Coupling & Cohesion Analyzer

Overview

This skill analyzes PHP codebases for coupling and cohesion metrics, helping identify architectural issues like unstable dependencies, low cohesion classes, and tightly coupled modules.

Metrics Reference

Metric	Formula	Target	Description
Ca (Afferent)	Incoming deps	-	Classes depending ON this
Ce (Efferent)	Outgoing deps	< 10	Classes this DEPENDS on
Instability (I)	Ce / (Ca + Ce)	0.0-1.0	0=stable, 1=unstable
Abstractness (A)	Abstract / Total	0.0-1.0	Ratio of interfaces
Distance (D)	|A + I - 1|	< 0.3	Distance from main sequence
LCOM	Methods not sharing fields	< 0.5	Lack of cohesion

Detection Patterns

Phase 1: Dependency Discovery

# Count imports per file (Efferent Coupling - Ce)
Grep: "^use " --glob "**/*.php"
# Group by file, count unique namespaces

# Find who imports a class (Afferent Coupling - Ca)
Grep: "use [A-Z][a-z]+\\\\[A-Z][a-z]+\\\\[A-Z]+" --glob "**/*.php"
# For each class, count files importing it

# Constructor dependencies
Grep: "__construct\(" --glob "**/*.php" -A 15
# Count injected dependencies

Phase 2: Efferent Coupling (Ce) Analysis

# Classes with high outgoing dependencies
# For each PHP file in src/:

# Count use statements
grep -c "^use " "$file"

# Count constructor parameters
grep -A 20 "__construct" "$file" | grep -c "private\|readonly"

# Count method parameters with type hints
grep -c "function.*[A-Z][a-z]+.*\$" "$file"

Thresholds:

• Ce < 5: Low coupling (good)
• Ce 5-10: Moderate coupling
• Ce 10-15: High coupling (warning)
• Ce > 15: Very high coupling (critical)

Phase 3: Afferent Coupling (Ca) Analysis

# Find highly depended-on classes
# For target class "User":

Grep: "use.*\\\\User;|use.*\\\\User as" --glob "**/*.php" --output_mode count

# Find classes imported across many modules
Grep: "use [A-Z]" --glob "**/*.php" --output_mode content
# Aggregate by imported class

High Ca Classes (> 20):

• May be stable core abstractions (good)
• May be God classes (bad)
• Should be interfaces, not concrete classes

Phase 4: Instability Index

// I = Ce / (Ca + Ce)
// I = 0: Maximally stable (many depend on it, depends on few)
// I = 1: Maximally unstable (few depend on it, depends on many)

# Calculate per package/namespace
# Example for src/Order/:

# Ce: outgoing dependencies from Order to other namespaces
grep -rh "^use " src/Order/ | grep -v "Order\\\\" | sort -u | wc -l

# Ca: incoming dependencies to Order from other namespaces
grep -rh "use.*Order\\\\" src/ | grep -v "src/Order/" | sort -u | wc -l

Stable Dependencies Principle:

• Unstable packages should depend on stable packages
• I(dependent) > I(dependency)

Phase 5: Abstractness Analysis

# Count interfaces and abstract classes per package
Grep: "^interface |^abstract class " --glob "**/Domain/**/*.php"

# Count concrete classes
Grep: "^class |^final class |^readonly class " --glob "**/Domain/**/*.php"

# Abstractness = abstract / total

Target Abstractness by Layer:

• Domain interfaces: A ≈ 0.3-0.5
• Application: A ≈ 0.2-0.3
• Infrastructure: A ≈ 0.1-0.2 (mostly concrete)

Phase 6: LCOM (Lack of Cohesion of Methods)

# LCOM measures how methods share instance variables
# High LCOM = methods don't share state = low cohesion

# For each class, analyze:
# 1. List all instance variables
# 2. For each method, list variables it uses
# 3. Calculate pairs of methods not sharing any variable

Grep: "private \$|private readonly" --glob "**/*.php"
Grep: "\$this->" --glob "**/*.php"

LCOM Calculation:

LCOM = (methods not sharing fields) / (total method pairs)

If class has 5 methods and 3 pairs share no fields:
LCOM = 3 / 10 = 0.3 (acceptable)

If class has 10 methods and 40 pairs share no fields:
LCOM = 40 / 45 = 0.89 (high - consider splitting)

