using System.Runtime.InteropServices;
using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;

namespace MyBenchmarks;

[MemoryDiagnoser(false)]
[ShortRunJob]
public class EnumerableExcept
{
    [Params(100, 10000, 1000000)]
    public int count;

    private IEnumerable<int> collection;
    
    private List<int> list;
    private int[] array;


    [GlobalSetup]
    public void GlobalSetup()
    {
        Random random = new Random(42);
        collection = Enumerable.Range(0, count).Select(i => random.Next());
        
        list = collection.ToList();
        array = collection.ToArray();
    }

    [Benchmark]
    public int Count_IEnumerable() => collection.Count(x => x % 2 == 0);

    [Benchmark]
    public int Count_List() => list.Count(x => x % 2 == 0);

    [Benchmark]
    public int Count_Array() => array.Count(x => x % 2 == 0);

    [Benchmark]
    public int Count_IEnumerable_New() => MyEnumerable.Count(collection, x => x % 2 == 0);

    [Benchmark]
    public int Count_List_New() => MyEnumerable.Count(list, x => x % 2 == 0);

    [Benchmark]
    public int Count_Array_New() => MyEnumerable.Count(array, x => x % 2 == 0);
}

public static class MyEnumerable
{

    public static int Count<TSource>(IEnumerable<TSource> collection, Func<TSource, bool> predicate)
    {
        ArgumentNullException.ThrowIfNull(collection);
        ArgumentNullException.ThrowIfNull(predicate);

        if (collection is TSource[] array) 
        {
            return SpanCount(array, predicate);
        }

        if (collection is List<TSource> list)
        {
            return SpanCount(CollectionsMarshal.AsSpan(list), predicate);
        }

        int count = 0;
        foreach (var item in collection)
        {
            if (predicate(item))
            {
                count++;
            }
        }

        return count;

        static int SpanCount(Span<TSource> span, Func<TSource, bool> predicate)
        {
            int count = 0;
            for (int i = 0; i < span.Length; i++)
            {
                if (predicate(span[i]))
                {
                    count++;
                }
            }

            return count;
        }
    }
}

public class Program
{
    public static void Main(string[] args)
    {
        var summary = BenchmarkRunner.Run<EnumerableExcept>();
    }
}