BUILD WITHATHAR
I architect production-grade SaaS systems end-to-end — from monorepo design and config-driven rendering engines to multi-tenant DNS automation, AI/RAG pipelines, and self-hosted captcha infrastructure. Solo lead on nine platforms in five years.
Engineers who ship entire products.
Senior Full-Stack Engineer with 5 years of experience architecting and building production-grade SaaS platforms from scratch — spanning real-time communication systems, AI/RAG pipelines, no-code website builders with automated DNS infrastructure, security/captcha infrastructure, AI chatbot services, embeddable developer tooling, and internal enterprise tooling (CRM, HRMS, Financial systems). Proven ability to own entire product surfaces end-to-end: from system architecture and monorepo design to cloud infrastructure provisioning, multi-tenancy, and payment integrations.
Practitioner of AI-augmented engineering — leverages Claude Code and AI agent workflows as a force multiplier to architect and ship systems that would traditionally require larger teams. Uses AI not as a code generator but as a collaborative engineering layer: breaking down complex system designs, validating architecture decisions, and accelerating delivery of production-grade platforms without compromising depth or quality.
Stack & competencies.
Experience & platforms.
Hashcash Consultants LLC
Sole lead developer responsible for designing and shipping nine production platforms from zero — real-time communication, AI knowledge retrieval, no-code publishing, security/captcha infrastructure, AI chatbots, embeddable developer tooling, CRM, HRMS, and financial reporting.
- Architected a full no-code website builder with a Studio editor and a separate generic rendering engine, enabling users to visually build, publish, and host websites end-to-end.
- Designed a section registry pattern — a shared component runtime across editor and renderer — so the same section definitions power both live preview and production render.
- Implemented config-driven pages: page structure, sections, and layout stored as JSON, consumed by a generic SSR/CSR hybrid renderer supporting both server-side and client-side data fetching per section.
- Built an undo/redo editor state engine and real-time preview system, giving users a WYSIWYG experience with full state reversibility.
- Engineered a theme variable abstraction layer supporting dynamic theming across all published sites without CSS duplication.
- Automated the full domain lifecycle: availability check → registrar purchase → AWS Route53 records → SSL provisioning → site deployment — all triggered from the UI.
- Designed a multi-tenant DNS architecture with per-tenant subdomain isolation, custom-domain CNAME mapping, and middleware-driven request routing.
- Integrated PayPal Subscriptions + Webhooks for plan management with idempotent webhook processing across activation, cancellation, and renewal events.
- Structured the codebase as a Turborepo monorepo with shared packages: UI library, section definitions, config schemas, and cross-environment SSR-safe utilities.
- Architected a Slack-like internal communication platform supporting real-time messaging, channels, threads, and presence indicators via Socket.io.
- Initially built P2P audio/video calling using raw WebRTC with Google STUN for NAT traversal; identified scalability limits for group calls and migrated to LiveKit — an open-source WebRTC SFU — for multi-participant calls with lower client-side media load.
- Integrated LiveKit rooms, participant tracks, and server-side room management APIs to handle dynamic join/leave, audio/video publishing, and subscriber management.
- Designed the real-time event model — message delivery, read receipts, typing indicators, online/offline state — with fault-tolerant Socket.io room management.
- Built a multi-tenant Retrieval-Augmented Generation (RAG) platform where each tenant configures a private knowledge base, accessible via an embedded chatbot widget.
- Designed the ingestion pipeline: web crawler → HTML parser → text chunker → OpenAI text-embedding-3-small → vector storage in MongoDB Atlas M10 (vector search cluster), with per-tenant namespace isolation.
- Implemented semantic retrieval: query embedding → Atlas Vector Search → top-K context retrieval → GPT-4 prompt assembly → response with cited source links.
- Architected multi-tenancy at the data layer: tenant-scoped vector collections, API key auth per tenant, and usage tracking for plan enforcement.
- Built a production AI chatbot backend that answers strictly Paybito-related questions using OpenAI ChatGPT, hard-wired to refuse off-topic and code-generation requests through deliberate system prompt design.
- Designed the data layer around a structured PayBito JSON knowledge base, injected as context into every chat completion — keeping responses grounded and reducing hallucination on pricing, plans, and product features.
- Implemented production hygiene: per-endpoint rate limits (50/15min on /api/ask vs 100/15min on read endpoints), input validation/sanitization, structured Winston logging, and dedicated health and data-verification endpoints.
- Architected a clean services / controllers / middleware split so the model layer (chatService) is swappable independently from the data loader (dataService) — enabling future model upgrades without touching business logic.
