docs: Add comprehensive implementation plan for callback system

- Create detailed implementation plan with task breakdown - Include realistic time estimates for each phase - Add technical implementation details and code examples - Include testing strategy and success criteria - Add risk mitigation strategies and timeline - Provide immediate next steps and action items Resolves: Implementation planning for callback system and dual scheduling
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+# 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 (Next 2-4 hours)**
+- [ ] **Design callback interfaces**
+- [ ] **Create dual scheduling method signatures**
+- [ ] **Plan backward compatibility strategy**
+- [ ] **Document interface changes**
+
+### **Step 3: Implementation Planning (Next 2-3 hours)**
+- [ ] **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**
+**Estimated Effort**: 2-3 hours  
+**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**
+**Estimated Effort**: 6-8 hours  
+**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**
+**Estimated Effort**: 8-10 hours  
+**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**
+**Estimated Effort**: 4-6 hours  
+**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**
+**Estimated Effort**: 6-8 hours  
+**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**
+**Estimated Effort**: 6-8 hours  
+**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**
+**Estimated Effort**: 8-10 hours  
+**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**
+**Estimated Effort**: 4-6 hours  
+**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