using System;
using System.Threading.Tasks;
using ConcurrencyTests.Api;
using Microsoft.EntityFrameworkCore;

namespace ConcurrencyTestsConsole
{
    public class Parent
    {
        public int Id { get; set; }
        public ICollection<Child> Children { get; set; }
    }

    public class Child
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public int ParentId { get; set; }
        public Parent Parent { get; set; }
    }

    public class AppDbContext : DbContext
    {
        public DbSet<Parent> Parents { get; set; }
        public DbSet<Child> Children { get; set; }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder.UseNpgsql("Host=localhost;Database=concurrency_tests;Username=postgres;Password=admin");
        }
    }

    class Program
    {
        static async Task CreateParent()
        {
            using (var db = new AppDbContext())
            {
                db.Parents.Add(new Parent());
                await db.SaveChangesAsync();
            }
        }

        static async Task DeleteParents()
        {
            using (var db = new AppDbContext())
            {
                await Task.Delay(1000);
                db.Parents.RemoveRange(db.Parents);
                await db.SaveChangesAsync();

                Console.WriteLine("Parent was deleted");
            }
        }

        static async Task CreateChild()
        {
            using (var db = new AppDbContext())
            {
                using (var transaction = db.Database.BeginTransaction())
                {
                    var parent = await db.Parents.FirstOrDefaultAsync();
                    if (parent == null)
                    {
                        Console.WriteLine("Parent cannot be null!");
                        return;
                    }

                    Console.WriteLine("Parent exists!");

                    await Task.Delay(3000);

                    db.Children.Add(new Child
                    {
                        Name = "dupa",
                        Parent = parent
                    });

                    Console.WriteLine("Trying to add a child with deleted parent");
                    await db.SaveChangesAsync();

                    Console.WriteLine("Child added");
                }
            }
        }

        static async Task Main()
        {
            await CreateParent();

            var createChildTask = CreateChild();
            var deleteParentsTask = DeleteParents();
            await Task.WhenAll(createChildTask, deleteParentsTask);
        }
    }
}