Theatrical themes in Long Day's Journey into Night?

I’ve just watched Sidney Lumet’s knockout 1962 film version of Eugene O’Neill’s play Long Day’s Journey into Night, with Katharine Hepburn and Ralph Richardson.

In addition to the dark autobiographical themes of addiction, family dysfunction, denial, and bitter blame, it seems to me that there is a strong theme pertaining to the theatre itself, and literature in general. I wondered if O’Neill might have even intended the family as a symbol of the decadence of literature in his time.

This turns out to be a very difficult subject to look up online. Searches for “theatre” in connection with the play bring up information about the play and productions of it, synopses, etc. I can’t seem to construct the right kind of search to find out if analysts think the play is (in part) about theatre or if this is just a delusion of my own.

If you’ve ever studied the play in school, or if you have references on the great moderns dramas, etc., and can point me to a discussion that might prove or disprove my thinking here, that’s what I’m looking for.