bDS/.github/copilot-instructions.md

GitHub Copilot Instructions for Blogging Desktop Server (bDS)

This document provides context and best practices for GitHub Copilot when working on this Electron + TypeScript + SQLite blogging application.

Project Overview

Blogging Desktop Server (bDS) is a desktop blogging application built with:

• Electron v28+ for cross-platform desktop
• TypeScript for all code (strict mode)
• React for the renderer UI
• Drizzle ORM for type-safe database access
• @libsql/client for SQLite (local database)
• Zustand for React state management

---

⚠️ MANDATORY: Test-First Development

STOP! Before writing ANY implementation code, you MUST:

1. Write a failing test first that describes the expected behavior
2. Run the test to confirm it fails (Red)
3. Write minimal code to make the test pass (Green)
4. Refactor while keeping tests green

No code without tests. No exceptions.

Tests must import and exercise the REAL implementation classes, not inline helper functions. Mock only external dependencies (database, filesystem), never the class under test.

See the TDD Requirements section for detailed guidelines.

---

⚠️ MANDATORY: Fix All Test Failures

You MUST investigate and fix ALL test failures before completing any task.

• Never leave tests failing, even if they appear unrelated to your changes
• If a test failure is pre-existing, fix it as part of your current work
• Run the full test suite (npm test) before considering any task complete
• If you cannot fix a test, explain why and propose a solution

Zero failing tests. No exceptions.

---

Architecture Principles

Separation of Concerns

1. Engine Classes (src/main/engine/): All business logic lives here

   • PostEngine: Blog post CRUD, file I/O, markdown handling
   • MediaEngine: Media import, metadata management
   • SyncEngine: Remote database synchronization
   • TaskManager: Async task queue with progress tracking

2. IPC Layer (src/main/ipc/): Bridge between main and renderer

   • Handlers call engine methods, never contain business logic
   • Always use ipcMain.handle for async operations

3. UI Components (src/renderer/components/): Presentation only

   • Components should be stateless where possible
   • Use Zustand store for shared state
   • Never call IPC directly from deeply nested components

File Storage Pattern

• Posts: Markdown files with YAML frontmatter in posts/ directory
• Media: Binary files with .meta JSON sidecar files in media/ directory
• Database: Index/cache only, source of truth is filesystem

TypeScript Best Practices

Type Safety

// ✅ DO: Use explicit return types for public methods
async function getPost(id: string): Promise<PostData | null> {
  // ...
}

// ✅ DO: Use discriminated unions for status types
type SyncStatus = 'pending' | 'syncing' | 'synced' | 'error';

// ✅ DO: Use Drizzle's inferred types
import { posts, type Post, type NewPost } from './schema';

// ❌ DON'T: Use `any` type
function processData(data: any) { } // Bad

// ❌ DON'T: Ignore null/undefined possibilities
const post = await getPost(id);
console.log(post.title); // Bad - post might be null

Async/Await Patterns

// ✅ DO: Use try-catch with specific error handling
try {
  await fileOperation();
} catch (error) {
  if (error instanceof Error && error.message.includes('ENOENT')) {
    // Handle file not found
  }
  throw error;
}

// ✅ DO: Use Promise.all for concurrent operations
const [posts, media] = await Promise.all([
  postEngine.getAllPosts(),
  mediaEngine.getAllMedia()
]);

// ❌ DON'T: Forget to await async operations
savePost(post); // Bad - fire and forget

Error Handling

// ✅ DO: Create typed error classes
class SyncError extends Error {
  constructor(
    message: string,
    public readonly code: 'AUTH_FAILED' | 'NETWORK_ERROR' | 'CONFLICT'
  ) {
    super(message);
    this.name = 'SyncError';
  }
}

// ✅ DO: Return result objects for operations that can fail
interface OperationResult<T> {
  success: boolean;
  data?: T;
  error?: string;
}

Electron Best Practices

IPC Communication

// ✅ DO: Use contextBridge for secure IPC exposure
// preload.ts
contextBridge.exposeInMainWorld('electronAPI', {
  posts: {
    getAll: () => ipcRenderer.invoke('posts:getAll'),
    create: (data: CreatePostInput) => ipcRenderer.invoke('posts:create', data),
  }
});

// ✅ DO: Validate all IPC inputs in main process
ipcMain.handle('posts:create', async (_event, data: unknown) => {
  const validated = validateCreatePostInput(data);
  return postEngine.createPost(validated);
});

// ❌ DON'T: Use nodeIntegration: true
// ❌ DON'T: Expose Node.js APIs directly to renderer

Window Management

// ✅ DO: Check window existence before sending messages
if (mainWindow && !mainWindow.isDestroyed()) {
  mainWindow.webContents.send('event', data);
}

// ✅ DO: Clean up IPC handlers on window close
mainWindow.on('closed', () => {
  ipcMain.removeHandler('posts:getAll');
});

Process Separation

// Main process: File system, database, native APIs
// Renderer process: UI only, no direct fs/db access

// ✅ DO: All file operations in main process
// src/main/engine/PostEngine.ts
await fs.writeFile(filePath, content);

// ❌ DON'T: Import 'fs' in renderer
// src/renderer/components/Editor.tsx
import fs from 'fs'; // Bad!

