Automate date formatting

Data contains a column "date range" that contains 2 months i.e. Oct 31,2019-Nov 30,2019 (November) and Dec 1,2019-Dec 31, 2019(December). Need to separate them in different columns under Post Period (December) and Pre Period (October) wrt to column "Revenue". I want to automate this process when I upload a file comparing any 2 months. Earlier month under "Pre Period" and later under "Post Period". Attached an example excel screenshot of the raw data and the processed data.

x<-data.frame("A"=c("book","mobile","tablet","desktop"),
              "B"=c("new york","chicago","london","paris"),
              "Date.Range"=c("Oct 31,2019-Nov 30,2019","Oct 31,2019-Nov 30,2019","Dec 1,2019-Dec 31, 2019","Dec 1,2019-Dec 31, 2019"),
              "Revenue"=c(542,837,1234,846))
dput(x)


structure(list(A = structure(c(1L, 3L, 4L, 2L), .Label = c("book", 
"desktop", "mobile", "tablet"), class = "factor"), B = structure(c(3L, 
1L, 2L, 4L), .Label = c("chicago", "london", "new york", "paris"
), class = "factor"), Date.Range = structure(c(2L, 2L, 1L, 1L
), .Label = c("Dec 1,2019-Dec 31, 2019", "Oct 31,2019-Nov 30,2019"
), class = "factor"), Revenue = c(542, 837, 1234, 846)), class = "data.frame", row.names = c(NA, 
-4L))

Raw Data.

Processed Data.