from multiprocessing import Queue
import os

class QueueFile(object):
  """ Class which implements a file-like interface and reads from a blocking
      multiprocessing queue.
  """
  def __init__(self, queue, name=None):
    self._queue = queue
    self._closed = False
    self._done = False
    self._buffer = ''
    self._total_size = 0
    self._name = name
    self.raised_exception = False
    self._exception_handlers = []

  def add_exception_handler(self, handler):
    self._exception_handlers.append(handler)

  def read(self, size=8192):
    if self._closed or self._done:
      return None

    while len(self._buffer) < size:
      result = self._queue.get(block=True)
      if result is None:
        self._done = True
        break

      if isinstance(result, Exception):
        self._closed = True
        self.raised_exception = True
        for handler in self._exception_handlers:
          handler(result)
          
        return

      self._buffer += result
      self._total_size += len(result)
    
    buf = self._buffer[0:size]
    self._buffer = self._buffer[size:]
    return buf

  def flush(self):
    pass

  def close(self):
    self._closed = True