Vũ Văn Hải

TypeScript, Express 5, PostgreSQL, Drizzle ORM, React 19, TanStack, Vercel AI SDK, Docker

• Designed and built the entire backend of a live CRM and course-commerce platform (200+ endpoints, 45 tables, 18 cron jobs) plus a 25-screen admin CRM; serves the sales and accounting teams, the CES Academy digital library and ~12 landing pages.
• Automated the full order lifecycle from bank transfer to legal invoice: SePay gateway (auto-reconciling webhooks, duplicate protection, a 24-hour revival window for late settlements) and MISA meInvoice e-invoices issued right after payment with 3 deduplication layers, reconciling exactly to the amount paid.
• Built an AI assistant that reads live CRM data for the operations team on the Vercel AI SDK: an agent loop with 18 read-only tools, every calculation done in SQL so the model never invents numbers, streamed answers with a per-step lookup trace; passed 4 rounds of adversarial review before merge.
• Shipped a daily "AI insights" panel on the dashboard: 10 SQL detectors surface findings (abnormal course cancellations, repeat buyers, optimal re-contact window, traffic sources with zero conversions...), the LLM only phrases them and every number in its sentence is machine-checked; each card links straight to the filtered list.
• Run marketing email to 11,000+ recipients on a DB-configured cron engine that sends in batches behind a circuit breaker; plus ~113 operations scripts (bank reconciliation, payment rescue, bulk import) that are idempotent and dry-run by default.

TypeScript, Hono 4, PostgreSQL, Drizzle ORM, BullMQ/Redis, Next.js 16, Zalo Mini App SDK

• Built the entire backend of a live platform (264 endpoints, 50 tables, 38 business modules, 6 background queues) serving the customer web app, internal CRM and Zalo Mini App at once - and delivered the Mini App end to end solo.
• Designed a tamper-evident audit log to accounting-record standards: HMAC-SHA-256 hash chain in PostgreSQL triggers, append-only enforced at the role level, a chain verification endpoint, and 3-tier retention ending in 10-year write-locked object storage.
• Resolved all concurrency conflicts without pessimistic locks: compare-and-swap via conditional UPDATE, partial unique indexes as business locks, atomic ceilings in WHERE; a 6-layer payment webhook sharing one commit path with manual confirmation.
• Modeled the pricing system: multi-rate VAT computed per tax bucket with DB-level CHECK constraints, 2-tier stacked promotions, and 3-stage price snapshots so order history never changes when configuration does; snapshot-based affiliate commissions.
• Built one auth layer for three clients with three token postures (httpOnly cookie, Bearer, Bearer + persisted session): refresh-token rotation with reuse detection and a 10-second grace window for multi-tab use, and client IP derived from the TCP peer address plus a CIDR allowlist so forged headers cannot poison the audit log or alerting.

C#, ASP.NET (.NET Framework), SQL Server, JavaScript

• Developed and maintained business web modules on an ASP.NET (.NET Framework) + SQL Server system serving enterprise customers, working directly in a legacy codebase.
• Wrote complex SQL queries and data-layer logic that reduced data inconsistencies; partnered with QA and business teams to analyze requirements, troubleshoot data issues and ship fixes to UAT and production.

.NET 8, ASP.NET Core, EF Core, PostgreSQL, SignalR, PayOS, Firebase, Docker, GitHub Actions

• Led 2 backend engineers in a 4-person team building a laundry-service platform for a real business: 5-layer architecture, 28 controllers, 5 user roles, SignalR realtime (chat, complaints, live driver tracking).
• Integrated PayOS (HMAC-SHA256-verified webhooks), Backblaze B2, Mapbox and Firebase push notifications; containerized with Docker and automated CI/CD on GitHub Actions, cutting deploy lead time by 35%.