using System;
using System.Linq;
using BenchmarkDotNet.Attributes;
using Microsoft.EntityFrameworkCore;

[MemoryDiagnoser]
[ReturnValueValidator] 
public class AverageBlogRanking
{
    [Params(1000)]
    public int NumBlogs; // number of records to write [once], and read [each pass]

    [GlobalSetup]
    public void Setup()
    {
        using var context = new BloggingContext();
        context.Database.EnsureDeleted();
        context.Database.EnsureCreated();
        context.SeedData(NumBlogs);
    }

    [Benchmark]
    public double LoadEntitiesNoTracking()
    {
        var sum = 0;
        var count = 0;
        using var ctx = new BloggingContext();
        foreach (var blog in ctx.Blogs.AsNoTracking())
        {
            sum += blog.Rating;
            count++;
        }

        return (double)sum / count;
    }

    [Benchmark]
    public double ProjectOnlyRanking()
    {
        var sum = 0;
        var count = 0;
        using var ctx = new BloggingContext();
        foreach (var rating in ctx.Blogs.Select(b => b.Rating))
        {
            sum += rating;
            count++;
        }

        return (double)sum / count;
    }

    [Benchmark(Baseline = true)]
    public double CalculateInDatabase()
    {
        using var ctx = new BloggingContext();
        return ctx.Blogs.Average(b => b.Rating);
    }

    public class BloggingContext : DbContext
    {
        public DbSet<Blog> Blogs { get; set; }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
            => optionsBuilder.UseSqlServer(@"Server=localhost;Database=Blogging;Trusted_Connection=True;TrustServerCertificate=true");

        public void SeedData(int numblogs)
        {
            Blogs.AddRange(
                Enumerable.Range(0, numblogs).Select(
                    i => new Blog
                    {
                        Name = $"Blog{i}",
                        Url = $"blog{i}.blogs.net",
                        CreationTime = new DateTime(2020, 1, 1),
                        Rating = i % 5
                    }));
            SaveChanges();
        }
    }

    public class Blog
    {
        public int BlogId { get; set; }
        public string Name { get; set; }
        public string Url { get; set; }
        public DateTime CreationTime { get; set; }
        public int Rating { get; set; }
    }
}

// .NET 8 Lowered C# Code unavailable due to errors:
error CS0234: The type or namespace name 'EntityFrameworkCore' does not exist in the namespace 'Microsoft' (are you missing an assembly reference?)
error CS0246: The type or namespace name 'DbContext' could not be found (are you missing a using directive or an assembly reference?)
error CS0246: The type or namespace name 'DbSet<>' could not be found (are you missing a using directive or an assembly reference?)
error CS0246: The type or namespace name 'DbContextOptionsBuilder' could not be found (are you missing a using directive or an assembly reference?)
error CS1674: 'AverageBlogRanking.BloggingContext': type used in a using statement must be implicitly convertible to 'System.IDisposable'.
error CS1061: 'AverageBlogRanking.BloggingContext' does not contain a definition for 'Database' and no accessible extension method 'Database' accepting a first argument of type 'AverageBlogRanking.BloggingContext' could be found (are you missing a using directive or an assembly reference?)
error CS0103: The name 'SaveChanges' does not exist in the current context

// .NET 8 IL Code unavailable due to errors:
error CS0234: The type or namespace name 'EntityFrameworkCore' does not exist in the namespace 'Microsoft' (are you missing an assembly reference?)
error CS0246: The type or namespace name 'DbContext' could not be found (are you missing a using directive or an assembly reference?)
error CS0246: The type or namespace name 'DbSet<>' could not be found (are you missing a using directive or an assembly reference?)
error CS0246: The type or namespace name 'DbContextOptionsBuilder' could not be found (are you missing a using directive or an assembly reference?)
error CS1674: 'AverageBlogRanking.BloggingContext': type used in a using statement must be implicitly convertible to 'System.IDisposable'.
error CS1061: 'AverageBlogRanking.BloggingContext' does not contain a definition for 'Database' and no accessible extension method 'Database' accepting a first argument of type 'AverageBlogRanking.BloggingContext' could be found (are you missing a using directive or an assembly reference?)
error CS0103: The name 'SaveChanges' does not exist in the current context