Allo Inventory — Reservation System

A concurrency-safe inventory reservation system for multi-warehouse fulfillment.

Built for Allo Health Engineering take-home exercise.

🔗 Live: https://allo-inventory-eight-lac.vercel.app

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Architecture

flowchart TD
    User(["👤 User / Browser"])

    subgraph Vercel ["▲ Vercel (Edge)"]
        UI["Next.js Frontend\nProduct Listing · Checkout"]
        API["Next.js API Routes\n/api/products\n/api/reservations\n/api/warehouses"]
        CRON["Cron Job\n/api/cron/expire-reservations\nRuns every 1 minute"]
    end

    subgraph Neon ["🐘 Neon (PostgreSQL)"]
        DB[("Database\nProduct · Inventory\nWarehouse · Reservation")]
    end

    subgraph Upstash ["⚡ Upstash (Redis)"]
        REDIS[("Redis Cache\nIdempotency Keys\n24h TTL")]
    end

    User -->|"HTTP Request"| UI
    UI -->|"fetch()"| API
    API -->|"SELECT FOR UPDATE\nPrisma ORM"| DB
    API -->|"Idempotency Check"| REDIS
    CRON -->|"Bulk release expired\nreservations"| DB
    API -.->|"Lazy expiry on\nevery GET /products"| DB

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Screenshots

Product Listing

Reserve Dialog

Reservation Checkout

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Tech Stack

Layer	Tech
Framework	Next.js (App Router)
Language	TypeScript
Database	PostgreSQL (Neon)
ORM	Prisma
Cache	Redis (Upstash) — idempotency
Hosting	Vercel

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Local Setup

git clone https://github.com/Smatypradish/allo-inventory.git
cd allo-inventory
npm install
cp .env.example .env   # fill in your credentials
npx prisma db push
npm run db:seed
npm run dev

Open http://localhost:3000

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Environment Variables

DATABASE_URL="postgresql://..."
UPSTASH_REDIS_REST_URL="https://..."
UPSTASH_REDIS_REST_TOKEN="..."
RESERVATION_TTL_MINUTES=10
CRON_SECRET="your-secret"

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API Reference

Method	Path	Description
GET	/api/products	List products with available stock
GET	/api/warehouses	List warehouses
POST	/api/reservations	Reserve units (409 if insufficient stock)
GET	/api/reservations/:id	Get reservation details
POST	/api/reservations/:id/confirm	Confirm purchase (410 if expired)
POST	/api/reservations/:id/release	Release / cancel reservation
GET	/api/cron/expire-reservations	Cron: expire stale reservations

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How It Works

1. Reserve — locks units for a configurable TTL (default 10 min) using SELECT ... FOR UPDATE
2. Confirm — marks units as permanently sold on payment success
3. Release — returns units to stock on cancellation or expiry

Concurrent requests for the last unit are serialised at the database level — exactly one gets 201, the other gets 409.

Expired reservations are released via:

• Lazy cleanup on every GET /api/products call
• Vercel Cron running every minute

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Project Structure

allo-inventory/
├── prisma/
│   ├── schema.prisma
│   └── seed.ts
├── src/
│   ├── app/
│   │   ├── page.tsx               # Product listing
│   │   ├── reservation/[id]/      # Checkout + countdown
│   │   └── api/
│   │       ├── products/
│   │       ├── warehouses/
│   │       ├── reservations/
│   │       └── cron/expire-reservations/
│   └── lib/
│       ├── prisma.ts
│       ├── redis.ts
│       ├── validators.ts
│       ├── idempotency.ts
│       └── utils.ts
├── vercel.json
└── .env.example