Rescuing Legacy ERP Logic: A Video-First Approach to SAP Customization Migration

The $3.6 trillion global technical debt crisis isn't caused by a lack of modern frameworks; it’s caused by the "Black Box" problem of legacy ERPs. When you look at a 20-year-old SAP customization, you aren't just looking at code—you're looking at calcified business logic that no living employee fully understands.

The traditional approach to rescuing legacy ERP logic involves months of manual "code archaeology," where expensive consultants bill thousands of hours to document what a system might be doing. It is a process designed for failure. Statistics show that 70% of legacy rewrites fail or significantly exceed their timelines, usually because the "source of truth" was lost a decade ago when the original architect retired.

TL;DR: Rescuing legacy ERP logic through video-first reverse engineering reduces modernization timelines from years to weeks by capturing real-world workflows and automatically generating documented React components and API contracts.

The High Cost of Manual Archaeology#

Most Enterprise Architects approach SAP or Oracle migrations by trying to read the underlying ABAP or PL/SQL. This is a mistake. In a system that has been patched, customized, and integrated over two decades, the code is often misleading.

The real business logic lives in the interaction between the user and the interface. 67% of legacy systems lack any form of up-to-date documentation. When you attempt a "Big Bang" rewrite without a clear understanding of these undocumented workflows, you aren't modernizing—you're guessing.

The Modernization Matrix#

Why Video is the New Source of Truth#

At Replay, we’ve shifted the paradigm from reading dead code to observing live execution. By recording real user workflows within these legacy ERP environments, we capture the "as-is" state of the business logic.

This isn't just a screen recording. Replay’s engine performs visual reverse engineering, mapping DOM elements, network requests, and state changes to modern architectural patterns. We transform a legacy "Z-transaction" in SAP into a documented, functional React component and a clean API contract.

💰 ROI Insight: Manual reverse engineering typically takes 40 hours per screen. With Replay’s automated extraction, that time is reduced to 4 hours—a 90% reduction in labor costs.

Technical Deep Dive: From SAP Screen to React Component#

When we talk about "rescuing" logic, we mean extracting the validation rules, data mapping, and UI constraints that are hidden behind proprietary ERP protocols.

Consider a standard legacy procurement form. In the old system, the logic for conditional field visibility might be buried in thousands of lines of procedural code. Replay identifies these patterns during the recording phase and generates a clean, type-safe implementation.

Example: Extracted Business Logic in TypeScript#

Below is an example of how Replay translates a legacy ERP workflow into a modern, maintainable React component.

typescript
// Generated by Replay AI Automation Suite
// Source: SAP ECC 6.0 - Transaction Z_PURCHASE_REQ
import React, { useState, useEffect } from 'react';
import { useForm } from 'react-hook-form';
import { LegacyERPClient } from '@internal/erp-bridge';

interface PurchaseRequest {
  reqId: string;
  departmentId: string;
  totalAmount: number;
  isUrgent: boolean;
  approverNotes?: string;
}

export const ModernizedPurchaseReq: React.FC = () => {
  const { register, handleSubmit, watch } = useForm<PurchaseRequest>();
  const [requiresHighLevelApproval, setApprovalLevel] = useState(false);

  const amount = watch('totalAmount');

  // Replay extracted this logic from the legacy 'Field-Exit' validation
  useEffect(() => {
    if (amount > 50000) {
      setApprovalLevel(true);
    } else {
      setApprovalLevel(false);
    }
  }, [amount]);

  const onSubmit = async (data: PurchaseRequest) => {
    // API Contract generated via Replay Blueprints
    await LegacyERPClient.submitRequest(data);
  };

  return (
    <form onSubmit={handleSubmit(onSubmit)} className="space-y-4">
      <input {...register('reqId')} placeholder="Request ID" className="ds-input" />
      <input {...register('totalAmount')} type="number" className="ds-input" />
      
      {requiresHighLevelApproval && (
        <div className="alert-warning">
          ⚠️ High-value request: Requires CFO sign-off (Extracted Logic)
        </div>
      )}
      
      <button type="submit" className="ds-button-primary">Submit to SAP Bridge</button>
    </form>
  );
};

This code isn't just a UI shell; it includes the business rules (like the $50,000 approval threshold) that were previously trapped in the legacy environment.

