LegacyRefactor

Legacy Code Refactor

Your 2,000-line controller isn't going to refactor itself. This agent systematically extracts god objects, splits fat controllers, and modernizes patterns—without breaking your production application.

The Legacy Code Trap

Every Rails monolith has them: the files nobody wants to touch. The ones with comments like # TODO: refactor this someday from 2018.

The God Model: User.rb with 3,000 lines and 47 concerns included
The Fat Controller: OrdersController with 2,000 lines of business logic
The Callback Hell: before_save chains that nobody understands
The Copy-Paste Virus: Same 50 lines duplicated in 12 different places

Everyone knows it needs fixing. Nobody has the time. And manual refactoring is terrifying because one wrong move breaks production.

How the Agent Works

1

Complexity Analysis

Maps your entire codebase to find the worst offenders.

→ Calculates cyclomatic complexity, lines of code, and coupling metrics
→ Identifies files with highest "change frequency + complexity" score
→ Prioritizes by impact: which refactors will save the most time?

2

Dependency Mapping

Understands what depends on what before touching anything.

→ Traces method calls, associations, and callback chains
→ Identifies safe extraction boundaries
→ Maps test coverage for each method being refactored

3

Service Object Extraction

Moves business logic from controllers and models to dedicated services.

→ Creates app/services/ with single-responsibility classes
→ Follows your team's existing patterns (or establishes new ones)
→ Maintains identical external behavior—no breaking changes

4

Concern Decomposition

Breaks bloated models into focused, reusable concerns.

→ Groups related methods by domain (e.g., User::Authentication, User::Billing)
→ Extracts shared behavior to app/models/concerns/
→ Reduces god model from 3,000 lines to 200 lines + focused concerns

5

Callback Untangling

Replaces implicit callback chains with explicit, testable code.

→ Maps the full before_save / after_commit execution chain
→ Converts to explicit service calls where appropriate
→ Keeps necessary callbacks but documents the "why"

6

Test Preservation

Ensures every refactor is backed by passing tests.

→ Runs existing tests after each micro-change
→ Adds characterization tests for untested legacy behavior
→ Creates unit tests for newly extracted services

7

Incremental PRs

Delivers small, reviewable changes—not a massive rewrite.

→ Each PR does one thing: extract one service, split one concern
→ PRs are ordered for safe merge sequence
→ Can pause at any point with a working codebase

What It Refactors

God Objects

Models with 1,000+ lines doing everything at once

Fat Controllers

Business logic that belongs in services or models

Callback Chains

Implicit side effects that make debugging impossible

Duplicated Code

Copy-pasted logic that drifts apart over time

Query Sprawl

Database queries scattered across controllers and views

Mixed Abstractions

HTTP, business logic, and DB in the same method

What This Is NOT

✗ Not a rewrite. We refactor incrementally, not "throw it away and start over."
✗ Not blind pattern application. We don't add service objects just because. Every change has a reason.
✗ Not "make it pretty." The goal is maintainability and velocity, not aesthetics.
✗ Not feature work. We don't change behavior—we reorganize structure while preserving functionality.

Typical Results

80%

reduction in largest file sizes

3x

faster onboarding for new devs

50%

fewer bugs in refactored areas

Stop Dreading That File

Your legacy code doesn't have to stay legacy. Let's break it down into something your team actually wants to work on.

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