synctable-no-changefeed.ts

/*
 *  This file is part of CoCalc: Copyright © 2020 Sagemath, Inc.
 *  License: MS-RSL – see LICENSE.md for details
 */

/*
Make a SyncTable which does not use a changefeed at all.

It does the initial database read as usual, and also
writes changes as usual, but does not use a changefeed
at all.   Instead changes are injected by calling
a function.

This is used, e.g., by a backend project for implementing a version
of SyncTable, where the project itself handles all changes,
not the database or hubs.   However, data is still persisted
to the central database.

Returned object is not cached in any way.
*/

import { EventEmitter } from "events";
import { SyncTable, Client } from "./synctable";
import { bind_methods } from "@cocalc/util/misc";

export function synctable_no_changefeed(
  query,
  options,
  client: Client,
  throttle_changes?: undefined | number,
): SyncTable {
  if (options == null) {
    options = [];
  }
  const client2 = new ClientNoChangefeed(client);
  return new SyncTable(query, options, client2, throttle_changes, true, false);
}

class ClientNoChangefeed extends EventEmitter {
  private client: Client;

  constructor(client) {
    super();

    bind_methods(this, [
      "query",
      "dbg",
      "query_cancel",
      "emit_connected",
      "emit_signed_in",
    ]);
    this.client = client;

    // These MUST be after the binds above, obviously.
    client.on("connected", this.emit_connected);
    client.on("signed_in", this.emit_signed_in);
  }

  private emit_connected(): void {
    this.emit("connected");
  }

  private emit_signed_in(): void {
    this.emit("signed_in");
  }

  public is_project(): boolean {
    return this.client.is_project();
  }

  public is_browser(): boolean {
    return this.client.is_browser();
  }

  public is_compute_server(): boolean {
    return this.client.is_compute_server();
  }

  public async touch_project(project_id: string): Promise<void> {
    await this.client.touch_project(project_id);
  }

  public is_connected(): boolean {
    return this.client.is_connected();
  }

  public is_signed_in(): boolean {
    return this.client.is_signed_in();
  }

  public server_time(): Date {
    return this.client.server_time();
  }

  public dbg(s: string): Function {
    return this.client.dbg(s);
  }

  public query(opts): void {
    if (opts.changes) {
      this.changefeed_query(opts);
    } else {
      this.client.query(opts);
    }
  }

  private changefeed_query(opts): void {
    opts.changes = false;
    this.client.query(opts);
  }

  public query_cancel(_): void {
    // no op since no changefeed.
    this.client.removeListener("connected", this.emit_connected);
    this.client.removeListener("signed_in", this.emit_signed_in);
  }

  public alert_message(opts): void {
    if (this.client.alert_message != null) {
      this.client.alert_message(opts);
    }
  }

  is_deleted = (_path: string, _project_id: string) => {
    // not implemented yet in general
    return undefined;
  };
}