Implement Calendar Integration for Event Attendance

[alx-sch]

Description

We need to allow users to sync events they are attending directly to their personal calendars (Google, Outlook, Apple, etc.). This ensures that once a user commits to an event in our app, it is reflected in their primary tools.

User Story

• As a user, when I click "Going" on an event, I want it automatically added to my external calendar.
• As a user, when I accept an invitation, I want the event details synced to my calendar.

Technical Requirements (MVP: One-Way Push)

1. Provider Authentication: Implement OAuth 2.0 flow for at least Google Calendar (optional Microsoft Outlook).

2. Attendance Trigger: Hook into the updateAttendance logic.

   • If status === 'attending', create the calendar event.
   • If status === 'not_going', delete the corresponding calendar event.

3. Data Mapping:

   • Title: Event Name
   • Time: Start and End ISO strings (must handle timezone conversion).
   • Location: Address or Google Map URL.
   • Description: Event details + "View in App" deep link.

Optional / Future Phase (Bi-Directional Sync)

• Webhook Integration: Set up listeners for external calendar changes.
• Logic: If a user deletes the event directly from their Google/Outlook calendar, our app should receive a notification and optionally prompt the user or automatically update their status to "Not Going" in our database.