I have this course controller for a aspnet core project i want to understand what is this for? using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;
using Project.Data;
using Project.Interfaces;
using Project.ViewModels;
using Project.Models;
using Project.Data.Enum;

namespace Project.Controllers
{
    public class CourseController : Controller
    {
        private readonly ICourseRepository _courseRepository;
        public CourseController(ICourseRepository courseRepository) /* ApplicationDbContext is our Database */
        {
            _courseRepository = courseRepository;
        }
        
      
       public async Task<IActionResult> Index( )
        {
            IEnumerable<Course> courses = await _courseRepository.GetAll( ); /* Bringing all the table from database and drop into your table */
    
            return View(courses);
        }


        public async Task<IActionResult> Detail(int id)
        {
            Course course = await _courseRepository.GetByIdAsync(id);
            return View(course);
        }
        
        public IActionResult Create()
        {
            return View( );
        }
        [HttpPost]
        public async Task<IActionResult> Create(Course course)
        {
            if (!ModelState.IsValid)
            {
                return View(course);
            }
            course.ImageURL = "https://s.udemycdn.com/home/top-categories/lohp-category-development-v2.jpg";

            
            _courseRepository.Add(course);
            return RedirectToAction("Index");
        }
        
        public async Task<IActionResult> Edit(int id)
        {
            var course = await _courseRepository.GetByIdAsync(id);
            if(course == null) return View("Error");
            var courseVM = new EditCourseViewModel
            {
                Title = course.Title,
                Description = course.Description,
                Image = course.ImageURL,
                CourseCategory = course.Category
            };
            return View(courseVM);
        }
        
        [HttpPost]
        public async Task<IActionResult> Edit(int id, EditCourseViewModel courseVM)
        {
            if(!ModelState.IsValid)
            {
                ModelState.AddModelError("","Failed to edit course");
                return View("Edit", courseVM);
            }
            var userCourse = await _courseRepository.GetByIdAsyncNoTracking(id);
            if(userCourse != null)
            {
                var course = new Course
                {
                    CourseID = id,
                    Title = courseVM.Title,
                    Description = courseVM.Description,
                    ImageURL = "Default",
                };
                _courseRepository.Update(course);
                return  RedirectToAction("Index");
            }
            else
            {
                return View(courseVM);
            }
        }    
        public async Task<IActionResult> Delete(int id)
        {
            var courseDetails = await _courseRepository.GetByIdAsync(id);
            if(courseDetails == null) return View("Error");
            return View(courseDetails);
        }
        [HttpPost, ActionName("Delete")]
        public async Task<IActionResult> DeleteCourse(int id)
        {
            var courseDetails = await _courseRepository.GetByIdAsync(id);
            if(courseDetails == null) return View("Error");

            _courseRepository.Delete(courseDetails);
            return RedirectToAction("Index");
        }

    }
}