ACRSpace – Multi-Tenant SaaS Inventory, POS & Billing Platform
Built at Param Divya
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Tech Stack
Architected and engineered an enterprise-grade multi-tenant, multi-warehouse B2B SaaS platform powering point-of-sale (POS), procurement, inventory control, automated billing, and ledger accounting with strict organization-level data isolation.
Key Impact & Engineering
- Architected a 'Two-Lock Door' authorization engine decoupling Subscription Entitlements (Limit Engine) from Enterprise RBAC across 50+ protected REST API routes with sub-millisecond permission checks and zero-downtime instant revocation.
- Cut API latency from 7s–9s to 300–800ms (and repeat lookups to 1–20ms) using a dual-layer waterfall cache (L1 In-Memory LRU <1ms + L2 Remote Redis) backed by a Promise Coalescing Stampede Shield preventing thundering herd database overload.
- Engineered multi-warehouse stock management featuring O(1) embedded warehouseStocks arrays with atomic MongoDB arrayFilters, x-warehouse-id header context, and automated plan-based location quota guards (WarehouseQuotaGuard).
- Engineered an append-only immutable StockMovement accounting ledger tracking Purchase, Sale, Return, Adjustment, and Multi-Warehouse Transfer operations with zero-ghost immutability.
- Built an ACID-compliant POS checkout & revision pipeline using MongoDB $session transactions for split payments, atomic stock deductions, and strict bounds checking preventing overselling.
- Integrated Razorpay subscription billing with a deterministic state machine, HMAC-SHA256 webhooks, automated PDF invoice generation, and an institutional Tally Prime XML export engine for CPA balance-sheet reconciliation.
- Designed a direct-to-cloud media upload pipeline using HMAC-SHA1 signatures and client-side HTML5 canvas interception, compressing 5MB smartphone photos down to ~150KB WebP assets before transit.
- Developed real-time cross-device & tab synchronization via browser BroadcastChannel API and tab-visibility heartbeat polling (/api/v1/sync/version), eliminating stale state without hard refreshes.
- Built serverless background worker queues and cron endpoints for Redis Audit Log Flushing, Subscription Expiration Sweeping (with Redis mutex locks), and Nightly MongoDB Aggregation Usage Reconciliation.
- Engineered an automated Fraud & Anti-Abuse engine featuring O(1) Redis Token Bucket velocity tracking, disposable email domain filtering, and a Mongoose Change Data Capture (CDC) audit system pushing pre-mutation snapshots to a Redis Outbox (batch-processed at 1,000 logs/batch).