"""This module defines a class for handling writing reponses."""

import exceptions

try: # backward compatibility for Python < 2.3
	True, False
except NameError:
	True, False = 1, 0
	bool = lambda x: x and True or False

debug = 0

class InvalidCommandSequence(exceptions.Exception):
	pass

class ASStreamOut:
	"""This is a response stream to the client.

	The key attributes of this class are:

	`_autoCommit`:
	    If True, the stream will automatically start sending data
	    once it has accumulated `_bufferSize` data. This means that
	    it will ask the response to commit itself, without developer
	    interaction. By default, this is set to False.
	`_bufferSize`:
	    The size of the data buffer. This is only used when autocommit
	    is True. If not using autocommit, the whole response is
	    buffered and sent in one shot when the servlet is done.
	`flush()`:
	    Send the accumulated response data now. Will ask the `Response`
	    to commit if it hasn't already done so.

	"""

	def __init__(self):
		self._autoCommit = False
		self._bufferSize = 8192
		self._committed = False
		self._needCommit = False
		self._chunks = []
		self._buffer=''
		self._chunkLen= 0
		self._closed = False

	def autoCommit(self):
		"""Get the auto commit mode."""
		return self._autoCommit

	def setAutoCommit(self, autoCommit=True):
		"""Set the auto commit mode."""
		self._autoCommit = bool(autoCommit)

	def bufferSize(self):
		"""Get the buffer size."""
		return self._bufferSize

	def setBufferSize(self, bufferSize=8192):
		"""Set the buffer size."""
		self._bufferSize = int(bufferSize)

	def flush(self):
		"""Flush stream.

		Send available data as soon as possible, i.e. *now*.

		Returns True if we are ready to send, otherwise False (i.e.,
		if the buffer is full enough).

		"""
		assert not self._closed, "Trying to flush when already closed"
		if debug:
			print ">>> Flushing ASStreamOut"
		if not self._committed:
			if self._autoCommit:
				if debug:
					print "ASSTreamOut.flush setting needCommit"
				self._needCommit = True
			return False
		try:
			self._buffer += ''.join(self._chunks)
		finally:
			self._chunks = []
			self._chunkLen = False
		return True

	def buffer(self):
		"""	Return accumulated data which has not yet been flushed.

		We want to be able to get at this data without having to call flush
		first, so that we can (for example) integrate automatic HTML validation.

		"""
		if self._buffer: # if flush has been called, return what was flushed:
			return self._buffer
		else: # otherwise return the buffered chunks
			return ''.join(self._chunks)

	def clear(self):
		"""Try to clear any accumulated response data.

		Will fail if the response is already sommitted.

		"""
		if debug:
			print ">>> strmOut clear called"
		if self._committed:
			raise InvalidCommandSequence()
		self._buffer = ''
		self._chunks = []
		self._chunkLen = 0

	def close(self):
		"""Close this buffer. No more data may be sent."""
		if debug:
			print ">>> ASStream close called"
		self.flush()
		self._closed = True
		self._committed = True
		self._autocommit = True

	def closed(self):
		"""Check whether we are closed to new data."""
		return self._closed

	def size(self):
		"""Return the current size of the data held here."""
		return self._chunkLen + len(self._buffer)

	def prepend(self, charstr):
		"""Add the attached string to front of the response buffer.

		Invalid if we are already committed.

		"""
		if self.committed() or self.closed():
			raise InvalidCommandSequence()
		if self._buffer:
			self._buffer = charstr + self._buffer
		else:
			self._chunks.insert(0, charstr)
			self._chunkLen += len(charstr)

	def pop(self, count):
		"""Remove count bytes from the front of the buffer."""
		if debug:
			print "AStreamOut popping %s" % count
		#should we check for an excessive pop length?
		assert count <= len(self._buffer)
		self._buffer = self._buffer[count:]

	def committed(self):
		"""Are we committed?"""
		return self._committed


	def needCommit(self):
		"""Request for commitment.

		Called by the `HTTPResponse` instance that is using this instance
		to ask if the response needs to be prepared to be delivered.
		The response should then commit it's headers, etc.

		"""
		return self._needCommit

	def commit(self, autoCommit=True):
		"""Called by the Response to tell us to go.

		If `_autoCommit` is True, then we will be placed into autoCommit mode.

		"""
		if debug:
			print ">>> ASStreamOut Committing"
		self._committed = True
		self._autoCommit = autoCommit
		self.flush()

	def write(self, charstr):
		"""Write a string to the buffer."""
		if debug:
			print ">>> ASStreamOut writing %s characters" % len(charstr)
		assert not self._closed, "Stream Already Closed"
		self._chunks.append(charstr)
		self._chunkLen += len(charstr)
		if self._autoCommit and self._chunkLen > self._bufferSize:
			if debug:
				print ">>> ASStreamOut.write flushing"
			self.flush()

