cfruby_public_library.rb

class Library
  attr_reader :shelf, :books
  def initialize
    @shelf = []
    @books = []
  end

  def report_all
    puts "Currently in the library we have #{Book.total} books."
  end

  def add_shelf(shelf)
    @shelf.push(self)
  end
end

class Shelf
  attr_reader :books
  def initialize(library)
    library.add_shelf(self)
    @books = []
  end

  def check_out(book)
    @books.delete(book)
    $count += -1
  end

  def return(book)
    @books.push(book)
  end
end

class Book
  attr_reader :shelf, :title

  $count = 0

  def initialize(title, library)
    @title = title
    @library = library
    $count += 1
  end

  def enshelf(shelf)
    @shelf = shelf
    shelf.return(self)
    puts "Thanks for returning your book!"
  end

  def unshelf
    @shelf.check_out(self)
    puts "Checking out #{title}..."
  end

  def self.total
    $count
  end
end

# COMMANDS =====

Utah = Library.new
Fantasy = Shelf.new(Utah)
Programming = Shelf.new(Utah)
Biography = Shelf.new(Utah)
dragons = Book.new("Dragons!", Utah)
rubywow = Book.new("Ruby!Wow!", Utah)
george = Book.new("The Life of George", Utah)
dragons.enshelf(Fantasy)
george.enshelf(Biography)
rubywow.enshelf(Programming)
Utah.report_all
dragons.unshelf
rubywow.unshelf
Utah.report_all