| 🎯 Focus | 🏗️ Architecture | 🤖 AI Integration | 🧪 Testing |
|---|---|---|---|
| Full-Stack Development | Multi-Tenant Systems | OpenAI GPT-4 | 100% Test Coverage |
| Enterprise Solutions | Real-time Features | Realtime API | E2E Testing |
| Polish Language Learning | Secure API Gateway | Stream Chat | TypeScript |
I am a Full-Stack Developer specializing in enterprise AI solutions and multi-tenant applications.
🎯 My Expertise:
- Modern Web Technologies - Next.js 16, React 19, TypeScript 5.9
- AI Integration - OpenAI GPT-4, Realtime API, Whisper, TTS, custom prompts
- Enterprise Architecture - Multi-tenant systems, secure APIs, payment processing
- Polish Language Learning - Combined technical & linguistic expertise with 20+ interactive learning modules
🚀 Current Project: PoliLex - A sophisticated AI-powered language learning platform demonstrating enterprise-level architecture, multi-tenancy, real-time AI integration, and production-ready DevOps practices.
Polish language learning platform with sophisticated full-stack architecture
Production-grade Stripe integration built with financial software engineering standards
A payment system engineered for correctness, security, and reliability—where money is involved, there's zero tolerance for bugs.
| Component | Responsibility | Design Pattern |
|---|---|---|
| Stripe Client Singleton | Centralized SDK configuration | Singleton with API version pinning |
| Error Handling Layer | Standardized error classification | Custom error types with user-safe messages |
| Retry Logic | Transient failure recovery | Exponential backoff with jitter |
| Idempotency Service | Duplicate operation prevention | Deterministic key generation |
| Webhook Handler | Asynchronous event processing | Event-driven with idempotency |
| Token Balance Calculator | Subscription credit management | Pure function with state preservation |
- Idempotency Guarantees — All Stripe API calls use deterministic idempotency keys (SHA-256 hashed from operation type, user ID, and relevant data) ensuring safe retries without duplicate charges
- Webhook Idempotency — Dual-layer event deduplication using in-memory cache (O(1) lookup) with database persistence for cross-restart consistency
- Fail-Open Design — Idempotency database checks fail-open to prevent blocking legitimate transactions during transient DB issues
- Token Balance Preservation — Subscription changes preserve top-up tokens using pure calculation:
newBalance = newCredits + max(0, currentBalance - oldCredits)
- Signature Verification — All webhook payloads verified against HMAC signatures before processing
- Price ID Validation — Two-layer validation: Zod schema format check + business logic allowlist verification
- User Authentication — Server actions enforce Clerk authentication with automatic sign-in redirects
- No Internal Secrets Exposed — User-facing error messages sanitized through dedicated
getUserErrorMessage()function
┌─────────────────────────────────────────────────────────────┐
│ Retry Strategy: Exponential Backoff with Jitter │
├─────────────────────────────────────────────────────────────┤
│ Attempt 0: baseDelay × 2⁰ = 1000ms + jitter (0-10%) │
│ Attempt 1: baseDelay × 2¹ = 2000ms + jitter (0-10%) │
│ Attempt 2: baseDelay × 2² = 4000ms + jitter (0-10%) │
│ Max Delay: Capped at configurable ceiling │
├─────────────────────────────────────────────────────────────┤
│ Retryable: 5xx errors, 429 rate limits, network timeouts │
│ Non-Retryable: 4xx client errors (card declined, invalid) │
└─────────────────────────────────────────────────────────────┘
| Event Type | Handler Action |
|---|---|
customer.subscription.created |
Allocate tier credits, set plan ID, sync Clerk metadata |
customer.subscription.updated |
Recalculate balance preserving top-ups, update tier |
customer.subscription.deleted |
Downgrade to free tier, clear subscription fields |
invoice.payment_succeeded |
Reset subscription credits on renewal, preserve top-ups |
invoice.payment_failed |
Update payment failure status, manage grace period |
checkout.session.completed |
Process one-time top-up purchases, increment balance |
- 100% Test Coverage — 177 tests covering all Stripe-related code paths
- External API Mocking Only — Tests mock Stripe SDK, Prisma, and Clerk, but execute all internal business logic with real implementations
- Financial Software Standards — Zero tolerance for test failures; all edge cases and error paths verified
- Concurrent Processing Tests — Race condition and duplicate event handling validated
