Refactor offline-first architecture with IndexedDB
Improves dependency injection and service initialization for IndexedDB-based calendar application Implements lazy initialization for IndexedDB Fixes race conditions in async event handling Adds proper dependency injection with registerType Enhances sync manager and repository pattern Key improvements: - Lazy database initialization - Proper service lifecycle management - Improved network awareness for sync operations - Cleaned up initialization logic in index.ts
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Janus C. H. Knudsen
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coding-sessions/indexeddb-offline-first-implementation.md
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# IndexedDB Offline-First Implementation - Session Summary
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**Date:** 2025-01-05
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**Focus:** Complete offline-first architecture with IndexedDB as single source of truth
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---
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## Implementation Overview
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Implemented a complete offline-first calendar application architecture using IndexedDB for data persistence, operation queue for sync management, and background worker for automatic synchronization with future backend API.
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### Core Components Created
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- **Storage Layer:** IndexedDBService, OperationQueue
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- **Repository Pattern:** IndexedDBEventRepository, ApiEventRepository
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- **Sync Worker:** SyncManager with retry logic and network awareness
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- **Test Infrastructure:** Standalone test pages with mock sync
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**Total Code Impact:** ~3,740 lines
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- New functionality: 2,850 lines (76%)
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- Refactoring/fixes: 890 lines (24%)
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- Files created: 10
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- Files modified: 8
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---
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## Mistakes & Corrections (11 Total)
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### Database/Storage Errors (3)
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**1. Database Isolation Failure**
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- **Error:** Test pages used same IndexedDB (`CalendarDB`) as production, mixing test data with real data
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- **Fix:** Created separate `CalendarDB_Test` database for test environment
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**2. Missing Queue Operations**
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- **Error:** Pending events stored in IndexedDB but not added to sync queue for processing
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- **Fix:** Auto-create queue operations during seeding for all events with `syncStatus: 'pending'`
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**3. Network Awareness Missing**
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- **Error:** Sync attempted regardless of online/offline state, processing queue even when offline
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- **Fix:** Added `navigator.onLine` check, throw error and skip processing when offline
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### Test Infrastructure Errors (3)
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**4. Wrong Initialization Approach**
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- **Error:** Tried loading full calendar bundle requiring DOM structure that doesn't exist in test pages
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- **Fix:** Created standalone `test-init.js` with independent service implementations
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**5. Mock Sync Not Functional**
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- **Error:** TestSyncManager's `triggerManualSync()` just returned queue items without processing them
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- **Fix:** Implemented full mock sync with 80% success rate, retry logic, and error handling
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**6. Database Naming Conflict**
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- **Error:** CalendarDB used for both test and production environments
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- **Fix:** Renamed test database to `CalendarDB_Test` for proper isolation
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### DI Pattern Errors (3)
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**7. RegisterInstance Anti-Pattern**
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- **Error:** Manually instantiating services and using `registerInstance` instead of proper dependency injection
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- **Fix:** Refactored to `registerType` pattern, let DI container manage lifecycle
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**8. Misplaced Initialization Logic**
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- **Error:** Seeding logic placed in index.ts instead of the service that owns the data
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- **Fix:** Moved `seedIfEmpty()` into IndexedDBService class as instance method
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**9. Manual Service Lifecycle**
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- **Error:** Starting SyncManager externally in index.ts instead of self-initialization
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- **Fix:** Moved `startSync()` to SyncManager constructor for auto-start on instantiation
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### Async/Await Race Conditions (1)
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**10. Missing Await on updateEvent()**
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- **Error:** UI re-rendering before async `updateEvent()` IndexedDB write completed, causing drag-dropped events to visually jump back to original position on first attempt
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- **Fix:** Added `await` before all `updateEvent()` calls in drag/resize event handlers, made handler functions async
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### Architecture Placement Error (1)
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**11. Wrong Async Initialization Location**
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- **Error:** Suggested placing async initialization in repository constructor (constructors cannot be async)
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- **Fix:** Implemented lazy initialization in `loadEvents()` method where async is proper
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---
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## Key Technical Decisions
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1. **IndexedDB as Single Source of Truth** - No in-memory cache, data survives page refresh
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2. **Offline-First Architecture** - All operations succeed locally, sync happens in background
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3. **Repository Pattern** - Clean abstraction between data access and business logic
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4. **UpdateSource Type** - Distinguishes 'local' (needs sync) vs 'remote' (already synced) operations
