStats(_nodeOperatorId);

        exitedSigningKeysCount = signingKeysStats.get(TOTAL_EXITED_KEYS_COUNT_OFFSET);
        depositedSigningKeysCount = signingKeysStats.get(TOTAL_DEPOSITED_KEYS_COUNT_OFFSET);
        maxSigningKeysCount = operatorTargetStats.get(MAX_VALIDATORS_COUNT_OFFSET);

        // Validate data boundaries invariants here to not use SafeMath in caller methods
        assert(maxSigningKeysCount >= depositedSigningKeysCount && depositedSigningKeysCount >= exitedSigningKeysCount);
    }

    function _applyNodeOperatorLimits(uint256 _nodeOperatorId)
        internal
        returns (uint256 oldMaxSigningKeysCount, uint256 newMaxSigningKeysCount)
    {
        Packed64x4.Packed memory signingKeysStats = _loadOperatorSigningKeysStats(_nodeOperatorId);
        Packed64x4.Packed memory operatorTargetStats = _loadOperatorTargetValidatorsStats(_nodeOperatorId);

        uint256 depositedSigningKeysCount = signingKeysStats.get(TOTAL_DEPOSITED_KEYS_COUNT_OFFSET);

        // It's expected that validators don't suffer from penalties most of the time,
        // so optimistically, set the count of max validators equal to the vetted validators count.
        newMaxSigningKeysCount = signingKeysStats.get(TOTAL_VETTED_KEYS_COUNT_OFFSET);

        if (operatorTargetStats.get(TARGET_LIMIT_MODE_OFFSET) != 0) {
            // apply target limit when it's active and the node operator is not penalized
            newMaxSigningKeysCount = Math256.max(
                // max validators count can't be less than the deposited validators count
                // even when the target limit is less than the current active validators count
                depositedSigningKeysCount,
                Math256.min(
                    // max validators count can't be greater than the vetted validators count
                    newMaxSigningKeysCount,
                    // SafeMath.add() isn't used below because the sum is always
                    // less or equal to 2 * UINT64_MAX
                    signingKeysStats.get(TOTAL_EXITED_KEYS_COUNT_OFFSET)
                        + operatorTargetStats.get(TARGET_VALIDATORS_COUNT_OFFSET)
                )
            );
        }

        oldMaxSigningKeysCount = operatorTargetStats.get(MAX_VALIDATORS_COUNT_OFFSET);
        if (oldMaxSigningKeysCount != newMaxSigningKeysCount) {
            operatorTargetStats.set(MAX_VALIDATORS_COUNT_OFFSET, newMaxSigningKeysCount);
            _saveOperatorTargetValidatorsStats(_nodeOperatorId, operatorTargetStats);
        }
    }

    function _getSigningKeysAllocationData(uint256 _keysCount)
        internal
        view
        returns (uint256 allocatedKeysCount, uint256[] memory nodeOperatorIds, uint256[] memory activeKeyCountsAfterAllocation)
    {
        uint256 activeNodeOperatorsCount = getActiveNodeOperatorsCount();
        nodeOperatorIds = new uint256[](activeNodeOperatorsCount);
        activeKeyCountsAfterAllocation = new uint256[](activeNodeOperatorsCount);
        uint256[] memory activeKeysCapacities = new uint256[](activeNodeOperatorsCount);

        uint256 activeNodeOperatorIndex;
        uint256 nodeOperatorsCount = getNodeOperatorsCount();
        uint256 maxSigningKeysCount;
        uint256 depositedSigningKeysCount;
        uint256 exitedSigningKeysCount;

        for (uint256 nodeOperatorId; nodeOperatorId < nodeOperatorsCount; ++nodeOperatorId) {
            (exitedSigningKeysCount, depositedSigningKeysCount, maxSigningKeysCount)
                = _getNodeOperator(nodeOperatorId);

            // the node operator has no available signing keys
            if (depositedSigningKeysCount == maxSigningKeysCount) continue;

            nodeOperatorIds[activeNodeOperatorIndex] = nodeOperatorId;
            activeKeyCountsAfterAllocation[activeNodeOperatorIndex] = depositedSigningKeysCount - exitedSigningKeysCount;
            activeKeysCapacities[activeNodeOperatorIndex] = maxSigningKeysCount - exitedSigningKeysCount;
            ++activeNodeOperatorIndex;
        }

        if (activeNodeOperatorIndex == 0) return (0, new uint256[](0), new uint256[](0));

        /// @dev shrink the length of the resulting arrays if some active node operators have no available keys to be deposited
        if (activeNodeOperatorIndex < activeNodeOperatorsCount) {
            assembly {
                mstore(nodeOperatorIds, activeNodeOperatorIndex)
                mstore(activeKeyCountsAfterAllocation, activeNodeOperatorIndex)
                mstore(activeKeysCapacities, activeNodeOperatorIndex)
            }
        }

        (allocatedKeysCount, activeKeyCountsAfterAllocation) =
            MinFirstAllocationStrategy.allocate(activeKeyCountsAfterAllocation, activeKeysCapacities, _keysCount);

