component-identification-sizing

# Component Identification and Sizing

This skill identifies architectural components (logical building blocks) in a codebase and calculates size metrics to assess decomposition feasibility and identify oversized components.

## How to Use

### Quick Start

Request analysis of your codebase:

- **"Identify and size all components in this codebase"**
- **"Find oversized components that need splitting"**
- **"Create a component inventory for decomposition planning"**
- **"Analyze component size distribution"**

### Usage Examples

**Example 1: Complete Analysis**

```
User: "Identify and size all components in this codebase"

The skill will:
1. Map directory/namespace structures
2. Identify all components (leaf nodes)
3. Calculate size metrics (statements, files, percentages)
4. Generate component inventory table
5. Flag oversized/undersized components
6. Provide recommendations
```

**Example 2: Find Oversized Components**

```
User: "Which components are too large?"

The skill will:
1. Calculate mean and standard deviation
2. Identify components >2 std dev or >10% threshold
3. Analyze functional areas within large components
4. Suggest specific splits with estimated sizes
```

**Example 3: Component Size Analysis**

```
User: "Analyze component sizes and distribution"

The skill will:
1. Calculate all size metrics
2. Generate size distribution summary
3. Identify outliers
4. Provide statistics and recommendations
```

### Step-by-Step Process

1. **Initial Analysis**: Start with complete component inventory
2. **Identify Issues**: Find components that need attention
3. **Get Recommendations**: Request actionable split/consolidation suggestions
4. **Monitor Progress**: Track component growth over time

## When to Use

Apply this skill when:

- Starting a monolithic decomposition effort
- Assessing codebase structure and organization
- Identifying components that are too large or too small
- Creating component inventory for migration planning
- Analyzing code distribution across components
- Preparing for component-based decomposition patterns

## Core Concepts

### Component Definition

A **component** is an architectural building block that:

- Has a well-defined role and responsibility
- Is identified by a namespace, package structure, or directory path
- Contains source code files (classes, functions, modules) grouped together
- Performs specific business or infrastructure functionality

**Key Rule**: Components are identified by **leaf nodes** in directory/namespace structures. If a namespace is extended (e.g., `services/billing` extended to `services/billing/payment`), the parent becomes a **subdomain**, not a component.

### Size Metrics

**Statements** (not lines of code):

- Count executable statements terminated by semicolons or newlines
- More accurate than lines of code for size comparison
- Accounts for code complexity, not formatting

**Component Size Indicators**:

- **Percent of codebase**: Component statements / Total statements
- **File count**: Number of source files in component
- **Standard deviation**: Distance from mean component size

## Analysis Process

### Phase 1: Identify Components

Scan the codebase directory structure:

1. **Map directory/namespace structure**
   - For Node.js: `services/`, `routes/`, `models/`, `utils/`
   - For Java: Package structure (e.g., `com.company.domain.service`)
   - For Python: Module paths (e.g., `app/billing/payment`)

2. **Identify leaf nodes**
   - Components are the deepest directories containing source files
   - Example: `services/BillingService/` is a component
   - Example: `services/BillingService/payment/` extends it, making `BillingService` a subdomain

3. **Create component inventory**
   - List each component with its namespace/path
   - Note any parent namespaces (subdomains)

### Phase 2: Calculate Size Metrics

For each component:

1. **Count statements**
   - Parse source files in component directory
   - Count executable statements (not comments, blank lines, or declarations alone)
   - Sum across all files in component

2. **Count files**
   - Total source files (`.js`, `.ts`, `.java`, `.py`, etc.)
   - Exclude test files, config files, documentation

3. **Calculate percentage**

   ```
   component_percent = (component_statements / total_statements) * 100
   ```

4. **Calculate statistics**
   - Mean component size: `total_statements / number_of_components`
   - Standard deviation: `sqrt(sum((size - mean)^2) / (n - 1))`
   - Component's deviation: `(component_size - mean) / std_dev`

