# Elixir script to calculate final grades

defmodule Test do
  @max_grade 100

  def grade(questions, right_answers)
    when is_integer(questions) and is_integer(right_answers)  do
    balls_per_question =
      if questions == 0 do
        0
      else
        @max_grade / questions
      end
    right_answers * balls_per_question
  end

  def test() do
    [
      grade(20, 20) == @max_grade,
      grade(19, 19) == @max_grade,
      grade(20, 19) < @max_grade,
      grade(19, 18) < @max_grade,
      grade(0, 20) == 0,
      grade(0, 19) == 0
    ]
  end
end

if Test.test() |> Enum.all?() do
  IO.puts "all tests passed"
end

IO.puts "original grade = #{Test.grade(20, 18)}"
IO.puts "new grade = #{Test.grade(19, 17)}"
IO.puts "----------------------------------------------"
IO.puts "(wrong answer removed) original grade = #{Test.grade(20, 17)}"
IO.puts "(wrong answer removed) new grade = #{Test.grade(19, 17)}"

# output:

$ elixir test.exs
all tests passed
original grade = 90.0
new grade = 89.47368421052633
----------------------------------------------
(wrong answer removed) original grade = 85.0
(wrong answer removed) new grade = 89.47368421052633