        /// @dev method NEVER allocates more keys than was requested
        assert(_keysCount >= allocatedKeysCount);
    }

    function _loadAllocatedSigningKeys(
        uint256 _keysCountToLoad,
        uint256[] memory _nodeOperatorIds,
        uint256[] memory _activeKeyCountsAfterAllocation
    ) internal returns (bytes memory pubkeys, bytes memory signatures) {
        (pubkeys, signatures) = SigningKeys.initKeysSigsBuf(_keysCountToLoad);

        uint256 loadedKeysCount = 0;
        uint256 depositedSigningKeysCountBefore;
        uint256 depositedSigningKeysCountAfter;
        uint256 keysCount;
        Packed64x4.Packed memory signingKeysStats;
        for (uint256 i; i < _nodeOperatorIds.length; ++i) {
            signingKeysStats = _loadOperatorSigningKeysStats(_nodeOperatorIds[i]);
            depositedSigningKeysCountBefore = signingKeysStats.get(TOTAL_DEPOSITED_KEYS_COUNT_OFFSET);
            depositedSigningKeysCountAfter =
                signingKeysStats.get(TOTAL_EXITED_KEYS_COUNT_OFFSET) + _activeKeyCountsAfterAllocation[i];

            if (depositedSigningKeysCountAfter == depositedSigningKeysCountBefore) continue;

            // For gas savings SafeMath.add() wasn't used on depositedSigningKeysCountAfter
            // calculation, so below we check that operation finished without overflow
            // In case of overflow:
            //   depositedSigningKeysCountAfter < signingKeysStats.get(TOTAL_EXITED_KEYS_COUNT_OFFSET)
            // what violates invariant:
            //   depositedSigningKeysCount >= exitedSigningKeysCount
            assert(depositedSigningKeysCountAfter > depositedSigningKeysCountBefore);

            keysCount = depositedSigningKeysCountAfter - depositedSigningKeysCountBefore;
            SIGNING_KEYS_MAPPING_NAME.loadKeysSigs(
                _nodeOperatorIds[i], depositedSigningKeysCountBefore, keysCount, pubkeys, signatures, loadedKeysCount
            );
            loadedKeysCount += keysCount;

            emit DepositedSigningKeysCountChanged(_nodeOperatorIds[i], depositedSigningKeysCountAfter);
            signingKeysStats.set(TOTAL_DEPOSITED_KEYS_COUNT_OFFSET, depositedSigningKeysCountAfter);
            _saveOperatorSigningKeysStats(_nodeOperatorIds[i], signingKeysStats);
            _updateSummaryMaxValidatorsCount(_nodeOperatorIds[i]);
        }

        assert(loadedKeysCount == _keysCountToLoad);

        Packed64x4.Packed memory summarySigningKeysStats = _loadSummarySigningKeysStats();
        summarySigningKeysStats.add(SUMMARY_DEPOSITED_KEYS_COUNT_OFFSET, loadedKeysCount);
        _saveSummarySigningKeysStats(summarySigningKeysStats);
    }

    /// @notice Returns the node operator by id
    /// @param _nodeOperatorId Node Operator id
    /// @param _fullInfo If true, name will be returned as well
    function getNodeOperator(uint256 _nodeOperatorId, bool _fullInfo)
        external
        view
        returns (
            bool active,
            string name,
            address rewardAddress,
            uint64 totalVettedValidators,
            uint64 totalExitedValidators,
            uint64 totalAddedValidators,
            uint64 totalDepositedValidators
        )
    {
        _onlyExistedNodeOperator(_nodeOperatorId);

        NodeOperator storage nodeOperator = _nodeOperators[_nodeOperatorId];

        active = nodeOperator.active;
        rewardAddress = nodeOperator.rewardAddress;
        name = _fullInfo ? nodeOperator.name : ""; // reading name is 2+ SLOADs

        Packed64x4.Packed memory signingKeysStats = _loadOperatorSigningKeysStats(_nodeOperatorId);

        totalVettedValidators = uint64(signingKeysStats.get(TOTAL_VETTED_KEYS_COUNT_OFFSET));
        totalExitedValidators = uint64(signingKeysStats.get(TOTAL_EXITED_KEYS_COUNT_OFFSET));
        totalAddedValidators = uint64(signingKeysStats.get(TOTAL_KEYS_COUNT_OFFSET));
        totalDepositedValidators = uint64(signingKeysStats.get(TOTAL_DEPOSITED_KEYS_COUNT_OFFSET));
    }

    /// @notice Returns the rewards distribution proportional to the effective stake for each node operator.
    /// @notice [DEPRECATED] The `penalized` array is no longer relevant and always contains only `false`.
    /// @param _totalRewardShares Total amount of reward shares to distribute.
    function getRewardsDistribution(uint256 _totalRewardShares)
        public
        view
        returns (address[] memory recipients, uint256[] memory shares, bool[] memory penalized)
    {
        uint256 nodeOperatorCount = getNodeOperatorsCount();

        uint256 activeCount = getActiveNodeOperatorsCount();
        recipients = new address[](activeCount);
        shares = new uint256[](activeCount);
        penalized = new bool[](activeCount);
        uint256 idx = 0;

        uint256 totalActiveValidatorsCount = 0;
        Packed64x4.Packed memory signingKeysStats;
        for (uint256 operatorId; operatorId < nodeOperatorCount; ++operatorId) {
            if (!getNodeOperatorIsActive(operatorId)) continue;

            signingKeysStats = _loadOperatorSigningKeysStats(operatorId);
            uint256 totalExitedValidators = signingKeysStats.get(TOTAL_EXITED_KEYS_COUNT_OFFSET);
            uint256 totalDepositedValidators = signingKeysStats.get(TOTAL_DEPOSITED_KEYS_COUNT_OFFSET);

