Modernizing Retail Inventory Logic: From AS/400 to React Native

70% of legacy rewrites fail or exceed their timelines, yet the global technical debt bill has ballooned to $3.6 trillion. In the retail sector, this debt is often anchored in AS/400 (IBM i) systems that have managed inventory logic reliably for decades but now act as an anchor, preventing the deployment of modern, high-performance mobile experiences.

TL;DR: Modernizing retail inventory systems from AS/400 to React Native no longer requires high-risk "Big Bang" rewrites; Visual Reverse Engineering allows teams to extract business logic directly from user workflows, reducing migration timelines from years to weeks.

The Retail Modernization Trap: Why AS/400 Logic is Hard to Kill#

For a VP of Engineering at a Tier-1 retailer, the AS/400 isn't just a server; it’s a black box containing thirty years of undocumented edge cases. Whether it’s complex SKU calculations, multi-warehouse allocation logic, or seasonal pricing overrides, the "source of truth" is often buried in RPG or COBOL code that no current employee fully understands.

The industry standard for "Modernizing Retail Inventory" has historically been a choice between two evils:

1. •The Big Bang Rewrite: A 18-24 month project that usually dies in the "requirements gathering" phase because 67% of legacy systems lack any form of documentation.
2. •The Strangler Fig Pattern: A safer but agonizingly slow approach that requires building expensive middleware wrappers around every legacy procedure.

Both approaches suffer from "Software Archaeology"—the manual, soul-crushing process of reading legacy code to understand what the system actually does. This manual extraction takes an average of 40 hours per screen. When you have 500+ inventory management screens, the math simply doesn't work.

Visual Reverse Engineering: A New Architectural Paradigm#

The future of modernization isn't rewriting from scratch; it’s understanding what you already have by observing it in motion. This is where Replay changes the trajectory. Instead of reading dead code, Replay records real user workflows within the legacy terminal or web-wrapped AS/400 interface.

By capturing the state changes, data inputs, and visual outputs, Replay’s AI Automation Suite performs "Visual Reverse Engineering." It treats the video as the source of truth, mapping the legacy "green screen" interactions directly to modern React Native components and API contracts.

Comparison of Modernization Strategies#

💰 ROI Insight: By moving from 40 hours of manual analysis to 4 hours of automated extraction per screen, a typical enterprise saves approximately 90% in engineering labor costs during the discovery and design phases.

From Green Screen to React Native: The Technical Workflow#

When modernizing retail inventory logic, the goal is to preserve the battle-tested business rules while discarding the obsolete interface. Replay facilitates this by generating documented React components and the underlying API contracts required to feed them.

Step 1: Recording the Source of Truth#

An SME (Subject Matter Expert) performs a standard inventory cycle—receiving a shipment, scanning a barcode, and updating stock levels—on the legacy system. Replay records this session, capturing not just the pixels, but the underlying data flow and state transitions.

Step 2: Logic Extraction and Blueprinting#

Replay’s AI analyzes the recording to identify patterns. It recognizes that a specific field in the AS/400 terminal corresponds to "Available to Promise" (ATP) logic. It then generates a Blueprint—a technical specification that bridges the gap between the legacy data structure and the desired React Native state.

Step 3: Code Generation#

Instead of a developer staring at a blank VS Code window, Replay generates the scaffolding. This includes the React Native UI components (using your organization's Design System from the Replay Library) and the TypeScript interfaces for the new microservices.

typescript
// Example: Generated React Native Hook for Inventory Update
// Extracted from AS/400 "Transaction 402" Workflow via Replay

import { useState, useEffect } from 'react';
import { InventoryService } from '@/services/inventory';

export const useInventoryLogic = (skuId: string) => {
  const [stockLevel, setStockLevel] = useState<number>(0);
  const [isAllocated, setIsAllocated] = useState<boolean>(false);

  // This logic was reverse-engineered from the legacy 'Warehouse-Out' workflow
  const handleStockUpdate = async (newCount: number) => {
    try {
      // API Contract generated by Replay based on legacy field mappings
      const response = await InventoryService.updateSKU(skuId, {
        quantity: newCount,
        transactionCode: 'WH_OUT_01', // Preserved legacy business logic
        timestamp: new Date().toISOString(),
      });
      
      setStockLevel(response.currentStock);
    } catch (error) {
      console.error("Failed to sync with legacy bridge:", error);
    }
  };

  return { stockLevel, handleStockUpdate, isAllocated };
};

Step 4: Technical Debt Audit#

Before deployment, Replay generates a Technical Debt Audit. This report identifies which parts of the legacy logic were successfully migrated and which "dead code" paths in the AS/400 were ignored because they are no longer used in real-world workflows.

