MYKOLA KOVALCHUK

Led development of a GenAI B2C e-commerce platform (customer app in Next.js, admin/back office in Angular, API in NestJS). Built a multi-provider payment layer using Adapter/Facade/Strategy (Stripe + Shopify) with webhook-driven order processing, enabling new providers without touching checkout logic. Implemented a config-driven funnel engine supporting multiple purchase funnels and partner channels with fast campaign iteration. Shipped frictionless onboarding (account created from payment email, OTP login across web/mobile, and duplicate account merge in a MongoDB transaction). Ran recurring billing for subscriptions via Stripe webhooks and cron-driven reminders, added upsell checkouts, made print rendering idempotent, moved PDF rendering to BullMQ with job recovery, and load-tested the end-to-end purchase funnel with k6.

Built and launched a Telegram Mini App iGaming product with 5 instant-win scratch-card games, integrating Telegram Stars deposits and TON withdrawals. Developed a configurable PixiJS scratch-card rendering engine (RenderTexture masks, alpha reveal thresholds, synchronized Spine win animations and sound), enabling new games to be created from configuration rather than new code. Implemented server-side purchase validation and a player wallet with Stars/transfer top-ups, address-validated TON withdrawals, and transaction/game history. Added geo-restriction handling, referral/deep-link codes, and optimized rendering for ~60 FPS inside Telegram WebView on iOS/Android/desktop.

Developed a browser-based trading terminal (FinTech) with real-time widgets and multi-broker trading across crypto, stocks, and forex. Reworked a market scanner to update thousands of instruments efficiently (one redraw per second instead of per tick) using virtual scrolling and batched updates. Offloaded Excel export into Web Workers with OffscreenCanvas charts to eliminate multi-second UI freezes for large datasets. Built a broker abstraction (Adapter/Strategy) and integrated multiple brokers/data providers behind a unified UI, while owning frontend architecture, releases, and mentorship in a small team.