            // validate invariant to not use SafeMath.sub()
            assert(totalDepositedValidators >= totalExitedValidators);
            uint256 activeValidatorsCount = totalDepositedValidators - totalExitedValidators;

            // SafeMath.add() isn't used below because the following is always true:
            // totalActiveValidatorsCount <= MAX_NODE_OPERATORS_COUNT * UINT64_MAX
            totalActiveValidatorsCount += activeValidatorsCount;

            recipients[idx] = _nodeOperators[operatorId].rewardAddress;
            // prefill shares array with 'key share' for recipient, see below
            shares[idx] = activeValidatorsCount;

            // [DEPRECATED] Penalized flag is no longer relevant. Always false.
            // penalized[idx] = false;

            ++idx;
        }

        if (totalActiveValidatorsCount == 0) return (recipients, shares, penalized);

        for (idx = 0; idx < activeCount; ++idx) {
            /// @dev unsafe division used below for gas savings. It's safe in the current case
            ///     because SafeMath.div() only validates that the divider isn't equal to zero.
            ///     totalActiveValidatorsCount guaranteed greater than zero.
            shares[idx] = shares[idx].mul(_totalRewardShares) / totalActiveValidatorsCount;
        }

        return (recipients, shares, penalized);
    }

    /// @notice Add `_quantity` validator signing keys to the keys of the node operator #`_nodeOperatorId`. Concatenated keys are: `_pubkeys`
    /// @dev Along with each key the DAO has to provide a signatures for the
    ///      (pubkey, withdrawal_credentials, 32000000000) message.
    ///      Given that information, the contract'll be able to call
    ///      deposit_contract.deposit on-chain.
    /// @param _nodeOperatorId Node Operator id
    /// @param _keysCount Number of signing keys provided
    /// @param _publicKeys Several concatenated validator signing keys
    /// @param _signatures Several concatenated signatures for (pubkey, withdrawal_credentials, 32000000000) messages
    function addSigningKeys(uint256 _nodeOperatorId, uint256 _keysCount, bytes _publicKeys, bytes _signatures) external {
        _addSigningKeys(_nodeOperatorId, _keysCount, _publicKeys, _signatures);
    }

    /// @notice Add `_quantity` validator signing keys of operator #`_id` to the set of usable keys. Concatenated keys are: `_pubkeys`. Can be done by node operator in question by using the designated rewards address.
    /// @dev Along with each key the DAO has to provide a signatures for the
    ///      (pubkey, withdrawal_credentials, 32000000000) message.
    ///      Given that information, the contract'll be able to call
    ///      deposit_contract.deposit on-chain.
    /// @param _nodeOperatorId Node Operator id
    /// @param _keysCount Number of signing keys provided
    /// @param _publicKeys Several concatenated validator signing keys
    /// @param _signatures Several concatenated signatures for (pubkey, withdrawal_credentials, 32000000000) messages
    /// @dev DEPRECATED use addSigningKeys instead
    function addSigningKeysOperatorBH(uint256 _nodeOperatorId, uint256 _keysCount, bytes _publicKeys, bytes _signatures)
        external
    {
        _addSigningKeys(_nodeOperatorId, _keysCount, _publicKeys, _signatures);
    }

    function _addSigningKeys(uint256 _nodeOperatorId, uint256 _keysCount, bytes _publicKeys, bytes _signatures) internal {
        _onlyExistedNodeOperator(_nodeOperatorId);
        _onlyNodeOperatorManager(msg.sender, _nodeOperatorId);

        _requireValidRange(_keysCount != 0 && _keysCount <= UINT64_MAX);

        Packed64x4.Packed memory signingKeysStats = _loadOperatorSigningKeysStats(_nodeOperatorId);
        uint256 totalSigningKeysCount = signingKeysStats.get(TOTAL_KEYS_COUNT_OFFSET);

        _requireValidRange(totalSigningKeysCount.add(_keysCount) <= UINT64_MAX);

        totalSigningKeysCount =
            SIGNING_KEYS_MAPPING_NAME.saveKeysSigs(_nodeOperatorId, totalSigningKeysCount, _keysCount, _publicKeys, _signatures);

        emit TotalSigningKeysCountChanged(_nodeOperatorId, totalSigningKeysCount);

        signingKeysStats.set(TOTAL_KEYS_COUNT_OFFSET, totalSigningKeysCount);
        _saveOperatorSigningKeysStats(_nodeOperatorId, signingKeysStats);

