class Haml::DynamicMerger

def count_newline(exps)
  count = 0
  exps.each do |exp|
    if exp == [:newline]
      count += 1
    else
      return count
    end
  end
  return count
end

def merge_dynamic(exps)
  # Merge exps only when they have both :static and :dynamic
  unless exps.any? { |type,| type == :static } && exps.any? { |type,| type == :dynamic }
    return exps
  end
  strlit_body = String.new
  exps.each do |type, arg|
    case type
    when :static
      strlit_body << arg.dump.sub!(/\A"/, '').sub!(/"\z/, '').gsub('\n', "\n")
    when :dynamic
      strlit_body << "\#{#{arg}}"
    when :newline
      # newline is added by `gsub('\n', "\n")`
    else
      raise "unexpected type #{type.inspect} is given to #merge_dynamic"
    end
  end
  [[:dynamic, "%Q\0#{strlit_body}\0"]]
end

def on_multi(*exps)
  exps = exps.dup
  result = [:multi]
  buffer = []
  until exps.empty?
    type, arg = exps.first
    if type == :dynamic && arg.count("\n") == 0
      buffer << exps.shift
    elsif type == :static && exps.size > (count = arg.count("\n")) &&
          exps[1, count].all? { |e| e == [:newline] }
      (1 + count).times { buffer << exps.shift }
    elsif type == :newline && exps.size > (count = count_newline(exps)) &&
          exps[count].first == :static && count == exps[count].last.count("\n")
      (count + 1).times { buffer << exps.shift }
    else
      result.concat(merge_dynamic(buffer))
      buffer = []
      result << compile(exps.shift)
    end
  end
  result.concat(merge_dynamic(buffer))
  result.size == 2 ? result[1] : result
end