Musify/backend/Core/Musify.Application/Users/FollowVisibility.cs

using Microsoft.EntityFrameworkCore;
using Musify.Application.Contracts;

namespace Musify.Application.Users
{
    public static class FollowVisibility
    {
        public static async Task<bool> CanViewFollowersAsync(
            IDatabase database,
            long? viewerId,
            long userId,
            CancellationToken cancellationToken)
        {
            if (viewerId is not { } viewer)
                return false;

            if (viewer == userId)
                return true;

            var mutualRows = await database.UserFollows
                .AsNoTracking()
                .CountAsync(f =>
                    (f.FollowerId == viewer && f.FollowedId == userId) ||
                    (f.FollowerId == userId && f.FollowedId == viewer),
                    cancellationToken);

            return mutualRows == 2;
        }
    }
}