David Serban

Delivered React and Next.js customer workflows with TypeScript, re-usable UI components, server-rendered views, and typed API integrations to keep navigation and complex forms consistent across features. Built Node.js and Python backend services using Express, Django, and FastAPI patterns (REST contracts, request validation, pagination, error handling, and clear boundaries between business logic and external integrations). Designed PostgreSQL data models and migration paths, profiled slow queries, and applied Redis caching for read-heavy endpoints to maintain responsiveness as datasets grew. Connected reporting screens to SQL-backed REST endpoints (search, sorting, and export) while keeping client query state and backend filtering consistent across releases. Implemented OAuth/JWT-based authentication and role-based authorization for React routes and backend endpoints, enforcing sensitive actions at the API layer. Integrated Kafka-backed async processing and webhook-driven updates with

Built TypeScript and React interfaces for payment operations, including accessible form components, reusable status components, and searchable transaction tables. Translated payment validation errors into actionable inline UI guidance, distinguishing business-rule failures from transient API connectivity errors within transaction flows. Connected operational screens to Java and Node.js backend APIs with validation and idempotent request handling to avoid conflicting payment-state transitions. Maintained backward-compatible API integrations as payload formats evolved, coordinating field mappings and regression scenarios before releases. Integrated asynchronous status updates driven by event-based services, handling Kafka message delays, duplicate callbacks, and out-of-order events while presenting clear pending/completed/failed states in the UI. Worked with SQL-backed transactional queries using server-side filtering, pagination, and consistency requirements to keep detailed payment vie

Developed React-based clinical workflow screens with reusable input components, responsive layouts, and field-level validation to help specialist users understand data-entry errors and incomplete records. Implemented paginated case search and filtering through SQL-backed endpoints with React table state, ensuring sensitive data fields were exposed only to authorized user views. Built Python web APIs for clinical data retrieval and prediction workflows with schema checks, access controls, and explicit response state handling before passing results to interactive interfaces. Modeled relational datasets and SQL transformations for dashboards and case views, checking null values, source consistency, and query behavior prior to exposing derived clinical information. Automated background import/processing jobs with checkpointing and retry handling so interrupted data flows could resume without duplicating completed work. Containerized frontend and backend services using Docker and maintained