Leveraging Visual Replay to Map Complex Logic in Legacy Financial Apps

70% of legacy rewrites fail or exceed their timelines. In the financial services sector, these failures aren't just missed deadlines—they are multi-million dollar write-offs that leave organizations tethered to $3.6 trillion in global technical debt. The traditional "Big Bang" rewrite is a relic of a slower era. Today, the bottleneck isn't the ability to write new code; it's the inability to understand the old code.

TL;DR: Leveraging visual replay transforms legacy modernization from a high-risk "archaeology" project into a streamlined extraction process, reducing the time to map complex financial logic from months to days.

The Archaeology Trap: Why Financial Modernization Stalls#

Most enterprise architects approach modernization like a treasure hunt without a map. They assign senior engineers to "code archaeology"—spending weeks digging through undocumented COBOL, Java, or .NET monoliths to find the business logic buried in 15-year-old subroutines.

The data is grim: 67% of legacy systems lack any meaningful documentation. When you ask a developer to modernize a complex loan origination screen or a high-frequency trading dashboard, they spend 40 hours per screen just trying to figure out what the "Submit" button actually triggers.

This is where Replay changes the paradigm. Instead of reading the code to find the logic, we record the behavior to generate the code.

Comparison: Modernization Methodologies#

Leveraging Visual Replay: From Black Box to React Components#

Leveraging visual replay means using the running application as the "source of truth." In financial apps—where validation logic, interest rate calculations, and regulatory checks are often hardcoded into the UI layer—recording a real user workflow allows Replay to extract the exact DOM structure, state transitions, and API calls.

💡 Pro Tip: Don't start with the source code. Start with the user's click path. The code tells you what could happen; the replay tells you what actually happens.

The Technical Debt Audit#

Before writing a single line of React, you need a technical debt audit. Replay's AI Automation Suite analyzes the recorded flows to identify redundant logic and orphaned API endpoints. In a recent engagement with a Tier 1 bank, leveraging visual replay identified that 40% of the legacy "Wealth Management" portal's code was never actually executed by users in production.

Step-by-Step: Extracting Logic from a Legacy Mortgage Application#

Step 1: Assessment and Recording#

The architect records a standard user journey—for example, a loan officer processing a mortgage application. Replay captures every interaction, state change, and network request. This "Visual Replay" becomes the blueprint for the new system.

Step 2: Component Extraction#

Replay's Blueprints editor takes the recording and identifies UI patterns. It doesn't just take a screenshot; it reconstructs the underlying component architecture.

typescript
// Example: Replay-generated React component from a legacy ASP.NET form
// The AI Automation Suite preserves the business logic and validation rules
import React, { useState, useEffect } from 'react';
import { ModernInput, CurrencyFormatter, ValidationLabel } from '@enterprise-ds/core';

export const LoanOriginationForm = ({ initialData, onValidate }) => {
  const [loanAmount, setLoanAmount] = useState(initialData?.amount || 0);
  const [interestRate, setInterestRate] = useState(initialData?.rate || 0.045);

  // Business logic extracted from legacy JS event listeners
  const calculateMonthlyPayment = (principal: number, rate: number) => {
    const monthlyRate = rate / 12;
    const termMonths = 360; // Extracted from legacy 'hdnTerm' field
    return (principal * monthlyRate) / (1 - Math.pow(1 + monthlyRate, -termMonths));
  };

  return (
    <div className="p-6 bg-white rounded-lg shadow-md">
      <ModernInput 
        label="Principal Amount"
        value={loanAmount}
        onChange={(val) => setLoanAmount(val)}
        type="currency"
      />
      <div className="mt-4">
        <p className="text-sm font-semibold">
          Estimated Monthly Payment: <CurrencyFormatter value={calculateMonthlyPayment(loanAmount, interestRate)} />
        </p>
      </div>
      {/* Replay identified this conditional logic from the legacy flow */}
      {loanAmount > 500000 && (
        <ValidationLabel type="warning">
          Requires Senior Underwriter Approval (Logic ID: REG-Z-104)
        </ValidationLabel>
      )}
    </div>
  );
};

