interface INodeOperatorsRegistry {
    /**
      * @notice Add node operator named `name` with reward address `rewardAddress` and staking limit `stakingLimit` validators
      * @param _name Human-readable name
      * @param _rewardAddress Ethereum 1 address which receives stETH rewards for this operator
      * @param _stakingLimit the maximum number of validators to stake for this operator
      * @return a unique key of the added operator
      */
    function addNodeOperator(string _name, address _rewardAddress, uint64 _stakingLimit) external returns (uint256 id);

    /**
      * @notice `_active ? 'Enable' : 'Disable'` the node operator #`_id`
      */
    function setNodeOperatorActive(uint256 _id, bool _active) external;

    /**
      * @notice Change human-readable name of the node operator #`_id` to `_name`
      */
    function setNodeOperatorName(uint256 _id, string _name) external;

    /**
      * @notice Change reward address of the node operator #`_id` to `_rewardAddress`
      */
    function setNodeOperatorRewardAddress(uint256 _id, address _rewardAddress) external;

    /**
      * @notice Set the maximum number of validators to stake for the node operator #`_id` to `_stakingLimit`
      */
    function setNodeOperatorStakingLimit(uint256 _id, uint64 _stakingLimit) external;

    /**
      * @notice Report `_stoppedIncrement` more stopped validators of the node operator #`_id`
      */
    function reportStoppedValidators(uint256 _id, uint64 _stoppedIncrement) external;

    /**
      * @notice Remove unused signing keys
      * @dev Function is used by the pool
      */
    function trimUnusedKeys() external;

    /**
      * @notice Returns total number of node operators
      */
    function getNodeOperatorsCount() external view returns (uint256);

    /**
      * @notice Returns number of active node operators
      */
    function getActiveNodeOperatorsCount() external view returns (uint256);

    /**
      * @notice Returns the n-th node operator
      * @param _id Node Operator id
      * @param _fullInfo If true, name will be returned as well
      */
    function getNodeOperator(uint256 _id, bool _fullInfo) external view returns (
        bool active,
        string name,
        address rewardAddress,
        uint64 stakingLimit,
        uint64 stoppedValidators,
        uint64 totalSigningKeys,
        uint64 usedSigningKeys);

    /**
      * @notice Returns the rewards distribution proportional to the effective stake for each node operator.
      * @param _totalRewardShares Total amount of reward shares to distribute.
      */
    function getRewardsDistribution(uint256 _totalRewardShares) external view returns (
        address[] memory recipients,
        uint256[] memory shares
    );

    event NodeOperatorAdded(uint256 id, string name, address rewardAddress, uint64 stakingLimit);
    event NodeOperatorActiveSet(uint256 indexed id, bool active);
    event NodeOperatorNameSet(uint256 indexed id, string name);
    event NodeOperatorRewardAddressSet(uint256 indexed id, address rewardAddress);
    event NodeOperatorStakingLimitSet(uint256 indexed id, uint64 stakingLimit);
    event NodeOperatorTotalStoppedValidatorsReported(uint256 indexed id, uint64 totalStopped);

    /**
     * @notice Selects and returns at most `_numKeys` signing keys (as well as the corresponding
     *         signatures) from the set of active keys and marks the selected keys as used.
     *         May only be called by the pool contract.
     *
     * @param _numKeys The number of keys to select. The actual number of selected keys may be less
     *        due to the lack of active keys.
     */
    function assignNextSigningKeys(uint256 _numKeys) external returns (bytes memory pubkeys, bytes memory signatures);

    /**
      * @notice Add `_quantity` validator signing keys to the keys of the node operator #`_operator_id`. 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 _operator_id Node Operator id
      * @param _quantity Number of signing keys provided
      * @param _pubkeys Several concatenated validator signing keys
      * @param _signatures Several concatenated signatures for (pubkey, withdrawal_credentials, 32000000000) messages
      */
    function addSigningKeys(uint256 _operator_id, uint256 _quantity, bytes _pubkeys, bytes _signatures) external;

    /**
      * @notice Removes a validator signing key #`_index` from the keys of the node operator #`_operator_id`
      * @param _operator_id Node Operator id
      * @param _index Index of the key, starting with 0
      */
    function removeSigningKey(uint256 _operator_id, uint256 _index) external;

    /**
      * @notice Returns total number of signing keys of the node operator #`_operator_id`
      */
    function getTotalSigningKeyCount(uint256 _operator_id) external view returns (uint256);

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

    /**
      * @notice Returns n-th signing key of the node operator #`_operator_id`
      * @param _operator_id 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 _operator_id, uint256 _index) external view returns
            (bytes key, bytes depositSignature, bool used);

    event SigningKeyAdded(uint256 indexed operatorId, bytes pubkey);
    event SigningKeyRemoved(uint256 indexed operatorId, bytes pubkey);
}
/**
 * @title Node Operator registry
 *
 * Node Operator registry manages signing keys and other node operator data.
 * It's also responsible for distributing rewards to node operators.
 */
function reportStoppedValidators(uint256 _id, uint64 _stoppedIncrement) external;

/**
 * @notice Report `_stoppedIncrement` more stopped validators of the node operator #`_id`
 */