pager.rb

# inherit from Enumerator
class Pager1 < Enumerator
  def initialize(url, page_size: 100, max_pages: Float::INFINITY, first_page: 0)
    @url = url
    super() do |receiver|
      page = first_page
      pages = []
      while page < (first_page + max_pages)
        get(page, page_size).each do |row|
          receiver.yield row
        end
        page += 1
      end
    end
  end

  # this simulates fetching a page of results from the url
  def get(page, size)
    puts "getting page #{page}" # some debug output to demonstrate this is done lazy
    (page * size)..(page * size + (size - 1))
  end
end



# done without inheritance
class Pager2
  attr_reader :url, :page_size, :max_pages, :first_page

  def initialize(url, page_size: 100, max_pages: Float::INFINITY, first_page: 0)
    @url = url
    @page_size = page_size
    @max_pages = max_pages
    @first_page = first_page
  end

  def each
    return enum_for(:each) unless block_given?

    page = first_page
    pages = []
    while page < (first_page + max_pages)
      get(page, page_size).each do |row|
        yield row
      end
      page += 1
    end
  end

  private

  # this simulates fetching a page of results from the url
  def get(page, size)
    puts "getting page #{page}" # some debug output to demonstrate this is done lazy
    (page * size)..(page * size + (size - 1))
  end
end


# same as pager2 but includes enumerable
class Pager3
  include Enumerable

  attr_reader :url, :page_size, :max_pages, :first_page

  def initialize(url, page_size: 100, max_pages: Float::INFINITY, first_page: 0)
    @url = url
    @page_size = page_size
    @max_pages = max_pages
    @first_page = first_page
  end

  def each
    return enum_for(:each).lazy unless block_given?

    page = first_page
    pages = []
    while page < (first_page + max_pages)
      get(page, page_size).each do |row|
        yield row
      end
      page += 1
    end
  end

  private

  # this simulates fetching a page of results from the url
  def get(page, size)
    puts "getting page #{page}" # some debug output to demonstrate this is done lazy
    (page * size)..(page * size + (size - 1))
  end
end

#
# Demonstrate both
#

pager = Pager1.new('url', page_size: 3, max_pages: 9, first_page: 1).lazy
pp pager.each.drop(4).take(2).to_a

puts

pager = Pager2.new('url', page_size: 3, max_pages: 9, first_page: 1)
pp pager.each.lazy.drop(4).take(2).to_a

puts

pager = Pager3.new('url', page_size: 3, max_pages: 9, first_page: 1)
pp pager.drop(4).take(2).to_a