Can I vibe code Gorilla ROI?

Build a lightweight replacement for Gorilla ROI using Python (FastAPI), Redis, and Google Apps Script.

1. SYSTEM ARCHITECTURE:
- Backend: FastAPI microservice deployed to Vercel or Render.
- Database/Cache: Upstash Redis for caching API payloads and token management.
- Frontend: Google Apps Script (GAS) deployed as a Custom Function container in Google Sheets.

2. BACKEND API ENGINE (Python):
- Use `python-amazon-sp-api` library to connect to Amazon Selling Partner API.
- Implement OAuth LWA (Login with Amazon) refresh token handling. Store refresh tokens securely in environment variables.
- Create endpoints:
  a) `GET /api/sales?sku={sku}&startDate={start}&endDate={end}`: Fetches sales summary for given SKU(s).
  b) `GET /api/inventory?sku={sku}`: Fetches current sellable, reserved, and inbound units.
  c) `GET /api/fees?sku={sku}`: Fetches Amazon estimated fulfillment and referral fees.
- Implement Redis caching key structure: `sp_api:{store_id}:{endpoint}:{params_hash}` with a 4-hour TTL to prevent hitting Amazon SP-API rate limits.
- Add rate limiting logic: Retry up to 3 times with exponential backoff on HTTP 429 status codes.

3. GOOGLE APPS SCRIPT INTEGRATION:
- Write custom functions in Apps Script:
  a) `=AMZ_SALES(sku, startDate, endDate)`
  b) `=AMZ_INVENTORY(sku)`
  c) `=AMZ_FEES(sku)`
- Implement `UrlFetchApp.fetch()` pointing to the FastAPI backend with an `X-API-Key` auth header.
- Parse JSON responses and return formatted 2D arrays so data populates grid cells cleanly.
- Add error handling in GAS: if the HTTP request times out or returns an error, output `'LOADING...'` or `'ERROR: ' + message` instead of breaking sheet calculation.

4. OUT OF SCOPE:
- Multi-tenant user login UI (single store key configuration via env vars).
- Native support for non-Amazon platforms.
- Complex historical data warehousing (rely on live API + Redis cache).

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