Prevent Duplicate Medication Reminders on Server Restart

[SrishtiSonam]

Problem

Currently, medication reminders can be triggered multiple times when:

• The server restarts, or
• Socket.IO reconnects occur

This happens because reminder scheduling relies on in-memory state, which is lost on restart. When the app rehydrates data, the same reminders may be scheduled again, leading to duplicate notifications. In a healthcare context, this is risky and can negatively impact patient safety.

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Proposed Idea / Solution

Introduce idempotent reminder scheduling with both in-memory and database-level safeguards.

Key Concepts

1. Deterministic Reminder Identity

   • Generate a stable reminder key using:

     userId + medicationId + scheduledTime
     

   • Prevents duplicate scheduling during runtime (e.g., Socket.IO reconnects).

2. Persistent Deduplication (DB-level)

   • Add an optional field to the Medication schema:
     • lastReminderSentAt
   • Before sending a reminder, check if it was already sent for that scheduled time.
   • Update this field only after a reminder is successfully delivered.

3. Safe Rehydration on Server Restart

   • On server startup:
     • Load only future medication schedules.
     • Schedule reminders only if they have not already been sent.
   • Ensures reminders are not duplicated after restarts.

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Why This Matters

• Patient safety: Prevents repeated reminders that could cause confusion or overdose.
• Reliability: Makes scheduling restart-safe and deterministic.
• Security-compliant: No secrets touched, no user data leakage.
• Non-breaking: Backward compatible with existing data.

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Scope

• Backend only
• No new dependencies
• No frontend changes
• No schema migration required (optional field with default)

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Files Likely Affected

• server/src/models/Medication.js
• server/src/services/schedulerService.js
• server/src/index.js
• (Optional) server/test/scheduler.test.js

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Open Questions

• Does the project currently have a preferred pattern for scheduler rehydration on startup?
• Is there an existing place where reminder state is persisted that this should integrate with?

I’m happy to take this up and submit a PR if the approach aligns with the maintainers’ direction.

[tirth-patel06]

Issue #54 open