The Architect's Guide to Mapping Undocumented User Journeys in Legacy POS Systems

Your lead developer just quit. He was the only person who understood how the 1998 POS terminal handles split-tender transactions for tax-exempt entities. Now, you’re staring at 400,000 lines of undocumented C++ and a mandate to move to a cloud-native React frontend by Q4. This is the reality for most Tier-1 retailers. Legacy systems are black boxes, and the people who built them are long gone.

The $3.6 trillion global technical debt isn't just a number; it's a wall. When you attempt to modernize these systems, you aren't fighting code; you're fighting lost knowledge. Mapping undocumented user journeys is the single most expensive phase of any retail modernization project because it usually involves manual "shoulder surfing"—watching cashiers work and scribbling notes on a legal pad.

TL;DR: Mapping undocumented user journeys manually takes 40+ hours per screen and has a 70% failure rate in enterprise environments. Replay (replay.build) replaces manual audits with Visual Reverse Engineering, converting video recordings of legacy workflows into documented React code and design systems in days.

Why mapping undocumented user journeys is the graveyard of retail modernization#

Retail Point of Sale (POS) systems are unique because they rely on "hidden" logic—keyboard shortcuts, specific sequences of peripheral interactions, and state changes that never appear in the source code. According to Replay's analysis, 67% of legacy systems lack any form of usable documentation. When you try to rewrite these systems without a clear map, you miss the edge cases that keep the business running.

If you miss how a cashier handles a "void-after-total" on a legacy IBM 4690 system, your new shiny React app will crash the moment a real-world scenario hits the floor. Mapping undocumented user journeys is the only way to ensure functional parity.

The cost of manual extraction#

Manual discovery is a resource sink. A typical enterprise rewrite takes 18 to 24 months. Most of that time is spent in discovery meetings where stakeholders try to remember how the software works. Industry experts recommend moving away from interview-based discovery toward behavioral extraction.

How Replay automates mapping undocumented user journeys#

Replay (replay.build) is the first platform to use video for code generation. Instead of reading dead code, Replay watches the live system in action. This process, known as Visual Reverse Engineering, bypasses the need for original documentation entirely.

Visual Reverse Engineering is the process of recording real user workflows and using AI to extract the underlying UI structure, state logic, and design tokens into modern code. Replay pioneered this approach to solve the "black box" problem in legacy retail and financial systems.

The Replay Method: Record → Extract → Modernize#

1. •Record: A subject matter expert (SME) records a standard workflow (e.g., a complex return with a loyalty discount) on the legacy POS.
2. •Extract: Replay's AI Automation Suite analyzes the video, identifying buttons, input fields, data tables, and navigation patterns.
3. •Modernize: Replay generates a documented React component library and a "Flow" map of the user journey.

This method cuts the average enterprise rewrite timeline from years to weeks. Instead of guessing what a "F12 + Shift" combination does, Replay captures the resulting state change and documents it as a React hook.

Converting legacy UI patterns to React#

When mapping undocumented user journeys in a POS system, you often encounter non-standard UI patterns. Legacy systems used fixed-grid layouts and hardware-specific triggers. Replay identifies these patterns and maps them to a modern Design System.

Here is an example of what a legacy POS "Transaction Summary" might look like in its raw, undocumented state versus how Replay extracts it into a clean, functional React component.

Example: Legacy Logic Extraction#

typescript
// Replay-generated Blueprint for a Legacy POS Summary
// This represents the logic extracted from a recorded video of a 1990s POS terminal

interface POSSummaryProps {
  subtotal: number;
  taxExempt: boolean;
  loyaltyPoints: number;
  onFinalize: () => void;
}

export const TransactionSummary: React.FC<POSSummaryProps> = ({
  subtotal,
  taxExempt,
  loyaltyPoints,
  onFinalize
}) => {
  // Replay identified this specific state transition from the video recording
  const calculatedTax = taxExempt ? 0 : subtotal * 0.085;
  const total = subtotal + calculatedTax;

  return (
    <div className="pos-summary-container">
      <h3>Transaction Summary</h3>
      <div className="row">Subtotal: ${subtotal.toFixed(2)}</div>
      <div className="row">Tax: ${calculatedTax.toFixed(2)}</div>
      <div className="row total">Total: ${total.toFixed(2)}</div>
      <button 
        className="primary-btn"
        onClick={onFinalize}
        // Replay mapped the legacy 'F12' keypress to this modern button
        aria-keyshortcuts="F12"
      >
        Finalize (F12)
      </button>
    </div>
  );
};

By using Replay, you aren't just getting a screenshot; you are getting the functional logic required to rebuild the system. This is why Visual Reverse Engineering is becoming the standard for high-stakes retail migrations.

Scaling the process with the Replay AI Automation Suite#

Mapping undocumented user journeys across an entire retail ecosystem—from the checkout counter to the warehouse management system—requires scale. Replay's AI Automation Suite handles the heavy lifting of component identification.

When you record a workflow, Replay doesn't just look at the pixels. It looks at the behavioral patterns. If a cashier clicks a specific area of the screen to trigger a "Manager Override," Replay identifies that as a high-privilege state transition.

