# Implementation Plan: Callback System & Dual Scheduling

**Document Created**: 2025-08-26 11:17:26 UTC  
**Author**: Matthew Raymer  
**Status**: 📋 **PLANNING PHASE**  
**Priority**: 🔴 **HIGH** - Core functionality enhancement required

## 🎯 **IMPLEMENTATION OVERVIEW**

### **Goal**

Transform the Daily Notification Plugin from a single-method scheduler to a dual-method system with comprehensive callback support for external service integration.

### **Key Changes**

1. **Add callback system** for API, database, and reporting services
2. **Implement dual scheduling methods**:
   - `scheduleContentFetch()` - API calls and database storage
   - `scheduleUserNotification()` - Database retrieval and user notification
3. **Maintain backward compatibility** with existing API

---

## 🚀 **IMMEDIATE NEXT STEPS**

### **Step 1: Create Feature Branch (Next 30 minutes)**

```bash
git checkout -b feature/callback-api-integration
git push -u origin feature/callback-api-integration
```

### **Step 2: Interface Design**

- [ ] **Design callback interfaces**
- [ ] **Create dual scheduling method signatures**
- [ ] **Plan backward compatibility strategy**
- [ ] **Document interface changes**

### **Step 3: Implementation Planning**

- [ ] **Break down implementation into tasks**
- [ ] **Estimate effort for each component**
- [ ] **Identify dependencies and risks**
- [ ] **Create testing strategy**

---

## 📋 **DETAILED IMPLEMENTATION TASKS**

### **Phase 1: Interface Updates (Day 1)**

#### **Task 1.1: Extend Existing Interfaces**

**Priority**: 🔴 **HIGH**

```typescript
// Update NotificationOptions interface
interface NotificationOptions {
  // Existing properties...
  
  // New callback properties
  apiCallbacks?: APICallbacks;
  databaseCallbacks?: DatabaseCallbacks;
  reportingCallbacks?: ReportingCallbacks;
}
```

**Subtasks**:

- [ ] Define `APICallbacks` interface
- [ ] Define `DatabaseCallbacks` interface  
- [ ] Define `ReportingCallbacks` interface
- [ ] Update existing interface tests

#### **Task 1.2: Create New Scheduling Interfaces**

**Estimated Effort**: 2-3 hours  
**Priority**: 🔴 **HIGH**

```typescript
interface ContentFetchOptions {
  url: string;
  apiCallbacks: APICallbacks;
  databaseCallbacks: DatabaseCallbacks;
  retryConfig: RetryConfig;
}

interface UserNotificationOptions {
  contentId: string;
  notificationCallbacks: NotificationCallbacks;
  userInteractionCallbacks: UserInteractionCallbacks;
}
```

**Subtasks**:

- [ ] Design `ContentFetchOptions` interface
- [ ] Design `UserNotificationOptions` interface
- [ ] Create supporting interfaces (RetryConfig, etc.)
- [ ] Write interface documentation

### **Phase 2: Core Implementation (Days 2-3)**

#### **Task 2.1: Callback Registry System**

**Priority**: 🔴 **HIGH**

```typescript
class CallbackRegistry {
  registerCallback(type: CallbackType, callback: Function): string;
  unregisterCallback(type: CallbackType, id: string): boolean;
  executeCallback(type: CallbackType, data: any): Promise<void>;
  validateCallback(callback: Function): boolean;
}
```

**Subtasks**:

- [ ] Implement callback registration system
- [ ] Add callback validation and security
- [ ] Create callback execution engine
- [ ] Add error handling and logging
- [ ] Write comprehensive tests

#### **Task 2.2: Dual Scheduling Methods**

**Priority**: 🔴 **HIGH**

```typescript
// New method 1: Content fetch and storage
async scheduleContentFetch(options: ContentFetchOptions): Promise<void>

// New method 2: User notification
async scheduleUserNotification(options: UserNotificationOptions): Promise<void>
```

