Feature Decomposition: User Notification System

Total Stories: 11 stories (1 investigation + 10 implementation)
Estimated Timeline: ~21 days (assuming 1 team)
Dependencies: Investigation story (1) must complete first; Stories 2-3 are foundation; Stories 4-8 depend on foundation

---

Story 1: 🔍 Email Delivery Provider Investigation [Investigation]

Estimated Size: 1 day
Priority: MUST HAVE (blocks architectural decisions)

As a technical lead,
I want to evaluate email delivery providers (SendGrid, AWS SES, Postmark, Mailgun),
So that we select a service that meets deliverability, cost, and compliance requirements.

Acceptance Criteria (starters):

• Document 3-4 provider options with pricing models
• Compare deliverability rates and reputation management
• Evaluate API complexity and integration effort
• Check compliance features (GDPR, CAN-SPAM, unsubscribe)
• Assess monitoring/analytics capabilities
• Recommend provider with rationale in decision document

Technical Notes:

• Consider transactional vs. marketing email needs
• Review existing infrastructure (AWS vs. other cloud)
• Check rate limits and scalability
• Estimate monthly volume to calculate costs

INVEST Check: All criteria met (timeboxed research)

---

Story 2: Notification Data Models & Database Schema [Foundation]

Estimated Size: 2 days
Priority: MUST HAVE (blocks all implementation stories)
Dependency: Story 1 (need to understand provider requirements)

As a developer,
I want database tables for notifications, preferences, and delivery tracking,
So that we can store notification data and user preferences.

Acceptance Criteria (starters):

• notifications table: id, user_id, type, channel, title, body, data (JSON), status, created_at
• notification_preferences table: user_id, channel, category, enabled, frequency
• notification_deliveries table: notification_id, channel, provider_id, status, sent_at, delivered_at, error
• Support for notification categories (account, billing, product_updates, system)
• Indexes on user_id, status, created_at for query performance
• Migration scripts with rollback support
• [Add more based on analytics requirements]

Technical Notes:

• Consider notification retention policy (archive old notifications)
• Add soft deletes for audit trail
• JSON field for flexible metadata per notification type
• Consider partitioning for high-volume systems

INVEST Check: All criteria met

---

Story 3: Notification Service Core [Foundation]

Estimated Size: 3 days
Priority: MUST HAVE (blocks delivery implementations)
Dependency: Story 2 (requires data models)

As a developer,
I want a notification service that queues and routes notifications to channels,
So that notifications can be sent reliably across email, push, and in-app.

Acceptance Criteria (starters):

• Service accepts notification requests with user_id, type, channel(s), payload
• Checks user preferences before routing to channels
• Queues notifications for async processing (background job)
• Routes to appropriate channel handler (email/push/in-app)
• Records delivery attempts with status tracking
• Implements retry logic for failed deliveries (3 attempts with backoff)
• Exposes status query API (get notification status by ID)
• [Add more based on observability requirements]

Technical Notes:

• Use job queue (Sidekiq, Bull, Celery depending on stack)
• Consider rate limiting per channel
• Build for extensibility (easy to add new channels)
• Log all notification events for debugging

INVEST Check: All criteria met

---

Story 4: Email Notification Implementation [Core]

Estimated Size: 3 days
Priority: MUST HAVE
Dependencies: Stories 2 + 3 (requires foundation)

As an end user or admin,
I want to receive email notifications for important events,
So that I stay informed even when not using the application.

Acceptance Criteria (starters):

• Integration with selected email provider (from Story 1)
• HTML email templates with responsive design
• Plain text fallback for all email types
• Unsubscribe link in footer (one-click unsubscribe)
• Handles delivery failures and bounce notifications
• Tracks open rates via pixel (optional, privacy-conscious)
• Supports batch sending for digest notifications
• [Add more based on template variety]

Technical Notes:

• Template engine (Handlebars, Jinja, etc.)
• CSS inlining for email client compatibility
• Preview text optimization
• Test across major email clients (Gmail, Outlook, Apple Mail)

INVEST Check: All criteria met

---

Story 5: Push Notification Implementation [Core]

Estimated Size: 2 days
Priority: MUST HAVE
Dependencies: Stories 2 + 3

As an end user,
I want to receive push notifications on my mobile device,
So that I get timely alerts about important events.

Acceptance Criteria (starters):

• Integration with push provider (FCM for Android, APNs for iOS)
• Device token registration and storage
• Handles expired/invalid tokens gracefully
• Supports rich notifications (title, body, icon, deep links)
• Badge count management for unread notifications
• Silent push for background data sync (if needed)
• [Add more based on platform-specific features]

Technical Notes:

• Use unified push service (Firebase Cloud Messaging or OneSignal)
• Handle token refresh on client side
• Test notification priority levels
• Consider notification grouping for multiple alerts

INVEST Check: All criteria met

---

Story 6: In-App Notification Feed [Core]

Estimated Size: 2 days
Priority: MUST HAVE
Dependencies: Stories 2 + 3

As an end user or admin,
I want to view a notification feed in the application,
So that I can review past alerts and take action.

