require "./pattern"

struct Time::Format
  # :nodoc:
  struct Formatter
    include Pattern

    getter io : IO
    getter time : Time

    def initialize(@time : Time, @io : IO)
    end

    def year : Nil
      pad4(time.year, '0')
    end

    def year_modulo_100 : Nil
      pad2(time.year % 100, '0')
    end

    def year_divided_by_100 : Nil
      io << time.year // 100
    end

    def full_or_short_year : Nil
      year
    end

    def calendar_week_year : Nil
      pad4(time.calendar_week[0], '0')
    end

    def calendar_week_year_modulo100 : Nil
      pad2(time.calendar_week[0] % 100, '0')
    end

    def month : Nil
      io << time.month
    end

    def month_zero_padded : Nil
      pad2 time.month, '0'
    end

    def month_blank_padded : Nil
      pad2 time.month, ' '
    end

    def month_name : Nil
      io << get_month_name
    end

    def month_name_upcase : Nil
      io << get_month_name.upcase
    end

    def short_month_name : Nil
      io << get_short_month_name
    end

    def short_month_name_upcase : Nil
      io << get_short_month_name.upcase
    end

    def calendar_week_week : Nil
      pad2(time.calendar_week[1], '0')
    end

    def day_of_month : Nil
      io << time.day
    end

    def day_of_month_zero_padded : Nil
      pad2 time.day, '0'
    end

    def day_of_month_blank_padded : Nil
      pad2 time.day, ' '
    end

    def day_name : Nil
      io << get_day_name
    end

    def day_name_upcase : Nil
      io << get_day_name.upcase
    end

    def short_day_name : Nil
      io << get_short_day_name
    end

    def short_day_name_upcase : Nil
      io << get_short_day_name.upcase
    end

    def short_day_name_with_comma? : Nil
      short_day_name
      char ','
      whitespace
    end

    def day_of_year_zero_padded : Nil
      pad3 time.day_of_year, '0'
    end

    def hour_24_zero_padded : Nil
      pad2 time.hour, '0'
    end

    def hour_24_blank_padded : Nil
      pad2 time.hour, ' '
    end

    def hour_12_zero_padded : Nil
      h = (time.hour % 12)
      pad2 (h == 0 ? 12 : h), '0'
    end

    def hour_12_blank_padded : Nil
      h = (time.hour % 12)
      pad2 (h == 0 ? 12 : h), ' '
    end

    def minute : Nil
      pad2 time.minute, '0'
    end

    def second : Nil
      pad2 time.second, '0'
    end

    def milliseconds : Nil
      pad3 time.millisecond, '0'
    end

    def microseconds : Nil
      pad6 time.nanosecond // 1000, '0'
    end

    def nanoseconds : Nil
      pad9 time.nanosecond, '0'
    end

    def second_fraction : Nil
      nanoseconds
    end

    def second_fraction?(fraction_digits : Int = 9) : Nil
      case fraction_digits
      when 0
      when 3 then char '.'; milliseconds
      when 6 then char '.'; microseconds
      when 9 then char '.'; nanoseconds
      else
        raise ArgumentError.new("Invalid fraction digits: #{fraction_digits}")
      end
    end

    def am_pm : Nil
      io << (time.hour < 12 ? "am" : "pm")
    end

    def am_pm_upcase : Nil
      io << (time.hour < 12 ? "AM" : "PM")
    end

    def day_of_week_monday_1_7 : Nil
      io << time.day_of_week.value
    end

    def day_of_week_sunday_0_6 : Nil
      io << time.day_of_week.value % 7
    end

    def unix_seconds : Nil
      io << time.to_unix
    end

    def time_zone(with_seconds = false) : Nil
      time_zone_offset(format_seconds: with_seconds)
    end

    def time_zone_z_or_offset(**options) : Nil
      if time.utc?
        io << 'Z'
      else
        time_zone_offset(**options)
      end
    end

    def time_zone_offset(force_colon = false, allow_colon = true, format_seconds = false, parse_seconds = true)
      time.zone.format(io, with_colon: force_colon, with_seconds: format_seconds)
    end

    def time_zone_colon(with_seconds = false) : Nil
      time_zone_offset(force_colon: true, format_seconds: with_seconds)
    end

    def time_zone_colon_with_seconds : Nil
      time_zone_colon(with_seconds: true)
    end

    def time_zone_gmt : Nil
      io << "GMT"
    end

    def time_zone_rfc2822 : Nil
      time_zone_offset(allow_colon: false)
    end

    def time_zone_gmt_or_rfc2822(**options) : Nil
      if time.utc? || time.location.name.in?("UT", "GMT")
        time_zone_gmt
      else
        time_zone_rfc2822
      end
    end

    def time_zone_name(zone = false) : Nil
      if zone
        io << time.zone.name
      else
        io << time.location
      end
    end

    def char(char, *alternatives) : Nil
      io << char
    end

    def char?(char, *alternatives)
      char(char, *alternatives)
    end

    def whitespace : Nil
      io << ' '
    end

    def get_month_name
      MONTH_NAMES[time.month - 1]
    end

    def get_short_month_name
      get_month_name[0, 3]
    end

    def get_day_name
      DAY_NAMES[time.day_of_week.value % 7]
    end

    def get_short_day_name
      get_day_name[0, 3]
    end

    def pad2(value, padding) : Nil
      io << padding if value < 10
      io << value
    end

    def pad3(value, padding) : Nil
      io << padding if value < 100
      pad2 value, padding
    end

    def pad4(value, padding) : Nil
      io << padding if value < 1000
      pad3 value, padding
    end

    def pad6(value, padding) : Nil
      io << padding if value < 100000
      io << padding if value < 10000
      pad4 value, padding
    end

    def pad9(value, padding) : Nil
      io << padding if value < 100000000
      io << padding if value < 10000000
      io << padding if value < 1000000
      pad6 value, padding
    end
  end
end