How a Global Retailer Modernized 50 POS Systems in a Single Quarter

The "Big Bang" rewrite is the most expensive way to fail in retail. Every year, enterprise organizations pour millions into legacy modernization, only to watch 70% of those projects exceed their timelines or fail entirely. When a Tier-1 retailer faced the daunting task of migrating 50 disparate Point of Sale (POS) systems—running everything from legacy .NET to obscure Delphi builds—the traditional 18-month roadmap was a non-starter.

They didn't have two years. They had three months.

By shifting from "manual archaeology" to visual reverse engineering, this retailer modernized 50 systems in a single quarter, reducing the average time-to-screen from 40 hours to just 4 hours.

TL;DR: By using Replay to record user workflows and automatically extract React components and API contracts, a major retailer bypassed the 18-month "Big Bang" rewrite cycle and modernized 50 legacy POS systems in 90 days.

The $3.6 Trillion Technical Debt Trap#

Global technical debt has ballooned to $3.6 trillion. In the retail sector, this debt is often physically manifested in POS systems that have been patched, wrapped, and layered for decades. These systems are "black boxes"—67% of legacy systems lack any meaningful documentation, and the original architects have long since left the building.

When you attempt to modernize these systems manually, your senior engineers spend 80% of their time acting as digital archaeologists rather than developers. They click through screens, take screenshots, try to find the corresponding stored procedure in a database from 2004, and guess at the business logic.

Why Traditional Modernization Fails#

The retailer in question realized that a manual rewrite of 50 systems would take decades. They needed a way to extract the "truth" of how their systems actually functioned in the field, not how the (missing) documentation said they functioned.

Moving from Black Box to Documented Codebase#

The core breakthrough was treating the video of a user session as the source of truth. Instead of reading brittle, 20-year-old source code, the team used Replay to record actual store clerks performing complex transactions: split payments, tax-exempt returns, and loyalty point redemptions.

Replay’s engine analyzes these recordings to identify UI patterns, state transitions, and underlying API calls. It then generates a "Blueprint"—a high-fidelity map of the legacy application's DNA.

Step 1: Workflow Recording#

The process began by capturing real-world usage. A clerk would perform a "Tax-Exempt Transaction." Replay doesn't just record pixels; it captures the DOM (if web-based) or the interaction layer (if desktop), mapping every click to a functional requirement.

Step 2: Component Extraction#

Once the workflow is captured, Replay’s AI Automation Suite identifies recurring UI elements. For this retailer, it meant identifying that "Button A" in the UK POS and "Button B" in the US POS performed the same functional logic. Replay extracted these into a unified Library (Design System).

Step 3: Logic Preservation#

The most dangerous part of retail modernization is losing "hidden" business logic—like specific regional tax calculations. Replay extracts these as API contracts and E2E tests, ensuring the new React-based system behaves exactly like the legacy one.

typescript
// Example: Generated React component from Replay extraction
// This component preserves the complex state logic captured during the recording
import React, { useState, useEffect } from 'react';
import { LegacyValidator } from './utils/validators'; 

export const POSCheckoutForm: React.FC<{ transactionId: string }> = ({ transactionId }) => {
  const [amount, setAmount] = useState<number>(0);
  const [isTaxExempt, setIsTaxExempt] = useState<boolean>(false);

  // Replay identified this specific business logic sequence from the legacy .NET trace
  const handlePayment = async () => {
    const isValid = LegacyValidator.validateTaxExemptStatus(amount, isTaxExempt);
    if (isValid) {
      const response = await fetch(`/api/v1/pos/process/${transactionId}`, {
        method: 'POST',
        body: JSON.stringify({ amount, isTaxExempt }),
      });
      // Handle response...
    }
  };

  return (
    <div className="modern-pos-container">
      <input 
        type="number" 
        value={amount} 
        onChange={(e) => setAmount(Number(e.target.value))} 
        placeholder="Enter Amount"
      />
      <label>
        Tax Exempt:
        <input 
          type="checkbox" 
          checked={isTaxExempt} 
          onChange={() => setIsTaxExempt(!isTaxExempt)} 
        />
      </label>
      <button onClick={handlePayment}>Complete Transaction</button>
    </div>
  );
};

The "Archaeology" vs. "Extraction" Math#

The reason this retailer modernized 50 systems so quickly comes down to the "40 vs 4" rule.

