module KPeg
  module Position
    # STANDALONE START

    def current_column(target=pos)
      if string[target] == "\n" && (c = string.rindex("\n", target-1) || -1)
        return target - c
      elsif c = string.rindex("\n", target)
        return target - c
      end

      target + 1
    end

    def position_line_offsets
      unless @position_line_offsets
        @position_line_offsets = []
        total = 0
        string.each_line do |line|
          total += line.size
          @position_line_offsets << total
        end
      end
      @position_line_offsets
    end

    if [].respond_to? :bsearch_index
      def current_line(target=pos)
        if line = position_line_offsets.bsearch_index {|x| x > target }
          return line + 1
        elsif target == string.size
          past_last = !string.empty? && string[-1]=="\n" ? 1 : 0
          return position_line_offsets.size + past_last
        end
        raise "Target position #{target} is outside of string"
      end
    else
      def current_line(target=pos)
        if line = position_line_offsets.index {|x| x > target }
          return line + 1
        elsif target == string.size
          past_last = !string.empty? && string[-1]=="\n" ? 1 : 0
          return position_line_offsets.size + past_last
        end
        raise "Target position #{target} is outside of string"
      end
    end

    def current_character(target=pos)
      if target < 0 || target > string.size
        raise "Target position #{target} is outside of string"
      elsif target == string.size
        ""
      else
        string[target, 1]
      end
    end

    KpegPosInfo = Struct.new(:pos, :lno, :col, :line, :char)

    def current_pos_info(target=pos)
      l = current_line target
      c = current_column target
      ln = get_line(l-1)
      chr = string[target,1]
      KpegPosInfo.new(target, l, c, ln, chr)
    end

    def lines
      string.lines
    end

    def get_line(no)
      loff = position_line_offsets
      if no < 0
        raise "Line No is out of range: #{no} < 0"
      elsif no >= loff.size
        raise "Line No is out of range: #{no} >= #{loff.size}"
      end
      lend = loff[no]-1
      lstart = no > 0 ? loff[no-1] : 0
      string[lstart..lend]
    end

    # STANDALONE END

  end
end
