smartstream/ts/smartstream.classes.smartduplex.ts

import * as plugins from './smartstream.plugins.js';
import { Duplex, type DuplexOptions } from 'stream';

export interface IStreamTools {
  truncate: () => void;
  push: (pipeObject: any) => void;
}

export interface IStreamWriteFunction<T, rT> {
  (chunkArg: T, toolsArg: IStreamTools): Promise<rT>;
}

export interface IStreamFinalFunction<rT> {
  (toolsArg: IStreamTools): Promise<rT>;
}

export interface ISmartDuplexOptions<TInput, TOutput> extends DuplexOptions {
  handleBackpressure?: boolean;
  readFunction?: () => Promise<void>;
  writeFunction?: IStreamWriteFunction<TInput, TOutput>;
  finalFunction?: IStreamFinalFunction<TOutput>;
  // Add other custom options if necessary
}

export class SmartDuplex<TInput = any, TOutput = any> extends Duplex {
  // STATIC
  static fromBuffer(buffer: Buffer, options?: ISmartDuplexOptions<any, any>): SmartDuplex {
    const smartDuplex = new SmartDuplex(options);
    process.nextTick(() => {
      smartDuplex.push(buffer);
      smartDuplex.push(null); // Signal the end of the data
    });
    return smartDuplex;
  }

  static fromObservable(
    observable: plugins.smartrx.rxjs.Observable<any>,
    options?: ISmartDuplexOptions<any, any>
  ): SmartDuplex {
    const smartStream = new SmartDuplex(options);
    smartStream.observableSubscription = observable.subscribe({
      next: (data) => {
        if (!smartStream.push(data) && smartStream.handleBackpressure) {
          // Pause the observable if the stream buffer is full
          smartStream.observableSubscription?.unsubscribe();
          smartStream.once('drain', () => {
            // Resume the observable when the stream buffer is drained
            smartStream.observableSubscription?.unsubscribe();
            smartStream.observableSubscription = observable.subscribe((data) => {
              smartStream.push(data);
            });
          });
        }
      },
      error: (err) => {
        smartStream.emit('error', err);
      },
      complete: () => {
        smartStream.push(null); // Signal the end of the data
      },
    });

    return smartStream;
  }

  static fromReplaySubject(
    replaySubject: plugins.smartrx.rxjs.ReplaySubject<any>,
    options?: DuplexOptions
  ): SmartDuplex {
    const smartStream = new SmartDuplex(options);
    let isBackpressured = false;

    // Subscribe to the ReplaySubject
    const subscription = replaySubject.subscribe({
      next: (data) => {
        const canPush = smartStream.push(data);
        if (!canPush) {
          // If push returns false, pause the subscription because of backpressure
          isBackpressured = true;
          subscription.unsubscribe();
        }
      },
      error: (err) => {
        smartStream.emit('error', err);
      },
      complete: () => {
        smartStream.push(null); // End the stream when the ReplaySubject completes
      },
    });

    // Listen for 'drain' event to resume the subscription if it was paused
    smartStream.on('drain', () => {
      if (isBackpressured) {
        isBackpressured = false;
        // Resubscribe to the ReplaySubject since we previously paused
        smartStream.observableSubscription = replaySubject.subscribe({
          next: (data) => {
            if (!smartStream.push(data)) {
              smartStream.observableSubscription?.unsubscribe();
              isBackpressured = true;
            }
          },
          // No need to repeat error and complete handling here because it's already set up above
        });
      }
    });

    return smartStream;
  }

  // INSTANCE
  private readFunction?: () => Promise<void>;
  private handleBackpressure: boolean;
  private writeFunction?: IStreamWriteFunction<TInput, TOutput>;
  private finalFunction?: IStreamFinalFunction<TOutput>;
  private observableSubscription?: plugins.smartrx.rxjs.Subscription;

  constructor(optionsArg?: ISmartDuplexOptions<TInput, TOutput>) {
    super(optionsArg);
    this.readFunction = optionsArg?.readFunction;
    this.writeFunction = optionsArg?.writeFunction;
    this.finalFunction = optionsArg?.finalFunction;
    this.handleBackpressure = optionsArg?.handleBackpressure ?? true;
  }

  public async _read(size: number): Promise<void> {
    if (this.readFunction) {
      await this.readFunction();
    }
  }

  public notBackpressured = true;
  public get backpressured(): boolean {
    return !this.notBackpressured;
  }
  public push(chunkArg?: TOutput | null): boolean {
    const result = super.push(chunkArg);
    if (!result && this.handleBackpressure) {
      this.notBackpressured = false;
      this.pause();
      // Listen for 'drain' event to resume
      this.once('drain', () => {
        this.notBackpressured = true;
        this.resume(); // Resume the source of data
      });
    }
    return result;
  }

  // Ensure the _write method types the chunk as TInput and encodes TOutput
  public async _write(chunk: TInput, encoding: string, callback: (error?: Error | null) => void) {
    if (!this.writeFunction) {
      return callback(new Error('No stream function provided'));
    }

    const tools: IStreamTools = {
      truncate: () => {
        this.push(null);
        callback();
      },
      push: (pushArg: TOutput) => this.push(pushArg),
    };

    try {
      const modifiedChunk = await this.writeFunction(chunk, tools);
      if (modifiedChunk) {
        this.push(modifiedChunk)
        if (this.backpressured && this.handleBackpressure) {
          this.once('drain', () => {
            callback();
          });
        } else {
          callback();
        }      
      } else {
        callback();
      }
    } catch (err) {
      callback(err);
    }
    return this.notBackpressured;
  }

  public async _final(callback: (error?: Error | null) => void) {
    if (this.finalFunction) {
      const tools: IStreamTools = {
        truncate: () => callback(),
        push: (pipeObject) => this.push(pipeObject),
      };

      try {
        const finalChunk = await this.finalFunction(tools);
        if (finalChunk) {
          this.push(finalChunk);
        }
      } catch (err) {
        callback(err);
      }
    } else {
      // nothing here
    }
    this.push(null);
    callback();
  }
}