Windsurf Case Study: Solo Developer Rebuilds Legacy PHP E-Commerce to Next.js in 10 Days
From Three Months to Ten Days: How One Developer Used Windsurf to Rewrite an Entire E-Commerce Backend
When freelance developer Marcus Chen inherited a 47,000-line legacy PHP e-commerce platform running on CodeIgniter 2, every agency he consulted quoted 12–14 weeks for a modern rewrite. The codebase had no tests, inconsistent naming conventions, and tightly coupled business logic embedded in views. Marcus completed the full migration to Next.js 14 with App Router, Prisma ORM, and Stripe integration in just 10 working days — using Windsurf as his AI-powered development environment. This case study breaks down the exact workflow, tools, and strategies that made this possible.
The Legacy Problem
- Stack: PHP 5.6, CodeIgniter 2.x, raw MySQL queries, jQuery spaghetti frontend- Scale: 47,000 lines across 312 files, 23 database tables, zero test coverage- Pain points: SQL injection vulnerabilities, no API layer, session-based cart with race conditions- Business constraint: The client’s hosting provider was deprecating PHP 5.6 support in 30 days
Why Windsurf
Unlike single-file AI assistants, Windsurf’s Cascade agent operates across the entire project context. For a migration of this scale, three capabilities proved decisive: multi-file editing with full codebase awareness, agentic workflows that chain reasoning across tasks, and automated test generation that validates migrated logic against the original behavior.
Step-by-Step Migration Workflow
Step 1: Install Windsurf and Initialize the Project
# Download Windsurf from windsurf.com and install
Open the legacy project alongside the new scaffolding
npx create-next-app@latest ecommerce-next —typescript —tailwind —app —src-dir
cd ecommerce-next
npm install prisma @prisma/client stripe @stripe/stripe-js next-auth
npx prisma init
Open both the legacy PHP directory and the new Next.js project in Windsurf’s workspace. Cascade can reference files across both directories simultaneously.
Step 2: Use Cascade to Reverse-Engineer the Database Schema
Instead of manually mapping 23 MySQL tables, Marcus used Cascade’s multi-file awareness to analyze every raw SQL query in the legacy codebase.
// Prompt to Cascade:
// “Analyze all SQL queries in /legacy/application/models/ and generate
// a complete Prisma schema with proper relations, indexes, and enums.”
// Cascade produced this in prisma/schema.prisma:
generator client {
provider = “prisma-client-js”
}
datasource db {
provider = “mysql”
url = env(“DATABASE_URL”)
}
model Product {
id Int @id @default(autoincrement())
sku String @unique @db.VarChar(64)
name String @db.VarChar(255)
slug String @unique @db.VarChar(255)
price Decimal @db.Decimal(10, 2)
compareAt Decimal? @db.Decimal(10, 2) @map(“compare_at_price”)
inventory Int @default(0)
categoryId Int @map(“category_id”)
category Category @relation(fields: [categoryId], references: [id])
orderItems OrderItem[]
createdAt DateTime @default(now()) @map(“created_at”)
updatedAt DateTime @updatedAt @map(“updated_at”)
@@map(“products”)
}
npx prisma db pull # Validate against existing database
npx prisma generate # Generate typed clientStep 3: Migrate Business Logic with Multi-File Editing
The legacy cart logic was spread across 8 PHP files with session manipulation, discount calculations, and tax rules. Marcus highlighted all 8 files in Windsurf's file tree and prompted Cascade:
// Prompt to Cascade:
// "Refactor all cart logic from these 8 PHP files into a single
// Next.js server action module at src/actions/cart.ts using Prisma.
// Preserve all discount tiers and tax calculation rules exactly."
// Generated: src/actions/cart.ts
“use server”;
import { prisma } from ”@/lib/prisma”;
import { getServerSession } from “next-auth”;
import { revalidatePath } from “next/cache”;
export async function addToCart(productId: number, quantity: number) {
const session = await getServerSession();
if (!session?.user?.id) throw new Error(“Unauthorized”);
const product = await prisma.product.findUniqueOrThrow({
where: { id: productId },
});
if (product.inventory < quantity) {
throw new Error(“Insufficient inventory”);
}
const existingItem = await prisma.cartItem.findUnique({
where: {
cartId_productId: {
cartId: session.user.cartId,
productId,
},
},
});
if (existingItem) {
await prisma.cartItem.update({
where: { id: existingItem.id },
data: { quantity: existingItem.quantity + quantity },
});
} else {
await prisma.cartItem.create({
data: {
cartId: session.user.cartId,
productId,
quantity,
unitPrice: product.price,
},
});
}
revalidatePath(“/cart”);
}
Cascade edited 14 dependent files simultaneously — updating imports, type references, and route handlers — in a single operation.
