using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;

BenchmarkSwitcher.FromAssembly(typeof(Tests).Assembly).Run(args);

[MemoryDiagnoser(false)]
[HideColumns("Job", "Error", "StdDev", "Median", "RatioSD")]
public class Tests
{
    private ILookup<int, string> _stringsByLength;

    [Params(1, 2, 3, 4, 5, 6, 7, 8)]
    public int ItemsPerGroup { get; set; }

    [GlobalSetup]
    public void Setup()
    {
        const int NumGroups = 10;

        var list = new List<string>();
        for (int i = 0; i < NumGroups; i++)
        {
            for (int item = 0; item < ItemsPerGroup; item++)
            {
                list.Add(new string((char)('a' + item), i + 1));
            }
        }

        _stringsByLength = list.ToLookup(s => s.Length);
    }

    [Benchmark]
    public int Sum()
    {
        int sum = 0;
        foreach (IGrouping<int, string> group in _stringsByLength)
        {
            foreach (string item in group)
            {
                sum += item.Length;
            }
        }
        return sum;
    }
}