using System;
using System.Collections.Generic;
using System.Linq;

public class Test
{
	public static void Main()
	{
		var samples = new[] {
			new Category { Id = 1, ParentCategoryId = 8, SortOrder = 1, Text = "Firefall" },
			new Category { Id = 2, ParentCategoryId = 8, SortOrder = 2, Text = "Left 4 Dead 2" },
			new Category { Id = 3, ParentCategoryId = 8, SortOrder = 3, Text = "Renegade X" },
			new Category { Id = 4, ParentCategoryId = 2, SortOrder = 2, Text = "Survival" },
			new Category { Id = 5, ParentCategoryId = 0, SortOrder = 1, Text = "General" },
			new Category { Id = 6, ParentCategoryId = 8, SortOrder = 4, Text = "Battlefield 4" },
			new Category { Id = 7, ParentCategoryId = 2, SortOrder = 1, Text = "Versus" },
			new Category { Id = 8, ParentCategoryId = 0, SortOrder = 2, Text = "Games" },
			new Category { Id = 9, ParentCategoryId = 0, SortOrder = 3, Text = "Army Restricted Area" },
			new Category { Id = 10, ParentCategoryId = 9, SortOrder = 1, Text = "Kool Kids Klub" }
		};
		
		var categories = new List<Category>(samples);
		
		// hierarchycal
		var categoryTree = CategoryTree.Create(categories, o => o.ParentCategoryId == 0);
		// recursively called Console.WriteLine on every node
		PrintNodes(categoryTree);
		
		Console.WriteLine(new string('-',80));
		
		var flatTree = categoryTree.Flatten();
		foreach(var category in flatTree) {
			Console.WriteLine(category.DisplayText);
		}
	}
	
	public static void PrintNodes(CategoryTree tree) {
		if (tree == null || !tree.Any()) return;
		
		foreach(var node in tree) {
			Console.WriteLine(node.DisplayText);
			PrintNodes(node.Children);
		}
	}
}

public class Category {
	public int Id { get; set; }
	public int ParentCategoryId { get; set; }
	public int SortOrder { get; set; }
	public string Text { get; set; }
}

public class CategoryNode : Category {
  public CategoryNode(Category category) {
  	Id = category.Id;
	ParentCategoryId = category.ParentCategoryId;
	SortOrder = category.SortOrder;
	Text = category.Text;
  }
   
  public CategoryTree Children { get; set; }
  public int Level { get; set;}
  public string DisplayText { 
   	get {
   	  return string.Concat(new string('.', Level*2), Text);	
 	}
  }
}

public class CategoryTree : IEnumerable<CategoryNode> {
	private List<CategoryNode> innerList = new List<CategoryNode>();
	
	public CategoryTree(IEnumerable<CategoryNode> nodes) {
		innerList = new List<CategoryNode>(nodes);	
	}
	
	public IEnumerator<CategoryNode> GetEnumerator()
    {
        return innerList.GetEnumerator();
    }

    System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
    {
        return this.GetEnumerator();
    }
    
	public IEnumerable<CategoryNode> Flatten() {
	  foreach(var category in innerList.OrderBy(o => o.SortOrder)) {
	  	yield return category;
	  	if (category.Children != null) {
	  	  foreach(var child in category.Children.Flatten()) {
	  		  yield return child;
	  	  }
	  	}
	  }
   }
   
   public static CategoryTree Create(IEnumerable<Category> categories, Func<Category, bool> parentPredicate, int level = 0) {
		var nodes = categories
			.Where(parentPredicate)
			.OrderBy(o => o.SortOrder)
			.Select(item => 
				new CategoryNode(item) { 
					Level = level,
					Children = Create(categories, o => o.ParentCategoryId == item.Id, level + 1)
				});
				
		return new CategoryTree(nodes);
	}
}