# Create by Brice PARENT, for whoever it could help (so, just me right now)
# Do whatever you want with it, and don't hesitate to drop a not here if
# it helped you, or if you have anything to say about it. Also, I'm not
# providing any support for it, so use at your own risk (but I might help
# if I've got some time) !

# When using unittest.setUpTestData to prefetch some data in the db, we should
# always take extra care when modify this data, as it will not be refreshed
# before the next tests.
# If we have to modify it, we have to re-set it manually before the end of the
# test (and in some cases, if we exit the test prematurely, the data will stay
# modified, potentially causing many side effects to future tests.
# Or we can use this context manager, which will operate the value change, and
# reverse it at the end (even if the test is exited prematurely).

# Usage :
# self.assertEqual(book.title, "My book's title")  # Initial title of the book
# with TestDataTempChange(book, "title", "My temporary title"):
#     self.assertEqual(book.title, "My temporary title")  # Your test here
#
# self.assertEqual(book.title, "My book's title")  # Back to initial title

class TestDataTempChange:
    def __init__(self, obj, prop, val):
        self.obj = obj
        self.prop = prop
        self.val = val

    def __enter__(self):
        # saving initial value
        self.init_val = getattr(self.obj, self.prop)
        # updating the object with new value
        setattr(self.obj, self.prop, self.val)
        self.obj.save()

    def __exit__(self, type_, value, traceback):
        # reverting the object's value to its initial value
        setattr(self.obj, self.prop, self.init_val)
        self.obj.save()