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import sys
import time
import unittest
import weakref

import IECore

class CancellerTest( unittest.TestCase ) :

	def testCheck( self ) :

		IECore.Canceller.check( None )

		c = IECore.Canceller()
		self.assertFalse( c.cancelled() )
		IECore.Canceller.check( c )
		c.cancel()
		self.assertTrue( c.cancelled() )

		with self.assertRaises( IECore.Cancelled ) :
			IECore.Canceller.check( c )

	def testFinally( self ) :

		def f() :

			c = IECore.Canceller()
			c.cancel()

			didFinally = False
			try :
				IECore.Canceller.check( c )
			finally :
				didFinally = True

			self.assertEqual( didFinally, True )

		self.assertRaises( IECore.Cancelled, f )

	def testCancelledClass( self ) :

		self.assertIsInstance( IECore.Cancelled(), RuntimeError )
		self.assertEqual( IECore.Cancelled.__module__, "IECore" )

	def testExceptionTranslation( self ) :

		def raiser( key ) :

			if key == "python" :
				raise IECore.Cancelled()
			else :
				c = IECore.Canceller()
				c.cancel()
				IECore.Canceller.check( c )

		c = IECore.LRUCache( raiser, 1 )

		with self.assertRaises( IECore.Cancelled ) as a :

			# Expected sequence of events is as follows :
			#
			# 1. `get()` enters C++.
			# 2. C++ enters back into Python, calling `raiser()`.
			# 3. `raiser()` raises a _python_ exception containing a _python_
			#    `IECore.Cancelled` object.
			# 4. `LRUCacheGetter` (in LRUCacheBinding.cpp) calls `translatePythonException()` to turn the
			#    Python exception back into an appropriate C++ one - a true instance of `IECore::Cancelled`.
			# 5. The C++ exception propagates back to `get()`, which translates it back into Python,
			#    yielding us an instance of `IECore.Cancelled`.
			#
			# If 4 or 5 fail to perform the appropriate translation, we'll end up with a generic
			# exception being thrown, meaning we can no longer determine that cancellation occurred.
			# And then bad things happen.

			c.get( "python" )

		with self.assertRaises( IECore.Cancelled ) as a :

			# Expected sequence of events is even more
			# convoluted :
			#
			# 1. `get()` enters C++.
			# 2. C++ enters back into Python, calling `raiser()`.
			# 3. `raiser()` calls `Canceller.check()` which throws `Cancelled` from C++.
			# 4. The C++ exception is translated back into Python.
			# 5. `LRUCacheGetter` (in LRUCacheBinding.cpp) calls `translatePythonException()` to turn the
			#    Python exception back into an appropriate C++ one - a true instance of `IECore::Cancelled`.
			# 6. The C++ exception propagates back to `get()`, which translates it back into Python,
			#    yielding us an instance of `IECore.Cancelled`.

			c.get( "c++" )

	def testElapsedTime( self ) :

		c = IECore.Canceller()
		time.sleep( 0.1 )
		self.assertEqual( c.elapsedTime(), 0.0 )

		c.cancel()
		time.sleep( 0.25 )
		t = c.elapsedTime()
		# Windows potentially sleeps less than the requested amount of time.
		# Testing indicates 1 millisecond should be enough margin to pass.
		self.assertGreaterEqual( t, 0.25 - 0.001 )
		# We'd like to `assertAlmostEqual( t, 0.25 )` as well, to check that are
		# units are seconds. But the load on CI machines is sometimes such that
		# we couldn't do that with any kind of reasonable epsilon. Instead, just
		# check that the units are in the right ballpark.
		self.assertLess( t, 2.0 )

		# Calling `cancel()` again shouldn't reset elapsed time.
		c.cancel()
		self.assertGreaterEqual( c.elapsedTime(), t )

	def testExceptionLifetime( self ) :

		c = IECore.Canceller()
		c.cancel()
		try :
			IECore.Canceller.check( c )
		except Exception as e :
			exception = e

		self.assertIsInstance( exception, IECore.Cancelled )
		w = weakref.ref( exception )
		del exception
		self.assertIsNone( w() )

		exception = IECore.Cancelled()
		self.assertIsInstance( exception, IECore.Cancelled )
		w = weakref.ref( exception )
		del exception
		self.assertIsNone( w() )

if __name__ == "__main__":
	unittest.main()