        _increaseValidatorsKeysNonce();
    }

    /// @notice Removes a validator signing key #`_index` from the keys of the node operator #`_nodeOperatorId`
    /// @param _nodeOperatorId Node Operator id
    /// @param _index Index of the key, starting with 0
    /// @dev DEPRECATED use removeSigningKeys instead
    function removeSigningKey(uint256 _nodeOperatorId, uint256 _index) external {
        _removeUnusedSigningKeys(_nodeOperatorId, _index, 1);
    }

    /// @notice Removes an #`_keysCount` of validator signing keys starting from #`_index` of operator #`_id` usable keys. Executed on behalf of DAO.
    /// @param _nodeOperatorId Node Operator id
    /// @param _fromIndex Index of the key, starting with 0
    /// @param _keysCount Number of keys to remove
    function removeSigningKeys(uint256 _nodeOperatorId, uint256 _fromIndex, uint256 _keysCount) external {
        _removeUnusedSigningKeys(_nodeOperatorId, _fromIndex, _keysCount);
    }

    /// @notice Removes a validator signing key #`_index` of operator #`_id` from the set of usable keys. Executed on behalf of Node Operator.
    /// @param _nodeOperatorId Node Operator id
    /// @param _index Index of the key, starting with 0
    /// @dev DEPRECATED use removeSigningKeys instead
    function removeSigningKeyOperatorBH(uint256 _nodeOperatorId, uint256 _index) external {
        _removeUnusedSigningKeys(_nodeOperatorId, _index, 1);
    }

    /// @notice Removes an #`_keysCount` of validator signing keys starting from #`_index` of operator #`_id` usable keys. Executed on behalf of Node Operator.
    /// @param _nodeOperatorId Node Operator id
    /// @param _fromIndex Index of the key, starting with 0
    /// @param _keysCount Number of keys to remove
    /// @dev DEPRECATED use removeSigningKeys instead
    function removeSigningKeysOperatorBH(uint256 _nodeOperatorId, uint256 _fromIndex, uint256 _keysCount) external {
        _removeUnusedSigningKeys(_nodeOperatorId, _fromIndex, _keysCount);
    }

    /// @notice Returns true if the given validator public key has already been reported as exiting.
    /// @dev The function hashes the input public key using keccak256 and checks if it exists in the _validatorProcessedLateKeys mapping.
    /// @param _publicKey The BLS public key of the validator (serialized as bytes).
    /// @return True if the validator exit for the provided key has been reported, false otherwise.
    function isValidatorExitingKeyReported(bytes _publicKey) public view returns (bool) {
        bytes32 processedKeyHash = keccak256(_publicKey);
        return _validatorProcessedLateKeys[processedKeyHash];
    }

    /// @notice Returns the number of seconds after which a validator is considered late for specified node operator.
    /// @dev The operatorId argument is ignored and present only to comply with the IStakingModule interface.
    /// @return uint256 The exit deadline threshold in seconds for all node operators.
    function exitDeadlineThreshold(uint256 /* operatorId */) public view returns (uint256) {
        return _exitDeadlineThreshold();
    }

    function _exitDeadlineThreshold() internal view returns (uint256) {
        return Packed64x4.Packed(EXIT_DELAY_STATS.getStorageUint256()).get(EXIT_DELAY_THRESHOLD_OFFSET);
    }

    /// @notice Returns the Timestamp before which validators reported as late will not result in penalties for their Node Operators..
    /// @return uint256 The cutoff timestamp used when evaluating late exits.
    function exitPenaltyCutoffTimestamp() public view returns (uint256) {
       return Packed64x4.Packed(EXIT_DELAY_STATS.getStorageUint256()).get(EXIT_PENALTY_CUTOFF_TIMESTAMP_OFFSET);
    }

    /// @notice Sets the validator exit deadline threshold and the reporting window for late exits.
    /// @dev Updates the cutoff timestamp before which a validator that was requested to exit cannot be reported as late.
    /// @param _threshold Number of seconds a validator has to exit after becoming eligible.
    /// @param _lateReportingWindow Additional number of seconds during which a late exit can still be reported.
    function setExitDeadlineThreshold(uint256 _threshold, uint256 _lateReportingWindow) external {
        _auth(MANAGE_NODE_OPERATOR_ROLE);
        _setExitDeadlineThreshold(_threshold, _lateReportingWindow);
    }

    function _setExitDeadlineThreshold(uint256 _threshold, uint256 _lateReportingWindow) internal {
        require(_threshold > 0, "INVALID_EXIT_DELAY_THRESHOLD");

        // Check for underflow protection before computing currentCutoffTimestamp
        require(block.timestamp >= _threshold + _lateReportingWindow, "CUTOFF_TIMESTAMP_UNDERFLOW");

        // Set the cutoff timestamp to the current time minus the threshold and reportingWindow period
        uint256 currentCutoffTimestamp = block.timestamp - _threshold - _lateReportingWindow;
        require(exitPenaltyCutoffTimestamp() <= currentCutoffTimestamp, "INVALID_EXIT_PENALTY_CUTOFF_TIMESTAMP");

