# Callback & Dual Scheduling Analysis

**Document Created**: 2025-08-26 11:17:26 UTC  
**Author**: Matthew Raymer  
**Status**: 🔄 **RESEARCH & ANALYSIS**  
**Priority**: 🔴 **HIGH** - Core functionality enhancement required

## 🎯 **REQUIREMENTS ANALYSIS**

### **User Feedback Summary**
> "BTW, I still think it's worth starting a branch where we use the notification plugin, but a note on the plugin itself: seems like it'll need a couple things. One is to accept some callbacks (eg. for API calls out to a reporting service and then saving in the DB). The other is that I believe we need two 'schedule' methods, one that does the call-API-store-in-DB function and the other that does the retrieve-from-DB-and-notify-user function."

### **Core Requirements Identified**
1. **Callback System**: Accept callbacks for external service integration
2. **Dual Scheduling**: Separate content fetch from user notification
3. **API Integration**: Support for external reporting services
4. **Database Operations**: Callback-based storage and retrieval

---

## 🔍 **CURRENT IMPLEMENTATION ANALYSIS**

### **Existing Scheduling Method**
```typescript
// Current single method approach
async scheduleDailyNotification(options: NotificationOptions): Promise<void>
```

**Current Behavior**:
- Single method handles both content fetching and notification scheduling
- Limited to basic URL fetching without callback support
- No separation of concerns between data operations and user notification
- Basic error handling without external service integration

### **Current API Call Handling**
```typescript
// Basic URL fetching in Android implementation
String url = call.getString("url", "");
// No callback support for API responses
// No database storage integration
// No external service reporting
```

### **Gap Analysis**
- ❌ **No callback mechanism** for external service integration
- ❌ **No dual scheduling** - single method handles everything
- ❌ **Limited API integration** - basic HTTP requests only
- ❌ **No database callback support** for storage operations
- ❌ **No reporting service integration** for analytics

---

## 🏗️ **PROPOSED ARCHITECTURE**

### **Dual Scheduling Methods**

#### **Method 1: Content Fetch & Storage**
```typescript
async scheduleContentFetch(options: ContentFetchOptions): Promise<void>
```

**Purpose**: Handle API calls and database storage
**Responsibilities**:
- Make API calls to external services
- Execute database storage callbacks
- Handle retry logic and fallbacks
- Report to analytics/reporting services
- Cache content for later use

#### **Method 2: User Notification**
```typescript
async scheduleUserNotification(options: UserNotificationOptions): Promise<void>
```

**Purpose**: Retrieve stored content and notify users
**Responsibilities**:
- Retrieve content from database/cache
- Execute user notification callbacks
- Handle notification display logic
- Manage user interaction callbacks
- Track notification engagement

### **Callback System Architecture**

#### **Callback Types**
```typescript
interface CallbackSystem {
  // API callbacks
  apiCallbacks: {
    onSuccess: (response: any) => Promise<void>;
    onError: (error: Error) => Promise<void>;
    onRetry: (attempt: number) => Promise<boolean>;
  };
  
  // Database callbacks
  databaseCallbacks: {
    onStore: (data: any) => Promise<void>;
    onRetrieve: (id: string) => Promise<any>;
    onError: (error: Error) => Promise<void>;
  };
  
  // Reporting callbacks
  reportingCallbacks: {
    onMetrics: (metrics: NotificationMetrics) => Promise<void>;
    onAnalytics: (event: string, data: any) => Promise<void>;
  };
}
```

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

---

## 🔧 **IMPLEMENTATION APPROACH**

### **Phase 1: Interface Updates**
**Estimated Effort**: 4-6 hours

1. **Extend existing interfaces**
   ```typescript
   interface NotificationOptions {
     // Existing properties...
     
     // New callback properties
     apiCallbacks?: APICallbacks;
     databaseCallbacks?: DatabaseCallbacks;
     reportingCallbacks?: ReportingCallbacks;
   }
   ```

2. **Create new scheduling interfaces**
   ```typescript
   interface ContentFetchOptions {
     url: string;
     apiCallbacks: APICallbacks;
     databaseCallbacks: DatabaseCallbacks;
     retryConfig: RetryConfig;
   }
   
   interface UserNotificationOptions {
     contentId: string;
     notificationCallbacks: NotificationCallbacks;
     userInteractionCallbacks: UserInteractionCallbacks;
   }
   ```

### **Phase 2: Core Implementation**
**Estimated Effort**: 12-16 hours

1. **Implement callback registry system**
   - Callback registration and validation
   - Execution engine with error handling
   - Lifecycle management

2. **Create dual scheduling methods**
   - `scheduleContentFetch()` implementation
   - `scheduleUserNotification()` implementation
   - Backward compatibility layer

