feat(dashboard): add instructor analytics dashboard (#562)

[CNduka001]

PR #562 feat(dashboard): Instructor analytics dashboard

• Enrollment trends chart
• Completion rate tracking
• Revenue breakdown
• Video watch time analytics

What changed

• Added GET /dashboard/instructors/:instructorId endpoint in src/dashboard/dashboard.controller.ts.
• Implemented getInstructorDashboard(instructorId) and supporting helpers in src/dashboard/dashboard.service.ts:
  • getInstructorRevenueBreakdown(instructorId) — revenue by currency, by course, and by payment method (completed payments only).
  • calculateEnrollmentTrends(courses, days=30) — daily enrollment buckets for the last 30 days (configurable).
  • calculateCompletionRate(courses) — overall and monthly completion rates (6-month window).
  • getInstructorVideoWatchTime(courses) — aggregates recorded video/watch events from analytics_events and falls back to progress-based estimates when events are absent.
• Registered AnalyticsEvent repository in src/dashboard/dashboard.module.ts.
• Added unit coverage in src/dashboard/dashboard.service.spec.ts to validate instructor dashboard generation and mocked query builders for payments and analytics.

API

GET /dashboard/instructors/:instructorId

Response (example):

{
  "instructorId": "instr-1",
  "revenue": { "totalRevenue": 120, "currency": "USD", "byCourse": [...], "byMethod": [...] },
  "enrollmentTrends": [{ "period": "2026-05-01", "count": 3 }, ...],
  "completionRate": { "overallRate": 0.25, "monthlyTrend": [...] },
  "videoWatchTime": { "totalWatchSeconds": 200, "byCourse": [...] },
  "courseSummary": [...],
  "generatedAt": "2026-06-01T...Z"
}

Testing

Unit tests were added/updated in src/dashboard/dashboard.service.spec.ts. To run the tests locally (project must have dev deps installed):

npm ci
npm test -- src/dashboard/dashboard.service.spec.ts --runInBand

How to smoke-test the endpoint locally

Start the application (depending on your local start script):

npm run start:dev

Then hit the endpoint (replace :instructorId with a real instructor UUID):

curl -H "Authorization: Bearer <token>" http://localhost:3000/dashboard/instructors/:instructorId

Notes for reviewers

• The video watch time logic first queries analytics_events for category = 'video' and action = 'watch' events with a numeric value representing watched seconds. If no events exist for a course, the service estimates watch time from enrollment progress and lesson durationSeconds.
• Revenue breakdown only considers payments with PaymentStatus.COMPLETED and uses the existing ReportingService for monthly recognition where appropriate.
• Performance: queries join payments -> course and group by currency/course/method. If you anticipate large datasets, we should consider adding batched endpoints or pre-aggregated views.
• Security: the controller route uses the existing DashboardService and inherits any guards on dashboard routes; consider restricting GET /dashboard/instructors/:instructorId to instructors or admins if desired.

Follow-ups

• Add a small API DTO to shape instructor dashboard responses (optional)
• Add pagination for byCourse revenue lists when an instructor has many courses
• Add end-to-end tests for event-driven watch-time reporting

Files touched (high-level)

• src/dashboard/dashboard.controller.ts
• src/dashboard/dashboard.service.ts
• src/dashboard/dashboard.module.ts
• src/dashboard/dashboard.service.spec.ts

Reviewer checklist

• Validate SQL grouping and indexes for payments and analytics_events queries (performance)
• Confirm access restrictions for instructor dashboards
• Verify that analytics_events contains video/watch events in expected shape before enabling the UI

Closes #562

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