Step 4: Automated Test Generation
With zero existing tests, Marcus needed confidence that migrated logic matched the original behavior. Cascade’s test generation analyzed both codebases to produce integration tests.
// Prompt to Cascade:
// “Generate integration tests for cart.ts that cover every discount
// tier and tax rule found in the legacy PHP cart controller.”
// Generated: src/actions/tests/cart.test.ts
import { addToCart, applyDiscount } from ”../cart”;
import { prisma } from ”@/lib/prisma”;
describe(“Cart Actions - Legacy Parity”, () => {
it(“applies 10% discount for orders over $100”, async () => {
const result = await applyDiscount({
subtotal: 150.0,
code: “SAVE10”,
});
expect(result.discount).toBe(15.0);
expect(result.total).toBe(135.0);
});
it(“rejects quantity exceeding inventory”, async () => {
await expect(addToCart(1, 9999)).rejects.toThrow(
“Insufficient inventory”
);
});
it(“calculates state tax for California orders”, async () => {
const tax = await calculateTax({
subtotal: 100.0,
state: “CA”,
});
expect(tax.rate).toBe(0.0725);
expect(tax.amount).toBe(7.25);
});
});
npm test — —coverageStep 5: API Route and Stripe Migration
// src/app/api/checkout/route.ts
import Stripe from "stripe";
const stripe = new Stripe(process.env.STRIPE_SECRET_KEY!);
export async function POST(req: Request) {
const { cartId } = await req.json();
const items = await prisma.cartItem.findMany({
where: { cartId },
include: { product: true },
});
const session = await stripe.checkout.sessions.create({
line_items: items.map((item) => ({
price_data: {
currency: "usd",
product_data: { name: item.product.name },
unit_amount: Math.round(Number(item.unitPrice) * 100),
},
quantity: item.quantity,
})),
mode: "payment",
success_url: `${process.env.NEXT_PUBLIC_URL}/order/success`,
cancel_url: `${process.env.NEXT_PUBLIC_URL}/cart`,
});
return Response.json({ url: session.url });
}Results: Day-by-Day Breakdown
| Day | Task | Files Touched | Cascade Operations |
|---|---|---|---|
| 1–2 | Schema migration, Prisma setup | 26 | 3 multi-file edits |
| 3–4 | Auth, user, and session migration | 18 | 5 workflows |
| 5–6 | Cart, checkout, Stripe integration | 34 | 8 multi-file edits |
| 7–8 | Admin dashboard, order management | 41 | 6 workflows |
| 9 | Test generation and bug fixes | 22 | 4 test generation runs |
| 10 | Deployment, DNS cutover, smoke tests | 8 | 2 config workflows |
| Issue | Cause | Solution |
|---|---|---|
| Cascade loses context on large files | File exceeds context window limit | Split files over 500 lines before prompting. Use @file references to include only relevant sections. |
| Prisma schema drift after manual edits | Schema and database out of sync | Run npx prisma db push --accept-data-loss in development, or npx prisma migrate dev for tracked migrations. |
| Multi-file edit modifies wrong import paths | Ambiguous module names across legacy and new code | Use explicit path aliases in tsconfig.json with @/ prefix. Remove legacy folder from workspace when not actively referencing it. |
| Test generation creates shallow mocks | Cascade defaults to unit test patterns | Specify "integration test with real database" in your prompt. Add // @cascade: no-mocks as a file-level hint. |
Can Windsurf handle migrations larger than 50,000 lines of code?
Yes, but strategy matters. For codebases exceeding 50,000 lines, break the migration into domain-bounded modules — such as auth, catalog, cart, and orders — and migrate each as a distinct Cascade workflow. Pin only the relevant legacy files for each module to keep context focused. Developers have reported successful migrations of codebases up to 200,000 lines using this modular approach over 4–6 weeks.
How does Windsurf’s Cascade differ from using ChatGPT or Copilot for migration tasks?
The critical difference is multi-file awareness. ChatGPT and Copilot operate on single-file or limited context windows. Cascade indexes your entire workspace and reasons across file boundaries — it understands that renaming a Prisma model field requires updating the schema, all queries referencing that field, API route handlers, and frontend components simultaneously. This cross-file reasoning eliminates the most time-consuming part of migration: tracking down and updating every reference manually.
What is the cost of Windsurf for a solo developer working on a project like this?
Windsurf offers a free tier with limited Cascade credits and a Pro plan that provides significantly more AI workflow capacity. For a 10-day intensive migration, the Pro plan is recommended as it provides sufficient Cascade operations for multi-file editing and test generation at scale. The cost is a fraction of what even a single week of agency billing would total, making it highly economical for solo developers tackling large rewrites.