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 IWriteAndTransformFunction<T, rT> {
  (chunkArg: T, toolsArg: IStreamTools): Promise<rT>;
}

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

export interface SmartStreamOptions<TInput, TOutput> extends DuplexOptions {
  readFunction?: () => Promise<void>;
  writeAndTransformFunction?: IWriteAndTransformFunction<TInput, TOutput>;
  finalFunction?: IStreamEndFunction<TOutput>;
  // Add other custom options if necessary
}

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

  static fromObservable(
    observable: plugins.smartrx.rxjs.Observable<any>,
    options?: DuplexOptions
  ): SmartDuplex {
    const smartStream = new SmartDuplex(options);
    smartStream.observableSubscription = observable.subscribe({
      next: (data) => {
        if (!smartStream.push(data)) {
          // 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 writeFunction?: IWriteAndTransformFunction<TInput, TOutput>;
  private finalFunction?: IStreamEndFunction<TOutput>;
  private observableSubscription?: plugins.smartrx.rxjs.Subscription;

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

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

  // 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) {
        if (!this.push(modifiedChunk)) {
          // Handle backpressure if necessary
        }
      }
      callback();
    } catch (err) {
      callback(err);
    }
  }

  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();
  }
}