SQLite & Drizzle ORM Best Practices

Schema Definition

// ✅ DO: Use proper column types and constraints
export const posts = sqliteTable('posts', {
  id: text('id').primaryKey(),
  title: text('title').notNull(),
  slug: text('slug').notNull().unique(),
  createdAt: integer('created_at', { mode: 'timestamp' }).notNull(),
  syncStatus: text('sync_status').$type<'pending' | 'synced'>().default('pending'),
});

// ✅ DO: Create indexes for frequently queried columns
// CREATE INDEX idx_posts_slug ON posts(slug);
// CREATE INDEX idx_posts_sync_status ON posts(sync_status);

Query Patterns

import { eq, and, desc, sql } from 'drizzle-orm';

// ✅ DO: Use Drizzle query builder
const drafts = await db
  .select()
  .from(posts)
  .where(eq(posts.status, 'draft'))
  .orderBy(desc(posts.updatedAt));

// ✅ DO: Use transactions for multi-table updates
await db.transaction(async (tx) => {
  await tx.update(posts).set({ status: 'published' }).where(eq(posts.id, id));
  await tx.insert(syncLog).values({ entityId: id, operation: 'update' });
});

// ❌ DON'T: Write raw SQL unless absolutely necessary
// ❌ DON'T: Use string interpolation in queries
const result = db.run(`SELECT * FROM posts WHERE id = '${id}'`); // SQL injection risk!

Connection Management

// ✅ DO: Use singleton pattern for database connection
let dbInstance: DatabaseConnection | null = null;

export function getDatabase(): DatabaseConnection {
  if (!dbInstance) {
    dbInstance = new DatabaseConnection();
  }
  return dbInstance;
}

// ✅ DO: Close connection gracefully on app quit
app.on('before-quit', async () => {
  await getDatabase().close();
});

Remote Sync Best Practices (Dropbox)

Sync Strategy

// ✅ DO: Track sync status per entity
interface SyncableEntity {
  syncStatus: 'pending' | 'syncing' | 'synced' | 'conflict';
  syncedAt: number | null;
  checksum: string;
}

// ✅ DO: Use checksums to detect conflicts
const localChecksum = calculateChecksum(localContent);
const remoteChecksum = await fetchRemoteChecksum(id);
if (localChecksum !== remoteChecksum) {
  // Handle conflict
}

// ✅ DO: Implement retry logic with exponential backoff
async function syncWithRetry(maxAttempts = 3): Promise<void> {
  for (let attempt = 1; attempt <= maxAttempts; attempt++) {
    try {
      await sync();
      return;
    } catch (error) {
      if (attempt === maxAttempts) throw error;
      await sleep(Math.pow(2, attempt) * 1000);
    }
  }
}

Offline-First Approach

// ✅ DO: Always write to local first
async function savePost(post: PostData): Promise<void> {
  // 1. Save to local file system
  await writePostFile(post);
  
  // 2. Update local database
  await updateLocalDatabase(post);
  
  // 3. Mark for sync (don't wait for network)
  await markForSync(post.id);
}

// ✅ DO: Queue sync operations
const syncQueue: SyncOperation[] = [];

function queueSync(operation: SyncOperation): void {
  syncQueue.push(operation);
  processSyncQueue(); // Non-blocking
}

// ✅ DO: Handle network state changes
window.addEventListener('online', () => {
  syncEngine.processPendingChanges();
});

Conflict Resolution

// ✅ DO: Implement clear conflict resolution strategy
type ConflictResolution = 'local-wins' | 'remote-wins' | 'manual';

interface ConflictInfo {
  entityId: string;
  localVersion: EntityVersion;
  remoteVersion: EntityVersion;
  resolution?: ConflictResolution;
}

// ✅ DO: Allow user to resolve conflicts manually when needed
async function resolveConflict(
  conflict: ConflictInfo,
  resolution: ConflictResolution
): Promise<void> {
  switch (resolution) {
    case 'local-wins':
      await pushLocalToRemote(conflict.entityId);
      break;
    case 'remote-wins':
      await pullRemoteToLocal(conflict.entityId);
      break;
    case 'manual':
      await showConflictResolutionUI(conflict);
      break;
  }
}

Sync Logging

// ✅ DO: Log all sync operations for debugging
await db.insert(syncLog).values({
  id: generateId(),
  entityType: 'post',
  entityId: postId,
  operation: 'push',
  status: 'success',
  timestamp: Date.now(),
});