In a manual modernization project, an architect spends approximately 40 hours per screen to:

1. •Identify the UI components.
2. •Map the data flow to the backend.
3. •Write the documentation.
4. •Create the Jira tickets for the frontend team.
5. •Write the initial React/Angular boilerplate.

With Replay, this process is compressed into 4 hours. The platform records the screen, generates the React code, creates the documentation, and audits the technical debt automatically.

💰 ROI Insight: For a 50-system rollout involving roughly 20 screens per system, the retailer saved over 36,000 man-hours. At an average senior developer rate, that’s a direct cost saving of approximately $5.4 million in labor alone.

Architecting for Regulated Environments#

For a global retailer, security wasn't negotiable. These POS systems handle PII (Personally Identifiable Information) and PCI-compliant transaction data. Replay's ability to run On-Premise and its SOC2/HIPAA-ready status allowed the retailer to record workflows in a sandbox environment using masked data, ensuring no sensitive information ever left their firewall.

Automated Documentation and E2E Tests#

One of the biggest pain points in legacy systems is the "Fear of Breaking." Developers are afraid to touch the code because there are no tests. As part of the extraction, Replay generates Playwright or Cypress E2E tests based on the recorded user flows.

typescript
// Generated E2E Test ensuring the new React POS matches legacy behavior
import { test, expect } from '@playwright/test';

test('Verify Tax-Exempt Workflow matches Legacy Trace #8842', async ({ page }) => {
  await page.goto('/checkout');
  await page.fill('input[type="number"]', '100.00');
  await page.click('text=Tax Exempt');
  await page.click('text=Complete Transaction');
  
  // The API contract generated by Replay expects this specific payload
  const request = await page.waitForRequest('**/api/v1/pos/process/*');
  expect(request.postDataJSON()).toMatchObject({
    amount: 100,
    isTaxExempt: true
  });
});

The Result: 50 Systems, 90 Days#

By the end of the quarter, the retailer had achieved what their consultants said was impossible:

• •50 Legacy POS variants consolidated into a single, modern React-based architecture.
• •Zero downtime during the transition, as each system was swapped out using a Strangler Fig pattern facilitated by the extracted API contracts.
• •100% Documentation coverage—every screen in the new system had a corresponding "Blueprint" in Replay showing exactly where the logic originated.

⚠️ Warning: Do not attempt to modernize without a "Source of Truth." If you rely on the memories of your longest-tenured developers, you are building on a foundation of sand.

Implementation Roadmap: The Replay Way#

Step 1: Assessment & Inventory#

Use Replay to audit your existing estate. Identify which of the 50 systems share common components. Our Technical Debt Audit feature will flag which systems are high-risk (e.g., those with no surviving source code).

Step 2: Recording the "Happy Path" and Edge Cases#

Assign subject matter experts (SMEs) to record the core workflows. For retail, this includes sales, returns, voids, and end-of-day reconciliation.

Step 3: Visual Extraction#

Use the Blueprints editor to refine the generated React components. Replay will automatically suggest components for your Library, ensuring consistency across all 50 modernized systems.

Step 4: Validation & Deployment#

Run the generated E2E tests against the new build. Because Replay provides the API Contracts, your frontend and backend teams can work in parallel, significantly accelerating the "days/weeks" timeline.

• •Library: Centralized repository of all extracted UI components.
• •Flows: Visual maps of how users move through the system.
• •Blueprints: The technical specification for every screen.
• •AI Automation: The engine that turns video into code.

Frequently Asked Questions#

How long does legacy extraction take?#

While a manual rewrite takes 18-24 months for an enterprise-grade system, Replay reduces this to 2-8 weeks per system. In the case of the 50 POS systems, the commonalities between systems allowed for parallel extraction, completing the entire fleet in 90 days.

What about business logic preservation?#

This is Replay's core strength. By recording the actual execution of the program, we capture the "as-is" state of the business logic. We generate API contracts and functional documentation that describe exactly how the legacy system handles data, preventing the "logic drift" that kills most rewrites.

Does Replay work with desktop applications?#

Yes. Replay is designed for complex enterprise environments. Whether it’s a mainframe terminal, a Java Swing app, a Delphi desktop client, or a legacy Silverlight web app, if a user can interact with it, Replay can reverse engineer it.

Can we export the code to our own stack?#

Absolutely. Replay generates standard, high-quality React code, TypeScript definitions, and OpenAPI specs. There is no vendor lock-in; the code is yours to own, commit to your repo, and maintain.

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Ready to modernize without rewriting? Book a pilot with Replay - see your legacy screen extracted live during the call.