# Architecture Patterns

**Domain:** Weekly Task Management Application
**Researched:** January 24, 2026

## Recommended Architecture

A weekly task management application with calendar integration follows a layered architecture pattern with distinct component boundaries. The architecture consists of:

1. **Frontend Layer** - User interface for weekly view, drag-and-drop functionality, and calendar integration
2. **Backend Layer** - API services for task and calendar data management
3. **Data Layer** - Database for storing tasks, events, and user preferences
4. **Integration Layer** - Services for Apple Calendar and Google Calendar synchronization

This structure enables scalability, maintainability, and supports the core requirement of displaying tasks and events in a single weekly view.

### Component Boundaries

| Component | Responsibility | Communicates With |
|-----------|---------------|-------------------|
| **Frontend** | User interface rendering, drag-and-drop operations, weekly view display | Backend API, Integration Layer |
| **Backend API** | Business logic, task/event management, authentication | Database, Integration Layer |
| **Database** | Persistent storage of tasks, events, calendar integrations, user data | Backend API |
| **Calendar Integration** | Sync with Apple Calendar and Google Calendar | Backend API, External Calendar APIs |

### Data Flow

1. User interacts with weekly view in frontend (drag-and-drop, add/remove tasks)
2. Frontend communicates changes to Backend API via RESTful services
3. Backend API processes business logic and validates data
4. Backend accesses Database for storage/retrieval of task/event data
5. For external calendar sync, Backend API communicates with Calendar Integration Layer
6. Calendar Integration Layer manages OAuth flows and data synchronization
7. Updates are pushed back to frontend for immediate UI refresh

## Patterns to Follow

### Pattern 1: Layered Architecture
**What:** Separation of concerns into distinct layers (presentation, business logic, data)
**When:** For scalable, maintainable codebase
**Example:**
```javascript
// Frontend layer
const WeeklyView = () => {
  // Renders weekly view with task/event cards
}

// Backend layer
const TaskService = {
  async createTask(taskData) {
    // Business logic validation
    const task = await database.saveTask(taskData);
    return task;
  }
}
```

### Pattern 2: Observer Pattern for Real-time Updates
**What:** Components notify each other of changes in real-time
**When:** For synchronous updates between frontend and backend when tasks are moved
**Example:**
```javascript
// Event emitter for task movement
const taskEmitter = new EventEmitter();
taskEmitter.on('taskMoved', (taskId, newDay) => {
  // Update UI immediately
  updateWeekView(taskId, newDay);
});
```

### Pattern 3: Service Layer for Calendar Integration
**What:** Encapsulate external calendar API interactions in dedicated services
**When:** For managing multiple calendar providers and complex sync logic
**Example:**
```javascript
class CalendarSyncService {
  async syncWithGoogle(calendarEvents) {
    // Handle Google Calendar OAuth flow
    // Update local DB with synced events
  }
  
  async syncWithApple(calendarEvents) {
    // Handle Apple Calendar integration
    // Update local DB with synced events
  }
}
```

## Anti-Patterns to Avoid

### Anti-Pattern 1: Monolithic Frontend
**What:** All UI logic bundled in single files without separation
**Why bad:** Makes maintenance difficult as application grows
**Instead:** Use component-based architecture with clear separation of concerns

### Anti-Pattern 2: Direct Database Access
**What:** Frontend components querying database directly
**Why bad:** Security vulnerabilities, tight coupling, scalability issues
**Instead:** Use API layer to mediate all data access

### Anti-Pattern 3: Inconsistent Calendar Sync Logic
**What:** Different sync approaches for different calendar providers
**Why bad:** Leads to data inconsistency and user confusion
**Instead:** Implement standardized sync protocols with clear error handling

## Scalability Considerations

| Concern | At 100 users | At 10K users | At 1M users |
|---------|--------------|--------------|-------------|
| Task Creation/Updates | Local caching with optimistic updates | Load balancer with database connection pooling | CDN for static assets, sharded database |
| Calendar Integration | Single-threaded sync per user | Parallel sync workers | Distributed sync services, queue processing |
| Concurrent Drag-and-Drop | Immediate updates with local state | Server-synchronized updates with conflict resolution | Real-time WebSocket connections for instant updates |

## Sources

- General software architecture principles from Martin Fowler's writings
- Layered architecture patterns commonly used in web applications
- Task management application design patterns from industry best practices
- Component-based architecture guidelines for scalable frontend development