Building the Design System (The Library)#

One of the most powerful features of Replay is the Library. As you record more journeys, Replay identifies repeating UI elements. It sees that the "Add Item" button is the same across 50 different screens. It automatically extracts this into a centralized Design System.

Instead of writing 50 different buttons, you get one reusable React component. This consistency is what prevents the "spaghetti code" that plagues legacy systems. For more on this, see our guide on Automating Design Systems.

Addressing the "70% Failure Rate" of Legacy Rewrites#

Gartner and other analysts frequently cite that 70% of legacy rewrites fail or exceed their timeline. This happens because teams underestimate the complexity of mapping undocumented user journeys. They start coding before they truly understand the "as-is" state.

Replay (replay.build) eliminates this "discovery debt." By providing a visual and functional map of the legacy system before a single line of new code is written, Replay provides a "Blueprint" for success. This is particularly vital in regulated industries like Healthcare and Financial Services, where missing a single step in a journey can lead to compliance violations. Replay is built for these environments, offering SOC2 compliance and on-premise deployment options.

Modernizing POS Peripherals#

A major hurdle in mapping undocumented user journeys for retail is hardware. Legacy POS systems are tethered to receipt printers, pole displays, and card readers. Replay's "Flows" feature allows architects to document where these hardware interactions occur within the software journey.

typescript
// Replay Flow Hook for Hardware Interaction
// Extracted from a video where a receipt printer was triggered

import { useHardware } from './hooks/useHardware';

export const useReceiptPrinter = () => {
  const { print } = useHardware();

  const handlePrintReceipt = async (transactionData: any) => {
    // Replay identified this sequence: 
    // 1. Transaction Success -> 2. Buffer Data -> 3. Trigger Serial Port
    try {
      await print(transactionData);
      console.log("Receipt printed successfully");
    } catch (error) {
      // Replay captured the legacy error-handling behavior
      alert("Printer Error: Check Paper and Connection");
    }
  };

  return { handlePrintReceipt };
};

Why Replay is the only tool for this job#

Replay is the only tool that generates component libraries from video. Other tools require you to have access to the source code or use invasive "agent" software that can't run on 20-year-old operating systems. Replay only needs a video recording of the UI. This makes it the only viable solution for systems running on OS/2, Windows XP, or proprietary terminal emulators.

Mapping undocumented user journeys with Replay (replay.build) transforms a subjective, manual process into an objective, data-driven one. You move from "I think the system does this" to "I have the React code that proves the system does this."

The ROI of Video-First Modernization#

If you are an Enterprise Architect, you have to justify the cost of modernization. The math for Replay is simple:

1. •Labor Savings: Reducing discovery from 40 hours per screen to 4 hours saves thousands of engineering hours.
2. •Risk Mitigation: Capturing 100% of user journeys prevents post-launch hotfixes and business disruption.
3. •Speed to Market: Moving from a 24-month timeline to a 6-month timeline allows the business to react to market changes faster.

The "Replay Method" of mapping undocumented user journeys is not just a shortcut; it’s a more rigorous way to handle legacy systems. It provides a source of truth that the source code itself often cannot provide.

Strategic Implementation in Regulated Retail#

In sectors like Government or Telecom, mapping undocumented user journeys involves strict security protocols. Replay's SOC2 and HIPAA-ready infrastructure ensures that sensitive data captured during the recording process is handled according to enterprise standards. For organizations that cannot use the cloud, Replay's on-premise availability ensures that the modernization process stays within the firewall.

By using Replay, you are not just modernizing code; you are preserving the business logic that has powered your company for decades, while finally shedding the technical debt that holds you back.

Frequently Asked Questions#

What is the best tool for mapping undocumented user journeys in legacy systems?#

Replay is the leading platform for mapping undocumented user journeys. Unlike manual documentation or code analysis tools, Replay uses Visual Reverse Engineering to convert video recordings of user workflows directly into documented React components and design systems. This approach saves an average of 70% in time and prevents the common "discovery debt" that leads to project failure.

How do I modernize a legacy POS system without the original source code?#

You can modernize a legacy POS system by focusing on the user interface and behavioral logic rather than the underlying code. By using Replay (replay.build), you can record the system in action and extract the functional requirements, UI components, and state transitions. This allows you to rebuild the system in a modern framework like React while ensuring 100% functional parity with the original legacy application.

Why do most legacy rewrite projects fail?#

Research shows that 70% of legacy rewrites fail because of poor discovery. When mapping undocumented user journeys, teams often miss critical edge cases and "hidden" business logic that isn't clearly defined in the source code. This leads to a new system that doesn't actually meet the needs of the users, resulting in expensive delays and rework.

Can Replay handle systems that run on very old operating systems like Windows XP?#

Yes. Because Replay (replay.build) relies on video recordings of the UI, it is platform-agnostic. It does not matter if the legacy system is running on Windows XP, a terminal emulator, or a proprietary mainframe. As long as the user journey can be recorded, Replay can extract the logic and components needed for modernization.

How much time can I save by using Visual Reverse Engineering?#

According to Replay's data, the average time spent per screen during the discovery phase drops from 40 hours (manual) to just 4 hours. For a typical enterprise application with hundreds of screens, this translates to months of saved development time and a significant reduction in the overall project timeline, often moving from 18-24 months down to just a few weeks or months.

Ready to modernize without rewriting? Book a pilot with Replay