Job Title: NestJS Backend Developer – High-Performance Car Bulk Import (ETL) The Challenge We are looking for a senior-level NestJS developer to build a robust, production-ready car data import engine for our vehicle marketplace. This isn't a simple "upload and save" task; we require a sophisticated streaming pipeline capable of processing massive datasets (CSV, XML, JSON) with minimal memory footprint and high reliability. Core Task Build a POST /imports/cars endpoint that: Automatic Format Detection: Handles multipart/form-data and identifies the file type (CSV, XML, or JSON) programmatically. Stream-Based Processing: Processes data using Node.js Streams / AsyncIterables. The application should never load the full file into RAM. Data Pipeline: Implements a clean Parse → Validate/Normalize → Map → Persist flow. Smart Idempotency: Ensures no duplicate vehicle records are created on re-imports (e.g., via unique VIN hashing or business-key indexing). Atomic Feedback: Returns a structured summary (total processed, success count, and a detailed array of failed rows with specific validation errors). Technical Stack & Requirements Framework: NestJS (TypeScript in Strict Mode). Architecture: Clean, SOLID principles; logic must reside in dedicated Services/Providers, keeping Controllers thin. Validation: Heavy usage of DTOs with class-validator. We are open to Zod for complex runtime schema enforcement within the stream. Streaming Tools: * CSV: csv-parser or fast-csv. XML: fast-xml-parser (streaming mode). JSON: stream-json. Database: MongoDB via Mongoose. Reliability: Proper backpressure handling and error boundaries to ensure one corrupt row doesn't crash the entire import process. Performance & Quality (Nice-to-Have) Progress Tracking: Experience with WebSockets (Socket.io) or Redis-based status tracking for long-running imports. Testing: High coverage with Jest (specifically unit tests for the mapping logic and integration tests for the stream). Cloud: Experience staging large files in AWS S3 before processing. What We Offer A highly focused, well-defined technical task. Clear acceptance criteria and a "no-fluff" development environment. Potential for ongoing collaboration on our core platform. How to Apply We value brevity and technical depth. Please provide: Relevant Experience: A 3-sentence summary of the largest/most complex import system you’ve built. Code Samples: A link to a GitHub repo or Gist showing a NestJS service or a streaming implementation. The "How-To": Briefly outline your strategy for handling backpressure and how you would structure the error-reporting object for a 100,000-row file. Note: Only applicants with demonstrated experience in NestJS and Node.js Streams will be considered.