require 'test_helper'

class QuestionPickerTest < ActiveSupport::TestCase
  QUESTIONS_COUNT = 100000
  ACCURACY_THRESHOLD_PERCENTS = 0.3

  ONE_ELEVENTH = 1.0 / 11 * 100

  setup do
    @question_picker = Exercises::QuestionPicker.new(
      ExerciseQuestion.all,
      exercise_sessions(:one).session_questions
    )
    @expected_question_frequencies = {
      exercise_questions(:question1) => ONE_ELEVENTH,
      exercise_questions(:question2) => ONE_ELEVENTH,
      exercise_questions(:question3) => ONE_ELEVENTH,
      exercise_questions(:question4) => ONE_ELEVENTH * 2,
      exercise_questions(:question5) => ONE_ELEVENTH * 3,
      exercise_questions(:question6) => 0,
      exercise_questions(:question7) => ONE_ELEVENTH,
      exercise_questions(:question8) => ONE_ELEVENTH * 2,
      exercise_questions(:question9) => 0,
      exercise_questions(:question10) => 0,
      exercise_questions(:question11) => 0,
    }
  end

  # passed with seed 7020
  test "question picker" do
    picked_questions = pick_questions
    total_sum = picked_questions.values.sum
    picked_questions.each do |question, question_count|
      frequency = question_count.to_f / total_sum * 100
      assert(
        question_frequency_correct?(question, frequency),
        "Frequency for question with id #{question.id} is not correct.
         Expected value: #{@expected_question_frequencies[question]}%, actual value: #{frequency}%
         (difference: #{(@expected_question_frequencies[question] - frequency).abs}%)"
      )
    end
  end

  private

    def question_frequency_correct?(question, frequency)
      expected_frequency = @expected_question_frequencies[question]
      expected_frequency == 0 ?
        frequency == 0 :
        (expected_frequency - frequency).abs < ACCURACY_THRESHOLD_PERCENTS
    end

    def pick_questions
      result = ExerciseQuestion.all.map { |q| [q, 0] }.to_h

      QUESTIONS_COUNT.times do
        question = @question_picker.pick
        result[question] += 1
      end

      result
    end
end