// ✅ DO: Implement sync status visibility in UI
const pendingCount = await syncEngine.getPendingChangesCount();
statusBar.setSyncStatus({ pending: pendingCount });

React & State Management

Zustand Patterns

// ✅ DO: Keep store slices focused
interface AppState {
  // UI state
  activeView: 'posts' | 'media' | 'settings';
  sidebarVisible: boolean;
  
  // Data
  posts: PostData[];
  media: MediaData[];
  
  // Actions
  setActiveView: (view: AppState['activeView']) => void;
  setPosts: (posts: PostData[]) => void;
}

// ✅ DO: Use selectors for derived state
const draftCount = useAppStore((state) => 
  state.posts.filter(p => p.status === 'draft').length
);

// ❌ DON'T: Store derived data
interface BadState {
  posts: PostData[];
  draftCount: number; // Bad - derived from posts
}

Component Patterns

// ✅ DO: Use composition over prop drilling
<EditorProvider postId={selectedPostId}>
  <EditorToolbar />
  <EditorContent />
  <EditorStatusBar />
</EditorProvider>

// ✅ DO: Separate container and presentation components
// Container: handles data fetching/IPC
// Presentation: pure rendering based on props

// ❌ DON'T: Put IPC calls in deeply nested components
const DeepComponent = () => {
  // Bad - hard to test and maintain
  const handleClick = async () => {
    await window.electronAPI.posts.save(data);
  };
};

File Naming Conventions

src/
  main/
    database/
      schema.ts        # Drizzle schema definitions
      connection.ts    # Database connection management
    engine/
      PostEngine.ts    # PascalCase for classes
      TaskManager.ts
    ipc/
      handlers.ts      # camelCase for modules
  renderer/
    components/
      Editor/
        Editor.tsx     # PascalCase for components
        Editor.css     # Matching CSS file
        index.ts       # Barrel exports
    store/
      appStore.ts      # camelCase for stores
    types/
      electron.d.ts    # Type declarations

Test-Driven Development (TDD) Requirements

⚠️ CRITICAL: This project follows STRICT Test-Driven Development.

Writing implementation code before tests is NOT acceptable. Pull requests without corresponding tests will be rejected.

All new features and bug fixes MUST have tests written BEFORE implementation.

The Golden Rule: Test Real Implementations

// ✅ CORRECT: Import and test the REAL class
import { PostEngine } from '../../src/main/engine/PostEngine';

describe('PostEngine', () => {
  let postEngine: PostEngine;

  beforeEach(() => {
    // Mock only external dependencies, NOT the class under test
    postEngine = new PostEngine(mockDatabase, mockFileSystem);
  });

  it('should create a post with generated slug from title', async () => {
    const result = await postEngine.createPost({ title: 'Hello World' });
    expect(result.slug).toBe('hello-world');
  });
});

// ❌ WRONG: Testing inline helper functions instead of real implementations
describe('PostEngine', () => {
  it('should generate slug', () => {
    // This tests a local function, not the actual PostEngine class!
    const generateSlug = (title: string) => title.toLowerCase().replace(/ /g, '-');
    expect(generateSlug('Hello World')).toBe('hello-world');
  });
});

TDD Workflow (Red-Green-Refactor)

// 1. RED: Write a failing test first that uses the REAL implementation
import { PostEngine } from '../../src/main/engine/PostEngine';

describe('PostEngine.createPost', () => {
  it('should create a post with generated slug from title', async () => {
    const postEngine = new PostEngine(mockDb, mockFs);
    const result = await postEngine.createPost({ title: 'Hello World' });
    expect(result.slug).toBe('hello-world');
  });
});

// 2. GREEN: Write minimal code in PostEngine to pass the test
// 3. REFACTOR: Improve the code while keeping tests green

Test File Structure

tests/
├── setup.ts                    # Global test configuration
├── utils/
│   ├── factories.ts           # Mock data factories
│   └── index.ts               # Utility exports
└── engine/
    ├── TaskManager.test.ts    # TaskManager unit tests
    ├── PostEngine.test.ts     # PostEngine unit tests
    ├── MediaEngine.test.ts    # MediaEngine unit tests
    └── SyncEngine.test.ts     # SyncEngine unit tests

Test Naming Conventions

// ✅ DO: Use descriptive test names that explain behavior
it('should generate slug from title with lowercase and hyphens', () => {});
it('should emit taskCompleted event when task finishes', () => {});
it('should return null when post not found', () => {});

// ❌ DON'T: Use vague test names
it('works', () => {});
it('test createPost', () => {});

Mock Factory Patterns

// ✅ DO: Use factory functions with overrides
import { createMockPost, createMockMedia } from '../utils/factories';

const post = createMockPost({ 
  title: 'Custom Title',
  status: 'published' 
});

