Code Quality Analyzer Skill

Expert guidance for identifying code smells, analyzing refactoring opportunities, and applying best practices to improve code maintainability and reduce duplication.

Code Smell Detection

1. Duplicate Code

Indicator: Same pattern appears 3+ times across files Impact: Maintenance burden increases, bugs must be fixed multiple places

// BAD: Error handling duplicated in PhotoService, GalleryService, SettingsService
class PhotoService {
  getPhotos() {
    return this.http.get<Photo[]>(url).pipe(
      catchError(error => {
        console.error('API error:', error);
        this.snackBar.open('Failed to load', 'OK');
        return throwError(() => error);
      })
    );
  }
}

// SOLUTION: Extract to base class
class BaseApiService {
  protected handleApiError<T>(message: string): (error: any) => Observable<T> {
    return (error: any) => {
      console.error('API error:', error);
      this.snackBar.open(message, 'OK');
      return throwError(() => error);
    };
  }
}

class PhotoService extends BaseApiService {
  getPhotos() {
    return this.http.get<Photo[]>(url).pipe(catchError(this.handleApiError('Failed to load photos')));
  }
}

2. Shotgun Surgery

Indicator: Change in one location requires changes in many places Solution: Centralize related logic

// BAD: Score formatting logic spread across 5 components
gallery.ts:      score.toFixed(1) + '/10'
photo-card.ts:   score.toFixed(1) + '/10'
photo-detail.ts: score.toFixed(1) + '/10'

// SOLUTION: Centralize in a pipe or utility
@Pipe({ name: 'score', standalone: true })
class ScorePipe implements PipeTransform {
  transform(score: number): string {
    return score.toFixed(1) + '/10';
  }
}

// Use in all templates:
// {{ photo.aggregate | score }}

3. Long Methods

Indicator: Method/function > 50 lines Solution: Extract sub-methods with clear names

// BAD: One 80-line method doing everything
method() {
  // Validate input
  // Load data
  // Transform data
  // Save to cache
  // Update UI
}

// SOLUTION: Extract into focused methods
private validateInput(): boolean { /* 5 lines */ }
private loadData(): Observable<Data> { /* 10 lines */ }
private transformData(data: Data): TransformedData { /* 5 lines */ }
private saveToCache(data: TransformedData): void { /* 3 lines */ }
private updateUI(data: TransformedData): void { /* 5 lines */ }

public execute(): void {
  if (!this.validateInput()) return;
  this.loadData()
    .pipe(
      map(data => this.transformData(data)),
      tap(data => this.saveToCache(data)),
      tap(data => this.updateUI(data))
    ).subscribe();
}

4. Feature Envy

Indicator: Method uses more data from another class than its own Solution: Move method to that class

// BAD: Component envies Photo model
class GalleryComponent {
  private getPhotoSummary(photo: Photo) {
    return `${photo.filename} - ${photo.aggregate.toFixed(1)} (${photo.category})`;
  }
}

// SOLUTION: Move to the class that owns the data
class Photo {
  getSummary(): string {
    return `${this.filename} - ${this.aggregate.toFixed(1)} (${this.category})`;
  }
}

5. Data Clumps

Indicator: Same 3+ parameters passed together across methods Solution: Create parameter object

// BAD: Passing same filter parameters repeatedly
fetchPhotos(category: string, minScore: number, sortBy: string, page: number) { }
countPhotos(category: string, minScore: number, sortBy: string, page: number) { }
exportPhotos(category: string, minScore: number, sortBy: string, page: number) { }

// SOLUTION: Create data object
interface PhotoFilter {
  category: string;
  minScore: number;
  sortBy: string;
  page: number;
}

fetchPhotos(filter: PhotoFilter) { }
countPhotos(filter: PhotoFilter) { }
exportPhotos(filter: PhotoFilter) { }

DRY Violation Detection

Pattern Recognition

Search for:

1. Line-for-line identical blocks (5+ lines appearing 3+ times)
2. Conceptually identical patterns (different variable names but same logic)
3. Copy-pasted methods with minor modifications
4. Repeated validation/transformation logic

Quick Detection Commands

# Find potential duplicates
grep -r "catchError" --include="*.service.ts" client/src/app/ | wc -l

# Look for repeated patterns
grep -r "pipe(" client/src/app/ --include="*.service.ts" | \
  grep -c "tap\|map\|catchError"

# Find repeated signal patterns
grep -r "signal<" --include="*.ts" client/src/app/ | wc -l

Refactoring Decision Tree

Is the code duplicated?

