Fix pricing, optimize orders, and add duplicate order

AI_LOG.md

@@ -5,21 +5,23 @@ Please be honest and detailed about your AI usage. Using AI is perfectly fine an
 ## Tools Used
 *(e.g., GitHub Copilot, ChatGPT, Claude, Cursor, etc.)*
 
-- 
-- 
+- ChatGPT Codex (GPT-5.6)
+- Command-line tools: Git, npm, Vitest, ESLint, TypeScript, Prisma and Next.js
 
 ## How did you use AI for this assessment?
 
 **Task 1: Pricing Logic Bug**
-- *Did you use AI to find the bug? If so, what prompt did you use?*
-- *Did you use AI to write the fix?*
+- I gave ChatGPT Codex the full challenge brief and repository URL. It inspected the pricing calculator and identified that the Pro/free-shipping branch incorrectly added the standard shipping rate to `discountCents` after shipping was already zeroed.
+- AI wrote the small fix and regression tests. I reviewed the expected totals for Pro, standard, and non-free-shipping cases.
 
 **Task 2: Dashboard Performance**
-- *How did you use AI here? Did you use it to identify the N+1 issue, or just to write the optimized query?*
+- AI identified the N+1 database pattern: one query loaded all orders and then one additional query ran for every order. It replaced this with one Prisma `findMany` query using a nested `include`, and added a compound `(userId, createdAt DESC)` index matching the dashboard filter and sort.
 
 **Task 3: Duplicate Order Feature**
-- *Did you use AI to write the API route, the client component, or both?*
-- *Did AI make any mistakes you had to fix manually?*
+- AI implemented both the authenticated API route and client component, plus a bulk cart-store action. The endpoint verifies order ownership and current product activity/stock, returns only fully available order lines, and reports skipped products.
+- The implementation was validated with TypeScript, ESLint, Vitest, Prisma validation, and a Next.js production build. The initial npm install required changing the cache directory because the default cache was unavailable in the execution environment; this was an environment issue, not an application-code issue.
 
 ## General Comments
 *(Any other thoughts on how AI helped or hindered you during this assessment?)*
+
+AI accelerated repository exploration, implementation, test design, and documentation. I used the generated changes as a starting point and relied on automated checks to verify that the final code remained type-safe and buildable.

README.md

@@ -20,6 +20,38 @@ Welcome to OrbitStack! This is a modern, Next.js-based e-commerce platform built
    npm run dev
    ```
 
+4. Open [http://localhost:3000](http://localhost:3000). Use one of the seeded user accounts shown by `npm run seed` to sign in.
+
+## Local database setup
+
+Start PostgreSQL with Docker, configure the connection, create the schema, and seed sample data:
+
+```bash
+docker compose up -d
+cp .env.example .env
+npx prisma db push
+npm run seed
+```
+
+Run the verification suite with:
+
+```bash
+npm test
+npm run lint
+npx tsc --noEmit
+npm run build
+```
+
+## Implemented fixes
+
+- Corrected stacked free-shipping logic so shipping is waived exactly once and never becomes a product discount.
+- Removed the dashboard's N+1 order-item queries by loading orders, items, and products in one Prisma query; added an index matching the user/date query.
+- Added an authenticated **Duplicate Order** action. It verifies ownership and current inventory, adds available order lines to the Zustand cart in one update, and clearly reports unavailable lines.
+
+## Remaining limitations
+
+- Duplicate Order validates stock at click time. As with any cart, availability can change before checkout, where the existing order endpoint validates stock again.
+
 ## The Challenge
 
 There are three tasks to complete. Please review the codebase and implement the fixes and features described below.

app/(auth)/login/page.tsx

@@ -2,7 +2,6 @@
 
 import { useState } from 'react';
 import { useRouter } from 'next/navigation';
-import { Button } from '@/components/ui/Button';
 
 const SEEDED_USERS = [
   { email: 'alice@orbitstack.dev', name: 'Alice Nakamura', tier: 'Pro' },

