/*!
 * Copyright 2024 Google LLC. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
import { EventEmitter } from 'events';
import { Database } from './database';
import { Session } from './session';
import { GetSessionCallback } from './session-factory';
import { ObservabilityOptions } from './instrument';
export declare const MUX_SESSION_AVAILABLE = "mux-session-available";
export declare const MUX_SESSION_CREATE_ERROR = "mux-session-create-error";
/**
 * Interface for implementing multiplexed session logic, it should extend the
 * {@link https://nodejs.org/api/events.html|EventEmitter} class
 *
 * @interface MultiplexedSessionInterface
 * @extends external:{@link https://nodejs.org/api/events.html|EventEmitter}
 *
 * @constructs MultiplexedSessionInterface
 * @param {Database} database The database to create a multiplexed session for.
 */
export interface MultiplexedSessionInterface extends EventEmitter {
    /**
     * When called creates a multiplexed session.
     *
     * @name MultiplexedSessionInterface#createSession
     */
    createSession(): void;
    /**
     * When called returns a multiplexed session.
     *
     * @name MultiplexedSessionInterface#getSession
     * @param {GetSessionCallback} callback The callback function.
     */
    getSession(callback: GetSessionCallback): void;
}
/**
 * Class used to manage connections to Spanner using multiplexed session.
 *
 * **You don't need to use this class directly, connections will be handled for
 * you.**
 *
 * @class
 * @extends {EventEmitter}
 */
export declare class MultiplexedSession extends EventEmitter implements MultiplexedSessionInterface {
    database: Database;
    refreshRate: number;
    _multiplexedSession: Session | null;
    _refreshHandle: NodeJS.Timer;
    _observabilityOptions?: ObservabilityOptions;
    constructor(database: Database);
    /**
     * Creates a new multiplexed session and manages its maintenance.
     *
     * This method initiates the session creation process by calling the `_createSession` method, which returns a Promise.
     */
    createSession(): void;
    /**
     * Creates a new multiplexed session.
     *
     * This method sends a request to the database to create a new session with multiplexing enabled.
     * The response from the database would be an array, the first value of the array will be containing the multiplexed session.
     *
     * @returns {Promise<void>} A Promise that resolves when the session has been successfully created and assigned, an event
     * `mux-session-available` will be emitted to signal that the session is ready.
     *
     * In case of error, an error will get emitted along with the error event.
     *
     * @private
     */
    _createSession(): Promise<void>;
    /**
     * Maintains the multiplexed session by periodically refreshing it.
     *
     * This method sets up a periodic refresh interval for maintaining the session. The interval duration
     * is determined by the @param refreshRate option, which is provided in days.
     * The default value is 7 days.
     *
     * @throws {Error} If the multiplexed session creation fails in `_createSession`, the error is caught
     * and ignored. This is because the currently active multiplexed session has a 30-day expiry, providing
     * the maintainer with four opportunities (one every 7 days) to refresh the active session.
     *
     * @returns {void} This method does not return any value.
     *
     */
    _maintain(): void;
    /**
     * Retrieves a session asynchronously and invokes a callback with the session details.
     *
     * @param {GetSessionCallback} callback - The callback to be invoked once the session is acquired or an error occurs.
     *
     * @returns {void} This method does not return any value, as it operates asynchronously and relies on the callback.
     *
     */
    getSession(callback: GetSessionCallback): void;
    /**
     * Acquires a session asynchronously, and prepares the transaction for the session.
     *
     * Once a session is successfully acquired, it returns the session object (which may be `null` if unsuccessful).
     *
     * @returns {Promise<Session | null>}
     * A Promise that resolves with the acquired session (or `null` if no session is available after retries).
     *
     */
    _acquire(): Promise<Session | null>;
    /**
     * Attempts to get a session, waiting for it to become available if necessary.
     *
     * Waits for the `MUX_SESSION_AVAILABLE` event or for the `MUX_SESSION_CREATE_ERROR`
     * to be emitted if the multiplexed session is not yet available. The method listens
     * for these events, and once `mux-session-available` is emitted, it resolves and returns
     * the session.
     *
     * In case of an error, the promise will get rejected and the error will get bubble up to the parent method.
     *
     * @returns {Promise<Session | null>} A promise that resolves with the current multiplexed session if available,
     * or `null` if the session is not available.
     *
     * @private
     *
     */
    _getSession(): Promise<Session | null>;
}