Code Pattern Extractor Agent Skill

Code Pattern Extractor

Overview

Systematically analyze code in directories or modules to identify recurring patterns, code duplication, and implementation patterns that can be abstracted into reusable components, utilities, or design patterns.

Workflow

1. Define Analysis Scope

Identify the code to analyze:

• Directory/module: Analyze all files in a specific directory
• File set: Analyze a specific set of related files
• Component: Analyze files related to a specific feature or component

Use Glob to find relevant files:

**/*.js, **/*.py, **/*.go, etc.

2. Scan for Code Duplication

Identify repeated code blocks that appear multiple times:

Look for:

• Similar function implementations with minor variations
• Repeated code blocks (>5 lines) across files
• Copy-pasted code with slight modifications
• Similar class structures or method patterns

Analysis criteria:

• Similarity threshold: >70% code similarity
• Minimum size: 5+ lines of code
• Frequency: Appears 3+ times

3. Identify Implementation Patterns

Find recurring implementation approaches:

Common patterns:

• API call patterns: Similar fetch/request handling
• Error handling: Repeated try-catch or error checking
• Data validation: Similar input validation logic
• Data transformation: Repeated mapping/filtering operations
• State management: Similar state update patterns
• Configuration: Repeated configuration setup

Example patterns to detect:

// Pattern: API call with error handling
async function fetchX() {
  try {
    const response = await fetch(url);
    if (!response.ok) throw new Error();
    return await response.json();
  } catch (error) {
    console.error(error);
    return null;
  }
}

4. Categorize Patterns

Group identified patterns by type and impact:

Categories:

• High-value: Appears frequently (5+ times), significant code size
• Medium-value: Appears moderately (3-4 times), moderate complexity
• Low-value: Appears rarely (2 times), simple code

Pattern types:

• Utility functions (data processing, formatting, validation)
• API/network patterns (requests, responses, error handling)
• UI patterns (component structures, event handling)
• Business logic patterns (calculations, rules, workflows)

5. Generate Pattern Catalog

Document each identified pattern:

Pattern entry format:

## Pattern: [Descriptive Name]

**Type**: [Utility/API/UI/Business Logic]
**Frequency**: [Number of occurrences]
**Impact**: [High/Medium/Low]

**Description**: [What the pattern does]

**Current implementations**:
- `file1.js:45-60` - [Brief context]
- `file2.js:120-135` - [Brief context]
- `file3.js:89-104` - [Brief context]

**Common variations**:
- [Variation 1 description]
- [Variation 2 description]

6. Generate Refactoring Suggestions

For each high-value pattern, provide refactoring recommendations:

Suggestion format:

### Refactoring: Extract [Pattern Name]

**Current state**: Pattern appears in [N] locations with [X]% code duplication

**Proposed solution**: Extract into [utility function/class/hook/module]

**Benefits**:
- Reduce code duplication by ~[N] lines
- Centralize logic for easier maintenance
- Improve testability

**Implementation approach**:
1. Create new file: `utils/[pattern-name].js`
2. Extract common logic with parameters for variations
3. Replace [N] occurrences with function calls
4. Add unit tests

**Estimated effort**: [Small/Medium/Large]

7. Generate Template Code

Create reusable template implementations for high-value patterns:

Template format:

/**
 * [Pattern description]
 *
 * @param {type} param1 - [Description]
 * @param {type} param2 - [Description]
 * @returns {type} [Description]
 */
function patternTemplate(param1, param2) {
  // Extracted common logic
  // Parameterized variations
  // Return standardized result
}

Include:

• Function signature with parameters for variations
• Documentation comments
• Error handling
• Type annotations (if applicable)
• Usage examples

Output Structure

Organize findings into a comprehensive report:

# Code Pattern Analysis: [Directory/Module Name]

## Summary
- Files analyzed: [N]
- Patterns identified: [N]
- High-value patterns: [N]
- Estimated duplication: [N] lines

## Pattern Catalog
[List of all identified patterns with details]

## Refactoring Suggestions
[Prioritized list of refactoring opportunities]

## Template Code
[Reusable implementations for high-value patterns]

## Next Steps
[Recommended actions prioritized by impact]

Pattern Detection Heuristics

Code duplication detection:

• Compare function bodies for structural similarity
• Ignore variable names and minor formatting differences
• Focus on logic flow and operations

Implementation pattern detection:

• Look for similar function signatures
• Identify repeated import patterns
• Find similar control flow structures (if-else, loops, try-catch)
• Detect repeated library usage patterns

Abstraction opportunities:

• Multiple functions with similar purpose but different parameters
• Repeated setup/teardown code
• Similar data transformations
• Parallel class hierarchies

Tips

• Start with high-frequency patterns for maximum impact
• Consider language-specific idioms when suggesting abstractions
• Balance DRY principle with code clarity (don't over-abstract)
• Include migration path in refactoring suggestions
• Prioritize patterns that improve maintainability, not just reduce lines
• Consider existing project architecture when suggesting abstractions
• Document trade-offs (flexibility vs. simplicity)
• For large codebases, analyze one module at a time