        Packed64x4.Packed memory stats = Packed64x4.Packed(0);
        stats.set(EXIT_DELAY_THRESHOLD_OFFSET, _threshold);
        stats.set(EXIT_PENALTY_CUTOFF_TIMESTAMP_OFFSET, currentCutoffTimestamp);
        EXIT_DELAY_STATS.setStorageUint256(stats.v);

        emit ExitDeadlineThresholdChanged(_threshold, _lateReportingWindow);
    }

    /// @notice Handles the triggerable exit event for a validator belonging to a specific node operator.
    /// @dev This function is called by the StakingRouter when a validator is triggered to exit using the triggerable
    ///      exit request on the Execution Layer (EL).
    /// @param _nodeOperatorId The ID of the node operator.
    /// @param _publicKey The public key of the validator being reported.
    /// @param _withdrawalRequestPaidFee Fee amount paid to send a withdrawal request on the Execution Layer (EL).
    /// @param _exitType The type of exit being performed.
    function onValidatorExitTriggered(
        uint256 _nodeOperatorId,
        bytes _publicKey,
        uint256 _withdrawalRequestPaidFee,
        uint256 _exitType
    ) external {
        _auth(STAKING_ROUTER_ROLE);

        emit ValidatorExitTriggered(_nodeOperatorId, _publicKey, _withdrawalRequestPaidFee, _exitType);
    }

    /// @notice Determines whether a validator's exit status should be updated and will have an effect on the Node Operator.
    /// @param _publicKey The public key of the validator.
    /// @param _proofSlotTimestamp The timestamp (slot time) when the validator was last known to be in an active ongoing state.
    /// @param _eligibleToExitInSec The number of seconds the validator was eligible to exit but did not.
    /// @return True if the validator has exceeded the exit deadline threshold and hasn't been reported yet.
    function isValidatorExitDelayPenaltyApplicable(
        uint256, // _nodeOperatorId
        uint256 _proofSlotTimestamp,
        bytes _publicKey,
        uint256 _eligibleToExitInSec
    ) external view returns (bool) {
        // Check if the key is already reported
        if (isValidatorExitingKeyReported(_publicKey)) {
            return false;
        }
        return _eligibleToExitInSec >= _exitDeadlineThreshold()
            && _proofSlotTimestamp - _eligibleToExitInSec >= exitPenaltyCutoffTimestamp();
    }

    /// @notice Handles tracking and penalization logic for a node operator who failed to exit their validator within the defined exit window.
    /// @dev This function is called by the StakingRouter to report the current exit-related status of a validator
    ///      belonging to a specific node operator. It marks the validator as processed to avoid duplicate reports.
    /// @param _nodeOperatorId The ID of the node operator whose validator's status is being delivered.
    /// @param _proofSlotTimestamp The timestamp (slot time) when the validator was last known to be in an active ongoing state.
    /// @param _publicKey The public key of the validator being reported.
    /// @param _eligibleToExitInSec The duration (in seconds) indicating how long the validator has been eligible to exit after request but has not exited.
    function reportValidatorExitDelay(
        uint256 _nodeOperatorId,
        uint256 _proofSlotTimestamp,
        bytes _publicKey,
        uint256 _eligibleToExitInSec
    ) external {
        _auth(STAKING_ROUTER_ROLE);
        require(_publicKey.length == 48, "INVALID_PUBLIC_KEY");

        // Check if exit delay exceeds the threshold
        require(_eligibleToExitInSec >= _exitDeadlineThreshold(), "EXIT_DELAY_BELOW_THRESHOLD");
        // Check if the proof slot timestamp is within the allowed reporting window
        require(_proofSlotTimestamp - _eligibleToExitInSec >= exitPenaltyCutoffTimestamp(), "TOO_LATE_FOR_EXIT_DELAY_REPORT");

        bytes32 processedKeyHash = keccak256(_publicKey);
        // Skip if key is already processed (i.e., not in NotProcessed state)
        if (_validatorProcessedLateKeys[processedKeyHash]) {
            return;
        }
        // Mark the validator exit key as processed
        _validatorProcessedLateKeys[processedKeyHash] = true;

        emit ValidatorExitStatusUpdated(_nodeOperatorId, _publicKey, _eligibleToExitInSec, _proofSlotTimestamp);
    }

    function _removeUnusedSigningKeys(uint256 _nodeOperatorId, uint256 _fromIndex, uint256 _keysCount) internal {
        _onlyExistedNodeOperator(_nodeOperatorId);
        _onlyNodeOperatorManager(msg.sender, _nodeOperatorId);

        // preserve the previous behavior of the method here and just return earlier
        if (_keysCount == 0) return;

