Task 3.0: Classical GoF Patterns Documentation and Examples (11.2.4)

[jburns24]

🎯 Task Overview

Task ID: 3.0
Parent Spec: docs/specs/01-spec-design-patterns-section/01-spec-design-patterns-section.md
Depends On: Task 1.0, Task 2.0 (conceptually independent, but sequential for consistency)
Status: Ready for Implementation
Estimated Time: 2-3 hours

This task implements comprehensive documentation for Classical Gang of Four Patterns (11.2.4), including Strategy, Factory, Observer, and Decorator patterns with working examples distributed across languages, explicit SOLID connections, and an interactive quiz.

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📋 Specification Context

Project Overview

This specification defines the remaining Design Patterns subsections for Chapter 11 (Application Development) of the DevOps Bootcamp. This task introduces selected Gang of Four patterns that directly relate to SOLID principles and are commonly used in production applications.

User Story

US-4: Recognizing Classical Patterns
As a senior CSCI student preparing for professional work, I want to recognize Strategy, Factory, Observer, and Decorator patterns in existing codebases so that I can understand and contribute to enterprise projects.

Functional Requirements

ID	Requirement
U4-FR1	The system shall explain Strategy Pattern with examples demonstrating swappable algorithms and explicit connection to Open/Closed Principle
U4-FR2	The system shall explain Factory Pattern with examples demonstrating object creation abstraction and explicit connection to Dependency Inversion Principle
U4-FR3	The system shall explain Observer Pattern with examples demonstrating event-driven communication between objects
U4-FR4	The system shall explain Decorator Pattern with examples demonstrating behavior extension and explicit connection to Open/Closed Principle
U4-FR5	The system shall organize pattern explanations by problem domain: Creational (Factory), Behavioral (Strategy, Observer), Structural (Decorator)
U4-FR6	The system shall explicitly connect each pattern to relevant SOLID principles with cross-references to 11.2.1 content
U4-FR7	The system shall provide pattern recognition exercises using real-world code snippets
U4-FR8	The system shall include a self-directed exercise for students to identify patterns in a production codebase of their choice
U4-FR9	The system shall include an interactive quiz testing pattern recognition across code snippets in multiple languages

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✅ Acceptance Criteria (Proof Artifacts)

The following artifacts must exist and be verified for task completion:

• Documentation: docs/11-application-development/11.2.4-classical-patterns.md exists with complete content including front-matter, pattern explanations organized by category (Creational/Behavioral/Structural), SOLID connections, and exercises
• Strategy Pattern: examples/ch11/classical-patterns/strategy/ contains working implementation with README and explicit connection to Open/Closed Principle
• Factory Pattern: examples/ch11/classical-patterns/factory/ contains working implementation with README and explicit connection to Dependency Inversion Principle
• Observer Pattern: examples/ch11/classical-patterns/observer/ contains working implementation with README demonstrating event-driven communication
• Decorator Pattern: examples/ch11/classical-patterns/decorator/ contains working implementation with README and explicit connection to Open/Closed Principle
• Quiz: src/quizzes/chapter-11/11.2.4/classical-patterns-quiz.js exists with multi-language pattern recognition questions following quizdown format
• CLI Verification: Tests pass in all example directories (using appropriate test command per language)
• SOLID Integration: Each pattern README includes explicit cross-reference to relevant section in 11.2.1

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📝 Sub-tasks

Documentation Tasks

• 3.1 Create documentation file docs/11-application-development/11.2.4-classical-patterns.md with front-matter (category: Application Development, technologies: Python/Go/TypeScript/Design Patterns, estReadingMinutes: 45, exercise definition)
• 3.2 Write introduction explaining Gang of Four patterns, their organization (Creational/Behavioral/Structural), and focus on patterns most relevant to SOLID principles
• 3.3 Write Strategy Pattern section (Behavioral) explaining swappable algorithms, explicit connection to Open/Closed Principle (extending behavior without modification), and cross-reference to 11.2.1
• 3.4 Write Factory Pattern section (Creational) explaining object creation abstraction, explicit connection to Dependency Inversion Principle (depending on abstractions), and cross-reference to 11.2.1
• 3.5 Write Observer Pattern section (Behavioral) explaining event-driven communication, one-to-many dependencies, and use cases (UI updates, event systems)
• 3.6 Write Decorator Pattern section (Structural) explaining dynamic behavior extension, explicit connection to Open/Closed Principle (adding responsibilities without modification), and cross-reference to 11.2.1
• 3.7 Add pattern recognition section with guidance on identifying these patterns in production codebases
• 3.8 Add self-directed exercise description for students to identify patterns in a production codebase of their choice