// ✅ DO: Create specialized factories for common scenarios
const draftPost = createMockPost({ status: 'draft' });
const publishedPost = createMockPublishedPost();
const imageMedia = createMockMedia({ mimeType: 'image/jpeg' });
const pdfMedia = createMockPdfMedia();

Testing Async Code

// ✅ DO: Use async/await in tests
it('should save post to filesystem', async () => {
  const post = createMockPost();
  await postEngine.createPost(post);
  
  expect(fs.writeFile).toHaveBeenCalled();
});

// ✅ DO: Test event emissions
it('should emit postCreated event', async () => {
  const handler = vi.fn();
  postEngine.on('postCreated', handler);
  
  await postEngine.createPost({ title: 'Test' });
  
  expect(handler).toHaveBeenCalledWith(
    expect.objectContaining({ title: 'Test' })
  );
});

// ✅ DO: Test error cases
it('should throw when file write fails', async () => {
  vi.mocked(fs.writeFile).mockRejectedValueOnce(new Error('ENOSPC'));
  
  await expect(postEngine.createPost({ title: 'Test' }))
    .rejects.toThrow('ENOSPC');
});

Mocking Dependencies

// ✅ DO: Mock at module level for consistent behavior
vi.mock('../../src/main/database', () => ({
  getDatabase: vi.fn(() => mockDatabase),
}));

vi.mock('fs/promises', () => ({
  readFile: vi.fn(),
  writeFile: vi.fn(),
  unlink: vi.fn(),
}));

// ✅ DO: Reset mocks between tests
beforeEach(() => {
  vi.clearAllMocks();
});

afterEach(() => {
  vi.restoreAllMocks();
});

Test Coverage Requirements

• Minimum coverage: 80% for engine classes
• Critical paths: 100% coverage for data mutations
• Edge cases: Null handling, empty arrays, error conditions

# Run tests with coverage
npm run test:coverage

# View coverage report
open coverage/index.html

When to Write Tests

Scenario	Test Requirement
New engine method	Unit tests BEFORE implementation
Bug fix	Failing test that reproduces bug FIRST
Refactoring	Ensure existing tests pass BEFORE and AFTER
IPC handler	Integration test with mocked engine
UI component	Behavior tests for user interactions

Test Commands

npm run test           # Run all tests once
npm run test:watch     # Run tests in watch mode
npm run test:coverage  # Generate coverage report
npm run test:ui        # Open Vitest UI

Vitest Configuration

Tests are configured in vitest.config.ts with:

• Global test utilities (describe, it, expect, vi)
• Node environment for main process tests
• Coverage reports via v8
• Custom setup file for Electron mocks

Testing Considerations

// ✅ DO: Design for testability
// - Engine classes should accept dependencies via constructor
// - Use interfaces for external dependencies
// - Keep pure business logic separate from I/O

class PostEngine {
  constructor(
    private db: DatabaseConnection,
    private fs: FileSystemAdapter, // Mockable
    private eventEmitter: EventEmitter
  ) {}
}

// ✅ DO: Use factory functions for test data
function createTestPost(overrides?: Partial<PostData>): PostData {
  return {
    id: 'test-id',
    title: 'Test Post',
    status: 'draft',
    ...overrides,
  };
}

// ✅ DO: Test pure functions in isolation
describe('generateSlug', () => {
  it('should convert to lowercase', () => {
    expect(generateSlug('Hello World')).toBe('hello-world');
  });
  
  it('should replace special characters', () => {
    expect(generateSlug('Hello, World!')).toBe('hello-world');
  });
});

Common Patterns in This Codebase

Creating a New Engine Method

// 1. Add method to engine class
async newOperation(input: InputType): Promise<OutputType> {
  // Validate input
  // Perform operation
  // Emit event for UI updates
  this.emit('operationCompleted', result);
  return result;
}

// 2. Add IPC handler
ipcMain.handle('entity:operation', async (_event, input) => {
  return engine.newOperation(input);
});

// 3. Expose in preload
entity: {
  operation: (input) => ipcRenderer.invoke('entity:operation', input),
}

// 4. Update store and UI

Adding a New Database Table

// 1. Define in schema.ts with proper types
export const newTable = sqliteTable('new_table', {
  id: text('id').primaryKey(),
  // ... columns
});

// 2. Export types
export type NewTableRow = typeof newTable.$inferSelect;
export type NewTableInsert = typeof newTable.$inferInsert;

// 3. Add CREATE TABLE to migrations in connection.ts
// 4. Create corresponding engine class

Security Reminders

• Never log sensitive data (auth tokens, passwords)
• Validate all IPC inputs before processing
• Use contextIsolation: true and sandbox: false only when necessary
• Store Dropbox auth tokens in secure storage, not in code
• Sanitize user input before rendering (XSS prevention)