        Packed64x4.Packed memory signingKeysStats = _loadOperatorSigningKeysStats(_nodeOperatorId);
        uint256 totalSigningKeysCount = signingKeysStats.get(TOTAL_KEYS_COUNT_OFFSET);
        // comparing _fromIndex.add(_keysCount) <= totalSigningKeysCount is enough as totalSigningKeysCount is always less than UINT64_MAX
        _requireValidRange(
            _fromIndex >= signingKeysStats.get(TOTAL_DEPOSITED_KEYS_COUNT_OFFSET)
                && _fromIndex.add(_keysCount) <= totalSigningKeysCount
        );

        totalSigningKeysCount =
            SIGNING_KEYS_MAPPING_NAME.removeKeysSigs(_nodeOperatorId, _fromIndex, _keysCount, totalSigningKeysCount);
        signingKeysStats.set(TOTAL_KEYS_COUNT_OFFSET, totalSigningKeysCount);
        emit TotalSigningKeysCountChanged(_nodeOperatorId, totalSigningKeysCount);

        uint256 vettedSigningKeysCount = signingKeysStats.get(TOTAL_VETTED_KEYS_COUNT_OFFSET);
        if (_fromIndex < vettedSigningKeysCount) {
            // decreasing the staking limit so the key at _index can't be used anymore
            signingKeysStats.set(TOTAL_VETTED_KEYS_COUNT_OFFSET, _fromIndex);
            emit VettedSigningKeysCountChanged(_nodeOperatorId, _fromIndex);
        }
        _saveOperatorSigningKeysStats(_nodeOperatorId, signingKeysStats);

        _updateSummaryMaxValidatorsCount(_nodeOperatorId);

        _increaseValidatorsKeysNonce();
    }

    /// @notice Returns total number of signing keys of the node operator #`_nodeOperatorId`
    function getTotalSigningKeyCount(uint256 _nodeOperatorId) external view returns (uint256) {
        _onlyExistedNodeOperator(_nodeOperatorId);
        Packed64x4.Packed memory signingKeysStats = _loadOperatorSigningKeysStats(_nodeOperatorId);
        return signingKeysStats.get(TOTAL_KEYS_COUNT_OFFSET);
    }

    /// @notice Returns number of usable signing keys of the node operator #`_nodeOperatorId`
    function getUnusedSigningKeyCount(uint256 _nodeOperatorId) external view returns (uint256) {
        _onlyExistedNodeOperator(_nodeOperatorId);

        Packed64x4.Packed memory signingKeysStats = _loadOperatorSigningKeysStats(_nodeOperatorId);
        return signingKeysStats.get(TOTAL_KEYS_COUNT_OFFSET).sub(signingKeysStats.get(TOTAL_DEPOSITED_KEYS_COUNT_OFFSET));
    }

    /// @notice Returns n-th signing key of the node operator #`_nodeOperatorId`
    /// @param _nodeOperatorId Node Operator id
    /// @param _index Index of the key, starting with 0
    /// @return key Key
    /// @return depositSignature Signature needed for a deposit_contract.deposit call
    /// @return used Flag indication if the key was used in the staking
    function getSigningKey(uint256 _nodeOperatorId, uint256 _index)
        external
        view
        returns (bytes key, bytes depositSignature, bool used)
    {
        bool[] memory keyUses;
        (key, depositSignature, keyUses) = getSigningKeys(_nodeOperatorId, _index, 1);
        used = keyUses[0];
    }

    /// @notice Returns n signing keys of the node operator #`_nodeOperatorId`
    /// @param _nodeOperatorId Node Operator id
    /// @param _offset Offset of the key, starting with 0
    /// @param _limit Number of keys to return
    /// @return pubkeys Keys concatenated into the bytes batch
    /// @return signatures Signatures concatenated into the bytes batch needed for a deposit_contract.deposit call
    /// @return used Array of flags indicated if the key was used in the staking
    function getSigningKeys(uint256 _nodeOperatorId, uint256 _offset, uint256 _limit)
        public
        view
        returns (bytes memory pubkeys, bytes memory signatures, bool[] memory used)
    {
        _onlyExistedNodeOperator(_nodeOperatorId);

        Packed64x4.Packed memory signingKeysStats = _loadOperatorSigningKeysStats(_nodeOperatorId);
        _requireValidRange(_offset.add(_limit) <= signingKeysStats.get(TOTAL_KEYS_COUNT_OFFSET));

        uint256 depositedSigningKeysCount = signingKeysStats.get(TOTAL_DEPOSITED_KEYS_COUNT_OFFSET);
        (pubkeys, signatures) = SigningKeys.initKeysSigsBuf(_limit);
        used = new bool[](_limit);

        SIGNING_KEYS_MAPPING_NAME.loadKeysSigs(_nodeOperatorId, _offset, _limit, pubkeys, signatures, 0);
        for (uint256 i; i < _limit; ++i) {
            used[i] = (_offset + i) < depositedSigningKeysCount;
        }
    }

    /// @notice Returns the type of the staking module
    function getType() external view returns (bytes32) {
        return TYPE_POSITION.getStorageBytes32();
    }

    function getStakingModuleSummary()
        external
        view
        returns (uint256 totalExitedValidators, uint256 totalDepositedValidators, uint256 depositableValidatorsCount)
    {
        Packed64x4.Packed memory summarySigningKeysStats = _loadSummarySigningKeysStats();
        totalExitedValidators = summarySigningKeysStats.get(SUMMARY_EXITED_KEYS_COUNT_OFFSET);
        totalDepositedValidators = summarySigningKeysStats.get(SUMMARY_DEPOSITED_KEYS_COUNT_OFFSET);
        depositableValidatorsCount = summarySigningKeysStats.get(SUMMARY_MAX_VALIDATORS_COUNT_OFFSET).sub(totalDepositedValidators);
    }

    function getNodeOperatorSummary(uint256 _nodeOperatorId)
        external
        view
        returns (
            uint256 targetLimitMode,
            uint256 targetValidatorsCount,
            uint256 stuckValidatorsCount,
            uint256 refundedValidatorsCount,
            uint256 stuckPenaltyEndTimestamp,
            uint256 totalExitedValidators,
            uint256 totalDepositedValidators,
            uint256 depositableValidatorsCount
    ) {
        _onlyExistedNodeOperator(_nodeOperatorId);