Acceptance Criteria (starters):

• Notification feed UI with unread indicator
• Paginated list of notifications (newest first)
• Mark as read/unread functionality
• Delete/dismiss notifications
• Deep linking to relevant pages (e.g., “New invoice” → invoice page)
• Real-time updates when new notifications arrive (WebSocket/polling)
• [Add more based on filtering requirements]

Technical Notes:

• Real-time updates via WebSocket or Server-Sent Events
• Fallback to polling if WebSocket unavailable
• Optimistic UI updates for better UX
• Consider notification persistence (how long to keep)

INVEST Check: All criteria met

---

Story 7: User Notification Preferences UI [Core]

Estimated Size: 2 days
Priority: MUST HAVE
Dependencies: Stories 2 + 4 + 5 + 6 (requires channels implemented)

As an end user or admin,
I want to configure which notifications I receive and how,
So that I only get alerts relevant to me.

Acceptance Criteria (starters):

• Settings page with notification categories (account, billing, updates, system)
• Toggle for each channel per category (email, push, in-app)
• Email frequency options (immediately, daily digest, weekly digest)
• Global “pause all notifications” option with duration
• Save preferences with immediate effect
• Clear explanation of each notification type
• [Add more based on granularity requirements]

Technical Notes:

• Admin users may have additional notification categories
• Consider smart defaults (important alerts enabled by default)
• Validate at least one channel enabled for critical alerts
• Store preferences in notification_preferences table

INVEST Check: All criteria met

---

Story 8: Admin-Specific Notifications [Core]

Estimated Size: 2 days
Priority: MUST HAVE
Dependencies: Stories 2-7 (requires full foundation)

As an admin,
I want to receive notifications about system events (new users, errors, usage spikes),
So that I can monitor and respond to issues quickly.

Acceptance Criteria (starters):

• Admin notification categories: user_activity, system_health, security, billing
• System event triggers (e.g., error rate > threshold)
• Configurable alert thresholds in admin settings
• Escalation rules (e.g., SMS for critical alerts)
• Admin-only notification feed with filtering
• Aggregate notifications to prevent alert fatigue
• [Add more based on monitoring needs]

Technical Notes:

• Integrate with monitoring tools (Sentry, Datadog)
• Consider PagerDuty/Opsgenie for on-call escalation
• Rate limiting to prevent notification storms
• Allow admins to delegate notification subscriptions

INVEST Check: All criteria met

---

Story 9: Notification Templates & Content Management [Enhancement]

Estimated Size: 2 days
Priority: SHOULD HAVE
Dependencies: Stories 4 + 5 + 6

As a product manager,
I want to edit notification content without code changes,
So that we can iterate on messaging quickly.

Acceptance Criteria (starters):

• Admin UI for managing notification templates
• Template editor with variable placeholders ({{user_name}}, {{action}})
• Preview notification in all channels before publishing
• Version history for templates with rollback
• A/B testing support for notification content
• Multi-language support (if applicable)
• [Add more based on content workflow]

Technical Notes:

• Store templates in database with versioning
• Template syntax validation to prevent errors
• Cache compiled templates for performance
• Consider approval workflow for template changes

INVEST Check: All criteria met
Note: Can be deferred to v2 if timeline pressure

---

Story 10: Notification Analytics Dashboard [Enhancement]

Estimated Size: 2 days
Priority: SHOULD HAVE
Dependencies: Stories 2-8 (requires delivery tracking data)

As a product manager,
I want to view notification metrics (sent, delivered, opened, clicked),
So that I can optimize notification strategy.

Acceptance Criteria (starters):

• Dashboard shows metrics per channel (email, push, in-app)
• Breakdown by notification category and user segment
• Delivery success rate and failure reasons
• Engagement metrics (open rate, click-through rate)
• Opt-out/unsubscribe trends over time
• Export data to CSV for deeper analysis
• [Add more based on reporting needs]

Technical Notes:

• Aggregate metrics via scheduled job (daily rollup)
• Consider data retention policy for raw events
• Use charting library (Chart.js, Recharts)
• Cache dashboard queries for performance

INVEST Check: All criteria met
Note: Can be deferred to v2 if timeline pressure

---

Story 11: Notification Rate Limiting & Spam Prevention [Enhancement]

Estimated Size: 2 days
Priority: SHOULD HAVE
Dependencies: Story 3 (requires notification service)

As a user,
I want protection from notification spam,
So that I’m not overwhelmed by excessive alerts.

