import threading
import queue
import time
import sys
import select
import random

__interval__ = .1

class Reader:
   def __init__(self, reader):
      self.reader = reader

   def read(self):
      q = queue.Queue(maxsize=1)

      class async_reader(threading.Thread):
         def __init__(self, q, foo):
            threading.Thread.__init__(self)
            self.q = q
            self.foo = foo
            self.stopping = False

         def stop(self):
            self.stopping = True

         def run(self):
            while not self.stopping:
               try:
                  self.q.put_nowait(self.foo())
               except queue.Full:
                  pass
               time.sleep(__interval__/2.0)

      reader = async_reader(q, self.reader.read)
      reader.start()
      try:
         while not reader.stopping:
            try:
               s = q.get(timeout=__interval__)
               if s:
                  s = s.lower().strip()
               yield s
            except queue.Empty:
               yield None
               pass
      except KeyboardInterrupt as e:
         reader.stop()
         reader.join()
         raise e

class StdinReader:
   def read(self):
      try:
         if select.select([sys.stdin,],[],[],__interval__/2.0)[0]:
            line = sys.stdin.readline()
            return line
      except Exception as e:
         pass
      return None

class RandomReader:
   def read(self):
      seed = random.randint(0, 99)
      if seed < 10:
         return "a"
      elif seed < 50:
         return "B"
      else:
         return "b"

class FileReader:
   def __init__(self, path):
      self.f = open(path, "r")

   def read(self):
      return self.f.readline()