Author of the "Imperfect Work" and Where to Find a Copy of It

In the writings of St. Alphonsus Liguori, e.g., *Dignity and Duties of the Priest*, he often makes mention of the author of the "Imperfect Work" without saying who this author is. I suspect that it is St. John Chrysostom. Does anyone know for sure? Also, I have tried many times to search the internet for this work, but have not found it. The second part of my question is: Is the "Imperfect Work" a book and where may I obtain a copy of it? Thank you.