[Backend] Implement Weight Tracking Service and Controller

[llinsss]

⚠️ This is a backend issue — work is done inside the backend/ folder

Description

The weight-tracking module has an entity (backend/src/weight-tracking/entities/weight-entry.entity.ts), a controller (weight-tracking.controller.ts), and a module file, but weight-tracking.service.ts does not exist. The controller has no service to delegate to, making all weight tracking endpoints non-functional.

Current State

• backend/src/weight-tracking/entities/weight-entry.entity.ts — entity exists
• backend/src/weight-tracking/weight-tracking.controller.ts — controller exists
• backend/src/weight-tracking/weight-tracking.module.ts — module exists
• backend/src/weight-tracking/weight-tracking.service.ts — missing

What Needs to Be Built

1. WeightTrackingService (weight-tracking.service.ts)

@Injectable()
export class WeightTrackingService {
  async addEntry(petId: string, dto: CreateWeightEntryDto): Promise<WeightEntry>
  async getHistory(petId: string, limit?: number): Promise<WeightEntry[]>
  async getLatest(petId: string): Promise<WeightEntry | null>
  async getTrend(petId: string): Promise<{ trend: 'gaining' | 'losing' | 'stable'; changeKg: number; periodDays: number }>
  async deleteEntry(id: string): Promise<void>
}

2. Trend Calculation Logic

• Compare the last 2 entries to determine direction
• Calculate changeKg and periodDays between entries
• Return stable if change is < 0.1 kg

3. Alert Integration

• If weight change exceeds a configurable threshold (e.g. >10% in 30 days), emit a notification via NotificationsService

4. Unit Tests (weight-tracking.spec.ts)

• Test trend calculation for gaining, losing, and stable cases
• Test alert threshold logic

Acceptance Criteria

• All CRUD operations work via the existing controller
• GET /weight-tracking/:petId/trend returns trend direction, change, and period
• Significant weight changes trigger a notification to the pet owner
• Unit tests cover trend and alert logic
• Service is registered in WeightTrackingModule

Files to Create / Modify

• backend/src/weight-tracking/weight-tracking.service.ts (new)
• backend/src/weight-tracking/weight-tracking.module.ts (modify — register service)
• backend/src/weight-tracking/weight-tracking.spec.ts (modify — add service tests)

Priority

Medium — module is wired but completely non-functional without the service

Estimated Effort

1–2 days

[pharuq411]

@pharuq411 has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

i will like to work this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @pharuq411 to this issue.

[drips-wave]

Congratulations, @pharuq411! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 2, 2026.

🧑‍💻 @pharuq411: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

Warning

When opening a PR, please link it to this issue to ensure it gets tracked accurately. Points are awarded when this issue is marked as completed by the maintainer.

🤠 Repo maintainers: Please keep an eye on the contributor's progress and review their work before the due date. You can manage this issue, including adjusting its complexity and points, here.

🌊 Happy Wave 🌊