turn-based-game-mcp: Instructions file for GitHub Copilot

TypeScript Development

Purpose

TypeScript patterns for type-safe code. Covers type definitions, generics, error handling, and module organization.

Type Definitions

Import/Export Patterns

• Import types with import type for type-only imports
• Export types separately from implementations
• Use barrel exports (index.ts) for clean imports
• Re-export shared types from @turn-based-mcp/shared

Shared Types and Constants

Always import types derived from shared constants - don't duplicate union types:

// ✅ Import types derived from constants
import type { Difficulty, GameType, PlayerId } from '@turn-based-mcp/shared'
import { DIFFICULTIES, DEFAULT_AI_DIFFICULTY, GAME_TYPES, PLAYER_IDS } from '@turn-based-mcp/shared'

// ✅ Use the imported types
const [aiDifficulty, setAiDifficulty] = useState<Difficulty>('medium')
const playerIds: PlayerId[] = Object.values(PLAYER_IDS)

// ❌ Don't define duplicate union types
type Difficulty = 'easy' | 'medium' | 'hard'  // This duplicates shared constants!
type PlayerId = 'player1' | 'player2' | 'ai'  // Use the derived type instead!

Key principle: Types are derived from constants using as const assertions:

// In shared/src/constants/game-constants.ts
export const DIFFICULTIES = ['easy', 'medium', 'hard'] as const
export type Difficulty = typeof DIFFICULTIES[number]  // 'easy' | 'medium' | 'hard'

Common types available from shared package:

• Difficulty - AI difficulty levels (derived from DIFFICULTIES)
• GameType - Supported game types (derived from GAME_TYPES)
• PlayerId - Player identifiers (derived from PLAYER_IDS)
• GameStatus - Game state values (derived from GAME_STATUSES)
• Game-specific interfaces: TicTacToeGameState, RPSGameState, etc.

Interface Design

• Use interfaces for object shapes and component props
• Include JSDoc comments for complex properties
• Make optional properties explicit with ?
• Use union types for enums and variants