extract-shared

name	extract-shared
description	Identify cross-project code duplication and generate candidates for a shared utility package.
argument-hint	[--scan|--report|--python|--node]

Shared Utilities Extractor

Scan your projects for duplicated patterns and identify candidates for extraction into a shared utility package.

Selecting Projects to Scan

Decide what to scan, in this order:

1. Paths passed as arguments — scan exactly those project directories.
2. A workspace root — if you keep several projects under one directory (e.g. ~/projects), scan each immediate subdirectory.
3. The current directory — if neither applies, this skill needs at least two projects to compare; ask the user to point it at a workspace root or a set of paths.

Arguments

Parse $ARGUMENTS:

• No arguments or --scan: Run full scan and report (default)
• --report: Show results from last scan without re-scanning
• --python: Only scan Python projects
• --node: Only scan Node.js projects

Process

Step 1: Define Search Patterns

Scan for these known duplication categories across the selected projects:

Category 1: Health Check Endpoints

Search for health endpoint implementations:

# Python
grep -rn "def health" --include="*.py" <path>
grep -rn "/health" --include="*.py" <path>

# Node/TypeScript
grep -rn "'/health'" --include="*.ts" --include="*.js" <path>
grep -rn "\"/health\"" --include="*.ts" --include="*.js" <path>

Category 2: Error Response Formats

Search for custom exception classes and error response patterns:

# Python
grep -rn "class.*Error.*Exception" --include="*.py" <path>
grep -rn "class.*APIError\|class.*AppError\|class.*ServiceError" --include="*.py" <path>

# Node/TypeScript
grep -rn "class.*Error extends" --include="*.ts" --include="*.js" <path>

Category 3: Configuration / Settings Patterns

Search for config loading patterns:

# Python
grep -rn "os.environ\|os.getenv\|environ.get" --include="*.py" <path> | head -10
grep -rn "class.*Config\|class.*Settings" --include="*.py" <path>

# Node/TypeScript
grep -rn "process.env" --include="*.ts" --include="*.js" <path> | head -10

Category 4: Authentication / Rate Limiting

# Python
grep -rn "rate.limit\|RateLimiter\|throttle" --include="*.py" <path>
grep -rn "auth.*decorator\|login_required\|verify_token" --include="*.py" <path>

# Node/TypeScript
grep -rn "rateLimit\|rate-limit" --include="*.ts" --include="*.js" <path>
grep -rn "authenticate\|verifyToken\|authMiddleware" --include="*.ts" --include="*.js" <path>

Category 5: Database Utilities

# Python
grep -rn "def get_db\|def create_tables\|def run_migration" --include="*.py" <path>
grep -rn "session.execute\|session.commit" --include="*.py" <path> | head -5

# Node/TypeScript
grep -rn "getConnection\|createPool\|query(" --include="*.ts" --include="*.js" <path>

Category 6: Encryption / Secrets Helpers

grep -rn "Fernet\|encrypt\|decrypt\|hashlib\|bcrypt" --include="*.py" <path>
grep -rn "crypto\|encrypt\|decrypt\|hash" --include="*.ts" --include="*.js" <path>

Category 7: Audit Logging

grep -rn "record_audit\|audit_log\|log_action\|telemetry" --include="*.py" <path>

Category 8: Docker Health Checks

grep -rn "healthcheck\|HEALTHCHECK" <path>/docker-compose*.yml <path>/Dockerfile 2>/dev/null

Step 2: Collect and Compare

For each category, collect the implementations found across projects. Use the Grep tool for each pattern across each project directory.

Group results by category and compare:

• How many projects implement this pattern?
• Are the implementations similar enough to share?
• What's the effort to extract vs. keep separate?

Step 3: Analyze Similarity

For patterns found in 2+ projects, read the actual implementation files and compare:

1. Read the relevant function/class from each project
2. Assess similarity (identical, similar with minor differences, fundamentally different)
3. Rate extraction feasibility: Easy (copy-paste), Medium (needs abstraction), Hard (too different)

Step 4: Report

## Cross-Project Duplication Report

### High-Value Extraction Candidates (found in 3+ projects)

#### 1. Health Check Endpoints
- **Projects:** api-service, web-app, dashboard, platform
- **Pattern:** GET /health returning {status: "healthy", service: "<name>"}
- **Similarity:** High — nearly identical implementations
- **Extraction effort:** Easy
- **Recommendation:** Create shared `health_check()` factory function

#### 2. Error Response Formats
- **Projects:** api-service, web-app
- **Pattern:** Custom exception classes with JSON error responses
- **Similarity:** Medium — same structure, different exception types
- **Extraction effort:** Medium
- **Recommendation:** Create shared base error classes with JSON serialization

### Medium-Value Candidates (found in 2 projects)

#### 3. Encryption Utilities
- **Projects:** api-service (Fernet), web-app (potential)
- **Similarity:** Low — only one project has it currently
- **Extraction effort:** Easy
- **Recommendation:** Extract if second project needs it

...

### Not Worth Extracting (domain-specific)

- Business-logic parsers unique to a single project
- Third-party integration sync code used by only one project
- Bespoke handlers unique to one product

### Proposed Shared Package Structure

If extracting a Python shared package (`shared-common`):

shared-common/ ├── pyproject.toml ├── shared_common/ │ ├── init.py │ ├── health.py # Health check endpoint factory │ ├── errors.py # Base error classes │ ├── config.py # Configuration loader │ ├── auth.py # Auth decorators │ ├── audit.py # Audit logging │ └── encryption.py # Encryption helpers └── tests/ └── ...

If extracting a Node shared package (`@yourorg/common`):

shared-common-node/ ├── package.json ├── src/ │ ├── health.ts │ ├── errors.ts │ ├── config.ts │ └── auth.ts └── tests/ └── ...

### Summary

| Category | Projects | Similarity | Effort | Priority |
|----------|----------|-----------|--------|----------|
| Health checks | 4 | High | Easy | HIGH |
| Error formats | 2 | Medium | Medium | MEDIUM |
| Config loading | 4 | Medium | Medium | MEDIUM |
| Rate limiting | 2 | Low | Medium | LOW |
| Encryption | 1+ | N/A | Easy | LOW |
| Audit logging | 2 | Medium | Medium | MEDIUM |
| Docker health | 3 | High | Easy | HIGH |

Total duplication categories: X
Worth extracting now: Y
Worth extracting later: Z
Domain-specific (keep separate): W

Error Handling

• If a project path doesn't exist, skip it
• If grep finds no matches in a category, report "No instances found"
• Large result sets: limit to first 10 matches per project per category
• Never modify any project files — this is analysis only

Notes

• This skill is read-only — it identifies duplication but does not extract or create packages
• Use the report to plan extraction work in a follow-up session
• Focus on patterns that appear in 3+ projects for highest ROI
• Domain-specific code (single-project business logic, one-off integrations) should stay in its project
• The proposed package structure is a recommendation — adjust based on actual findings
• Run this quarterly or before starting a new project