- Single Source of Truth —
tokenBalancefield is authoritative; no derived calculations in business logic - Tier-Based Allocation — Credits mapped from price IDs via environment-configured lookup table
- Top-Up Preservation — One-time purchases survive subscription changes through stateless balance calculation
- Transaction Audit Trail — All balance mutations recorded with Stripe event IDs for reconciliation
| Category | Technology / Tools | Purpose |
|---|---|---|
| Frontend | Next.js 16, React 19 | Core application shell and interactive UI |
| TypeScript 5.9 | Type-safe client-side development | |
| Tailwind CSS 4, ShadCN | Design system, layout, and reusable UI components | |
| Lexical Editor, Framer Motion | Rich authoring experience and high-quality motion | |
| Backend & Infrastructure | Prisma 7, PostgreSQL, Supabase | Type-safe data access and relational persistence |
| Clerk Auth, Stripe, Stream Chat, Redis | Authentication, payments, real-time messaging, cache | |
| Testing & Quality | Jest, React Testing Library | Unit and integration coverage for components & logic |
| Playwright | End-to-end browser regression on critical journeys | |
| k6, Artillery | Load and performance validation for APIs and flows | |
| TypeScript (strict), Prisma, Zod, @t3-oss/env-nextjs | Static typing and schema validation across the stack | |
| ESLint, Prettier, import-sorting plugins | Automated linting, formatting, and code consistency | |
| AI & Integrations | OpenAI GPT-4, DALL-E 3 | Language processing and image generation |
| OpenAI Realtime API, Whisper API, OpenAI TTS | Real-time voice, speech-to-text, and text-to-speech | |
| Stream Chat | Real-time chat and collaboration |
- Authentication & Database Integration - Sophisticated user management with role-based access control
- Company portals with isolated data and secure tenant boundaries
- Multi-Organization Support - Seamless switching between different company portals
- Permission Management - Granular access control for teachers, students, and admins
- Data Isolation - Company-specific data segregation with secure tenant boundaries
- Zuplo API Gateway - Secure API management, rate limiting, and enterprise-grade security
- Enterprise Security - Role-based access control & secure authentication
- Performance Optimized - SSR, edge caching, optimized database queries
- Comprehensive Testing - Unit, integration, and E2E test coverage
- GPT-4 Integration - Personalized instruction and content generation
- OpenAI Realtime API - Voice conversations with real-time streaming responses
- Whisper API - Audio transcription for podcasts and video content
- Text-to-Speech (TTS) - AI-generated audio pronunciation
- Stream Chat - Real-time messaging with AI assistance
- Custom AI Prompts - Specialized language learning prompts and instructions
Grammar Labs:
- Aspect Master - Verb aspect practice with quizzes, challenges, and timeline visualization
- Reflexive Lab - Reflexive verb journeys with categories and templates
- Preposition Lab - Interactive preposition challenges with case governance
- Motion Lab - Verbs of motion (unidirectional/multidirectional pairs)
- Verb Prefixes - Perfective prefix forms and transformations
- Conjugator - Interactive Kanban board for verb conjugation practice
Vocabulary & Practice:
- Counting - Grammatical cases through counting 1-21 with contextual examples
- Adjectives - Comparative forms and interactive exercises
- Adverbs - Comparative and superlative forms practice
- Nouns - Auto-generated flashcards with translations
- Occupations - 5 interactive games (Flashcards, Quiz, Memory, Drag & Drop, Sentence Builder)
- Word Wizard - AI-assisted vocabulary building with audio pronunciation
- Flashcards - Customizable flashcards with example sentences
- Cases - Grammatical case mastery through fill-in-the-blank exercises
- Days & Months - Temporal vocabulary practice
- Genealogy - Interactive family tree drag-and-drop game
Interactive Content:
- Lexical Editor - Rich text editing with collaborative features
- PDF Processing - Document processing and annotation
- Portable Documents - PDF viewer with highlighting capabilities
- Podcasts - Audio content with transcription
- Videos - Video learning with interactive features
- Audio Transcript - Speech-to-text processing
Community & Social:
- Real-time Chat - Stream Chat integration for user communication
- Memory Games - Polish language memory recall activities
- Jira Integration - Project management and task tracking
