server.ts

import { Logger, LoggerService } from '@nestjs/common/services/logger.service';
import { loadPackage } from '@nestjs/common/utils/load-package.util';
import {
  connectable,
  EMPTY,
  from as fromPromise,
  isObservable,
  Observable,
  ObservedValueOf,
  of,
  Subject,
  Subscription,
} from 'rxjs';
import { catchError, finalize } from 'rxjs/operators';
import { NO_EVENT_HANDLER } from '../constants';
import { BaseRpcContext } from '../ctx-host/base-rpc.context';
import { IncomingRequestDeserializer } from '../deserializers/incoming-request.deserializer';
import {
  ClientOptions,
  KafkaOptions,
  MessageHandler,
  MicroserviceOptions,
  MqttOptions,
  MsPattern,
  NatsOptions,
  ReadPacket,
  RedisOptions,
  RmqOptions,
  TcpOptions,
  WritePacket,
} from '../interfaces';
import { ConsumerDeserializer } from '../interfaces/deserializer.interface';
import { ConsumerSerializer } from '../interfaces/serializer.interface';
import { IdentitySerializer } from '../serializers/identity.serializer';
import { transformPatternToRoute } from '../utils';

export abstract class Server {
  protected readonly messageHandlers = new Map<string, MessageHandler>();
  protected readonly logger: LoggerService = new Logger(Server.name);
  protected serializer: ConsumerSerializer;
  protected deserializer: ConsumerDeserializer;

  public addHandler(
    pattern: any,
    callback: MessageHandler,
    isEventHandler = false,
    extras: Record<string, any> = {},
  ) {
    const normalizedPattern = this.normalizePattern(pattern);
    callback.isEventHandler = isEventHandler;
    callback.extras = extras;

    if (this.messageHandlers.has(normalizedPattern) && isEventHandler) {
      const headRef = this.messageHandlers.get(normalizedPattern);
      const getTail = (handler: MessageHandler) =>
        handler?.next ? getTail(handler.next) : handler;

      const tailRef = getTail(headRef);
      tailRef.next = callback;
    } else {
      this.messageHandlers.set(normalizedPattern, callback);
    }
  }

  public getHandlers(): Map<string, MessageHandler> {
    return this.messageHandlers;
  }

  public getHandlerByPattern(pattern: string): MessageHandler | null {
    const route = this.getRouteFromPattern(pattern);
    return this.messageHandlers.has(route)
      ? this.messageHandlers.get(route)
      : null;
  }

  public send(
    stream$: Observable<any>,
    respond: (data: WritePacket) => unknown | Promise<unknown>,
  ): Subscription {
    let dataBuffer: WritePacket[] = null;
    const scheduleOnNextTick = (data: WritePacket) => {
      if (!dataBuffer) {
        dataBuffer = [data];
        process.nextTick(async () => {
          for (const item of dataBuffer) {
            await respond(item);
          }
          dataBuffer = null;
        });
      } else if (!data.isDisposed) {
        dataBuffer = dataBuffer.concat(data);
      } else {
        dataBuffer[dataBuffer.length - 1].isDisposed = data.isDisposed;
      }
    };
    return stream$
      .pipe(
        catchError((err: any) => {
          scheduleOnNextTick({ err });
          return EMPTY;
        }),
        finalize(() => scheduleOnNextTick({ isDisposed: true })),
      )
      .subscribe((response: any) => scheduleOnNextTick({ response }));
  }

  public async handleEvent(
    pattern: string,
    packet: ReadPacket,
    context: BaseRpcContext,
  ): Promise<any> {
    const handler = this.getHandlerByPattern(pattern);
    if (!handler) {
      return this.logger.error(
        `${NO_EVENT_HANDLER} Event pattern: ${JSON.stringify(pattern)}.`,
      );
    }
    const resultOrStream = await handler(packet.data, context);
    if (isObservable(resultOrStream)) {
      const connectableSource = connectable(resultOrStream, {
        connector: () => new Subject(),
        resetOnDisconnect: false,
      });
      connectableSource.connect();
    }
  }

  public transformToObservable<T>(
    resultOrDeferred: Observable<T> | Promise<T>,
  ): Observable<T>;
  public transformToObservable<T>(
    resultOrDeferred: T,
  ): never extends Observable<ObservedValueOf<T>>
    ? Observable<T>
    : Observable<ObservedValueOf<T>>;
  public transformToObservable(resultOrDeferred: any) {
    if (resultOrDeferred instanceof Promise) {
      return fromPromise(resultOrDeferred);
    }

    if (isObservable(resultOrDeferred)) {
      return resultOrDeferred;
    }

    return of(resultOrDeferred);
  }

  public getOptionsProp<
    T extends MicroserviceOptions['options'],
    K extends keyof T,
  >(obj: T, prop: K, defaultValue: T[K] = undefined) {
    return obj && prop in obj ? obj[prop] : defaultValue;
  }

  protected handleError(error: string) {
    this.logger.error(error);
  }

  protected loadPackage<T = any>(
    name: string,
    ctx: string,
    loader?: Function,
  ): T {
    return loadPackage(name, ctx, loader);
  }

  protected initializeSerializer(options: ClientOptions['options']) {
    this.serializer =
      (options &&
        (
          options as
            | RedisOptions['options']
            | NatsOptions['options']
            | MqttOptions['options']
            | TcpOptions['options']
            | RmqOptions['options']
            | KafkaOptions['options']
        ).serializer) ||
      new IdentitySerializer();
  }

  protected initializeDeserializer(options: ClientOptions['options']) {
    this.deserializer =
      (options &&
        (
          options as
            | RedisOptions['options']
            | NatsOptions['options']
            | MqttOptions['options']
            | TcpOptions['options']
            | RmqOptions['options']
            | KafkaOptions['options']
        ).deserializer) ||
      new IncomingRequestDeserializer();
  }

  /**
   * Transforms the server Pattern to valid type and returns a route for him.
   *
   * @param  {string} pattern - server pattern
   * @returns string
   */
  protected getRouteFromPattern(pattern: string): string {
    let validPattern: MsPattern;

    try {
      validPattern = JSON.parse(pattern);
    } catch (error) {
      // Uses a fundamental object (`pattern` variable without any conversion)
      validPattern = pattern;
    }
    return this.normalizePattern(validPattern);
  }

  protected normalizePattern(pattern: MsPattern): string {
    return transformPatternToRoute(pattern);
  }
}