legacy-code-refactorer

Purpose

Plan safe, incremental refactorings of complex, untested legacy codebases using proven methodologies (Mikado Method, Characterization Testing, Strangler Fig pattern, Seams) without breaking production behavior.

When to Use

• Refactoring sprawling 3,000-line "God classes" or legacy spaghetti functions.
• Untangling deeply coupled monolithic code with zero existing unit tests.
• Modernizing ancient callback-hell or global-state architectures into clean, testable interfaces.

What to Analyze

1. Characterization Tests (Golden Master): Capture existing behavior with black-box snapshot tests before touching code.
2. Mikado Graph: Map dependency prerequisites to identify leaf nodes that can be refactored safely first.
3. Seam Identification: Find places where behavior can be intercepted and mocked without editing core logic.
4. Extract Interface & Dependency Injection: Replace direct static class instantiation with injected interfaces.
5. Incremental Verification: Ensure every micro-step leaves the codebase in a releasable, passing state.

Output Format

• Mikado Refactoring Dependency Tree: Step-by-step ordered graph of prerequisite tasks.
• Characterization Test Harness: Safety-net test verifying existing input/output contracts.
• Before / After Code Diffs: Clean step-by-step refactoring transformations.

Avoid

• Attempting a "Big Bang" rewrite from scratch that never reaches production.
• Refactoring internal logic before establishing characterization test safety nets.