Delphi to React Transition: Solving the $1.2M Hidden Logic Gap in Aerospace Apps

The average aerospace firm spends $1.2 million per legacy application just trying to figure out what the code actually does before they even write a single line of React. In mission-critical environments where Delphi 7 or XE2 systems still manage flight logistics, parts inventory, or maintenance scheduling, the "black box" problem isn't just a technical debt issue—it’s a massive financial leak.

When you decide to move from delphi to react, you aren't just changing languages; you are attempting to port decades of undocumented business logic, hidden event triggers, and complex VCL (Visual Component Library) behaviors into a modern, state-driven architecture. The "hidden logic gap" refers to the 67% of legacy systems that lack any meaningful documentation, leading to the 70% failure rate of enterprise rewrites.

TL;DR: Transitioning from delphi to react fails when teams treat it as a manual code rewrite; Replay eliminates the $1.2M "discovery gap" by using visual reverse engineering to extract documented React components and business logic directly from user workflows in days, not years.

The High Cost of "Archaeological" Modernization#

Most enterprise architects approach a delphi to react transition through manual "code archaeology." They hire expensive consultants to sit with subject matter experts (SMEs), watch them use the legacy app, and try to map Pascal procedures to TypeScript functions.

This manual process is where the $1.2M gap originates. An average enterprise screen takes 40 hours to manually document, design, and re-code. In a complex aerospace ERP with 300+ screens, you are looking at 12,000 man-hours before accounting for testing and integration.

The Modernization Matrix: Comparing Approaches#

Why Delphi to React Transitions Stall#

Delphi was revolutionary because of its tight coupling between the UI and the database via the VCL. However, that same coupling is what makes modernizing to React a nightmare. In a legacy Delphi app, a

change event might trigger a chain reaction of database triggers, global variable updates, and hidden form calculations that no one on your current team fully understands.

The Documentation Gap#

With $3.6 trillion in global technical debt, the aerospace industry is particularly vulnerable. Many of the original developers who built these Delphi systems in the late 90s have retired. The "source of truth" isn't the code—it's the behavior of the application during a live user session.

⚠️ Warning: Attempting to rewrite Delphi logic by only reading the

text

.pas

and

text

.dfm

files often misses "ghost logic"—behaviors that only trigger under specific runtime conditions or user sequences.

Bridging the Gap with Replay#

Replay changes the paradigm from "reading code" to "observing execution." By recording real user workflows within the legacy Delphi application, Replay’s engine performs visual reverse engineering. It identifies the UI patterns, captures the data flow, and generates documented React components that mirror the actual business requirements.

Step 1: Visual Recording#

Instead of interviewing SMEs, you record them performing their daily tasks—processing a flight manifest or a parts order. Replay captures every state change, API call (if any), and UI transition.

Step 2: Logic Extraction#

Replay analyzes the recording to identify the "Blueprints" of the application. It maps the Delphi VCL components to their modern React equivalents, ensuring that the layout and the underlying logic remain intact.

Step 3: Code Generation#

The platform generates clean, production-ready TypeScript and React code. This isn't "spaghetti code" output; it’s structured, modular, and follows modern best practices.

typescript
// Example: Generated React component from a Delphi 'Parts Inventory' screen
// Replay identified the TDBGrid and TActionList logic to produce this:

import React, { useState, useEffect } from 'react';
import { Button, Table, Modal } from '@/components/ui'; // From your Replay Library
import { useInventoryLogic } from './hooks/useInventoryLogic';

export const PartsInventoryDashboard: React.FC = () => {
  const { parts, loading, updateStock } = useInventoryLogic();
  const [isDetailOpen, setIsDetailOpen] = useState(false);

  // Replay preserved the 'OnDrawCell' conditional logic from Delphi
  const getRowStatus = (stockLevel: number) => {
    return stockLevel < 10 ? 'bg-red-100' : 'bg-green-100';
  };

  return (
    <div className="p-6 space-y-4">
      <h1 className="text-2xl font-bold">Aerospace Parts Registry</h1>
      <Table 
        data={parts}
        onRowClick={() => setIsDetailOpen(true)}
        rowClassName={(row) => getRowStatus(row.stock)}
      />
      <Button onClick={() => updateStock()}>
        Sync with Global Logistics
      </Button>
    </div>
  );
};

Solving the $1.2M Logic Gap#

The "Hidden Logic Gap" is essentially the cost of uncertainty. When you move delphi to react, the uncertainty lies in the "middle-tier" logic often buried in Delphi's form files. Replay's AI Automation Suite audits this technical debt automatically.