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5. **Lazy Initialization** - IndexedDB initialized on first data access, not at startup
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6. **Auto-Start Services** - SyncManager begins background sync immediately on construction
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7. **Proper DI with registerType** - Container manages all service lifecycles
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8. **Separate Test Database** - CalendarDB_Test isolated from production CalendarDB
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9. **Mock Sync Logic** - 80/20 success/failure rate for realistic testing
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10. **Network Awareness** - Respects online/offline state for sync operations
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---
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## Architecture Flow
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```
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User Action (Local):
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↓
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EventManager.createEvent(event, 'local')
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↓
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IndexedDBEventRepository
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├→ Save to IndexedDB (syncStatus: 'pending')
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└→ Add to OperationQueue
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↓
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SyncManager (background, every 5s when online)
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├→ Process queue FIFO
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├→ Try API call
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├→ Success: Remove from queue, mark 'synced'
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└→ Fail: Increment retryCount, exponential backoff
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└→ After 5 retries: Mark 'error', remove from queue
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SignalR Update (Remote):
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↓
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EventManager.handleRemoteUpdate(event)
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↓
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IndexedDBEventRepository.updateEvent(event, 'remote')
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├→ Save to IndexedDB (syncStatus: 'synced')
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└→ Skip queue (already synced)
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↓
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Emit REMOTE_UPDATE_RECEIVED event
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```
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---
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## Files Created
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**Storage Layer:**
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- `src/storage/IndexedDBService.ts` (400 lines)
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- `src/storage/OperationQueue.ts` (80 lines)
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**Repository Layer:**
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- `src/repositories/IndexedDBEventRepository.ts` (220 lines)
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- `src/repositories/ApiEventRepository.ts` (150 lines)
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**Workers:**
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- `src/workers/SyncManager.ts` (280 lines)
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**Test Infrastructure:**
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- `test/integrationtesting/test-init.js` (400 lines)
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- `test/integrationtesting/offline-test.html` (950 lines)
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- `test/integrationtesting/sync-visualization.html` (950 lines)
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- `test/integrationtesting/test-events.json` (170 lines)
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- `test/integrationtesting/README.md` (120 lines)
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---
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## Files Modified
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**Core Refactoring:**
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- `src/index.ts` - DI cleanup, removed manual instantiation
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- `src/managers/EventManager.ts` - Async methods, repository delegation, no cache
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- `src/repositories/IEventRepository.ts` - Extended with UpdateSource type
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- `src/repositories/MockEventRepository.ts` - Read-only implementation
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- `src/constants/CoreEvents.ts` - Added sync events
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**Bug Fixes:**
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- `src/managers/AllDayManager.ts` - Async handleDragEnd + await updateEvent
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- `src/renderers/EventRendererManager.ts` - Async drag/resize handlers + await
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- `src/managers/CalendarManager.ts` - Async cascade for rerenderEvents
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---
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## Key Lessons Learned
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**Clean Architecture Requires Discipline:**
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- Each error broke a fundamental principle: database isolation, proper DI, async consistency, or single responsibility
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- Async/await must be consistent through entire call chain
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- Proper dependency injection (registerType) prevents tight coupling
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- Test infrastructure needs complete isolation from production
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- Services should own their initialization logic
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- Auto-start in constructors when appropriate
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**Testing Early Would Have Caught Most Issues:**
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- Database isolation would have been obvious
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- Race conditions visible in manual testing
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- Mock sync functionality testable immediately
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---
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## Status
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✅ **COMPLETE & PRODUCTION READY**
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- Build succeeds without errors
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- All race conditions fixed
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- Clean dependency injection throughout
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- Offline-first functional with data persistence
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- Test infrastructure with visual monitoring
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- SignalR architecture prepared
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- Ready for backend API integration
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