WorthCars

A marketplace where sellers list a car with an asking price and a minimum they'll actually consider, buyers submit offers, and both sides negotiate from their dashboard — with a notification the moment the other side responds.

Stack

• Next.js 14 (App Router) + Tailwind CSS, deployed to Vercel
• Supabase for everything: Auth (email/password), Postgres (listings, offers, notifications), and Storage (listing photos). No other paid service is required.
• NHTSA vPIC API (free, no key) powers the optional "auto-fill from VIN" helper on the create-listing form.

How the offer flow works

• A listing has an asking_price and a minimum_offer. The minimum is shown to buyers directly on the listing — an offer below it is rejected automatically, before the seller ever sees it.
• A valid offer starts in pending_seller. The seller can accept, counter, or decline.
• A counter flips the offer to pending_buyer — the buyer gets an in-app notification and can accept, counter back, or the offer stays open until they do (they can also withdraw it at any point while it's open).
• Accepting marks the listing sold and auto-declines any other open offers on it (each of those buyers gets notified).
• The full back-and-forth is logged in offer_events so the UI can show the negotiation history, not just the current state.

See lib/offers.ts for the state machine and lib/db.ts for the raw data access.

Setup

1. npm install
2. Copy .env.example to .env.local and fill in your Supabase project's URL + keys.
3. Run supabase/schema.sql against your Supabase project (SQL editor) — it creates the tables, enables RLS, sets up the profiles-on-signup trigger, and creates the public listing-photos storage bucket.
4. In the Supabase dashboard, under Authentication → Email, confirm whether you want email confirmation required for signup (app/signup/page.tsx handles both cases — if confirmation is on, it shows a "check your email" screen instead of logging the user straight in).
5. npm run dev

Notifications

In-app only for now (bell icon in the nav, polls every 30s). Email/SMS notifications would need a provider like Resend or Twilio — that's a new ongoing cost, so it's intentionally not wired up; ask before adding it.

Architecture notes

• No separate "buyer" vs "seller" account type — any signed-in user can list a car and make offers on others' listings from the same account.
• All offer/listing state changes happen server-side (API routes using the Supabase service-role key) after checking the caller is the buyer or seller involved — RLS policies on the tables are a read-time backstop, not the only authorization check.
• Prices are stored in cents everywhere (lib/money.ts has the only two conversion points) to avoid floating-point rounding on money.