plugins_status.ts

/*
 * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
 * or more contributor license agreements. Licensed under the Elastic License
 * 2.0 and the Server Side Public License, v 1; you may not use this file except
 * in compliance with, at your election, the Elastic License 2.0 or the Server
 * Side Public License, v 1.
 */

import { BehaviorSubject, Observable, combineLatest, of } from 'rxjs';
import {
  map,
  distinctUntilChanged,
  switchMap,
  debounceTime,
  timeoutWith,
  startWith,
} from 'rxjs/operators';
import { isDeepStrictEqual } from 'util';

import { PluginName } from '../plugins';
import { ServiceStatus, CoreStatus, ServiceStatusLevels } from './types';
import { getSummaryStatus } from './get_summary_status';

const STATUS_TIMEOUT_MS = 30 * 1000; // 30 seconds

interface Deps {
  core$: Observable<CoreStatus>;
  pluginDependencies: ReadonlyMap<PluginName, PluginName[]>;
}

export class PluginsStatusService {
  private readonly pluginStatuses = new Map<PluginName, Observable<ServiceStatus>>();
  private readonly update$ = new BehaviorSubject(true);
  private readonly defaultInheritedStatus$: Observable<ServiceStatus>;
  private newRegistrationsAllowed = true;

  constructor(private readonly deps: Deps) {
    this.defaultInheritedStatus$ = this.deps.core$.pipe(
      map((coreStatus) => {
        return getSummaryStatus(Object.entries(coreStatus), {
          allAvailableSummary: `All dependencies are available`,
        });
      })
    );
  }

  public set(plugin: PluginName, status$: Observable<ServiceStatus>) {
    if (!this.newRegistrationsAllowed) {
      throw new Error(
        `Custom statuses cannot be registered after setup, plugin [${plugin}] attempted`
      );
    }
    this.pluginStatuses.set(plugin, status$);
    this.update$.next(true); // trigger all existing Observables to update from the new source Observable
  }

  public blockNewRegistrations() {
    this.newRegistrationsAllowed = false;
  }

  public getAll$(): Observable<Record<PluginName, ServiceStatus>> {
    return this.getPluginStatuses$([...this.deps.pluginDependencies.keys()]);
  }

  public getDependenciesStatus$(plugin: PluginName): Observable<Record<PluginName, ServiceStatus>> {
    const dependencies = this.deps.pluginDependencies.get(plugin);
    if (!dependencies) {
      throw new Error(`Unknown plugin: ${plugin}`);
    }

    return this.getPluginStatuses$(dependencies).pipe(
      // Prevent many emissions at once from dependency status resolution from making this too noisy
      debounceTime(25)
    );
  }

  public getDerivedStatus$(plugin: PluginName): Observable<ServiceStatus> {
    return this.update$.pipe(
      debounceTime(25), // Avoid calling the plugin's custom status logic for every plugin that depends on it.
      switchMap(() => {
        // Only go up the dependency tree if any of this plugin's dependencies have a custom status
        // Helps eliminate memory overhead of creating thousands of Observables unnecessarily.
        if (this.anyCustomStatuses(plugin)) {
          return combineLatest([this.deps.core$, this.getDependenciesStatus$(plugin)]).pipe(
            map(([coreStatus, pluginStatuses]) => {
              return getSummaryStatus(
                [...Object.entries(coreStatus), ...Object.entries(pluginStatuses)],
                {
                  allAvailableSummary: `All dependencies are available`,
                }
              );
            })
          );
        } else {
          return this.defaultInheritedStatus$;
        }
      })
    );
  }

  private getPluginStatuses$(plugins: PluginName[]): Observable<Record<PluginName, ServiceStatus>> {
    if (plugins.length === 0) {
      return of({});
    }

    // TODO: broken during Node 16 upgrade
    // @ts-expect-error
    return this.update$.pipe(
      switchMap(() => {
        const pluginStatuses = plugins
          .map((depName) => {
            const pluginStatus = this.pluginStatuses.get(depName)
              ? this.pluginStatuses.get(depName)!.pipe(
                  timeoutWith(
                    STATUS_TIMEOUT_MS,
                    this.pluginStatuses.get(depName)!.pipe(
                      startWith({
                        level: ServiceStatusLevels.unavailable,
                        summary: `Status check timed out after ${STATUS_TIMEOUT_MS / 1000}s`,
                      })
                    )
                  )
                )
              : this.getDerivedStatus$(depName);
            return [depName, pluginStatus] as [PluginName, Observable<ServiceStatus>];
          })
          .map(([pName, status$]) =>
            status$.pipe(map((status) => [pName, status] as [PluginName, ServiceStatus]))
          );

        return combineLatest(pluginStatuses).pipe(
          map((statuses) => Object.fromEntries(statuses)),
          distinctUntilChanged(isDeepStrictEqual)
        );
      })
    );
  }

  /**
   * Determines whether or not this plugin or any plugin in it's dependency tree have a custom status registered.
   */
  private anyCustomStatuses(plugin: PluginName): boolean {
    if (this.pluginStatuses.get(plugin)) {
      return true;
    }

    return this.deps.pluginDependencies
      .get(plugin)!
      .reduce((acc, depName) => acc || this.anyCustomStatuses(depName), false as boolean);
  }
}