/**
 * @license
 * Copyright 2022 Google Inc.
 * SPDX-License-Identifier: Apache-2.0
 */

import type {Protocol} from 'devtools-protocol';

import type {TargetFilterCallback} from '../api/Browser.js';
import {type CDPSession, CDPSessionEvent} from '../api/CDPSession.js';
import {EventEmitter} from '../common/EventEmitter.js';
import {assert} from '../util/assert.js';
import {Deferred} from '../util/Deferred.js';

import type {CdpCDPSession} from './CDPSession.js';
import type {Connection} from './Connection.js';
import type {CdpTarget} from './Target.js';
import {
  type TargetFactory,
  TargetManagerEvent,
  type TargetManager,
  type TargetManagerEvents,
} from './TargetManager.js';

/**
 * FirefoxTargetManager implements target management using
 * `Target.setDiscoverTargets` without using auto-attach. It, therefore, creates
 * targets that lazily establish their CDP sessions.
 *
 * Although the approach is potentially flaky, there is no other way for Firefox
 * because Firefox's CDP implementation does not support auto-attach.
 *
 * Firefox does not support targetInfoChanged and detachedFromTarget events:
 *
 * - https://bugzilla.mozilla.org/show_bug.cgi?id=1610855
 * - https://bugzilla.mozilla.org/show_bug.cgi?id=1636979
 *   @internal
 */
export class FirefoxTargetManager
  extends EventEmitter<TargetManagerEvents>
  implements TargetManager
{
  #connection: Connection;
  /**
   * Keeps track of the following events: 'Target.targetCreated',
   * 'Target.targetDestroyed'.
   *
   * A target becomes discovered when 'Target.targetCreated' is received.
   * A target is removed from this map once 'Target.targetDestroyed' is
   * received.
   *
   * `targetFilterCallback` has no effect on this map.
   */
  #discoveredTargetsByTargetId = new Map<string, Protocol.Target.TargetInfo>();
  /**
   * Keeps track of targets that were created via 'Target.targetCreated'
   * and which one are not filtered out by `targetFilterCallback`.
   *
   * The target is removed from here once it's been destroyed.
   */
  #availableTargetsByTargetId = new Map<string, CdpTarget>();
  /**
   * Tracks which sessions attach to which target.
   */
  #availableTargetsBySessionId = new Map<string, CdpTarget>();
  #targetFilterCallback: TargetFilterCallback | undefined;
  #targetFactory: TargetFactory;

  #attachedToTargetListenersBySession = new WeakMap<
    CDPSession | Connection,
    (event: Protocol.Target.AttachedToTargetEvent) => Promise<void>
  >();

  #initializeDeferred = Deferred.create<void>();
  #targetsIdsForInit = new Set<string>();

  constructor(
    connection: Connection,
    targetFactory: TargetFactory,
    targetFilterCallback?: TargetFilterCallback
  ) {
    super();
    this.#connection = connection;
    this.#targetFilterCallback = targetFilterCallback;
    this.#targetFactory = targetFactory;

    this.#connection.on('Target.targetCreated', this.#onTargetCreated);
    this.#connection.on('Target.targetDestroyed', this.#onTargetDestroyed);
    this.#connection.on(
      CDPSessionEvent.SessionDetached,
      this.#onSessionDetached
    );
    this.setupAttachmentListeners(this.#connection);
  }

  setupAttachmentListeners(session: CDPSession | Connection): void {
    const listener = (event: Protocol.Target.AttachedToTargetEvent) => {
      return this.#onAttachedToTarget(session, event);
    };
    assert(!this.#attachedToTargetListenersBySession.has(session));
    this.#attachedToTargetListenersBySession.set(session, listener);
    session.on('Target.attachedToTarget', listener);
  }

  #onSessionDetached = (session: CDPSession) => {
    this.removeSessionListeners(session);
    this.#availableTargetsBySessionId.delete(session.id());
  };

  removeSessionListeners(session: CDPSession): void {
    if (this.#attachedToTargetListenersBySession.has(session)) {
      session.off(
        'Target.attachedToTarget',
        this.#attachedToTargetListenersBySession.get(session)!
      );
      this.#attachedToTargetListenersBySession.delete(session);
    }
  }

  getAvailableTargets(): ReadonlyMap<string, CdpTarget> {
    return this.#availableTargetsByTargetId;
  }

  getChildTargets(_target: CdpTarget): ReadonlySet<CdpTarget> {
    return new Set();
  }

  dispose(): void {
    this.#connection.off('Target.targetCreated', this.#onTargetCreated);
    this.#connection.off('Target.targetDestroyed', this.#onTargetDestroyed);
  }

  async initialize(): Promise<void> {
    await this.#connection.send('Target.setDiscoverTargets', {
      discover: true,
      filter: [{}],
    });
    this.#targetsIdsForInit = new Set(this.#discoveredTargetsByTargetId.keys());
    await this.#initializeDeferred.valueOrThrow();
  }

  #onTargetCreated = async (
    event: Protocol.Target.TargetCreatedEvent
  ): Promise<void> => {
    if (this.#discoveredTargetsByTargetId.has(event.targetInfo.targetId)) {
      return;
    }

    this.#discoveredTargetsByTargetId.set(
      event.targetInfo.targetId,
      event.targetInfo
    );

    if (event.targetInfo.type === 'browser' && event.targetInfo.attached) {
      const target = this.#targetFactory(event.targetInfo, undefined);
      target._initialize();
      this.#availableTargetsByTargetId.set(event.targetInfo.targetId, target);
      this.#finishInitializationIfReady(target._targetId);
      return;
    }

    const target = this.#targetFactory(event.targetInfo, undefined);
    if (this.#targetFilterCallback && !this.#targetFilterCallback(target)) {
      this.#finishInitializationIfReady(event.targetInfo.targetId);
      return;
    }
    target._initialize();
    this.#availableTargetsByTargetId.set(event.targetInfo.targetId, target);
    this.emit(TargetManagerEvent.TargetAvailable, target);
    this.#finishInitializationIfReady(target._targetId);
  };

  #onTargetDestroyed = (event: Protocol.Target.TargetDestroyedEvent): void => {
    this.#discoveredTargetsByTargetId.delete(event.targetId);
    this.#finishInitializationIfReady(event.targetId);
    const target = this.#availableTargetsByTargetId.get(event.targetId);
    if (target) {
      this.emit(TargetManagerEvent.TargetGone, target);
      this.#availableTargetsByTargetId.delete(event.targetId);
    }
  };

  #onAttachedToTarget = async (
    parentSession: Connection | CDPSession,
    event: Protocol.Target.AttachedToTargetEvent
  ) => {
    const targetInfo = event.targetInfo;
    const session = this.#connection.session(event.sessionId);
    if (!session) {
      throw new Error(`Session ${event.sessionId} was not created.`);
    }

    const target = this.#availableTargetsByTargetId.get(targetInfo.targetId);

    assert(target, `Target ${targetInfo.targetId} is missing`);

    (session as CdpCDPSession)._setTarget(target);
    this.setupAttachmentListeners(session);

    this.#availableTargetsBySessionId.set(
      session.id(),
      this.#availableTargetsByTargetId.get(targetInfo.targetId)!
    );

    parentSession.emit(CDPSessionEvent.Ready, session);
  };

  #finishInitializationIfReady(targetId: string): void {
    this.#targetsIdsForInit.delete(targetId);
    if (this.#targetsIdsForInit.size === 0) {
      this.#initializeDeferred.resolve();
    }
  }
}