- Company Portals - Multi-tenant learning environments with blogs, videos, and PDFs
Source of Truth:
- Database-Driven Pricing - Centralized database table serves as the single source of truth for all OpenAI model costs
- Manual Admin Management - Pricing is manually updated by administrators through a secure admin interface (no automated scraping or external API dependencies)
- Performance Optimization - Server-side pricing cached with configurable TTL for optimal performance, with immediate cache invalidation after updates
- Resilience - Fallback pricing values available if database is temporarily unavailable (with appropriate logging and warnings)
Security Practices:
- Defense in Depth - Multi-layer security approach combining application-level authorization checks with database-level access controls
- Row-Level Security - Database policies enforce role-based access control, ensuring only authorized administrators can modify pricing data
- Read Access - Authenticated users can read active pricing information required for cost calculations
- Write Access - Strictly limited to authorized administrators through verified authentication mechanisms
- Secure Initialization - Seed scripts use secure service-level connections for initial data population
- Token-Based Authorization - Admin privileges verified through secure token claims validated at both application and database layers
- Rich Text Editing - Full-featured Lexical editor with markdown support, tables, lists, and formatting
- YouTube Integration - Embed YouTube videos directly in editor content with resizable player controls
- Audio/Podcast Integration - Seamless audio embedding with Supabase storage integration
- Audio playback controls with custom player interface
- Podcast image support with signed URL generation
- Audio transcription workflow integration
- Video Content Creation - Link videos to editor content for bilingual text generation
- Speech-to-Text - Built-in speech recognition plugin for voice input
- Auto-Embed Plugin - Automatic detection and embedding of YouTube URLs
- Collaborative Features - Real-time editing capabilities with history tracking
- Export Capabilities - Export editor content to blog posts and learning materials
- Dedicated Company Portals - Isolated multi-tenant environments for each teaching organization
- Blog Management System - Full-featured blog with Lexical editor integration
- Rich text blog posts with embedded media
- Tag-based categorization and filtering
- Comments and reactions system
- Nested comment threads with real-time updates
- Author profiles and post attribution
- Draft and published post status management
- Video Library Management - Comprehensive video content system
- YouTube video integration with metadata
- Difficulty level categorization (A1-C2)
- Category organization (Grammar, Vocabulary, Pronunciation, etc.)
- Bilingual text support (Polish/English)
- Video transcription and summaries
- Thumbnail and duration tracking
- Publishing workflow
- Resource Management - Centralized content hub
- PDF document management
- Resource organization by company
- Access control and permissions
- Dashboard Analytics - Company-specific insights and user management
- Multi-User Support - Role-based access for teachers, admins, and students
- Tenant Isolation - Secure data segregation between different companies
PoliLex is validated with a full testing pipeline that combines automated tests, static analysis, and load testing.
Every change is validated through:
- Automated unit and integration suites using Jest and React Testing Library for components and business logic
- End-to-end regression tests with Playwright for critical user journeys in the browser
- Load and performance exercises with k6 and Artillery focused on core APIs, server-side operations, and caching behavior
- Strict static typing and schema validation with TypeScript (strict mode), Prisma, Zod, and @t3-oss/env-nextjs for data, inputs, and configuration
- Automated linting and formatting with ESLint, Prettier, and import-sorting to enforce consistent, production-grade code quality
| Education | Training | Specialization |
| Boolean UK Graduate Full-stack development fundamentals |
JS Mastery Graduate (Feb 2024) - Advanced React & Next.js Masterclass |
Polish Language Enthusiast Combined technical expertise with language learning |
💡 Always learning, always building. Currently exploring advanced AI integration and enterprise-scale applications.