# A class for calculating locations (line, column) in a string based
# on an offset.
class StringLocations
  def initialize(string)
    @string, @string_length = string, string.length
    @line_lengths = @string.split(/\n/).map {|l| l.length}
    @start_pos_of_line = [0]
    @line_lengths.each do |l|
      @start_pos_of_line << @start_pos_of_line.last + l + 1
    end
  end

  def location(offset)
    l = line(offset)
    return l, column(offset, l)
  end

  def column(offset, l = nil)
    l ||= line(offset)
    offset - @start_pos_of_line[l-1]
  end

  def line(offset)
    if offset >= @string_length
      raise "#{offset} is larger than the string size #{@string_length}"
    end
    line_index(offset) + 1
  end

  # Find the index to the line where the given offset can be found. Assumes
  # the start_pos_of_line array has been extended so that offset is covered.
  def line_index(offset)
    index = nil
    for index in (0...(@start_pos_of_line.length))
      if @start_pos_of_line[index] <= offset && 
	  @start_pos_of_line[index+1] > offset
	break
      end
    end
    index
  end
end