AggregationController.cs

using System.Linq;
using System.Threading.Tasks;
using HwProj.APIGateway.API.Models;
using HwProj.AuthService.Client;
using HwProj.Models.CoursesService.ViewModels;
using Microsoft.AspNetCore.Mvc;

namespace HwProj.APIGateway.API.Controllers;

public class AggregationController : ControllerBase
{
    protected readonly IAuthServiceClient AuthServiceClient;

    protected AggregationController(IAuthServiceClient authServiceClient)
    {
        AuthServiceClient = authServiceClient;
    }

    protected string? UserId =>
        Request.HttpContext.User.Claims
            .FirstOrDefault(claim => claim.Type.ToString() == "_id")
            ?.Value;

    protected async Task<CoursePreviewView[]> GetCoursePreviews(CoursePreview[] courses)
    {
        var getMentorsTasks = courses.Select(t => AuthServiceClient.GetAccountsData(t.MentorIds)).ToList();
        await Task.WhenAll(getMentorsTasks);
        var mentorDTOs = getMentorsTasks.Select(t => t.Result);

        var result = courses.Zip(mentorDTOs, (course, mentors) =>
            new CoursePreviewView
            {
                Id = course.Id,
                Name = course.Name,
                GroupName = course.GroupName,
                IsCompleted = course.IsCompleted,
                Mentors = mentors.Where(t => t != null).ToArray()
            }).ToArray();

        return result;
    }
}