Acceptance Criteria (starters):

• Rate limits per channel (e.g., max 10 emails/hour per user)
• Notification deduplication (don’t send identical alerts twice)
• Smart batching for similar notifications (e.g., “3 new comments”)
• Global cool-down period after user dismisses notification
• Admin tools to monitor and adjust rate limits
• Override for critical/urgent notifications
• [Add more based on abuse scenarios]

Technical Notes:

• Use Redis or similar for rate limit counters
• Fingerprint notifications for deduplication
• Consider user behavior (adjust limits for power users)
• Log rate limit violations for abuse detection

INVEST Check: All criteria met
Note: Can be deferred to v2 if timeline pressure

---

Implementation Strategy

Phase 1: Investigation & Foundation (Days 1-6)

• Day 1: Story 1 (investigation) - 1 day
• Days 2-3: Story 2 (data models) - 2 days
• Days 4-6: Story 3 (notification service) - 3 days
• Enables: Core architecture ready for channel implementations

Phase 2: Channel Implementations (Days 7-12)

• Days 7-9: Story 4 (email) - 3 days
• Days 10-11: Story 5 (push) - 2 days (can overlap with email)
• Days 10-11: Story 6 (in-app feed) - 2 days (can overlap with push)
• Parallelization: Stories 5 + 6 with 2 developers → 2 days instead of 4
• Enables: All notification channels functional

Phase 3: User Experience (Days 13-18)

• Days 13-14: Story 7 (preferences UI) - 2 days
• Days 15-16: Story 8 (admin notifications) - 2 days
• Days 17-18: Story 11 (rate limiting) - 2 days
• Enables: MVP shippable (core notification system complete)

Phase 4: Enhancements (Days 19-22)

• Days 19-20: Story 9 (template management) - 2 days
• Days 21-22: Story 10 (analytics) - 2 days
• Parallelization: Stories 9 + 10 with 2 developers → 2 days instead of 4
• Enables: Full-featured notification system

MVP Definition: Stories 1-8 + 11 = Core notification system (18 days)
Full Feature: All 11 stories (22 days)

Parallelization Opportunities:

• Phase 2: Stories 5 + 6 with 2 developers → 2 days savings
• Phase 4: Stories 9 + 10 with 2 developers → 2 days savings
• Best case with strategic parallelization: ~16 days total

---

Risk Mitigation

Technical Risks:

• Email deliverability issues → Complete Story 1 thoroughly; choose provider with strong reputation management
• Push token management complexity → Use established SDK (Firebase, OneSignal) rather than direct APNs/FCM
• Real-time notification delays → Implement fallback to polling if WebSocket fails; consider Server-Sent Events
• Database performance under load → Add indexes early (Story 2); consider read replicas for notification feed queries
• Third-party provider outages → Implement circuit breakers and fallback providers for critical notifications
• Notification spam and abuse → Prioritize Story 11 (rate limiting) in MVP if abuse is likely

Scope Risks:

• Email template variety could explode → Start with 3-5 core templates, add more later
• Admin notification requirements unclear → Story 8 may expand once admins see possibilities; timebox to 2 days
• Multi-language support → Not included in current scope; add as separate story if needed
• SMS channel requests → Not included; can add as Story 12 following same pattern as email/push
• Analytics requirements grow → Story 10 focused on basic metrics; advanced analytics as separate feature

User Experience Risks:

• Notification fatigue → Prioritize Story 11 (rate limiting) and smart defaults in Story 7
• Poor email rendering → Test across email clients early (Story 4)
• Mobile push permission denial → Implement graceful degradation to email/in-app

Recommendation: Build Stories 1-8 first (MVP), validate with end users and admins, then prioritize Stories 9-11 based on feedback.

---

Definition of Done

Each story is complete when:

• Code reviewed and merged to main branch
• Unit tests written and passing (>80% coverage for core service)
• Integration tests cover happy path + error scenarios
• Manual QA completed across affected channels
• Database migrations tested (up and down)
• Documentation updated (API docs, user guides, admin docs)
• Performance tested under expected load (e.g., 1000 notifications/minute)
• Security review passed (especially for email links, unsubscribe)
• Monitoring/alerting configured (error rates, delivery failures)
• Stakeholder demo completed and approved

---

Cross-Cutting Concerns

Security Considerations:

• Sanitize user data in notification content (prevent XSS in in-app notifications)
• Validate email addresses before sending (prevent abuse)
• Implement signed unsubscribe tokens (prevent unauthorized opt-outs)
• Rate limit notification API endpoints (prevent spam)
• Encrypt sensitive data in notification payloads
• Audit log for admin actions (template changes, preference overrides)

Compliance Considerations:

• CAN-SPAM Act: Unsubscribe link in all marketing emails
• GDPR: Allow users to export notification history; delete on account deletion
• CCPA: Provide notification data in data export requests
• Consider adding consent checkboxes during signup for marketing notifications

Scalability Considerations:

• Background job queue for async processing (critical for performance)
• Database indexing on frequently queried fields
• Caching for user preferences (reduce DB load)
• Consider notification archive strategy (move old notifications to cold storage)
• Monitor queue depth and processing lag

Observability:

• Log all notification events (created, sent, delivered, failed, opened)
• Metrics: notification volume, delivery success rate, processing latency
• Alerts: queue backup, high failure rate, provider errors
• Distributed tracing for debugging delivery issues