test task

test.rb

data = {
  'mon_1_open': '09:00',
  'mon_1_close': '13:00',
  'tue_1_open': '09:00',
  'tue_1_close': '13:00',
  'wed_1_open': '16:00',
  'wed_1_close': '20:00',
  'thu_1_open': '09:00',
  'thu_1_close': '13:00',
  'fri_1_open': '09:00',
  'fri_1_close': '13:00',
  'sat_1_open': '09:00',
  'sat_1_close': '14:00',
  'mon_2_open': '16:00',
  'mon_2_close': '20:00',
  'tue_2_open': '16:00',
  'tue_2_close': '20:00'
}

def parse(data={})
  splitted = data.each_with_object({}) { |(k, v),res| res[k.to_s.split('_')] = v }
  # => {["mon", "1", "open"]=>"09:00", ["mon", "1", "close"]=>"13:00", ...}
  grouped = splitted.group_by { |k, v| [k[0], k[1]] }
  # => {["mon", "1"]=>[[["mon", "1", "open"], "09:00"], [["mon", "1", "close"], "13:00"]], ...}
  with_full_time = grouped.each_with_object({}) do |(k, v), res|
    time = Array.new(2)
    v.each do |data_line|
      state_line, t = data_line
      time[0] = t if state_line[2] == 'open'
      time[1] = t if state_line[2] == 'close'
    end
    res[k] = time.join(' - ')
  end
  # => {["mon", "1"]=>"09:00 - 13:00", ["tue", "1"]=>"09:00 - 13:00", ...}
  reversed = with_full_time.each_with_object({}) { |(k, v), res| res[v] = [*res[v], k[0]]  }
  # => {"09:00 - 13:00"=>["mon", "tue", "thu", "fri"], "16:00 - 20:00"=>["wed", "mon", "tue"], "09:00 - 14:00"=>["sat"]}
  reversed.map { |k, v| "#{v.join(', ')} => #{k}" }
end

puts parse(data)

# Sorry no sorting by days, no periods
# mon, tue, thu, fri => 09:00 - 13:00
# wed, mon, tue => 16:00 - 20:00
# sat => 09:00 - 14:00