Code Example Tasks (Multi-Language)

• 3.9 Create Strategy Pattern Python example in examples/ch11/classical-patterns/strategy/ with pyproject.toml, src/ (different algorithm implementations), README.md with OCP connection, and tests
• 3.10 Create Factory Pattern Go example in examples/ch11/classical-patterns/factory/ with go.mod, factory.go (creation abstraction), README.md with DIP connection, and tests
• 3.11 Create Observer Pattern TypeScript example in examples/ch11/classical-patterns/observer/ with package.json, tsconfig.json, src/ (subject/observer implementation), README.md, and tests
• 3.12 Create Decorator Pattern Python example in examples/ch11/classical-patterns/decorator/ with pyproject.toml, src/ (base component + decorators), README.md with OCP connection, and tests

Quiz and Verification Tasks

• 3.13 Create interactive quiz src/quizzes/chapter-11/11.2.4/classical-patterns-quiz.js with 8-10 questions covering pattern recognition from code snippets in multiple languages, SOLID connections, and when to use each pattern
• 3.14 Verify Strategy and Decorator Python examples run successfully with uv run main.py and tests pass with uv run pytest
• 3.15 Verify Factory Go example runs successfully with go run main.go and tests pass with go test ./...
• 3.16 Verify Observer TypeScript example runs successfully with npm run start and tests pass with npm test
• 3.17 Embed quiz in documentation using Docsify quiz syntax and verify it renders correctly with npm start

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📁 Relevant Files

Files to Create

Documentation:

• docs/11-application-development/11.2.4-classical-patterns.md - Main documentation
• src/quizzes/chapter-11/11.2.4/classical-patterns-quiz.js - Interactive quiz

Strategy Pattern (Python):

• examples/ch11/classical-patterns/strategy/pyproject.toml - Python dependencies
• examples/ch11/classical-patterns/strategy/src/strategy.py - Strategy interface and implementations
• examples/ch11/classical-patterns/strategy/src/main.py - Executable demo
• examples/ch11/classical-patterns/strategy/tests/test_strategy.py - Unit tests
• examples/ch11/classical-patterns/strategy/README.md - Setup, explanation, and OCP connection

Factory Pattern (Go):

• examples/ch11/classical-patterns/factory/go.mod - Go module definition
• examples/ch11/classical-patterns/factory/factory.go - Factory interface and implementations
• examples/ch11/classical-patterns/factory/main.go - Executable demo
• examples/ch11/classical-patterns/factory/factory_test.go - Unit tests
• examples/ch11/classical-patterns/factory/README.md - Setup, explanation, and DIP connection

Observer Pattern (TypeScript):

• examples/ch11/classical-patterns/observer/package.json - Dependencies
• examples/ch11/classical-patterns/observer/tsconfig.json - TypeScript config
• examples/ch11/classical-patterns/observer/src/observer.ts - Observer interface
• examples/ch11/classical-patterns/observer/src/subject.ts - Subject implementation
• examples/ch11/classical-patterns/observer/src/main.ts - Executable demo
• examples/ch11/classical-patterns/observer/tests/observer.test.ts - Unit tests
• examples/ch11/classical-patterns/observer/README.md - Setup and explanation

Decorator Pattern (Python):

• examples/ch11/classical-patterns/decorator/pyproject.toml - Python dependencies
• examples/ch11/classical-patterns/decorator/src/decorator.py - Component interface and decorators
• examples/ch11/classical-patterns/decorator/src/main.py - Executable demo
• examples/ch11/classical-patterns/decorator/tests/test_decorator.py - Unit tests
• examples/ch11/classical-patterns/decorator/README.md - Setup, explanation, and OCP connection

Files to Reference

• docs/11-application-development/11.2.1-solid-principles.md - SOLID principles (for explicit cross-references)
• examples/ch11/solid-exercises/ - Example of existing code structure
• src/quizzes/chapter-11/11.2.1/solid-principles-quiz.js - Example quiz format to follow

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🎓 Repository Standards

Code Example Standards (Multi-Language)

Python (Strategy, Decorator):

• Python 3.11+ with uv for dependency management
• Use pyproject.toml for project configuration
• Testing with pytest: uv run pytest
• Type hints where appropriate
• Follow PEP 8 style guidelines

Go (Factory):

• Go 1.21+ with Go modules
• Standard Go project layout
• Testing with built-in package: go test ./...
• Follow Go best practices (gofmt, golint)

TypeScript (Observer):

• Node.js 20+ with npm/package.json
• TypeScript with strict mode enabled
• Testing with Jest: npm test
• Follow TypeScript best practices

General:

