class Sprockets::Concatenation

def initialize
  @source_lines = []
  @source_file_mtimes = {}
end

def mtime
  @source_file_mtimes.values.max
end

def record(source_line)
  source_lines << source_line
  record_mtime_for(source_line.source_file)
  source_line
end

def record_mtime_for(source_file)
  @source_file_mtimes[source_file] ||= source_file.mtime
end

def save_to(filename)
  timestamp = mtime
  File.open(filename, "w") { |file| file.write(to_s) }
  File.utime(timestamp, timestamp, filename)
  true
end

def to_s
  source_lines.join
end