💰 ROI Insight: By moving from a 40-hour-per-screen manual process to a 4-hour-per-screen automated process with Replay, an enterprise can save over $1M in developer salaries and opportunity costs on a standard 200-screen application.

Preserving Complex Business Logic#

In aerospace, a calculation for "Weight and Balance" or "Fuel Burn" cannot be "mostly correct." It must be exact. Replay generates E2E tests and API contracts based on the legacy system's actual outputs, ensuring that your new React frontend interacts with your backend exactly as the Delphi client did.

typescript
// Generated E2E Test to ensure logic parity during Delphi to React transition
describe('Weight and Balance Logic Parity', () => {
  it('should match legacy Delphi output for Boeing 747-8 loadouts', () => {
    cy.visit('/weight-balance');
    cy.get('[data-testid="cargo-input"]').type('45000');
    cy.get('[data-testid="fuel-input"]').type('120000');
    
    // The expected value 0.285 was extracted from the recorded Delphi session
    cy.get('[data-testid="cg-result"]').should('contain', '0.285');
  });
});

Implementing the Transition: A 3-Step Tutorial#

Step 1: Assessment and Library Mapping#

Before the delphi to react transition begins, use Replay to audit your existing UI. Replay's "Library" feature identifies recurring patterns across your Delphi forms. If you have 50 different versions of a "Search" button, Replay consolidates them into a single, standardized React component in your new Design System.

Step 2: Workflow Recording (The "Source of Truth")#

Deploy the Replay recorder to your power users. As they navigate the legacy Delphi app, Replay builds a "Flow" map. This map is a visual architecture of your entire system, showing how users actually move from screen to screen—often revealing that 30% of your legacy features are never even used.

Step 3: Blueprint Extraction and Export#

Select a flow and hit "Extract." Replay’s Blueprints editor allows you to refine the generated React code before it hits your repository. You get:

• •Documented React components
• •TypeScript interfaces for all data structures
• •API contracts (Swagger/OpenAPI)
• •A full technical debt audit

💡 Pro Tip: Focus your first sprint on the "High Value/Low Complexity" flows identified by Replay to show immediate ROI to stakeholders.

Security and Compliance in Regulated Industries#

For Aerospace, Government, and Healthcare, cloud-only solutions are often a non-starter. Replay is built for these environments:

• •SOC2 & HIPAA Ready: Data privacy is baked into the extraction process.
• •On-Premise Available: Keep your source code and recordings within your own secure perimeter.
• •Air-Gapped Compatibility: Modernize sensitive systems without exposing them to the public internet.

The Future of Modernization is Understanding#

The 18-month average enterprise rewrite timeline is a relic of an era where we had to manually decode the past. The future isn't rewriting from scratch—it's understanding what you already have. By using video as the source of truth for reverse engineering, Replay allows you to bridge the gap from delphi to react without the "archaeological" tax.

• •Document without archaeology: Stop digging through 20-year-old
  text

  .pas
  files.
• •Modernize without rewriting: Use the logic you already have, just in a better wrapper.
• •From black box to documented codebase: Finally understand your enterprise's core logic.

Frequently Asked Questions#

How long does a Delphi to React transition take with Replay?#

While a manual rewrite of a complex application typically takes 18-24 months, Replay customers typically see a 70% reduction in timeline. Most core extractions are completed in days or weeks, allowing the team to focus on new feature development rather than just playing catch-up.

Does Replay handle complex Delphi business logic or just the UI?#

Replay captures the interaction between the UI and the data layer. It generates the functional logic required to maintain the same state transitions and data handling found in the legacy application. While some highly specific low-level driver integrations may require manual tweaking, the bulk of business logic is preserved and documented.

What about the database? Delphi apps are often heavily tied to SQL Server or Oracle.#

Replay generates the API contracts based on the data observed during user sessions. This allows you to build a modern API layer (using Node.js, Python, or .NET) that mirrors the data requirements of the legacy system, facilitating a smoother transition of the data layer.

Is the generated React code maintainable?#

Yes. Unlike "low-code" platforms that output proprietary "mush," Replay generates standard TypeScript and React code using your organization's design system and coding standards. It is indistinguishable from code written by a senior frontend engineer.

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