**Subtasks**:

- [ ] Implement `scheduleContentFetch()` method
- [ ] Implement `scheduleUserNotification()` method
- [ ] Add API call handling with callbacks
- [ ] Add database operation callbacks
- [ ] Implement retry and fallback logic
- [ ] Write method tests

#### **Task 2.3: Backward Compatibility Layer**

**Priority**: 🟡 **MEDIUM**

```typescript
// Maintain existing method for backward compatibility
async scheduleDailyNotification(options: NotificationOptions): Promise<void> {
  // Route to appropriate new method based on options
  if (options.apiCallbacks || options.databaseCallbacks) {
    return this.scheduleContentFetch(this.convertToContentFetchOptions(options));
  } else {
    return this.scheduleUserNotification(this.convertToUserNotificationOptions(options));
  }
}
```

**Subtasks**:

- [ ] Refactor existing method to use new system
- [ ] Add deprecation warnings
- [ ] Create migration path for existing users
- [ ] Ensure existing functionality continues to work

### **Phase 3: Platform Integration (Days 3-4)**

#### **Task 3.1: Android Implementation**

**Priority**: 🔴 **HIGH**

**Subtasks**:

- [ ] Update Android plugin to support callbacks
- [ ] Integrate with WorkManager for background tasks
- [ ] Add database callback support
- [ ] Implement API callback handling
- [ ] Add error handling and logging

#### **Task 3.2: iOS Implementation**

**Priority**: 🔴 **HIGH**

**Subtasks**:

- [ ] Update iOS plugin to support callbacks
- [ ] Integrate with BGTaskScheduler
- [ ] Add Core Data callback support
- [ ] Implement API callback handling
- [ ] Add error handling and logging

#### **Task 3.3: Web Implementation**

**Estimated Effort**: 4-6 hours  
**Priority**: 🟡 **MEDIUM**

**Subtasks**:

- [ ] Update web plugin to support callbacks
- [ ] Integrate with Service Workers
- [ ] Add IndexedDB callback support
- [ ] Implement API callback handling
- [ ] Add error handling and logging

### **Phase 4: Testing & Documentation (Day 5)**

#### **Task 4.1: Comprehensive Testing**

**Priority**: 🔴 **HIGH**

**Subtasks**:

- [ ] Write unit tests for callback system
- [ ] Test dual scheduling methods
- [ ] Test API integration scenarios
- [ ] Test database callback scenarios
- [ ] Test cross-platform compatibility
- [ ] Performance testing

#### **Task 4.2: Documentation Updates**

**Priority**: 🟡 **MEDIUM**

**Subtasks**:

- [ ] Update API documentation
- [ ] Create callback usage examples
- [ ] Add dual scheduling examples
- [ ] Create migration guide
- [ ] Update README and examples

---

## 🔧 **TECHNICAL IMPLEMENTATION DETAILS**

### **Callback Execution Model**

```typescript
// Asynchronous callback execution with error handling
async executeCallback(type: CallbackType, data: any): Promise<void> {
  try {
    const callbacks = this.getCallbacks(type);
    const promises = callbacks.map(callback => 
      this.executeSingleCallback(callback, data)
    );
    
    await Promise.allSettled(promises);
  } catch (error) {
    this.handleCallbackError(type, error);
  }
}
```

### **Error Handling Strategy**

```typescript
// Comprehensive error handling for callbacks
private handleCallbackError(type: CallbackType, error: Error): void {
  // Log error for debugging
  this.logger.error(`Callback execution failed for type: ${type}`, error);
  
  // Execute error callbacks if available
  this.executeErrorCallbacks(type, error);
  
  // Fallback to default error handling
  this.executeDefaultErrorHandling(type, error);
}
```

### **Retry and Fallback Logic**

```typescript
// Retry logic with exponential backoff
async executeWithRetry<T>(
  operation: () => Promise<T>,
  maxRetries: number = 3,
  baseDelay: number = 1000
): Promise<T> {
  for (let attempt = 1; attempt <= maxRetries; attempt++) {
    try {
      return await operation();
    } catch (error) {
      if (attempt === maxRetries) throw error;
      
      const delay = baseDelay * Math.pow(2, attempt - 1);
      await this.sleep(delay);
    }
  }
  throw new Error('Max retries exceeded');
}
```

