Agent Skills: Add New File

Add New File

This skill guides you through adding new files to the codebase while maintaining architectural consistency and code quality standards.

Quick Reference

When adding a new file to this project:

1. Determine the scope - What domain/concern does this file address?
2. Follow module pattern - Create types.ts, constants.ts, main logic file
3. Externalize constants - All magic strings/numbers go in constants.ts
4. Keep functions small - Max 20 lines of logic per function
5. Use proper imports - node: prefix, import type, .ts extensions
6. Write co-located tests - Create .test.ts alongside source

See references/architecture-principles.md for comprehensive guidelines.

Adding a New Module

When creating a new module (e.g., cache/, auth/, logger/):

Step 1: Create Module Directory

module-name/
├── types.ts          # Type definitions only
├── constants.ts      # Externalized constants
├── module-name.ts    # Core logic
└── module-name.test.ts  # Tests

Step 2: Define Types First

Create types.ts:

export interface ModuleConfig {
  enabled: boolean;
  timeout: number;
}

export type ModuleState = "idle" | "active" | "error";

Step 3: Externalize Constants

Create constants.ts:

export const DEFAULT_TIMEOUT_MS = 5000;
export const MODULE_CONFIG_FILE = "module-config.json";
export const ERROR_INVALID_CONFIG = "Invalid module configuration";

Step 4: Implement Core Logic

Create module-name.ts:

import { existsSync, readFileSync } from "node:fs";
import { join } from "node:path";
import type { ModuleConfig } from "./types.ts";
import { DEFAULT_TIMEOUT_MS, MODULE_CONFIG_FILE } from "./constants.ts";

export const loadModuleConfig = (dir: string): ModuleConfig => {
  const configPath = join(dir, MODULE_CONFIG_FILE);
  if (!existsSync(configPath)) {
    return { enabled: true, timeout: DEFAULT_TIMEOUT_MS };
  }
  return JSON.parse(readFileSync(configPath, "utf-8"));
};

Step 5: Write Tests

Create module-name.test.ts following Vitest patterns in the reference doc.

Adding a Utility File

For standalone utilities that don't need a full module:

1. Place in appropriate existing module or create utils/ if needed
2. Create utils/helper.ts and utils/helper.test.ts
3. Extract any constants to the parent module's constants.ts
4. Keep functions small and composable

Pre-Flight Checklist

Before creating files, verify:

• ✅ Correct location - File belongs in right module/directory
• ✅ Constants identified - Know what values need externalizing
• ✅ Types defined - Clear interfaces for inputs/outputs
• ✅ Single responsibility - File has one clear purpose
• ✅ Dependencies mapped - Know what to import

Post-Creation Checklist

After creating files, verify:

• ✅ All imports use node: prefix for built-ins
• ✅ Type imports use import type
• ✅ Relative imports include .ts extension
• ✅ All exports have explicit return types
• ✅ Constants externalized to constants.ts
• ✅ Functions under 20 lines of logic
• ✅ Tests created and passing
• ✅ Code follows style guide (see reference doc)
• ✅ No console.log statements (use client.tui)

Common Patterns

Configuration Module

config/
├── types.ts       # ConfigOptions, ConfigSchema
├── constants.ts   # CONFIG_FILE_NAME, DEFAULT_VALUES
├── config.ts      # loadConfig(), saveConfig()
└── config.test.ts

Business Logic Module

processor/
├── types.ts          # ProcessorInput, ProcessorOutput
├── constants.ts      # MAX_RETRIES, TIMEOUT_MS
├── processor.ts      # process(), validate()
└── processor.test.ts

Utility Module

utils/
├── string-utils.ts      # String manipulation helpers
├── string-utils.test.ts
├── path-utils.ts        # Path manipulation helpers
└── path-utils.test.ts

Detailed Guidelines

For comprehensive information on:

• Complete constants externalization rules with examples
• Full code style guide (imports, functions, naming, formatting)
• Error handling patterns
• Testing patterns with Vitest
• File system operation patterns

Read: references/architecture-principles.md

Verification Commands

After creating new files:

bun run typecheck   # Verify TypeScript types
bun run lint        # Check code style
bun run test        # Run tests
bun run build       # Ensure it builds