Paiza 練習問題 : [翌営業日 - その1](https://paiza.jp/works/mondai/dateset/working_day_1?language_uid=ruby)

main.rb

require File.join(__dir__, 'lib', 'workdays')

# eg. 10 1 FRI
# => 10月4日
workday = WorkDay.new(*gets.chomp.split)
month, day = workday.next_workday

puts "#{month}月#{day}日"

next_workday.rb

# frozen_string_literal: true

# 月, 日, 曜日から「翌営業日」を算出
class WorkDay
  WEEK = %w[SUN MON TUE WED THU FRI SAT]
  WORK_DAY = %w[MON TUE WED THU FRI]
  NON_WORK_DAY = %w[SUN SAT]
  SHORT_MONTH = [2, 4, 6, 9, 11] # 30日終わりの月 (厳格さは求めないので2月も同じ扱いにする)
  LONG_MONTH = [1, 3, 5, 7, 8, 10, 12] # 31日終わりの月

  private_constant :WEEK, :SHORT_MONTH, :LONG_MONTH, :WORK_DAY, :NON_WORK_DAY

  def initialize(month, day, week)
    @month = month.to_i
    @day = day.to_i
    @wday_index = WEEK.index(week) # WEEK 定数を modulo(WEEK.size) で参照するカウンタ

    # 外部からの入力によって設定する値が決まるので インスタンス変数として定義
    @last_day_of_month =
      if SHORT_MONTH.include?(@month)
        30
      elsif LONG_MONTH.include?(@month)
        31
      end
  end

  def next_workday
    # 2月28日の次の日は必ず 3月1日扱いにする
    if february_28?
      @month = 3
      @day = 1
      @wday_index += 1

      return find_workday!
    end

    @day += 1
    @wday_index += 1

    find_workday!
  end

  private

  def february_28?
    [@month, @day].eql?([2, 28])
  end

  def non_workday?
    NON_WORK_DAY.include?(wday_index_as_string)
  end

  def workday?
    WORK_DAY.include?(wday_index_as_string)
  end

  def wday_index_as_string
    WEEK.at(@wday_index.modulo(WEEK.size))
  end

  # 「日」加算時、「3月32日」のような値になってないか検査
  def day_out_of_bounce?
    @day > @last_day_of_month
  end

  # 「12月32日」のような値になっていれば「1月1日」と翌月に変換する
  def adjust_day_month_bounce!
    return [@month, @day] unless day_out_of_bounce?

    @month += 1
    @day = 1

    if @month > 12
      @month = 1
    end

    [@month, @day]
  end

  # 月日 (@month, @day) が営業日になるまで日を進めて探す
  def find_workday!
    adjust_day_month_bounce!

    loop do
      break adjust_day_month_bounce! if workday?

      @wday_index += 1
      @day += 1
      adjust_day_month_bounce!
    end
  end
end

next_workday_spec.rb

# frozen_string_literal: true

describe WorkDay do
  context '#next_workday' do
    subject { WorkDay.new(month, day, week).next_workday }

    shared_examples 'next_workday' do
      it { is_expected.to eq expected }
    end

    context '2月28日(水)' do
      it_behaves_like 'next_workday' do
        let(:month) { 2 }
        let(:day) { 28 }
        let(:week) { 'WED' }
        let(:expected) { [3, 1] }
      end
    end

    context '2月28日(金)' do
      it_behaves_like 'next_workday' do
        let(:month) { 2 }
        let(:day) { 28 }
        let(:week) { 'FRI' }
        let(:expected) { [3, 3] }
      end
    end

    context '2月28日(土)' do
      it_behaves_like 'next_workday' do
        let(:month) { 2 }
        let(:day) { 28 }
        let(:week) { 'SAT' }
        let(:expected) { [3, 2] }
      end
    end

    context '3月4日(金)' do
      it_behaves_like 'next_workday' do
        let(:month) { 3 }
        let(:day) { 4 }
        let(:week) { 'FRI' }
        let(:expected) { [3, 7] }
      end
    end

    context '3月31日(金)' do
      it_behaves_like 'next_workday' do
        let(:month) { 3 }
        let(:day) { 31 }
        let(:week) { 'FRI' }
        let(:expected) { [4, 3] }
      end
    end

    context '7月7日(土)' do
      it_behaves_like 'next_workday' do
        let(:month) { 7 }
        let(:day) { 7 }
        let(:week) { 'SAT' }
        let(:expected) { [7, 9] }
      end
    end

    context '8月9日(日)' do
      it_behaves_like 'next_workday' do
        let(:month) { 8 }
        let(:day) { 9 }
        let(:week) { 'SUN' }
        let(:expected) { [8, 10] }
      end
    end

    context '12月31日(土)' do
      it_behaves_like 'next_workday' do
        let(:month) { 12 }
        let(:day) { 31 }
        let(:week) { 'SAT' }
        let(:expected) { [1, 2] }
      end
    end

    context '12月31日(日)' do
      it_behaves_like 'next_workday' do
        let(:month) { 12 }
        let(:day) { 31 }
        let(:week) { 'SUN' }
        let(:expected) { [1, 1] }
      end
    end

    context '12月31日(月)' do
      it_behaves_like 'next_workday' do
        let(:month) { 12 }
        let(:day) { 31 }
        let(:week) { 'MON' }
        let(:expected) { [1, 1] }
      end
    end
  end
end