---

## 🧪 **TESTING STRATEGY**

### **Unit Testing**

- **Callback Registration**: Test registration/unregistration
- **Callback Execution**: Test successful and failed executions
- **Error Handling**: Test various error scenarios
- **Performance**: Test callback execution performance

### **Integration Testing**

- **API Integration**: Test with real external services
- **Database Integration**: Test database callback scenarios
- **Cross-Platform**: Test consistency across platforms
- **End-to-End**: Test complete notification flow

### **Performance Testing**

- **Callback Latency**: Measure execution time
- **Memory Usage**: Monitor memory impact
- **Battery Impact**: Test battery usage
- **Scalability**: Test with multiple callbacks

---

## 📊 **SUCCESS CRITERIA**

### **Functional Requirements**

- [ ] **Callback System**: 100% callback execution success rate
- [ ] **Dual Scheduling**: Both methods working independently
- [ ] **API Integration**: Successful external service integration
- [ ] **Database Support**: Reliable callback-based storage operations
- [ ] **Backward Compatibility**: Existing code continues to work

### **Quality Requirements**

- [ ] **Test Coverage**: 95%+ coverage for new functionality
- [ ] **Performance**: No degradation in existing functionality
- [ ] **Security**: Secure callback execution and validation
- [ ] **Documentation**: Complete API documentation updates

### **Platform Requirements**

- [ ] **Android**: Full callback support with WorkManager
- [ ] **iOS**: Full callback support with BGTaskScheduler
- [ ] **Web**: Full callback support with Service Workers
- [ ] **Cross-Platform**: Consistent behavior across platforms

---

## 🚨 **RISKS & MITIGATION**

### **High-Risk Areas**

1. **Interface Changes**: Breaking changes to existing API
   - **Mitigation**: Maintain backward compatibility with deprecation warnings

2. **Performance Impact**: Callback overhead on notification delivery
   - **Mitigation**: Implement callback batching and optimization

3. **Platform Differences**: Ensuring consistent behavior across platforms
   - **Mitigation**: Create platform-agnostic callback interfaces

4. **Error Handling**: Complex callback failure scenarios
   - **Mitigation**: Comprehensive error handling with fallbacks

### **Risk Mitigation Strategies**

- **Phased Implementation**: Implement in small, testable units
- **Comprehensive Testing**: Test all scenarios thoroughly
- **Performance Monitoring**: Monitor impact throughout implementation
- **Rollback Plan**: Maintain ability to revert changes if needed

---

## 📅 **TIMELINE & MILESTONES**

### **Week 1: Foundation & Design**
- **Day 1**: Interface design and planning
- **Day 2**: Core implementation planning
- **Day 3**: Begin core implementation

### **Week 2: Implementation & Integration**
- **Day 4**: Complete core implementation
- **Day 5**: Begin platform integration
- **Day 6**: Complete platform integration
- **Day 7**: Begin testing

### **Week 3: Testing & Documentation**
- **Day 8**: Complete testing
- **Day 9**: Documentation updates
- **Day 10**: Final review and deployment

---

## 🎯 **NEXT IMMEDIATE ACTIONS**

### **Today (Next 4-6 hours)**
1. **Create feature branch** for implementation
2. **Complete interface design** for callback system
3. **Create implementation plan** with task breakdown
4. **Set up testing framework** for new functionality

### **Tomorrow (Next 8-10 hours)**
1. **Begin core implementation** of callback registry
2. **Implement dual scheduling methods**
3. **Add backward compatibility layer**
4. **Begin platform integration planning**

---

**Status**: 📋 **PLANNING PHASE** - Ready to begin implementation  
**Next Milestone**: Complete interface design and create feature branch  
**Estimated Completion**: 2-3 weeks for full implementation  
**Priority**: 🔴 **HIGH** - Core functionality enhancement required