using System;

using Microsoft.EntityFrameworkCore;

using System.Linq;

​

public class Product

{

    public Guid Id { get; set; }

    public string Title { get; set; }

    public Guid CategoryId { get; set; }

    public double OrderNumber { get; set; }

    public int RX { get; set; }

    public int RY { get; set; }

}

public class MyDbContext : DbContext

{

    public MyDbContext(DbContextOptions<MyDbContext> options)

        : base(options)

    {

        Database.EnsureCreated();

    }

​

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)

    {

    }

​

    protected override void OnModelCreating(ModelBuilder modelBuilder)

    {

    }

    public DbSet<Product> Products { get; set; }

}

public class Program

{

    private static Product CreateProduct(Guid categoryId,string title)

    {

        return new Product

            {

                CategoryId = categoryId,

                Title = title

            };

    }

    public static void Main()

    {

        //config database context by sqlite

        var options = new DbContextOptionsBuilder<MyDbContext>()

                .UseInMemoryDatabase(databaseName: "Test")

                .Options;

​

        using (var context = new MyDbContext(options))

        {

            var business = new ProductBusiness(context);

            var categoryId = Guid.NewGuid();

            var firstProductId = business.Append(CreateProduct(categoryId,"first product"));

            business.Append(CreateProduct(categoryId,"Second product"));

            var thirdProductId = business.Prepend(CreateProduct(categoryId,"Third product"));

            business.InsertAfter(firstProductId.Id,CreateProduct(categoryId,"forth product"));

            business.InsertBefore(thirdProductId.Id,CreateProduct(categoryId,"fifth product"));

            business.InsertBefore(firstProductId.Id,thirdProductId,false);

​

            context.Products

                .OrderBy(x => x.OrderNumber)

                .ToList()

                .ForEach(x => {

                    Console.WriteLine(x.Title +" , " +  x.RX.ToString() + " , " +  x.RY.ToString() );

                });

        }

    }

}

​

public class ProductBusiness

{

    private MyDbContext _dbContext;

    private decimal insertUnit = Decimal.Parse(".0");

    private const decimal appendUnit = 1;

​

    public ProductBusiness(MyDbContext dbContext)

    {

        this._dbContext = dbContext;

    }

    public Product InsertAfter(Guid id,Product product,bool insert=true)

    {

        var previousProduct = _dbContext.Products

            .Where(x => x.CategoryId == product.CategoryId && x.Id==id)

            .FirstOrDefault();

        if(previousProduct == null)

            throw new Exception("Product not found");

        var nextProduct = _dbContext.Products

            .Where(x => x.CategoryId == product.CategoryId && x.OrderNumber >= previousProduct.OrderNumber)

            .OrderBy(x => x.OrderNumber)

            .Skip(1)

            .Take(1)

            .FirstOrDefault();

        var rx = previousProduct.RX + (nextProduct!= null?nextProduct.RX : 1);

        var ry = nextProduct!= null ? nextProduct.RY + previousProduct.RY : 1;

        var newOrderNumber = rx/ry;

        product.RX = rx;

        product.RY = ry;

        product.OrderNumber = newOrderNumber;

        if(insert)

            _dbContext.Add<Product>(product);

        _dbContext.SaveChanges();

        return product;

    }

    public Product InsertBefore(Guid id,Product product,bool insert=true)

    {

        var nextProduct = _dbContext.Products

            .Where(x => x.CategoryId == product.CategoryId && x.Id==id)

            .FirstOrDefault();

        if(nextProduct == null)

            throw new Exception("Product not found");

        var prevProduct = _dbContext.Products

            .Where(x => x.CategoryId == product.CategoryId && x.OrderNumber <= nextProduct.OrderNumber)

            .OrderByDescending(x => x.OrderNumber)

            .Skip(1)

            .Take(1)

            .FirstOrDefault();

        var rx = nextProduct.RX + (prevProduct!= null ? prevProduct.RX : -1);

        var ry = prevProduct != null ? (prevProduct.RY+nextProduct.RY) : 1;

        var newOrderNumber = rx/ry;

        product.RX = rx;

        product.RY = ry;

        product.OrderNumber = newOrderNumber;

        if(insert)

        _dbContext.Add<Product>(product);

        _dbContext.SaveChanges();

        return product;

    }

    public Product Append(Product product)

    {

        var lastProduct = _dbContext.Products

            .Where(x => x.CategoryId == product.CategoryId)

            .OrderByDescending(x => x.OrderNumber)

            .FirstOrDefault();

        var rx = lastProduct != null ? lastProduct.RX+1 : 1;

        var ry = 1;

        var newOrderNumber = rx/ry;

        product.RX = rx;

        product.RY = ry;

        product.OrderNumber = newOrderNumber;

        _dbContext.Add<Product>(product);

        _dbContext.SaveChanges();

        return product;

    }

    public Product Prepend(Product product)

    {

        var lastProduct = _dbContext.Products

            .Where(x => x.CategoryId == product.CategoryId)

            .OrderBy(x => x.OrderNumber)

            .FirstOrDefault();

        var rx = lastProduct != null ? lastProduct.RX-1 : 1;

        var ry = 1;

        var newOrderNumber = rx/ry;

        product.RX = rx;

        product.RY = ry;

        product.OrderNumber = newOrderNumber;

        _dbContext.Add<Product>(product);

        _dbContext.SaveChanges();

        return product;

    }

    public void Remove(Product product)

    {

        _dbContext.Remove<Product>(product);

        _dbContext.SaveChanges();

    }

}