module Pattern
  # roll-up - iterating through an ordered array and rolling up 
  #           related entries into a single entry
  #
  #   require '/Users/chiefwahoo/rails/patterns/patterns.rb'
  #   class Array; include Pattern; end
  #
  #   class Person 
  #     attr_accessor :name, :address 
  #     def initialize(name, address) 
  #       @name = name; @address = address; 
  #     end 
  #   end
  #
  #    # Assumes items are grouped by "key" in this case Person's name
  #    people = []
  #    people << Person.new("Compton, Kevin", "123 Mockingbird Lane")
  #    people << Person.new("Compton, Kevin", "9823 Beach View Drive")
  #    people << Person.new("Compton, Jessica", "823 City Park Avenue")
  #    people << Person.new("Compton, Megan", "123 California")
  #    people << Person.new("Compton, Megan", "876 Mount Vista")
  #
  #   rollup_items = []
  #
  #   people.rollup(
  #       Proc.new {|person| person.name}, 
  #       Proc.new {|person| "User #{person.name} has residences at: "},
  #       Proc.new {|container, person| container << " #{person.address};" },
  #       Proc.new {|container| 
  #           rollup_items << container; 
  #           puts "Detail is : #{container}" }
  #       )
  #    
  #    ### OUTPUT ###
  #    Detail is : User Compton, Kevin has residences at:  123 Mockingbird Lane; 9823 Beach View Drive;
  #    Detail is : User Compton, Jessica has residences at:  823 City Park Avenue; 9824 Beach View Drive;
  #    Detail is : User Compton, Keith has residences at:  777 College Avenue;
  #    Detail is : User Compton, Megan has residences at:  123 California; 876 Mount Vista;
  #    => nil
  #    irb(main):098:0> rollup_items
  #    => ["User Compton, Kevin has residences at:  123 Mockingbird Lane; 9823 Beach View Drive;", "User Compton, Jessica has residences at:  823 City Park Avenue; 9824 Beach View Drive;", "User Compton, Keith has residences at:  777 College Avenue;", "User Compton, Megan has residences at:  123 California; 876 Mount Vista;"]
  #    
   def rollup(bookmark_detail_proc, initialize_item_proc, merge_into_item_proc, finalize_item_proc)
     saved_bookmark = nil
     current_item = nil

     self.each do |line|
       current_bookmark = bookmark_detail_proc.call(line) 
       if saved_bookmark != current_bookmark
         finalize_item_proc.call(current_item) unless current_item.nil?

         saved_bookmark = current_bookmark  
         current_item = initialize_item_proc.call(line)
       end

       merge_into_item_proc.call(current_item, line)
     end 
     finalize_item_proc.call(current_item) unless current_item.nil?
   end
end