app/api/orders/[id]/duplicate/route.ts

@@ -0,0 +1,73 @@
+import { NextResponse } from 'next/server';
+import { getSession } from '@/lib/auth/session';
+import { prisma } from '@/lib/db/client';
+import type { ApiResponse, CartItem } from '@/types';
+
+interface DuplicateOrderResult {
+  items: CartItem[];
+  unavailableItems: string[];
+}
+
+export async function POST(
+  _request: Request,
+  { params }: { params: Promise<{ id: string }> }
+) {
+  try {
+    const session = await getSession();
+    if (!session) {
+      return NextResponse.json<ApiResponse<null>>(
+        { data: null, error: 'Unauthorized' },
+        { status: 401 }
+      );
+    }
+
+    const { id } = await params;
+    const order = await prisma.order.findFirst({
+      where: { id, userId: session.id },
+      select: {
+        items: {
+          select: {
+            quantity: true,
+            product: true,
+          },
+        },
+      },
+    });
+
+    if (!order) {
+      return NextResponse.json<ApiResponse<null>>(
+        { data: null, error: 'Order not found' },
+        { status: 404 }
+      );
+    }
+
+    const availableItems: CartItem[] = [];
+    const unavailableItems: string[] = [];
+
+    for (const item of order.items) {
+      if (item.product.active && item.product.stock >= item.quantity) {
+        availableItems.push({ product: item.product, quantity: item.quantity });
+      } else {
+        unavailableItems.push(item.product.name);
+      }
+    }
+
+    if (availableItems.length === 0) {
+      return NextResponse.json<ApiResponse<null>>(
+        { data: null, error: 'None of the items in this order are currently available' },
+        { status: 409 }
+      );
+    }
+
+    return NextResponse.json<ApiResponse<DuplicateOrderResult>>({
+      data: { items: availableItems, unavailableItems },
+      error: null,
+    });
+  } catch (error) {
+    console.error('[POST /api/orders/[id]/duplicate]', error);
+    return NextResponse.json<ApiResponse<null>>(
+      { data: null, error: 'Failed to duplicate order' },
+      { status: 500 }
+    );
+  }
+}

app/api/orders/route.ts

@@ -5,7 +5,7 @@ import { listOrders } from '@/lib/orders/queries';
 import { computeOrderTotals } from '@/lib/pricing/calculator';
 import type { ApiResponse } from '@/types';
 
-export async function GET(request: NextRequest) {
+export async function GET() {
   try {
     const session = await getSession();
     if (!session) {

app/cart/page.tsx

@@ -1,5 +1,4 @@
 import type { Metadata } from 'next';
-import { CartItem } from '@/components/cart/CartItem';
 import { CartSummaryPage } from '@/components/cart/CartSummaryPage';
 
 export const metadata: Metadata = {

app/dashboard/page.tsx

@@ -1,4 +1,5 @@
 import type { Metadata } from 'next';
+import Link from 'next/link';
 import { redirect } from 'next/navigation';
 import { getSession } from '@/lib/auth/session';
 import { listOrders } from '@/lib/orders/queries';
@@ -43,9 +44,9 @@ export default async function DashboardPage() {
         <div className="rounded-xl border border-space-700 bg-space-900 py-16 text-center text-lunar-400">
           <div className="mb-3 text-4xl">🌑</div>
           <p>No orders yet.</p>
-          <a href="/products" className="mt-2 block text-sm text-moon-gold hover:underline">
+          <Link href="/products" className="mt-2 block text-sm text-moon-gold hover:underline">
             Start shopping →
-          </a>
+          </Link>
         </div>
       ) : (
         <ul className="space-y-4">
@@ -59,4 +60,3 @@ export default async function DashboardPage() {
     </div>
   );
 }
-

app/products/page.tsx

@@ -1,4 +1,5 @@
 import type { Metadata } from 'next';
+import Link from 'next/link';
 import { prisma } from '@/lib/db/client';
 import { ProductGrid } from '@/components/products/ProductGrid';
 import type { Product } from '@/types';
@@ -40,16 +41,16 @@ export default async function ProductsPage({
 
         {}
         <div className="flex flex-wrap gap-2">
-          <a
+          <Link
             href="/products"
             className={`rounded-lg px-3 py-1.5 text-sm transition-colors ${
               !category ? 'bg-moon-gold text-space-950 font-medium' : 'bg-space-800 text-lunar-400 hover:text-lunar-100'
             }`}
           >
             All
-          </a>
+          </Link>
           {categories.map((cat) => (
-            <a
+            <Link
               key={cat}
               href={`/products?category=${cat}`}
               className={`rounded-lg px-3 py-1.5 text-sm capitalize transition-colors ${
@@ -59,7 +60,7 @@ export default async function ProductsPage({
               }`}
             >
               {cat}
-            </a>
+            </Link>
           ))}
         </div>
       </div>

components/cart/CartDrawer.tsx

@@ -1,7 +1,7 @@
 'use client';
 
-import { useState, useEffect } from 'react';
 import { useCartStore } from '@/store/cart';
+import { useHydrated } from '@/lib/utils/useHydrated';
 import { CartItem } from './CartItem';
 import { CartSummary } from './CartSummary';
 import { Button } from '@/components/ui/Button';
@@ -13,14 +13,10 @@ interface CartDrawerProps {
 }
 
 export function CartDrawer({ open, onClose }: CartDrawerProps) {
-  const [mounted, setMounted] = useState(false);
+  const mounted = useHydrated();
   const { items, itemCount } = useCartStore();
   const count = itemCount();
 
-  useEffect(() => {
-    setMounted(true);
-  }, []);
-
   const displayedItems = mounted ? items : [];
   const displayedCount = mounted ? count : 0;
 

components/cart/CartSummaryPage.tsx

@@ -1,20 +1,16 @@
 'use client';
 
