uCommerce categories

using System;
using System.Collections.Generic;
using System.Linq;
using UCommerce.EntitiesV2;


public class categories
{
    /// <summary>
    /// Gets a list of products that are in all categories specified
    /// </summary>
    /// <param name="categories">a comma-delited string of categories</param>
    public List<Product> GetProductsInCategories(string categories)
    {
        List<Product> productsInCategories = new List<Product>();
        List<List<Product>> allProducts = new List<List<Product>>();

        try
        {
            // Break the comma delimited string into an array of filter strings
            string[] filters = categories.Split(',');

            foreach (string filter in filters)
            {
                List<Product> productsInCategory = GetProductsInCategory(filter);
                allProducts.Add(productsInCategory);
            }

            // Create a list of sortable products (required by the FindDuplicates() method below)
            var allSortableProducts = new List<List<SortableProduct>>();
            foreach (List<Product> productList in allProducts)
            {
                var sortableProducts = new List<SortableProduct>();
                foreach (Product thisProduct in productList)
                {
                    var sortableProduct = new SortableProduct {product = thisProduct};
                    sortableProducts.Add(sortableProduct);
                }
                allSortableProducts.Add(sortableProducts);
            }

            // Filter products that are in all categories
            SortedDictionary<SortableProduct, bool>.KeyCollection common = FindDuplicates(allSortableProducts);
            if (common.Count > 0)
            {
                // Convert back to a List<Product>
                List<SortableProduct> sortableProducts = common.ToList();
                foreach (SortableProduct sortableProduct in sortableProducts)
                {
                    productsInCategories.Add(sortableProduct.product);
                }
            }
        }
        catch (Exception ex)
        {
        }

        return productsInCategories;
    }

    private List<Product> GetProductsInCategory(string category)
    {
        List<Product> productsInCategory = new List<Product>();

        try
        {
            Category cat = Category.SingleOrDefault(x => x.Name.ToLower() == category.ToLower());
            if (cat != null)
            {
                productsInCategory = cat.Products.Where(x => x.DisplayOnSite).ToList();
            }
        }
        catch (Exception ex)
        {
            productsInCategory = null;
        }
        return productsInCategory;
    }

    /// <summary>
    /// Gets the items that are common to all lists in the list of items
    /// Taken from http://stackoverflow.com/questions/41159/fastest-way-to-find-common-items-across-multiple-lists-in-c-sharp?rq=1
    /// </summary>
    private SortedDictionary<T, bool>.KeyCollection FindDuplicates<T>(List<List<T>> items)
    {
        SortedDictionary<T, bool> current_common = new SortedDictionary<T, bool>(),
            common = new SortedDictionary<T, bool>();

        foreach (List<T> list in items)
        {
            if (current_common.Count == 0)
            {
                foreach (T item in list)
                {
                    common[item] = true;
                }
            }
            else
            {
                foreach (T item in list)
                {
                    if (current_common.ContainsKey(item))
                    {
                        common[item] = true;
                    }
                }
            }

            if (common.Count == 0)
            {
                current_common.Clear();
                break;
            }

            SortedDictionary<T, bool> swap = current_common;

            current_common = common;
            common = swap;
            common.Clear();
        }

        return current_common.Keys;
    }
}

public class SortableProduct : IComparable
{
    public Product product;

    public int ProductId
    {
        get { return product.Id; }
    }

    public int CompareTo(object obj)
    {
        SortableProduct item = obj as SortableProduct;
        if (item != null)
        {
            SortableProduct other = item;
            return other.ProductId.CompareTo(this.ProductId);
        }
        else
        {
            return 0;
        }
    }
}