SHOPIFY INVENTORY SYNC APP ARCHITECTURE

APP SETUP (shopify.app.toml)
→ Scopes: write_inventory,read_inventory,write_products,webhook
→ OAuth redirect: https://inventory-sync-app.example.com/auth/callback
→ API version: 2024-07

WEBHOOK STRUCTURE
→ Topic: inventory_levels/update (triggers on stock change)
→ Batching: Groups updates into 50-item batches (rate limit: 2 calls/second)
→ Retry logic: Exponential backoff 60/120/300 seconds (drop after 3 failures)
→ Dead letter queue: Failed syncs logged to Postgres for manual review

SYNC WORKFLOW
1. Warehouse system POSTs inventory delta to sync-app endpoint
2. App validates request signature (HMAC-SHA256)
3. Transforms warehouse SKU → Shopify variant ID (via mapping table)
4. Batch updates via Shopify GraphQL (updateProductVariants mutation)
5. Logs audit trail: warehouse_qty → shopify_qty, timestamp, user
6. Webhook fires: inventory_levels/update (notifies Shopify subscribers)

CONFLICT RESOLUTION
→ Shopify is source of truth during sales (prevents oversell)
→ Warehouse update is applied only if shopify_inventory > 0
→ Tie-breaker: Last-write-wins with 5-second debounce
→ Mismatch alert: Email if delta exceeds 10% of warehouse count

TESTING
→ Shopify CLI: shopify app dev (localhost:3000)
→ Mock webhooks via CLI: shopify webhooks trigger inventory_levels/update
→ Load test: 10k inventory updates in 10 seconds (verify batching + rate limits)

DEPLOYMENT
→ Environment: Node.js 20 + Express on Vercel
→ Database: Postgres for mappings, audit trail
→ Monitoring: Sentry for error tracking, DataDog for webhook latency
→ Production first sync: Runs incrementally over 24 hours (avoids rate limit burst)