        Packed64x4.Packed memory operatorTargetStats = _loadOperatorTargetValidatorsStats(_nodeOperatorId);

        targetLimitMode = operatorTargetStats.get(TARGET_LIMIT_MODE_OFFSET);
        targetValidatorsCount = operatorTargetStats.get(TARGET_VALIDATORS_COUNT_OFFSET);
        stuckValidatorsCount = 0;
        refundedValidatorsCount = 0;
        stuckPenaltyEndTimestamp = 0;

        (totalExitedValidators, totalDepositedValidators, depositableValidatorsCount) =
            _getNodeOperatorValidatorsSummary(_nodeOperatorId);
    }

    function _getNodeOperatorValidatorsSummary(uint256 _nodeOperatorId) internal view returns (
        uint256 totalExitedValidators,
        uint256 totalDepositedValidators,
        uint256 depositableValidatorsCount
    ) {
        uint256 totalMaxValidators;
        (totalExitedValidators, totalDepositedValidators, totalMaxValidators) = _getNodeOperator(_nodeOperatorId);

        depositableValidatorsCount = totalMaxValidators - totalDepositedValidators;
    }

    /// @notice [DEPRECATED] Penalty logic removed. Always returns `false`.
    /// @dev _nodeOperatorId Ignored.
    /// @return Always returns `false`.
    function isOperatorPenalized(uint256 /* _nodeOperatorId */) public pure returns (bool) {
        return false;
    }

    /// @notice [DEPRECATED] Penalty logic removed. Always returns `true`.
    /// @dev _nodeOperatorId Ignored.
    /// @return Always returns `true`.
    function isOperatorPenaltyCleared(uint256 /* _nodeOperatorId */) public pure returns (bool) {
        return true;
    }

    /// @notice Returns total number of node operators
    function getNodeOperatorsCount() public view returns (uint256) {
        return TOTAL_OPERATORS_COUNT_POSITION.getStorageUint256();
    }

    /// @notice Returns number of active node operators
    function getActiveNodeOperatorsCount() public view returns (uint256) {
        return ACTIVE_OPERATORS_COUNT_POSITION.getStorageUint256();
    }

    /// @notice Returns if the node operator with given id is active
    function getNodeOperatorIsActive(uint256 _nodeOperatorId) public view returns (bool) {
        return _nodeOperators[_nodeOperatorId].active;
    }

    /// @notice Returns up to `_limit` node operator ids starting from the `_offset`.
    function getNodeOperatorIds(uint256 _offset, uint256 _limit)
        external
        view
        returns (uint256[] memory nodeOperatorIds) {
        uint256 nodeOperatorsCount = getNodeOperatorsCount();
        if (_offset >= nodeOperatorsCount || _limit == 0) return;
        nodeOperatorIds = new uint256[](Math256.min(_limit, nodeOperatorsCount - _offset));
        for (uint256 i = 0; i < nodeOperatorIds.length; ++i) {
            nodeOperatorIds[i] = _offset + i;
        }
    }

    /// @notice Returns a counter that MUST change it's value when any of the following happens:
    ///     1. a node operator's deposit data is added
    ///     2. a node operator's deposit data is removed
    ///     3. a node operator's ready-to-deposit data size is changed
    ///     4. a node operator was activated/deactivated
    ///     5. a node operator's deposit data is used for the deposit
    function getNonce() external view returns (uint256) {
        return KEYS_OP_INDEX_POSITION.getStorageUint256();
    }

    /// @notice Returns a counter that MUST change its value whenever the deposit data set changes.
    ///     Below is the typical list of actions that requires an update of the nonce:
    ///     1. a node operator's deposit data is added
    ///     2. a node operator's deposit data is removed
    ///     3. a node operator's ready-to-deposit data size is changed
    ///     4. a node operator was activated/deactivated
    ///     5. a node operator's deposit data is used for the deposit
    ///     Note: Depending on the StakingModule implementation above list might be extended
    /// @dev DEPRECATED use getNonce() instead
    function getKeysOpIndex() external view returns (uint256) {
        return KEYS_OP_INDEX_POSITION.getStorageUint256();
    }

    /// @notice distributes rewards among node operators
    /// @return the amount of stETH shares distributed among node operators
    function _distributeRewards() internal returns (uint256 distributed) {
        IStETH stETH = IStETH(getLocator().lido());

        uint256 sharesToDistribute = stETH.sharesOf(address(this));
        if (sharesToDistribute == 0) {
            return;
        }