The 4-Step Methodology for Rescuing Legacy ERP#

Modernization fails when it is treated as a coding problem. It must be treated as a knowledge-capture problem.

Step 1: Workflow Assessment#

Identify the critical "Happy Path" and "Edge Case" workflows in your ERP. Instead of reading documentation that hasn't been updated since 2012, we identify the power users who actually operate the system daily.

Step 2: Visual Recording with Replay#

Users perform their standard tasks while Replay records the session. Our platform captures the metadata of every interaction—every click, every data entry, and every error message returned by the legacy backend.

Step 3: Automated Extraction & Audit#

Replay’s AI Automation Suite analyzes the recording. It identifies:

• •UI Patterns: To be mapped to your new Design System (Library).
• •Data Schemas: To generate API contracts and Swagger documentation.
• •Technical Debt Audit: Identifying redundant fields and dead logic paths.

Step 4: Blueprint Generation#

The output is a "Blueprint"—a functional, documented specification of the legacy screen. This includes E2E tests (Cypress/Playwright) that ensure the new system behaves exactly like the old one, providing a safety net for the migration.

⚠️ Warning: Never attempt to modernize an ERP module without first generating E2E tests from the existing system. Without a baseline, you cannot prove functional parity.

Bridging the Documentation Gap#

One of the most significant pain points in ERP migration is the "Black Box" backend. While the UI is what users see, the API contracts are what developers need. Replay generates these contracts automatically by observing the data flow during the recording process.

yaml
# Generated API Contract from Replay Flow analysis
openapi: 3.0.0
info:
  title: Legacy ERP Procurement Bridge
  version: 1.0.0
paths:
  /api/v1/purchase-requests:
    post:
      summary: Extracted from Z_PURCHASE_REQ workflow
      requestBody:
        content:
          application/json:
            schema:
              type: object
              properties:
                dept_code: { type: string, example: "FIN-01" }
                cost_center: { type: string, pattern: "^[0-9]{4}$" }
                amount: { type: number }

By providing these artifacts upfront, Replay eliminates the "discovery phase" that typically consumes 30-40% of a modernization budget.

Built for Regulated Environments#

We understand that ERP systems in Financial Services, Healthcare, and Government cannot simply be "recorded" to a public cloud. Replay is built with security as a first-class citizen:

• •SOC2 & HIPAA Ready: Data handling meets the highest enterprise standards.
• •On-Premise Availability: Keep your sensitive business logic within your own firewall.
• •PII Masking: Automated redaction of sensitive data during the recording and extraction process.

The Future Isn't Rewriting—It's Understanding#

The 18-month average enterprise rewrite timeline is a relic of a pre-AI era. When you use Replay, you are moving from a world of manual interpretation to a world of automated understanding. You are no longer guessing what "Z_FIN_TRANS_OLD_V2" does; you are seeing it in action and receiving the documented React code to replace it.

Modernization is no longer about the "Big Bang." It’s about surgical extraction. By capturing the visual and functional reality of your legacy ERP, you can migrate screen-by-screen, workflow-by-workflow, with 70% less effort and near-zero risk of logic loss.

Frequently Asked Questions#

How long does legacy extraction take?#

While a manual audit can take months, a Replay-assisted extraction typically takes 4 hours per complex screen. A full module migration that used to take 18 months can now be completed in 4 to 8 weeks.

What about business logic preservation?#

Replay captures the intent and the outcome of user actions. By monitoring network calls and state changes, we identify the underlying rules (e.g., "If Country is US, Tax must be X") and document them in the generated code and Blueprints.

Does Replay require access to my legacy source code?#

No. Replay is a visual reverse engineering platform. It works by observing the application as it runs. This is particularly valuable for systems where the source code is lost, proprietary, or too convoluted to analyze statically.

Can Replay handle terminal-based or "Green Screen" ERPs?#

Yes. Our visual engine is designed to interpret a wide variety of interfaces, from legacy web portals to terminal emulators, translating them into modern web standards.

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