• YES -> 5+ line blocks in 3+ places?
  • Base class (behavior inheritance)
  • Utility function (stateless logic)
  • Injectable service (stateful behavior)

Is it a cross-cutting concern?

• YES (error handling, logging, caching):
  • Base service class or HTTP interceptor
  • Angular pipe for display formatting

Does one class know too much about another?

• YES: Move responsibility to appropriate class

Are parameters always passed together?

• YES: Create parameter object or data class

Refactoring Patterns

Pattern 1: Base Class Extraction

Use when: Multiple classes share behavior, have same parent interface

// Extract common error handling
class BaseApiService {
  protected http = inject(HttpClient);
  protected snackBar = inject(MatSnackBar);

  protected handleError<T>(message: string): (error: any) => Observable<T> {
    return (error) => {
      console.error(`API error:`, error);
      this.snackBar.open(message, 'OK', { duration: 3000 });
      return throwError(() => error);
    };
  }
}

Pattern 2: Utility Function Extraction

Use when: Stateless transformation logic, calculation, formatting

// Extract score formatting utility
export function formatScore(score: number, maxScore = 10): string {
  return `${score.toFixed(1)}/${maxScore}`;
}

export function formatPercentage(value: number): string {
  return `${(value * 100).toFixed(0)}%`;
}

// Use in any component
displayScore = computed(() => formatScore(this.$photo().aggregate));

Pattern 3: Injectable Service Extraction

Use when: Stateful logic, caching, complex operations, needs dependencies

// Extract caching service
@Injectable({ providedIn: 'root' })
class PhotoCacheService {
  private cache = new Map<string, Photo[]>();

  get(key: string, factory: () => Observable<Photo[]>): Observable<Photo[]> {
    if (this.cache.has(key)) {
      return of(this.cache.get(key)!);
    }
    return factory().pipe(
      tap(data => this.cache.set(key, data))
    );
  }

  invalidate(key?: string): void {
    key ? this.cache.delete(key) : this.cache.clear();
  }
}

Refactoring Verification

After refactoring, verify:

• No increase in file count (or justified increase)
• npx ng build compiles cleanly from client/
• No change in public API (backward compatible)
• Code is simpler, not more complex
• Duplicated code removed (not just moved)

When NOT to Refactor

• Code is about to be deleted anyway
• Refactoring would break public API
• Code is isolated/rarely changed
• Not truly duplicated (coincidental similarity)

Examples

User says: "Find duplicated error handling across services"

1. Search: grep -r "catchError" --include="*.service.ts" client/src/app/ -- find 8 occurrences
2. Analyze: 6 of 8 use identical error notification pattern
3. Report: "6 services duplicate error handling -> extract to BaseApiService.handleError()"
4. Propose: Base class with shared catchError operator
5. Verify: All child classes extend base, build succeeds

User says: "This code feels messy, help me clean it up"

1. Read the file -- identify code smells (long methods, data clumps, feature envy)
2. Categorize: 2 long methods (>50 lines), 1 data clump (filter params)
3. Propose refactoring with decision tree: stateless -> utility, stateful -> service
4. Apply changes, verify no public API breakage

Common Issues

Issue	Cause	Solution
Refactoring breaks child classes	Base class method signature changed	Check ALL child classes before modifying base
"False positive" duplication	Coincidentally similar but semantically different code	Only refactor truly duplicated logic, not coincidental similarity
Over-abstraction	Extracting a helper used only once	Only extract when pattern appears 3+ times
Refactoring breaks tests	Mocks tied to old implementation	Update test mocks to match new structure