Fix inconsistent voting permission checks

[RounakChoudhary]

Summary

Refactored and centralized voting logic across question and answer endpoints to ensure consistent validation, reputation handling, and response behavior.

This fixes inconsistencies where newer /upvote and /downvote routes bypassed reputation checks and some routes attempted to call updateReputation() on unpopulated author references.

Changes Made

Centralized voting logic

• Added shared voting service in server/services/voting.js

• Moved duplicated vote handling into reusable helpers:

  • voteOnContent
  • applyVoteChange
  • sendVoteResponse

Consistent authorization & validation

• Enforced req.user.canVote() across all voting endpoints
• Added validation for allowed vote types (upvote / downvote)
• Added self-vote prevention

Reputation handling fixes

• Populated content authors before reputation updates
• Ensured updateReputation() is only called on populated author documents
• Fixed reputation delta calculations during vote toggles

Notification improvements

• Centralized vote notification creation
• Prevented notifications for self-votes

Route/controller cleanup

• Removed duplicated voting logic from:

  • server/routes/questions.js
  • server/controllers/answersController.js

• Unified response format across vote APIs

Tests

Added tests covering:

• vote toggling behavior
• low-reputation vote rejection
• reputation updates on populated author documents

Fixed Issues

• Low-reputation users could vote through newer endpoints
• Inconsistent validation across voting APIs
• Potential runtime errors from calling updateReputation() on ObjectId
• Duplicate voting logic across routes/controllers

Result

All voting endpoints now:

• enforce the same authorization rules
• validate voting consistently
• safely update reputation
• return standardized responses

[vercel]

@RounakChoudhary is attempting to deploy a commit to the anglenobida003-8112's projects Team on Vercel.

A member of the Team first needs to authorize it.

[RounakChoudhary]

This PR addresses Issue #6 by centralizing voting logic, enforcing consistent vote validation, and fixing reputation update handling across all voting endpoints.

Please review the changes and let me know if any modifications are needed. If everything looks good, kindly consider merging the PR.