import StringIO
"""
SimpleChannel. Kept simple and small..
"""

class SCAccesor:
	"""An accesor over a SimpleChannel"""
	def __init__(self, strtuple):
		self.readfrom, self.writeto = strtuple
		self.rpos = self.wpos = 0
		
	def _handle_rpos(self, func, args):
		self.readfrom.seek(self.rpos)
		ret = func(*args)
		self.rpos = self.readfrom.tell()
		return ret
	
	def _handle_wpos(self, func, args):
		self.writeto.seek(self.wpos)
		ret = func(*args)
		self.wpos = self.writeto.tell()
		return ret
		
	def read(self, *args):
		return self._handle_rpos(self.readfrom.read, args)
	
	def readline(self, *args):
		return self._handle_rpos(self.readfrom.readline, args)
	
	def write(self, *args):
		return self._handle_wpos(self.writeto.write, args)
	
	def seek(self, *args):
		#return self._handle_pos(self.file.seek, args)
		raise 'must implement'
	
	def tell(self, *args):
		#return self._keep_pos(self.file.tell, args)
		raise 'must implement'
	
	def truncate(self, *args):
		#return self._keep_pos(self.file.truncate, args)
		raise 'must implement'
	
	def close(self):
		#do something here
		self.readfrom = self.writefrom = None
		
		
class SimpleChannel:
	"""
	A Channel for accessing a file at two places.. as a bidireccional socket
	"""
	def __init__(self, twoway=False, strclass=StringIO.StringIO):
		self.twoway = twoway
		self.st1 = strclass()
		if self.twoway:
			self.st2 = strclass()
		else:
			self.st2 = None
			
	def get_reader(self):
		return ( SCAccesor( (self.st1, self.st2) ))
	def get_writer(self):
		return ( SCAccesor( (self.st2, self.st1) ))
	def likepopen(self):
		return (self.get_reader(), self.get_writer())


if __name__=='__main__':
	import unittest
	
	class genTester(unittest.TestCase):
		def _test_instances(self, reader, writer):
			"""
			This is used to check that any instance keep it's position pointer
			"""
			t = writer.write('hola carlos')
			t = reader.read(5)
			self.assertEqual(t, 'hola ')
			t = writer.write(' -> chau')
			t = reader.read()
			self.assertEqual(t, 'carlos -> chau')
	
	
	class testChannel(genTester):
		"""Test Channel"""
		def test_1(self):
			"""Test that a channel reader/writer works as I want :-)"""
			c = SimpleChannel()
			r = c.get_reader()
			w = c.get_writer()
			self._test_instances(r,w)
		def test_twosided(self):
			"""Test bi-dir"""
			c = SimpleChannel(True)
			r = c.get_reader()
			w = c.get_writer()
			self._test_instances(r,w)
			self._test_instances(w,r)
	
	suite = unittest.TestSuite()
	suite.addTest(unittest.makeSuite(testChannel))
	unittest.TextTestRunner(verbosity=2).run(suite)