class ChangeTaxonsToNestedSet < ActiveRecord::Migration
  def self.up
    add_column :taxons, :lft, :integer
    add_column :taxons, :rgt, :integer

    Taxon.reset_column_information # So the new root ids get saved

    Taxon.class_eval do
      # adapted from awesome nested set to use "position" information
      indices = {}

      left_column_name = "lft"
      right_column_name = "rgt"
      quoted_parent_column_name = "parent_id"
      scope = lambda{|node|}

      set_left_and_rights = lambda do |node|
        # set left
        node[left_column_name] = indices[scope.call(node)] += 1
        # find
        find(:all, :conditions => ["#{quoted_parent_column_name} = ?", node], :order => "position ASC").each{|n| set_left_and_rights.call(n) }
        # set right
        node[right_column_name] = indices[scope.call(node)] += 1
        node.save!
      end

      # Find root node(s)
      find(:all, :conditions => "#{quoted_parent_column_name} IS NULL", :order => "position ASC").each do |root_node|
        # setup index for this scope
        indices[scope.call(root_node)] ||= 0
        set_left_and_rights.call(root_node)
      end
    end
  end

  def self.down
    remove_column :taxons, :lft
    remove_column :taxons, :rgt
  end
end