module Haml::TempleLineCounter

def self.count_lines(exp)
  type, *args = exp
  case type
  when :multi
    args.map { |a| count_lines(a) }.reduce(:+) || 0
  when :dynamic, :code
    args.first.count("\n")
  when :static
    0 # It has not real newline "\n" but escaped "\\n".
  when :case
    arg, *cases = args
    arg.count("\n") + cases.map do |cond, e|
      (cond == :else ? 0 : cond.count("\n")) + count_lines(e)
    end.reduce(:+)
  when :escape
    count_lines(args[1])
  when :newline
    1
  else
    raise UnexpectedExpression.new("[HAML BUG] Unexpected Temple expression '#{type}' is given!")
  end
end