        (address[] memory recipients, uint256[] memory shares,) =
            getRewardsDistribution(sharesToDistribute);

        for (uint256 idx; idx < recipients.length; ++idx) {
            /// @dev skip ultra-low amounts processing to avoid transfer zero amount in case of a penalty
            if (shares[idx] < 2) continue;
            stETH.transferShares(recipients[idx], shares[idx]);
            distributed = distributed.add(shares[idx]);
            emit RewardsDistributed(recipients[idx], shares[idx]);
        }
    }

    function getLocator() public view returns (ILidoLocator) {
        return ILidoLocator(LIDO_LOCATOR_POSITION.getStorageAddress());
    }

    /// @notice [DEPRECATED] Stuck penalty delay logic removed. Always returns 0.
    /// @return Always returns 0.
    function getStuckPenaltyDelay() public pure returns (uint256) {
        return 0;
    }

    /// @dev Get the current reward distribution state, anyone can monitor this state
    /// and distribute reward (call distributeReward method) among operators when it's `ReadyForDistribution`
    function getRewardDistributionState() public view returns (RewardDistributionState) {
        uint256 state = REWARD_DISTRIBUTION_STATE.getStorageUint256();
        return RewardDistributionState(state);
    }

    function _updateRewardDistributionState(RewardDistributionState _state) internal {
        REWARD_DISTRIBUTION_STATE.setStorageUint256(uint256(_state));
        emit RewardDistributionStateChanged(_state);
    }

    function _increaseValidatorsKeysNonce() internal {
        uint256 keysOpIndex = KEYS_OP_INDEX_POSITION.getStorageUint256() + 1;
        KEYS_OP_INDEX_POSITION.setStorageUint256(keysOpIndex);
        /// @dev [DEPRECATED] event preserved for tooling compatibility
        emit KeysOpIndexSet(keysOpIndex);
        emit NonceChanged(keysOpIndex);
    }

    function _loadSummarySigningKeysStats() internal view returns (Packed64x4.Packed memory) {
        return _nodeOperatorSummary.summarySigningKeysStats;
    }

    function _saveSummarySigningKeysStats(Packed64x4.Packed memory _val) internal {
        _nodeOperatorSummary.summarySigningKeysStats = _val;
    }

    function _loadOperatorTargetValidatorsStats(uint256 _nodeOperatorId) internal view returns (Packed64x4.Packed memory) {
        return _nodeOperators[_nodeOperatorId].targetValidatorsStats;
    }

    function _saveOperatorTargetValidatorsStats(uint256 _nodeOperatorId, Packed64x4.Packed memory _val) internal {
        _nodeOperators[_nodeOperatorId].targetValidatorsStats = _val;
    }


    function _loadOperatorSigningKeysStats(uint256 _nodeOperatorId) internal view returns (Packed64x4.Packed memory) {
        return _nodeOperators[_nodeOperatorId].signingKeysStats;
    }

    function _saveOperatorSigningKeysStats(uint256 _nodeOperatorId, Packed64x4.Packed memory _val) internal {
        _nodeOperators[_nodeOperatorId].signingKeysStats = _val;
    }

    function _requireAuth(bool _pass) internal pure {
        require(_pass, "APP_AUTH_FAILED");
    }

    function _requireNotSameValue(bool _pass) internal pure {
        require(_pass, "VALUE_IS_THE_SAME");
    }

    function _requireValidRange(bool _pass) internal pure {
        require(_pass, "OUT_OF_RANGE");
    }

    function _onlyCorrectNodeOperatorState(bool _pass) internal pure {
        require(_pass, "WRONG_OPERATOR_ACTIVE_STATE");
    }

    function _auth(bytes32 _role) internal view {
        _requireAuth(canPerform(msg.sender, _role, new uint256[](0)));
    }

    function _authP(bytes32 _role, uint256[] _params) internal view {
        _requireAuth(canPerform(msg.sender, _role, _params));
    }

    function _onlyNodeOperatorManager(address _sender, uint256 _nodeOperatorId) internal view {
        bool isRewardAddress = _sender == _nodeOperators[_nodeOperatorId].rewardAddress;
        bool isActive = _nodeOperators[_nodeOperatorId].active;
        _requireAuth((isRewardAddress && isActive) || canPerform(_sender, MANAGE_SIGNING_KEYS, arr(_nodeOperatorId)));
    }

    function _onlyExistedNodeOperator(uint256 _nodeOperatorId) internal view {
        _requireValidRange(_nodeOperatorId < getNodeOperatorsCount());
    }

    function _onlyValidNodeOperatorName(string _name) internal pure {
        require(bytes(_name).length > 0 && bytes(_name).length <= MAX_NODE_OPERATOR_NAME_LENGTH, "WRONG_NAME_LENGTH");
    }

    function _onlyValidRewardAddress(address _rewardAddress) internal view {
        _onlyNonZeroAddress(_rewardAddress);
        // The Lido address is forbidden explicitly because stETH transfers on this contract will revert
        // See onExitedAndStuckValidatorsCountsUpdated() and StETH._transferShares() for details
        require(_rewardAddress != getLocator().lido(), "LIDO_REWARD_ADDRESS");
    }

    function _onlyNonZeroAddress(address _a) internal pure {
        require(_a != address(0), "ZERO_ADDRESS");
    }
}