Step 3: API Contract Generation#

Financial systems are notorious for having "chatty" front-ends that make dozens of undocumented calls to SOAP or REST services. Leveraging visual replay allows you to intercept these calls and automatically generate OpenAPI (Swagger) specifications.

yaml
# Generated API Contract from Replay Flow
openapi: 3.0.0
info:
  title: Legacy Mortgage API (Extracted)
  version: 1.0.1
paths:
  /api/v1/underwriting/validate:
    post:
      summary: Extracted from 'btnSubmit_Click' event
      requestBody:
        content:
          application/json:
            schema:
              type: object
              properties:
                applicantId: {type: string}
                creditScore: {type: integer}
                dtiRatio: {type: number}

⚠️ Warning: Never trust legacy documentation. In 90% of financial services projects, the actual API payload differs from the documentation by at least three critical fields.

The ROI of Understanding Over Rewriting#

The cost of manual screen migration is roughly 40 hours per screen. This includes discovery, component building, logic mapping, and testing. Replay reduces this to 4 hours per screen.

For a standard enterprise application with 100 screens:

• •Manual Approach: 4,000 hours (~$600,000 in developer salary)
• •Replay Approach: 400 hours (~$60,000 in developer salary)
• •Direct Savings: $540,000 and 10 months of time-to-market.

💰 ROI Insight: Leveraging visual replay typically yields a 70% time saving on the "Discovery and Design" phase of modernization.

Built for the Regulated Enterprise#

Financial services, healthcare, and government agencies cannot use "black box" AI tools that send data to the public cloud. Replay is built for these environments:

• •SOC2 & HIPAA Ready: Compliance is baked into the platform.
• •On-Premise Deployment: Keep your sensitive financial data within your own VPC or data center.
• •Audit Trails: Every component generated by Replay is traceable back to the original video recording, providing a clear "Chain of Logic" for regulators.

Challenging the "Big Bang" Wisdom#

The "Big Bang" rewrite is a vanity project that CTOs use to justify massive budgets, but it rarely delivers value to the business. The future of enterprise architecture isn't about throwing away the past; it's about translating it.

By leveraging visual replay, you treat your legacy system as a highly detailed specification. You aren't "migrating" code; you are "observing and extracting" value. This allows for a Strangler Fig approach on steroids—where you can replace individual screens or flows in days, not months, while maintaining 100% parity with the business logic that has kept the company running for decades.

Key Features of the Replay Platform:#

• •Library (Design System): Automatically group extracted components into a unified React library.
• •Flows (Architecture): Visualize the user journey and the underlying data dependencies.
• •Blueprints (Editor): Fine-tune the AI-generated code to match your internal coding standards.
• •E2E Test Generation: Replay generates Playwright or Cypress tests based on the recorded user flows, ensuring the new system behaves exactly like the old one.

Frequently Asked Questions#

How long does legacy extraction take?#

While a manual audit of a complex financial module can take 3-6 months, leveraging visual replay allows you to map the same flows in 2-4 weeks. The actual "recording" takes as long as the user journey; the "extraction" of React components and API contracts happens in near real-time via our AI Automation Suite.

What about business logic preservation?#

This is the primary advantage of Replay. Traditional rewrites lose logic because developers don't see the "edge cases" hidden in the code. Replay captures the system's response to these edge cases visually. If a specific input triggers a specific regulatory warning, Replay captures that state transition and generates the corresponding logic in the modern component.

Can Replay handle mainframe-backed web apps?#

Yes. As long as the application is accessible via a browser or a terminal emulator with a web interface, Replay can record the interaction. It doesn't matter if the backend is a 40-year-old mainframe or a modern microservice; Replay focuses on the "Contract of the UI."

Is the generated code maintainable?#

Unlike "low-code" platforms that output spaghetti code, Replay generates clean, documented React/TypeScript. You own the code. It’s built to your standards, using your design system components, and is fully editable in the Blueprints editor before it ever hits your repository.

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