using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public class ProductVariantModel

    {

        public string Name { get; set; }

​

        public string Options { get; set; }

    }

​

    public class CreateModel

    {

        public string Name { get; set; }

        public IList<ProductVariantModel> Variants { get; set; }

    }

    public class ProductVariantOption {

        public string Name { get; set; }

    }

    private static ProductVariantOption BuildModel(string[] modelParts) {

        if (modelParts.Length == 1) {

            return new ProductVariantOption {

                Name = modelParts.Single()

            };  

        }

        var baseName = modelParts.First();

        var variantParts = string.Join('/', modelParts.Skip(1));

        return new ProductVariantOption {

            Name = $"{baseName}-{variantParts}"

        }; 

    }

    public static IList<ProductVariantOption> GetVariants(CreateModel model) {

        // Prepare all possible variables from the model in advance

        var allVariables = model.Variants.Select(v => v.Options.Split(",")).ToArray();

        var initialParts = new List<string[]> { new[] { model.Name } };

        // Generate cross product for every subsequent variant with initial list as a seed

        // Every iteration of aggregate produces all possible combination of models with the new variant

        var allModels = allVariables.Aggregate(initialParts, (variantsSoFar, variableValues) =>

            variantsSoFar

                .SelectMany(variant => variableValues.Select(variableValue => variant.Append(variableValue).ToArray()))

                .ToList()

        );

        // Map all lists of model parts into ProductVariantOption

        return allModels.Select(BuildModel).ToList();

    }

    public static void Main()

    {

        var testModel = new CreateModel {

            Name = "Jean",

            Variants = new List<ProductVariantModel> {

                new ProductVariantModel {

                    Name = "Color",

                    Options = "Grey,Black"

                },

                new ProductVariantModel {

                    Name = "Size",

                    Options = "X,XL"

                },

                new ProductVariantModel {

                    Name = "Stretch",

                    Options = "Low,High,Mid"

                }

            }

        };

        var productOptions = GetVariants(testModel);

        Console.WriteLine(string.Join("\n", productOptions.Select(it => it.Name)));

    }

}