- Built a self-hosted, Paybito-branded captcha service to replace a leaky npm slider-captcha package — moving all puzzle state server-side so positions and salts never reach the client, eliminating client-side forgery.
- Implemented a Cloudflare Turnstile / hCaptcha-compatible integration surface: customer apps embed a script tag; customer backends call POST /v1/siteverify with secret + token — a drop-in shape any team already familiar with reCAPTCHA can adopt without retraining.
- Designed the token lifecycle as JWT issue + atomic single-use consume against Redis, so a verification token can only be exchanged once even under race conditions.
- Architected an iframe-based challenge UI: only the iframe ever talks to /v1/internal/{generate,solve}; the loader on the host page never sees puzzle state — preventing reverse-engineering through DevTools.
- Layered defense: origin enforcement against per-site allowed_origins, IP allowlists, per-site rate limits, and pluggable abuse rules. MySQL for sites/audit/abuse, Redis for sessions/tokens.
- Built an internal admin dashboard for managing customer apps, sitekeys, secrets, abuse rules, and usage metrics, with full audit logging.
- Architected a multi-tenant feedback collection service where any client app drops in a ~10KB JS widget via a single script tag and routes feedback/bug reports into a central triage dashboard.
- Designed a dual-auth architecture: x-feedback-app-key header for public widget submissions (per-application keys, no user login required), JWT in httpOnly cookies for the dashboard side — keeping the two attack surfaces fully isolated.
- Built the embeddable widget as a standalone ES5 script with no build step or framework — exposes window.FeedbackWidget.{open, close, configure} so host apps control placement entirely.
- Implemented per-app status workflows (new → open → in_progress → resolved / wont_fix), type filters (feedback / bug / suggestion / other), full-text search, and per-application stats for dashboard cards.
- Set up an idempotent SQL migration runner with a _migrations tracking table — safe to re-run, no destructive sync.
- Stack: Node.js + Express, MySQL 8 (mysql2 pool), EJS + Tailwind CDN, bcryptjs, JWT cookie auth, single-process deploy.
- Designed and built a full CRM from scratch covering lead pipeline, deal stages, contact management, activity tracking, and sales reporting dashboards.
- Implemented role-based access control (RBAC), multi-stage pipeline views, and automated follow-up task creation on deal state transitions.
- Built a full-featured HRMS covering employee onboarding, attendance tracking, leave management, payroll calculation, and organizational hierarchy.
- Implemented an approval-workflow engine for leave requests and integrated with the financial reporting layer for payroll output.
- Engineered a dynamic Profit & Loss system that aggregates financial data across departments and produces configurable P&L statements, cost-center breakdowns, and trend reports in real time.
- Built the formula engine for dynamic line-item computation and export pipelines for management reporting.
Architecture highlights.
Monorepo + Turborepo
Structured multi-product codebases with shared packages, incremental builds, and cross-package type safety — enabling reuse across editor, renderer, and API layers without coupling.
Generic Rendering Engine
A config-driven, section-agnostic engine that consumes a page JSON schema and dynamically resolves registered section components — SSR, CSR, and hybrid data fetching per section.
Domain Lifecycle State Machine
Modeled domain provisioning as an explicit state machine — available → purchased → DNS configured → SSL issued → deployed → active — with automated transitions and rollback handling.
Multi-tenant Middleware
Request-time tenant resolution via subdomain / custom-domain matching, injecting tenant context into downstream handlers without per-route tenant checks.
WebRTC → LiveKit Migration
Evolved BitoLink calling from raw WebRTC P2P (STUN) to a LiveKit SFU — unlocking scalable multi-party calls, server-side track routing, and reduced client bandwidth.
RAG Ingestion Pipeline
An async, queue-based ingestion pipeline supporting large site crawls with retry logic, duplicate URL detection, chunk-overlap tuning, and per-tenant embedding namespacing.
Captcha Token Lifecycle
Designed JWT issue + atomic single-use consume against Redis so a verification token can only be exchanged once even under race conditions — server-side puzzle state, iframe-isolated UI.
Embeddable Widget Pattern
Standalone ES5 widgets (Feedback Central, captcha loader, RAG chatbot) with zero build step — host apps drop in a script tag, widget posts to a dual-auth API surface.
Editor State Engine
Command-pattern undo/redo for the website builder editor — granular reversibility of section edits, reordering, style changes, and content updates.
AI-Augmented Engineering
Claude Code and AI agent workflows as a collaborative layer across system design, validation, and implementation — enabling solo delivery of platform-scale systems.
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Available for senior full-stack, platform engineering, and staff-level roles. Avg reply: under 24h.