Feat: Music Compatibility Scores

[kellenGary]

Summary

Implement music compatibility scores that show how similar two users' music tastes are when viewing a profile.

Background

• When viewing another user's profile, there should be a section showing a compatibility/similarity score with the current user.
• The score can be derived from overlapping listening history, shared song streaks, liked albums in common, followed artists in common, and genre overlap.
• This is a core social feature that encourages discovery and connection between users.

Scope

Backend (C# API)

• Design and implement a compatibility scoring algorithm that considers:
  • Overlapping listening history (shared tracks)
  • Shared song streaks
  • Liked albums in common
  • Followed artists in common
  • Genre overlap from top artists
• Create an API endpoint: GET /users/{userId}/compatibility that returns the score and a breakdown of contributing factors.
• Optimize the query for performance — this needs to be fast enough for profile page loads.

Frontend (React Native)

• Add a "Music Compatibility" section to the user profile page.
• Display the overall score (e.g., percentage or visual meter).
• Show a breakdown of what contributes to the score (e.g., "12 artists in common," "8 shared tracks").
• Design the component to be visually engaging and consistent with the app's design system.

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Definition of Done

• Algorithm implemented: A scoring algorithm exists that computes compatibility based on overlapping listening history, streaks, liked albums, followed artists, and genres.
• API endpoint created: GET /users/{userId}/compatibility returns a score and factor breakdown for the authenticated user vs. the target user.
• Profile UI added: The user profile page shows a "Music Compatibility" section with the score.
• Breakdown displayed: The UI shows contributing factors (e.g., "X artists in common," "Y shared tracks").
• Performance acceptable: The compatibility score loads within a reasonable time (< 2 seconds) on a profile page.
• Score range defined: The score uses a clear, understandable scale (e.g., 0–100%).
• Edge cases handled: If there is insufficient data to compute a score (new user, no overlap), an appropriate message is shown instead of 0% or a broken state.
• Self-profile: The compatibility section is hidden or shows a special state on the user's own profile.
• Build passes: Both the C# API and the frontend compile without errors.
• Verified with test data: Tested with users who have overlapping and non-overlapping listening data to confirm the score behaves correctly.