• All examples must be self-contained with README, tests, and dependency management
• Assume ARM-based macOS development environment
• No external service dependencies
• Clear executable demos with main files

Documentation Standards

• Front-Matter: Include YAML metadata with category, technologies (Python/Go/TypeScript/Design Patterns), estReadingMinutes: 45, exercises
• Organization: Group patterns by GoF category (Creational, Behavioral, Structural)
• SOLID Connections: Each pattern must explicitly reference relevant SOLID principle from 11.2.1
• Cross-References: Use markdown links like [Open/Closed Principle](11-application-development/11.2.1-solid-principles.md#open-closed-principle-ocp)
• Header Levels: Use H2 (##) for navigation-visible sections, H3 (###) as default within sections
• Code Snippets: Include short code examples in documentation showing pattern structure

Quiz Standards

• Format: Follow existing quizdown format from src/quizzes/chapter-11/11.2.1/solid-principles-quiz.js
• Question Types: Pattern recognition from code snippets (Python/Go/TypeScript), SOLID connections, when to use each pattern
• Question Count: 8-10 questions covering all four patterns
• Multi-Language: Include code snippets in different languages to reinforce language-agnostic concepts
• Feedback: Explain why answers are correct/incorrect and reinforce SOLID connections

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🔗 Related Documentation

• Full Spec: docs/specs/01-spec-design-patterns-section/01-spec-design-patterns-section.md
• Complete Task List: docs/specs/01-spec-design-patterns-section/01-tasks-design-patterns-section.md
• Previous Tasks:
  • Issue Task 1.0: Data Layer Patterns Documentation and Examples (11.2.2) #816 - Task 1.0: Data Layer Patterns
  • Issue Task 2.0: Business Logic Patterns Documentation and Examples (11.2.3) #821 - Task 2.0: Business Logic Patterns
• Project Overview: CLAUDE.md (repository root)
• Style Guide: STYLE.md (repository root)

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🤖 AI Agent Instructions

Implementation Approach

1. Start with Documentation: Create markdown file with proper front-matter and GoF organization structure
2. Write Pattern Explanations: For each pattern, clearly explain the problem it solves, the solution, and explicit SOLID connection
3. Build Examples by Pattern: Complete one pattern at a time (documentation + code + tests) before moving to next
4. Emphasize SOLID Connections: Make explicit cross-references to 11.2.1 showing how patterns embody principles
5. Test Multi-Language Setup: Ensure you have Python (uv), Go, and Node.js/TypeScript environments working
6. Create Quiz Last: Quiz should test pattern recognition across multiple languages
7. Verify All Integration: Test complete documentation with all code examples and quiz

Pattern Implementation Suggestions

Strategy Pattern (Python):

• Example: Payment processing with different payment methods (CreditCard, PayPal, Bitcoin)
• Show how adding new payment method doesn't modify existing code (OCP)

Factory Pattern (Go):

• Example: Database connection factory supporting multiple databases (PostgreSQL, MySQL, SQLite)
• Show how client depends on interface, not concrete implementations (DIP)

Observer Pattern (TypeScript):

• Example: Stock price monitoring with multiple displays (chart, table, alert)
• Show event-driven updates when stock price changes

Decorator Pattern (Python):

• Example: Coffee shop with base coffee and decorators (milk, sugar, whipped cream)
• Show how adding features doesn't modify base component (OCP)

Quality Checklist

• All code follows language-specific best practices
• Each README includes explicit SOLID principle connection
• Cross-references to 11.2.1 use correct anchor links
• All tests pass in their respective environments
• Documentation clearly organizes patterns by GoF category
• Quiz includes code snippets from multiple languages
• Pattern recognition section provides practical guidance
• Self-directed exercise is clear and actionable

Multi-Language Testing Commands

# Strategy Pattern (Python)
cd examples/ch11/classical-patterns/strategy
uv run main.py
uv run pytest

# Factory Pattern (Go)
cd examples/ch11/classical-patterns/factory
go run main.go
go test ./...

# Observer Pattern (TypeScript)
cd examples/ch11/classical-patterns/observer
npm install
npm run start
npm test

# Decorator Pattern (Python)
cd examples/ch11/classical-patterns/decorator
uv run main.py
uv run pytest

Success Criteria

This task is complete when:

1. All 17 sub-tasks are checked off
2. All proof artifacts exist and are verified
3. Tests pass in all four example directories (Python, Go, TypeScript)
4. Each pattern README explicitly cross-references relevant SOLID principle in 11.2.1
5. Quiz includes pattern recognition questions with multi-language code snippets
6. npm start successfully renders documentation with embedded quiz
7. Documentation follows bootcamp conventions and clearly organizes patterns by GoF category