Phase 7: Dependency Cycles Detection

# Find circular dependencies between packages

# Build dependency graph
# For each namespace A, find dependencies to namespace B
# If B also depends on A → cycle

# Package A imports from B
Grep: "namespace Order|use Payment\\\\" --glob "**/Order/**/*.php"

# Package B imports from A
Grep: "namespace Payment|use Order\\\\" --glob "**/Payment/**/*.php"

# If both match → circular dependency

Report Format

# Coupling & Cohesion Analysis Report

## Package Metrics

| Package | Ce | Ca | I | A | D | Status |
|---------|----|----|---|---|---|--------|
| Domain/User | 3 | 25 | 0.11 | 0.40 | 0.29 | ✅ Stable |
| Domain/Order | 8 | 18 | 0.31 | 0.35 | 0.04 | ✅ Good |
| Application/Order | 15 | 5 | 0.75 | 0.10 | 0.15 | ✅ Unstable (OK) |
| Infrastructure/Persistence | 22 | 3 | 0.88 | 0.05 | 0.07 | ⚠️ High Ce |

**Legend:**
- Ce = Efferent coupling (outgoing)
- Ca = Afferent coupling (incoming)
- I = Instability (0=stable, 1=unstable)
- A = Abstractness
- D = Distance from main sequence

## Main Sequence Diagram

Abstractness (A) 1.0 ┌───────────────────────────────────┐ │ Zone of Uselessness │ │ ╲ │ 0.5 │ ╲ Main Sequence │ │ Domain/User ● │ │ ╲ Domain/Order │ │ ● ╲ │ 0.0 │ ╲ Infra/Persist │ │ Zone of Pain ● ●App/Order │ └───────────────────────────────────┘ 0.0 1.0 Instability (I)

## Critical Issues

### COUP-001: High Efferent Coupling
- **Package:** `src/Application/Order/`
- **Ce:** 22 (threshold: 15)
- **Dependencies:**
  - Domain/Order (4 classes)
  - Domain/User (3 classes)
  - Domain/Payment (2 classes)
  - Domain/Shipping (3 classes)
  - Infrastructure/Persistence (4 classes)
  - Infrastructure/Messaging (3 classes)
  - External/Stripe (3 classes)
- **Issue:** Too many external dependencies
- **Refactoring:**
  - Split into focused use cases
  - Introduce facades/mediators
  - Use domain events instead of direct calls
- **Skills:** `acc-create-use-case`, `acc-create-mediator`

### COUP-002: Unstable Package Depends on Unstable
- **Violation:** Stable Dependencies Principle
- **Package:** `Domain/Order` (I=0.31)
- **Depends on:** `Application/Reporting` (I=0.82)
- **Issue:** Stable domain depends on unstable application
- **Refactoring:** Invert dependency, use interface

### COUP-003: Circular Dependency
- **Packages:** `Order` ↔ `Payment`
- **Order → Payment:**
  - `Order.php` imports `PaymentService`
- **Payment → Order:**
  - `PaymentProcessor.php` imports `OrderRepository`
- **Refactoring:**
  - Introduce shared interface in Domain
  - Use domain events for communication
- **Skills:** `acc-create-domain-event`

## Warning Issues

### COUP-004: Low Cohesion Class
- **File:** `src/Application/Service/OrderService.php`
- **LCOM:** 0.78 (threshold: 0.5)
- **Methods:** 12
- **Shared fields:** Only 2 fields used across all methods
- **Issue:** Class has multiple responsibilities
- **Refactoring:** Split into focused classes
  - `OrderCreationService`
  - `OrderValidationService`
  - `OrderNotificationService`
- **Skills:** `acc-create-use-case`, `acc-create-domain-service`

### COUP-005: Zone of Pain
- **Package:** `src/Infrastructure/Legacy/`
- **Metrics:** I=0.15, A=0.05
- **Issue:** Stable concrete package (hard to change, many depend on it)
- **Refactoring:** Extract interfaces, increase abstractness

### COUP-006: High Afferent on Concrete
- **Class:** `src/Domain/Order/Order.php`
- **Ca:** 45 (many classes depend on it)
- **Type:** Concrete class
- **Issue:** Changes affect 45 dependents
- **Refactoring:** Ensure class is stable, consider interface