3. **Add callback execution logic**
   - API call handling with callbacks
   - Database operation callbacks
   - Reporting service integration

### **Phase 3: Platform Integration**
**Estimated Effort**: 8-12 hours

1. **Android implementation**
   - WorkManager integration for background tasks
   - Callback execution in native code
   - Database callback support

2. **iOS implementation**
   - BGTaskScheduler integration
   - Callback handling in Swift
   - Core Data callback support

3. **Web implementation**
   - Service Worker integration
   - Browser notification callbacks
   - IndexedDB callback support

---

## 📊 **COMPLEXITY ASSESSMENT**

### **Technical Complexity**: 🔴 **HIGH**
- **Architecture Changes**: Significant interface redesign required
- **Platform Integration**: Need to implement across Android/iOS/Web
- **Callback Management**: Complex lifecycle and error handling
- **Backward Compatibility**: Must maintain existing API functionality

### **Business Complexity**: 🟡 **MEDIUM**
- **User Impact**: Existing users need migration path
- **Testing Requirements**: Comprehensive callback testing needed
- **Documentation**: Significant API documentation updates required
- **Training**: Team needs to understand new callback patterns

### **Risk Factors**: 🔴 **HIGH**
- **Interface Changes**: Breaking changes to existing API
- **Performance Impact**: Callback overhead on notification delivery
- **Platform Differences**: Ensuring consistent behavior across platforms
- **Error Handling**: Complex callback failure scenarios

---

## 🚀 **RECOMMENDED IMPLEMENTATION STRATEGY**

### **1. Research & Design Phase (Days 1-2)**
- [ ] **Complete callback system design**
- [ ] **Create interface mockups**
- [ ] **Design migration strategy**
- [ ] **Plan testing approach**

### **2. Core Implementation Phase (Days 2-4)**
- [ ] **Implement callback registry system**
- [ ] **Create dual scheduling methods**
- [ ] **Add callback execution logic**
- [ ] **Implement error handling**

### **3. Platform Integration Phase (Days 4-5)**
- [ ] **Android callback integration**
- [ ] **iOS callback integration**
- [ ] **Web callback integration**
- [ ] **Cross-platform testing**

### **4. Testing & Documentation Phase (Day 5)**
- [ ] **Comprehensive callback testing**
- [ ] **Performance validation**
- [ ] **API documentation updates**
- [ ] **Migration guide creation**

---

## 🔒 **SECURITY CONSIDERATIONS**

### **Callback Security**
- **Input Validation**: Validate all callback parameters
- **Sandboxing**: Execute callbacks in controlled environment
- **Rate Limiting**: Prevent callback abuse
- **Authentication**: Validate callback sources

### **Data Security**
- **Encryption**: Encrypt sensitive data in callbacks
- **Access Control**: Limit callback access to necessary data
- **Audit Logging**: Log all callback executions
- **Error Handling**: Prevent information leakage in errors

---

## 📈 **PERFORMANCE IMPACT**

### **Callback Overhead**
- **Execution Time**: Additional 10-50ms per callback
- **Memory Usage**: Callback registry storage
- **Battery Impact**: Minimal on modern devices
- **Network Impact**: Depends on callback implementation

### **Optimization Strategies**
- **Callback Batching**: Execute multiple callbacks together
- **Async Execution**: Non-blocking callback execution
- **Caching**: Cache callback results where appropriate
- **Lazy Loading**: Load callbacks only when needed

---

## 🧪 **TESTING STRATEGY**

### **Unit Testing**
- **Callback Registration**: Test callback 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 callback execution time
- **Memory Usage**: Monitor memory impact of callbacks
- **Battery Impact**: Test battery usage with callbacks
- **Scalability**: Test with multiple concurrent callbacks

---

## 📚 **REFERENCES & RESOURCES**

### **Design Patterns**
- **Observer Pattern**: For callback registration and execution
- **Strategy Pattern**: For different callback execution strategies
- **Factory Pattern**: For creating different callback types
- **Chain of Responsibility**: For callback execution flow

### **Platform-Specific Resources**
- **Android**: WorkManager, AlarmManager, Room database
- **iOS**: BGTaskScheduler, UNCalendarNotificationTrigger, Core Data
- **Web**: Service Workers, IndexedDB, Browser Notifications API

### **Best Practices**
- **Error Handling**: Comprehensive error handling for callbacks
- **Performance**: Optimize callback execution for mobile devices
- **Security**: Secure callback execution and data handling
- **Testing**: Thorough testing of callback scenarios

---

**Next Steps**: Complete callback system design and create implementation plan  
**Estimated Timeline**: 3-5 days for full implementation  
**Success Criteria**: Dual scheduling methods working with full callback support  
**Risk Level**: 🔴 **HIGH** - Requires careful planning and implementation