module ICalPal
  # Child class of DateTime that adds support for relative dates (<em><b>R</b>elative<b>D</b>ate<b>T</b>ime</em>).
  class RDT < DateTime

    # Create a new RDT from a Time object
    #
    # @param t [Time] The Time object
    #
    # @return [RDT] a new RDT
    def self.from_time(t)
      new(*t.to_a[0..5].reverse, Rational((t.gmt_offset / 3600), 24))
    end

    # Create a new RDT from seconds since epoch
    #
    # @param s [Integer] Seconds since the Unix epoch (Thu Jan  1 00:00:00 UTC 1970)
    #
    # @return [RDT] a new RDT
    def self.from_epoch(s)
      from_time(Time.at(s))
    end

    # Create a new RDT from seconds since iCal epoch
    #
    # @param s [Integer] Seconds since the iCal epoch (Jan  1 00:00:00 UTC 2001)
    #
    # @return [RDT] a new RDT
    def self.from_itime(s)
      from_epoch(s + ITIME)
    end

    # Convert a String to an RDT
    #
    # @param str [String] can be +yesterday+, +today+, +tomorrow+,
    #  <code>+N</code>, or +-N+.  Otherwise use DateTime.parse.
    #
    # @return [RDT] a new RDT
    def self.conv(str)
      case str
      when 'yesterday' then $today.add(-1)
      when 'today' then $today
      when 'tomorrow' then $today.add(1)
      when /^\+([0-9]+)/ then $today + Regexp.last_match(1).to_i
      when /^-([0-9]+)/ then $today - Regexp.last_match(1).to_i
      else parse(str)
      end
    end

    # Add a number of days accounting for daylight saving time changes
    #
    # @param days [Integer] Number of days to add
    # @return [RDT] A new RDT
    def add(days)
      n = self + days
      t = Time.parse("#{n.year}-#{n.month}-#{n.day} #{n.hour}:#{n.min}:#{n.sec}")
      RDT.from_time(t)
    end

    # Values can be +day before yesterday+, +yesterday+,
    # +today+, +tomorrow+, +day after tomorrow+, or the result from
    # strftime
    #
    # @return [String] A string representation of self relative to
    #  today.
    def to_s
      return strftime($opts[:df]) if $opts && $opts[:df] && $opts[:nrd]
      return super unless $today && $opts

      case (self - $today).floor
      when -2 then 'day before yesterday'
      when -1 then 'yesterday'
      when 0 then 'today'
      when 1 then 'tomorrow'
      when 2 then 'day after tomorrow'
      else strftime($opts[:df]) if $opts && $opts[:df]
      end
    end

    alias inspect to_s

    # @see Time.to_a
    #
    # @return [Array] Self as an array
    def to_a
      [ year, month, day, hour, min, sec ]
    end

    # @return [Integer] Seconds since epoch
    def to_i
      to_time.to_i
    end

    # @param z [Integer] Optional UTC offset
    # @return [RDT] Self at 00:00:00
    def day_start(z = zone)
      RDT.new(year, month, day, 0, 0, 0, z)
    end

    # @param z [Integer] Optional UTC offset
    # @return [RDT] Self at 23:59:59
    def day_end(z = zone)
      RDT.new(year, month, day, 23, 59, 59, z)
    end

    # @return [Array] Only the year, month and day of self
    def ymd
      [ year, month, day ]
    end

    # @return [Array] Only the hour, min and sec of self
    def hms
      [ hour, min, sec ]
    end

  end
end