### Phase 3: Identify Size Issues

**Oversized Components** (candidates for splitting):

- Exceeds 30% of total codebase (for small apps with <10 components)
- Exceeds 10% of total codebase (for large apps with >20 components)
- More than 2 standard deviations above mean
- Contains multiple distinct functional areas

**Undersized Components** (candidates for consolidation):

- Less than 1% of codebase (may be too granular)
- Less than 1 standard deviation below mean
- Contains only a few files with minimal functionality

**Well-Sized Components**:

- Between 1-2 standard deviations from mean
- Represents a single, cohesive functional area
- Appropriate percentage for application size

## Output Format

### Component Inventory Table

```markdown
## Component Inventory

| Component Name  | Namespace/Path               | Statements | Files | Percent | Status       |
| --------------- | ---------------------------- | ---------- | ----- | ------- | ------------ |
| Billing Payment | services/BillingService      | 4,312      | 23    | 5%      | ✅ OK        |
| Reporting       | services/ReportingService    | 27,765     | 162   | 33%     | ⚠️ Too Large |
| Notification    | services/NotificationService | 1,433      | 7     | 2%      | ✅ OK        |
```

**Status Legend**:

- ✅ OK: Well-sized (within 1-2 std dev from mean)
- ⚠️ Too Large: Exceeds size threshold or >2 std dev above mean
- 🔍 Too Small: <1% of codebase or <1 std dev below mean

### Size Analysis Summary

```markdown
## Size Analysis Summary

**Total Components**: 18
**Total Statements**: 82,931
**Mean Component Size**: 4,607 statements
**Standard Deviation**: 5,234 statements

**Oversized Components** (>2 std dev or >10%):

- Reporting (33% - 27,765 statements) - Consider splitting into:
  - Ticket Reports
  - Expert Reports
  - Financial Reports

**Well-Sized Components** (within 1-2 std dev):

- Billing Payment (5%)
- Customer Profile (5%)
- Ticket Assignment (9%)

**Undersized Components** (<1 std dev):

- Login (2% - 1,865 statements) - Consider consolidating with Authentication
```

### Component Size Distribution

```markdown
## Component Size Distribution
```

Component Size Distribution (by percent of codebase)

[Visual representation or histogram if possible]

Largest: ████████████████████████████████████ 33% (Reporting)
████████ 9% (Ticket Assign)
██████ 8% (Ticket)
██████ 6% (Expert Profile)
█████ 5% (Billing Payment)
████ 4% (Billing History)
...

````

### Recommendations

```markdown
## Recommendations

### High Priority: Split Large Components

**Reporting Component** (33% of codebase):
- **Current**: Single component with 27,765 statements
- **Issue**: Too large, contains multiple functional areas
- **Recommendation**: Split into:
  1. Reporting Shared (common utilities)
  2. Ticket Reports (ticket-related reports)
  3. Expert Reports (expert-related reports)
  4. Financial Reports (financial reports)
- **Expected Result**: Each component ~7-9% of codebase

### Medium Priority: Review Small Components

**Login Component** (2% of codebase):
- **Current**: 1,865 statements, 3 files
- **Consideration**: May be too granular if related to broader authentication
- **Recommendation**: Evaluate if should be consolidated with Authentication/User components

### Low Priority: Monitor Well-Sized Components

Most components are appropriately sized. Continue monitoring during decomposition.
````

## Analysis Checklist

**Component Identification**:

- [ ] Mapped all directory/namespace structures
- [ ] Identified leaf nodes (components) vs parent nodes (subdomains)
- [ ] Created complete component inventory
- [ ] Documented namespace/path for each component

**Size Calculation**:

- [ ] Counted statements (not lines) for each component
- [ ] Counted source files (excluding tests/configs)
- [ ] Calculated percentage of total codebase
- [ ] Calculated mean and standard deviation

**Size Assessment**:

- [ ] Identified oversized components (>threshold or >2 std dev)
- [ ] Identified undersized components (<1% or <1 std dev)
- [ ] Flagged components for splitting or consolidation
- [ ] Documented size distribution

**Recommendations**:

- [ ] Suggested splits for oversized components
- [ ] Suggested consolidations for undersized components
- [ ] Prioritized recommendations by impact
- [ ] Created architecture stories for refactoring

## Implementation Notes

### For Node.js/Express Applications

Components typically found in:

- `services/` - Business logic components
- `routes/` - API endpoint components
- `models/` - Data model components
- `utils/` - Utility components
- `middleware/` - Middleware components

**Example Component Identification**:

```
services/
├── BillingService/          ← Component (leaf node)
│   ├── index.js
│   └── BillingService.js
├── CustomerService/          ← Component (leaf node)
│   └── CustomerService.js
└── NotificationService/      ← Component (leaf node)
    └── NotificationService.js
```

### For Java Applications

Components identified by package structure:

- `com.company.domain.service` - Service components
- `com.company.domain.model` - Model components
- `com.company.domain.repository` - Repository components

**Example Component Identification**:

```
com.company.billing.payment   ← Component (leaf package)
com.company.billing.history   ← Component (leaf package)
com.company.billing           ← Subdomain (parent of payment/history)
```

### Statement Counting

**JavaScript/TypeScript**:

- Count statements terminated by `;` or newline
- Include: assignments, function calls, returns, conditionals, loops
- Exclude: comments, blank lines, declarations without assignment

**Java**:

- Count statements terminated by `;`
- Include: method calls, assignments, returns, conditionals
- Exclude: class/interface declarations, comments, blank lines

**Python**:

- Count executable statements (not comments or blank lines)
- Include: assignments, function calls, returns, conditionals
- Exclude: docstrings, comments, blank lines

## Fitness Functions

After identifying and sizing components, create automated checks:

### Component Size Threshold

```javascript
// Alert if any component exceeds 10% of codebase
function checkComponentSize(components, threshold = 0.1) {
  const totalStatements = components.reduce((sum, c) => sum + c.statements, 0)
  return components
    .filter((c) => c.statements / totalStatements > threshold)
    .map((c) => ({
      component: c.name,
      percent: ((c.statements / totalStatements) * 100).toFixed(1),
      issue: 'Exceeds size threshold',
    }))
}
```

### Standard Deviation Check

```javascript
// Alert if component is >2 standard deviations from mean
function checkStandardDeviation(components) {
  const sizes = components.map((c) => c.statements)
  const mean = sizes.reduce((a, b) => a + b, 0) / sizes.length
  const stdDev = Math.sqrt(sizes.reduce((sum, size) => sum + Math.pow(size - mean, 2), 0) / (sizes.length - 1))

  return components
    .filter((c) => Math.abs(c.statements - mean) > 2 * stdDev)
    .map((c) => ({
      component: c.name,
      deviation: ((c.statements - mean) / stdDev).toFixed(2),
      issue: 'More than 2 standard deviations from mean',
    }))
}
```

## Best Practices

### Do's ✅

- Use statements, not lines of code
- Identify components as leaf nodes only
- Calculate both percentage and standard deviation
- Consider application size when setting thresholds
- Document namespace/path for each component
- Create visual size distribution if possible

### Don'ts ❌

- Don't count test files in component size
- Don't treat parent directories as components
- Don't use fixed thresholds without considering app size
- Don't ignore small components (may need consolidation)
- Don't skip standard deviation calculation
- Don't mix infrastructure and domain components in same analysis

## Next Steps

After completing component identification and sizing:

1. **Apply Gather Common Domain Components Pattern** - Identify duplicate functionality
2. **Apply Flatten Components Pattern** - Remove orphaned classes from root namespaces
3. **Apply Determine Component Dependencies Pattern** - Analyze coupling between components
4. **Create Component Domains** - Group components into logical domains

## Notes

- Component size thresholds vary by application size
- Small apps (<10 components): 30% threshold may be appropriate
- Large apps (>20 components): 10% threshold is more appropriate
- Standard deviation is more reliable than fixed percentages
- Well-sized components are 1-2 standard deviations from mean
- Oversized components often contain multiple functional areas that can be split