## Class Metrics

### High Coupling Classes (Ce > 10)

| Class | Ce | Layer | Recommendation |
|-------|----|----|----------------|
| OrderService | 18 | Application | Split responsibilities |
| ReportGenerator | 15 | Application | Use query service |
| UserController | 12 | Presentation | Extract handlers |
| ImportProcessor | 14 | Infrastructure | Use adapter pattern |

### Low Cohesion Classes (LCOM > 0.5)

| Class | LCOM | Methods | Fields | Recommendation |
|-------|------|---------|--------|----------------|
| OrderManager | 0.82 | 15 | 4 | Split by responsibility |
| UserService | 0.71 | 12 | 3 | Extract domain logic |
| ReportHelper | 0.68 | 8 | 2 | Group related methods |

## Dependency Diagram

```mermaid
graph TD
    subgraph "Stable (I < 0.3)"
        DO[Domain/Order<br/>I=0.31, A=0.35]
        DU[Domain/User<br/>I=0.11, A=0.40]
    end

    subgraph "Unstable (I > 0.7)"
        AO[Application/Order<br/>I=0.75, A=0.10]
        IO[Infrastructure/Order<br/>I=0.88, A=0.05]
    end

    AO --> DO
    AO --> DU
    IO --> AO
    IO --> DO

    style DO fill:#90EE90
    style DU fill:#90EE90
    style AO fill:#FFD700
    style IO fill:#FFB6C1

Recommendations

Immediate Actions

1. Break circular dependencies with events
2. Split high Ce classes (> 15 dependencies)
3. Extract interfaces for high Ca concrete classes

Short-term

4. Split low cohesion classes (LCOM > 0.5)
5. Move unstable code away from stable packages
6. Increase abstractness in Zone of Pain packages

Metrics Targets

Metric	Current	Target
Max Ce per class	22	< 10
Avg LCOM	0.45	< 0.3
Circular deps	2	0
Zone of Pain packages	3	0

## Coupling Reduction Strategies

### High Efferent Coupling

```php
// BAD: High Ce
class OrderService
{
    public function __construct(
        private UserRepository $users,
        private ProductRepository $products,
        private PaymentGateway $payment,
        private ShippingService $shipping,
        private NotificationService $notifications,
        private InventoryService $inventory,
        private TaxCalculator $tax,
        private DiscountService $discounts,
    ) {}
}

// GOOD: Lower Ce via Facade
class OrderService
{
    public function __construct(
        private OrderDependencies $deps,
    ) {}
}

// Or split into focused classes
class CreateOrderUseCase { /* uses only 3 deps */ }
class CalculateOrderUseCase { /* uses only 2 deps */ }

Circular Dependencies

// BAD: Circular
// Order depends on Payment
// Payment depends on Order

// GOOD: Domain events
class Order
{
    public function pay(): void
    {
        $this->recordEvent(new OrderPaidEvent($this->id));
    }
}

class PaymentSubscriber
{
    public function __invoke(OrderPaidEvent $event): void
    {
        $this->paymentService->record($event->orderId);
    }
}

Quick Analysis Commands

# Coupling analysis
echo "=== High Efferent Coupling (Ce) ===" && \
for f in $(find src -name "*.php"); do \
  count=$(grep -c "^use " "$f" 2>/dev/null || echo 0); \
  [ $count -gt 10 ] && echo "$f: $count imports"; \
done && \
echo "=== Circular Dependencies ===" && \
for ctx in Order User Payment; do \
  for other in Order User Payment; do \
    [ "$ctx" != "$other" ] && \
    grep -l "use.*${other}\\\\" src/${ctx}/**/*.php 2>/dev/null | head -1 && \
    grep -l "use.*${ctx}\\\\" src/${other}/**/*.php 2>/dev/null | head -1; \
  done; \
done

Integration

Works with:

• acc-detect-code-smells — God Class detection
• acc-structural-auditor — Architecture analysis
• acc-grasp-knowledge — GRASP principles (Low Coupling, High Cohesion)
• acc-create-mediator — Reduce coupling via mediator

References

• "Agile Software Development" (Robert C. Martin) — Package Coupling Principles
• "Object-Oriented Metrics in Practice" (Lanza, Marinescu)
• "A Metrics Suite for Object Oriented Design" (Chidamber, Kemerer) — LCOM metric