module Timing
  grammar NaturalTimeLanguage

    rule expression
      space* moment:moment space* zone_info:zone_info? space* <Expression>
    end

    rule zone_info
      zone_offset /
      zone_name
    end

    rule moment
      timestamp /
      time_ago /
      moment_at_time /
      before_from_moment /
      date_moment
    end

    rule date_moment
      named_moment / 
      last_next_day_name / 
      day_month_name_year / 
      year_month_day /
      beginning_end_interval
    end

    rule named_moment
      now / today / tomorrow / yesterday
    end

    rule last_next_day_name
      direction:last_next space* day_name:day_name space* including_today:'including today'? <LastNextDayName>
    end

    rule day_month_name_year
      day:integer space* month:month_name space* year:integer? space* <DayMonthNameYear>
    end

    rule year_month_day
      year:integer '-' month:integer '-' day:integer <YearMonthDay>
    end

    rule beginning_end_interval
      direction:beginning_end space* interval_type:interval <BeginningEndInterval>
    end

    rule time_ago
      number:integer space* interval_type:interval space* 'ago' <TimeAgo>
    end

    rule moment_at_time
      moment:date_moment space* 'at' space* time:hour_minute_second <MomentAtTime>
    end

    rule before_from_moment
      number:integer space* interval_type:interval space* direction:before_from space* moment:moment <BeforeFromMoment>
    end

    rule timestamp
      [\d]4..4 '-' [\d]2..2 '-' [\d]2..2 space* 't'? space* [\d]2..2 ':' [\d]2..2 ':' [\d]2..2 <Timestamp>
    end

    rule now
      'now' <Now>
    end

    rule today
      'today' <Today>
    end

    rule tomorrow
      'tomorrow' <Tomorrow>
    end

    rule yesterday
      'yesterday' <Yesterday>
    end

    rule last_next
      last / next
    end

    rule last
      'last' <LastNext>
    end

    rule next
      'next' <LastNext>
    end

    rule beginning_end
      beginning_of / end_of
    end

    rule beginning_of
      direction:'beginning' space* 'of' <BeginningEnd>
    end

    rule end_of
      direction:'end' space* 'of' <BeginningEnd>
    end

    rule before_from
      before / from
    end

    rule before
      'before' <BeforeFrom>
    end

    rule from
      'from' <BeforeFrom>
    end

    rule interval
      second_interval / 
      minute_interval / 
      hour_interval / 
      day_interval / 
      week_interval / 
      month_interval / 
      year_interval
    end

    rule second_interval
      'second' 's'? <SecondInterval>
    end

    rule minute_interval
      'minute' 's'? <MinuteInterval>
    end

    rule hour_interval
      'hour' 's'? <HourInterval>
    end

    rule day_interval
      'day' 's'? <DayInterval>
    end

    rule week_interval
      'week' 's'?  <WeekInterval>
    end

    rule month_interval
      'month' 's'?  <MonthInterval>
    end

    rule year_interval
      'year' 's'?  <YearInterval>
    end

    rule day_name
      long_day_name / short_day_name
    end

    rule long_day_name
      'sunday'    <DayName> /
      'monday'    <DayName> /
      'tuesday'   <DayName> /
      'wednesday' <DayName> /
      'thursday'  <DayName> /
      'friday'    <DayName> /
      'saturday'  <DayName>
    end

    rule short_day_name
      'sun' <DayName> /
      'mon' <DayName> /
      'tue' <DayName> /
      'wed' <DayName> /
      'thu' <DayName> /
      'fri' <DayName> /
      'sat' <DayName>
    end

    rule month_name
      long_month_name / short_month_name
    end

    rule long_month_name
      'january'   <MonthName> /
      'february'  <MonthName> /
      'march'     <MonthName> /
      'april'     <MonthName> /
      'may'       <MonthName> /
      'june'      <MonthName> /
      'july'      <MonthName> /
      'august'    <MonthName> /
      'september' <MonthName> /
      'october'   <MonthName> /
      'november'  <MonthName> /
      'december'  <MonthName>
    end

    rule short_month_name
      'jan' <MonthName> /
      'feb' <MonthName> /
      'mar' <MonthName> /
      'apr' <MonthName> /
      'may' <MonthName> /
      'jun' <MonthName> /
      'jul' <MonthName> /
      'aug' <MonthName> /
      'sep' <MonthName> /
      'oct' <MonthName> /
      'nov' <MonthName> /
      'dec' <MonthName>
    end

    rule zone_offset
      [+-] [\d]2..2 ':'? [\d]2..2 <ZoneOffset>
    end

    rule zone_name
      'utc' <ZoneName>
    end

    rule hour_minute_second
      [\d]2..2 ':' [\d]2..2 (':' [\d]2..2)? <HourMinuteSecond> /
      'beginning' <HourMinuteSecond> /
      'end' <HourMinuteSecond>
    end

    rule integer
      [\d]+ <Int>
    end

    rule space
      [\s\t\n]
    end

  end
end