-import { useState, useEffect } from 'react';
 import { useCartStore } from '@/store/cart';
+import { useHydrated } from '@/lib/utils/useHydrated';
 import { CartItem } from './CartItem';
 import { CartSummary } from './CartSummary';
 import { Button } from '@/components/ui/Button';
 import Link from 'next/link';
 
 export function CartSummaryPage() {
-  const [mounted, setMounted] = useState(false);
+  const mounted = useHydrated();
   const { items, clearCart } = useCartStore();
 
-  useEffect(() => {
-    setMounted(true);
-  }, []);
-
   const displayedItems = mounted ? items : [];
 
   if (displayedItems.length === 0) {

components/checkout/CheckoutForm.tsx

@@ -1,27 +1,25 @@
 'use client';
 
-import { useState, useEffect } from 'react';
+import { useState } from 'react';
+import Link from 'next/link';
 import { useRouter } from 'next/navigation';
 import { useCartStore } from '@/store/cart';
 import { CartSummary } from '@/components/cart/CartSummary';
 import { DiscountInput } from './DiscountInput';
 import { Button } from '@/components/ui/Button';
 import { formatCents } from '@/lib/utils/format';
 import type { PricingResult } from '@/types';
+import { useHydrated } from '@/lib/utils/useHydrated';
 
 export function CheckoutForm() {
   const router = useRouter();
-  const [mounted, setMounted] = useState(false);
+  const mounted = useHydrated();
   const { items, clearCart } = useCartStore();
   const [pricing, setPricing] = useState<PricingResult | null>(null);
   const [appliedCode, setAppliedCode] = useState<string | null>(null);
   const [loading, setLoading] = useState(false);
   const [error, setError] = useState<string | null>(null);
 
-  useEffect(() => {
-    setMounted(true);
-  }, []);
-
   const handleDiscountApplied = (code: string, result: PricingResult) => {
     setAppliedCode(code);
     setPricing(result);
@@ -61,7 +59,7 @@ export function CheckoutForm() {
   if (!mounted || items.length === 0) {
     return (
       <div className="py-12 text-center text-lunar-400">
-        Your cart is empty. <a href="/products" className="text-moon-gold hover:underline">Browse products</a>
+        Your cart is empty. <Link href="/products" className="text-moon-gold hover:underline">Browse products</Link>
       </div>
     );
   }

components/dashboard/DuplicateOrderButton.tsx

@@ -0,0 +1,56 @@
+'use client';
+
+import { useState } from 'react';
+import { useCartStore } from '@/store/cart';
+import { Button } from '@/components/ui/Button';
+import type { ApiResponse, CartItem } from '@/types';
+
+interface DuplicateOrderButtonProps {
+  orderId: string;
+}
+
+interface DuplicateOrderResult {
+  items: CartItem[];
+  unavailableItems: string[];
+}
+
+export function DuplicateOrderButton({ orderId }: DuplicateOrderButtonProps) {
+  const addItems = useCartStore((state) => state.addItems);
+  const [loading, setLoading] = useState(false);
+  const [message, setMessage] = useState<string | null>(null);
+
+  async function duplicateOrder() {
+    setLoading(true);
+    setMessage(null);
+
+    try {
+      const response = await fetch(`/api/orders/${orderId}/duplicate`, { method: 'POST' });
+      const result = (await response.json()) as ApiResponse<DuplicateOrderResult>;
+
+      if (!response.ok || !result.data) {
+        throw new Error(result.error ?? 'Unable to duplicate order');
+      }
+
+      addItems(result.data.items);
+      const skipped = result.data.unavailableItems.length;
+      setMessage(
+        skipped > 0
+          ? `Added available items; ${skipped} unavailable item${skipped === 1 ? '' : 's'} skipped.`
+          : 'Order added to cart.'
+      );
+    } catch (error) {
+      setMessage(error instanceof Error ? error.message : 'Unable to duplicate order');
+    } finally {
+      setLoading(false);
+    }
+  }
+
+  return (
+    <div className="flex flex-col items-end gap-2">
+      <Button type="button" size="sm" loading={loading} onClick={duplicateOrder}>
+        Duplicate Order
+      </Button>
+      {message && <p className="text-right text-xs text-lunar-400" role="status">{message}</p>}
+    </div>
+  );
+}

components/dashboard/OrderCard.tsx

@@ -2,6 +2,7 @@ import { formatCents, formatDate, relativeDate, shortOrderId } from '@/lib/utils
 import { Badge } from '@/components/ui/Badge';
 import { Card } from '@/components/ui/Card';
 import { OrderItemRow } from './OrderItemRow';
+import { DuplicateOrderButton } from './DuplicateOrderButton';
 import type { Order, OrderStatus } from '@/types';
 
 interface OrderCardProps {
@@ -67,7 +68,9 @@ export function OrderCard({ order }: OrderCardProps) {
         </div>
       </div>
 
-      {}
+      <div className="flex justify-end border-t border-space-700 pt-4">
+        <DuplicateOrderButton orderId={order.id} />
+      </div>
     </Card>
   );
 }