BOGOF discount for ZERO2W

checkout.rb

@@ -21,9 +21,7 @@ class Checkout
   end
 
   def total
-    @items.reduce(0.00) do |running_total, item|
-      running_total + AVAILABLE_ITEMS[item]
-    end
+    pre_discount_total - current_discount
   end
 
   private
@@ -31,4 +29,20 @@ class Checkout
   def valid_item?(item)
     return AVAILABLE_ITEMS.keys.include?(item)
   end
+
+  def current_discount
+    # BOGOF ZERO2W
+    discount = (@items.count(:ZERO2W) / 2.0).floor * AVAILABLE_ITEMS[:ZERO2W]
+
+
+    # TODO: Bulk PICO2
+
+    return discount
+  end
+
+  def pre_discount_total
+    @items.reduce(0.00) do |running_total, item|
+      running_total + AVAILABLE_ITEMS[item]
+    end
+  end
 end

main.rb

@@ -7,3 +7,38 @@ checkout.add(:ZERO2W)
 
 puts checkout.items # ["PI5", "ZERO2W"]
 puts checkout.total # 75.00
+
+
+checkout = Checkout.new()
+checkout.add(:ZERO2W)
+checkout.add(:ZERO2W)
+
+puts checkout.total # 15.00
+
+
+checkout = Checkout.new()
+checkout.add(:ZERO2W)
+checkout.add(:ZERO2W)
+checkout.add(:ZERO2W)
+
+puts checkout.total # 30.00
+
+
+checkout = Checkout.new()
+checkout.add(:PICO2)
+checkout.add(:PICO2)
+checkout.add(:PICO2)
+
+puts checkout.total # 10.50
+
+
+checkout = Checkout.new()
+checkout.add(:PI5)
+checkout.add(:ZERO2W)
+checkout.add(:ZERO2W)
+checkout.add(:PICO2)
+checkout.add(:PICO2)
+checkout.add(:PICO2)
+checkout.add(:PICO2)
+
+puts checkout.total # 89.00

tests.rb

@@ -34,4 +34,22 @@ class TestCheckout < Minitest::Test
   def test_that_an_empty_checkout_total_is_zero
     assert_equal 0.00, @checkout.total
   end
+
+  # Discounts
+
+  def test_that_bogof_applied
+    4.times do
+      @checkout.add(:ZERO2W)
+    end
+
+    assert_equal 30.00, @checkout.total
+  end
+
+  def test_that_bogof_applied_with_odd_number
+    5.times do
+      @checkout.add(:ZERO2W)
+    end
+
+    assert_equal 45.00, @checkout.total
+  end
 end