module ActiveRecord
  class Base
    # This method lets you iterate over the results of a .find, in groups.
    # (Basically an interface to LIMIT.)
    # Anything you can pass as options to .find, you can pass here. 
    # Example 1:
    #   Order.each_by(100, :conditions => { :cc_processed_at => nil }) do |order|
    #     # do stuff with order
    #   end
    # Example 2:
    #   Person.each_by(50, :order => 'name') do |person, index|
    #     # do stuff with person and index
    #   end
    # Pass :update => true in the options to print a message before each group is
    # fetched from the db.
    #
    # Author: Elliot Winkler <elliot.winkler@gmail.com>
    # Source: http://snippets.dzone.com/posts/show/5461
    def self.each_by(group_size, options={}, &blk)
      update = options.delete(:update) || false
      num_records = count(options.except(:from))
      return 0 if num_records == 0
      #raise "Number of records: #{num_records}"
      also_pass_offset = (blk.arity == 2)
      0.step(num_records, group_size) do |offset|
        find_options = { :offset => offset, :limit => group_size }.merge(options)
        if update
          if num_records == 1
            puts ">> Reading the only record."
          else
            start_offset = offset + 1
            end_offset   = offset + group_size
            end_offset   = num_records if num_records < end_offset
            puts ">> Reading records #{start_offset}-#{end_offset}."
          end
        end 
        find(:all, find_options).each do |record|
          also_pass_offset ? blk.call(record, offset) : blk.call(record)
        end
      end
      num_records
    end
  end
end