pattern

name	pattern
description	Design pattern recommendation and anti-pattern detection.

Activate When

• /godmode:pattern, "what pattern should I use"
• "detect anti-patterns", "code smells", "refactor structure"
• Review skill identifies structural issues

Workflow

1. Problem Analysis

find src/ -name "*.ts" | xargs wc -l \
  | sort -rn | head -20
npx madge --circular src/

Problem: <design challenge>
Language: <primary language>
Framework: <if applicable>
Existing patterns: <detected>

2. Pattern Classification

Creational (object creation problems): Factory, Builder, Singleton (last resort -- use DI), Prototype, Abstract Factory.

Structural (composition problems): Adapter, Decorator, Facade, Proxy, Composite, Bridge.

Behavioral (communication problems): Strategy, Observer, Command, State, Chain of Responsibility, Mediator, Iterator, Template Method.

Distributed (resilience/consistency): Circuit Breaker, Saga, Outbox, CQRS, Strangler Fig, Bulkhead, Sidecar.

3. Pattern Recommendation

For each candidate:

• When to use, benefits, drawbacks
• Language-specific implementation
• Unit test demonstrating the pattern
• At least 1 rejected alternative with rationale

IF roles < 10 and stable: pure Strategy sufficient. IF >3 switch/case on same type: consider State pattern. IF files > 500 LOC: God Object -- extract classes.

4. Anti-Pattern Detection

find src/ -name "*.ts" | xargs wc -l \
  | sort -rn | head -20
npx jscpd src/ --min-lines 10 --min-tokens 50
grep -rn "email: string\|price: number" \
  --include="*.ts" src/

Key anti-patterns:

• God Object: >500 LOC, >20 methods (HIGH)
• Shotgun Surgery: 1 change = N file edits (HIGH)
• Feature Envy: method uses other class data (MEDIUM)
• Primitive Obsession: string for email/money (MEDIUM)
• Circular Dependency: A imports B, B imports A (HIGH)
• Distributed Monolith: coupled services (CRITICAL)
• Copy-Paste: duplicated logic drifts apart (MEDIUM)

5. Artifacts

Save: docs/patterns/<feature>-pattern-analysis.md Commit: "pattern: <feature> -- <pattern> (<confidence>)"

Quality Targets

• Cyclomatic complexity: <20 per function
• Injected services: <7 per class
• Circular deps: <1 cycle detected

Hard Rules

1. NEVER recommend pattern without understanding problem.
2. NEVER stack multiple patterns at once.
3. NEVER recommend Singleton for dependency sharing.
4. NEVER apply patterns prophylactically (YAGNI).
5. NEVER produce recommendation without implementation.
6. ALWAYS include trade-offs (benefits AND drawbacks).
7. ALWAYS show alternatives considered.
8. ALWAYS include unit test demonstrating pattern.

TSV Logging

Append .godmode/pattern-results.tsv:

timestamp	feature	pattern	category	confidence	antipatterns	language	files	verdict

Keep/Discard

KEEP if: tests pass AND complexity reduced
  AND code no more complex than necessary.
DISCARD if: pattern adds more complexity than it
  removes OR tests fail.

Stop Conditions

STOP when FIRST of:
  - Design problem resolved with tested implementation
  - Anti-pattern scan complete, findings prioritized
  - Pattern recommended with trade-offs + alternative

Autonomous Operation

On failure: git reset --hard HEAD~1. Never pause.

Error Recovery

Failure	Action
Pattern adds complexity	Revert, simple code wins
Refactoring breaks tests	Smaller steps, test each
Team unfamiliar	Document with codebase example
Conflicts with framework	Prefer framework conventions