⚠️ Warning: Attempting to migrate 100% of legacy code is a common pitfall. Our data shows that up to 40% of legacy retail logic is "zombie code"—routines that run but serve no current business purpose. Visual Reverse Engineering filters this out by focusing on active workflows.

Preserving Integrity in Regulated Environments#

For industries like Healthcare retail or Government-contracted manufacturing, modernization isn't just a speed game; it’s a compliance game. One of the primary reasons "Modernizing Retail Inventory" stalls is the fear of breaking SOC2 or HIPAA compliance during the transition.

Replay is built for these high-stakes environments. It offers:

• •On-Premise Deployment: Keep your sensitive inventory data within your own firewall.
• •SOC2 & HIPAA Ready: Automated documentation provides a clear audit trail of how logic was moved from System A to System B.
• •E2E Test Generation: Replay doesn't just give you code; it generates the End-to-End tests based on the original recording to ensure the new React Native app behaves exactly like the legacy system.

typescript
// Example: Automated E2E Test generated from Replay recording
// Validates that the new React Native flow matches the legacy AS/400 workflow

describe('Inventory Receiving Flow', () => {
  it('should update stock levels correctly after barcode scan', async () => {
    await device.launchApp();
    await element(by.id('sku-input')).typeText('SKU-99283');
    await element(by.id('scan-button')).tap();
    
    // Logic check: Legacy system required a +1 increment on scan
    // Replay extracted this requirement and generated the following assertion
    await expect(element(by.id('stock-count'))).toHaveText('101');
    
    // Validate API contract integrity
    const lastRequest = await MockServer.getLastRequest('/v1/inventory/sync');
    expect(lastRequest.body.increment).toBe(1);
  });
});

Moving Beyond "Archaeological Engineering"#

The manual approach to modernization is essentially "Archaeological Engineering." You hire expensive consultants to dig through layers of digital sediment, hoping to find the "why" behind a specific line of RPG code.

Replay turns this process on its head. By using Video as the source of truth, you bypass the need for perfect documentation. You don't need to know how the AS/400 calculates tax for a multi-state shipment if you can record the system doing it and extract the resulting logic.

Key Benefits of the Replay Approach:#

• •Library (Design System): Ensure your new React Native inventory app looks like a modern tool, not a mobile version of a 1990s terminal.
• •Flows (Architecture): Visualize the entire inventory lifecycle before writing a single line of backend code.
• •Blueprints (Editor): Fine-tune the extracted logic to remove legacy constraints (like 8-character field limits).
• •AI Automation Suite: Automatically generate the documentation that the original developers forgot to write 20 years ago.

💡 Pro Tip: Start your modernization journey with the "most painful" screen. In retail, this is usually the Returns Processing or Inter-store Transfer logic. These screens are often the most complex and least documented.

Frequently Asked Questions#

How long does legacy extraction take with Replay?#

While a manual audit takes weeks, a Replay recording takes as long as the workflow itself. Once recorded, the AI extraction of components and contracts typically happens in hours. Most enterprise teams see a functional prototype of their modernized inventory screen within 3 to 5 days.

What about business logic preservation?#

This is Replay’s core strength. By recording the inputs and outputs of the legacy system, we capture the behavioral logic. If the legacy system requires a specific sequence of three "Enter" key presses to commit a transaction, Replay identifies that sequence and encapsulates it into a single, clean API call in the modern React Native frontend.

Does this require access to the AS/400 source code?#

No. Replay performs Visual Reverse Engineering. We look at the interface and the data layer interactions. This is critical for companies that have lost their source code or are using third-party legacy software where the source is proprietary.

How does this handle complex retail edge cases?#

Retail is all about edge cases (e.g., "If it's Tuesday and the item is in the clearance zone, apply a 10% discount unless it's a holiday"). By recording these specific scenarios, Replay documents the logic for each. You can build a comprehensive library of "Flows" that cover every exception the legacy system handles.

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