gistfile1.rb

  constraints(SoftwareFilter) do
    constraints(CategoriesFilter) do
      match ':software/:controller/:category1/:category2/:category3/:category4/c(.:format)', :action => :index
      match ':software/:controller/:category1/:category2/:category3/:category4/c(/:id(.:format))', :action => :show
      match ':software/:controller/:category1/:category2/:category3/:category4/c(/:action(/:id(.:format)))'
      match ':software/:controller/:category1/:category2/:category3/c(.:format)', :action => :index
      match ':software/:controller/:category1/:category2/:category3/c(/:id(.:format))', :action => :show
      match ':software/:controller/:category1/:category2/:category3/c(/:action(/:id(.:format)))'
      match ':software/:controller/:category1/:category2/c(.:format)', :action => :index
      match ':software/:controller/:category1/:category2/c(/:id(.:format))', :action => :show
      match ':software/:controller/:category1/:category2/c(/:action(/:id(.:format)))'
      match ':software/:controller/:category1/c(.:format)', :action => :index
      match ':software/:controller/:category1/c(/:id(.:format))', :action => :show
      match ':software/:controller/:category1/c(/:action(/:id(.:format)))'
    end
  end
  
  constraints(CategoriesFilter) do
    match ':controller/:category1/:category2/:category3/:category4/c(.:format)', :action => :index
    match ':controller/:category1/:category2/:category3/:category4/c(/:id(.:format))', :action => :show
    match ':controller/:category1/:category2/:category3/:category4/c(/:action(/:id(.:format)))'
    match ':controller/:category1/:category2/:category3/c(.:format)', :action => :index
    match ':controller/:category1/:category2/:category3/c(/:id(.:format))', :action => :show
    match ':controller/:category1/:category2/:category3/c(/:action(/:id(.:format)))'
    match ':controller/:category1/:category2/c(.:format)', :action => :index
    match ':controller/:category1/:category2/c(/:id(.:format))', :action => :show
    match ':controller/:category1/:category2/c(/:action(/:id(.:format)))'
    match ':controller/:category1/c(.:format)', :action => :index
    match ':controller/:category1/c(/:id(.:format))', :action => :show
    match ':controller/:category1/c(/:action(/:id(.:format)))'
  end

class CategoriesFilter
  def self.matches?(request)
    match = (!request.params[:category1] || (request.params[:category1] && level1.include?(request.params[:category1]))) &&
            (!request.params[:category2] || (request.params[:category2] && level2.include?(request.params[:category2]))) &&
            (!request.params[:category3] || (request.params[:category3] && level3.include?(request.params[:category3]))) &&
            (!request.params[:category4] || (request.params[:category4] && level4.include?(request.params[:category4])))
  end
  
  def self.level1
    @@level1 ||= level1_cats.collect(&:permalink)
  end
  
  def self.level2
    @@level2 ||= level2_cats.collect(&:permalink)
  end
  
  def self.level3
    @@level3 ||= level3_cats.collect(&:permalink)
  end
  
  def self.level4
    @@level4 ||= level4_cats.collect(&:permalink)
  end
  
  def self.level1_cats
    Category.roots
  end
  
  def self.level2_cats
    Category.where(:parent_id => level1_cats.collect(&:id))
  end
  
  def self.level3_cats
    Category.where(:parent_id => level2_cats.collect(&:id))
  end
  
  def self.level4_cats
    Category.where(:parent_id => level3_cats.collect(&:id))
  end
end