I would like to watch the Bungaku Shoujo movie at some point, but I don't want spoilers for the novels. Skimming over the Wikipedia page, it seems that some events haven't happened yet as of the end of the fourth novel, while other events seem to correspond to earlier novels. There may be other spoilers, some of them major, and that also makes me afraid to research this topic too deeply on my own.
Which novels provide the major plot points for the movie? Please use spoiler tags as appropriate.