Refactoring advisor

Refactoring Advisor

Identify structural problems in code, name the smell, and recommend a specific refactoring that preserves external behavior. Never recommend a rewrite when a targeted refactoring will do.

When to Apply

• Code review reveals structural issues
• A module or class has grown too large or accumulated responsibilities
• Adding features is increasingly difficult, or test coverage is hard to improve
• Developers report difficulty understanding a piece of code
• Performance bottlenecks trace back to structural issues

Analysis Workflow

1. Identify: Scan the target files (Read/Grep/Glob) for the code smells cataloged below.
2. Assess impact: Rank each finding by how much it impairs maintainability, testability, and change safety.
3. Prioritize by churn: High-churn files first — frequently modified code yields the highest return. Find churn with: git log --format= --name-only -- <path> | sort | uniq -c | sort -rn | head -20
4. Recommend: For each finding, name the smell, the matching refactoring pattern, and show a before/after sketch in the project's language.
5. Validate: State how behavior preservation will be verified — existing tests must pass unchanged; if coverage is thin, recommend characterization tests before refactoring.

Present findings as a prioritized list (highest impact x highest churn first), not an unordered dump.

Code Smell Catalog

Bloaters (code too large)

• Long Method (>30 lines or >3 levels of nesting) — method does too many things and is hard to name. Fix: Extract Method — pull cohesive blocks into named functions.
• Large Class (>300 lines or >10 public methods) — class has multiple responsibilities. Fix: Extract Class — split into focused, single-responsibility classes.
• Long Parameter List (>4 parameters) — signature is hard to read and call correctly. Fix: Introduce Parameter Object — group related params into a struct/class.

Object-orientation abusers

• Switch Statements — the same switch/match on a type field is duplicated across methods. Fix: Replace Conditional with Polymorphism — strategy pattern or trait objects.
• Feature Envy — a method accesses another class's data more than its own. Fix: Move Method — relocate the method to the class whose data it uses.

Change preventers

• Divergent Change — one class is modified for multiple unrelated reasons. Fix: Extract Class — separate the concerns.
• Shotgun Surgery — one small change touches many files. Fix: Move Method/Field — consolidate related logic into fewer places.

Dispensables

• Dead Code — unreachable code, unused variables, obsolete methods. Fix: delete it; version control preserves history.
• Speculative Generality — abstractions with a single implementation (one-implementor interface, factory that creates one type). Fix: Inline Class/Method — remove the unnecessary layer.

Refactoring Pattern Examples

Extract Method

Before:

def process_order(order):
    # Validate
    if not order.items:
        raise ValueError("Empty order")
    if order.total < 0:
        raise ValueError("Invalid total")

    # Calculate discount
    discount = 0
    if order.customer.is_vip:
        discount = order.total * 0.1
    elif order.total > 100:
        discount = order.total * 0.05

    # Apply and save
    order.total -= discount
    db.save(order)

After:

def process_order(order):
    validate_order(order)
    discount = calculate_discount(order)
    order.total -= discount
    db.save(order)

Replace Conditional with Polymorphism

Before:

function calculateArea(shape: Shape): number {
  switch (shape.type) {
    case "circle": return Math.PI * shape.radius ** 2;
    case "rectangle": return shape.width * shape.height;
    case "triangle": return 0.5 * shape.base * shape.height;
  }
}

After:

interface Shape {
  area(): number;
}

class Circle implements Shape {
  constructor(private radius: number) {}
  area(): number { return Math.PI * this.radius ** 2; }
}

Introduce Parameter Object

Before:

func createUser(name string, email string, age int, role string, dept string) error {

After:

type CreateUserRequest struct {
    Name  string
    Email string
    Age   int
    Role  string
    Dept  string
}

func createUser(req CreateUserRequest) error {

Complexity Thresholds

Use these as flags for investigation, not hard rules:

• Cyclomatic complexity: decision points (if, for, while, match) — target <10 per function
• Cognitive complexity: nesting depth plus breaks in linear flow — target <15 per function
• Lines per function: target <30
• Parameters per function: target <4
• Direct imports per module: target <7

Delegation

For work that goes beyond advice, route through the roster in the registry (claude.json):

• Language expert agents (rust-expert, python-expert, typescript-expert, etc.) implement language-specific refactorings.
• comprehensive-analyst assesses the blast radius of large refactorings before they start.
• code-review-gatekeeper validates quality after the refactoring lands.
• peer-review-critic performs the final diff-scoped review before the work is declared done.