planes.rb

SIZES = Hash.new(0) # return zero for any unknown size
SIZES[:small] = 1
SIZES[:medium] = 2
SIZES[:large] = 3

class Plane
  attr_accessor :type, :size
  attr_reader :priority

  def initialize(options={})
    @type = options[:type]
    @size = options[:size]
    @priority = SIZES[@size]
  end
end

class PrivatePlane < Plane
  def initialize(options={})
    super(options.update(:type => 'Private'))
    @priority = 10 + SIZES[@size]
  end
end

class CommercialPlane < Plane
  def initialize(options={})
    super(options.update(:type => 'Commercial'))
    @priority = 100 + SIZES[@size]
  end
end

class AirForceOne < Plane
  def initialize(options={})
    super(options.update(:type => 'Air Force One'))
    @priority = 1_000_000
  end
end

class PlaneQueue
  attr_reader :queue
  
  def initialize
    @queue = []
  end
  
  def <<(plane)
    @queue.unshift(plane)
  end
  
  def next_plane_to_land
    @queue.sort{ |p1,p2| p2.priority <=> p1.priority }.shift
  end
  
  def inspect
    @queue.inspect
  end
  
end

if __FILE__ == $0 # run tests
  require 'test/unit'
  
  class PlaneTests < Test::Unit::TestCase
    
    def test_default_types
      assert_equal 'Private', PrivatePlane.new.type
      assert_equal 'Commercial', CommercialPlane.new.type
    end

    def test_default_priorities
      assert_equal 10, PrivatePlane.new.priority
      assert_equal 100, CommercialPlane.new.priority
    end

    def test_larger_size_has_higher_priority
      small_plane = PrivatePlane.new(:size => :small)
      medium_plane = PrivatePlane.new(:size => :medium)
      assert medium_plane.priority > small_plane.priority
    end
        
    def test_commercial_has_higher_priority_than_private_regardless_of_size
      private_plane = PrivatePlane.new(:size => :large)
      commericial_plane = CommercialPlane.new(:size => :small)
      assert commericial_plane.priority > private_plane.priority
    end
    
    def test_air_force_one_has_highest_priority
      other_plane = CommercialPlane.new(:size => :large)
      air_force_one = AirForceOne.new
      assert air_force_one.priority > other_plane.priority
    end
    
  end
  
  class PlaneQueueTests < Test::Unit::TestCase
    
    def setup
      @queue = PlaneQueue.new
    end
    
    def test_empty_queue
      assert_equal nil, @queue.next_plane_to_land
    end

    def test_large_size_has_higher_priority
      @queue << CommercialPlane.new(:size => :small)
      @queue << CommercialPlane.new(:size => :large)
      @queue << CommercialPlane.new(:size => :medium)
      assert_equal :large, @queue.next_plane_to_land.size
    end
    
    def test_commericial_has_higher_priority
      @queue << PrivatePlane.new
      @queue << CommercialPlane.new
      @queue << PrivatePlane.new
      assert_equal CommercialPlane, @queue.next_plane_to_land.class
    end
    
  end
  
end