R: Add/duplicate rows to a dataframe and replace column values when condition is met

Question

I have two dataframes named TableA and TableB (reproducible example below).

Within TableA$D, whenever the value is NA, I would like to do two things:

1.) Add/duplicate the relevant rows "n" times, where "n" is defined by how many rows are in TableB.

2.) With the rows duplicated, replace the "NA"'s in TableA$D with the values from TableB.

Sometimes TableB will have 7 values, sometimes 100, and there is no prior knowledge of what values will appear in TableB.

A <- c("foo", "foo bar", "foo bar", "bar")
B <- c("bar", "foo", "bar bar", "foo")
C <- c("foo", "foo", "foo", "foo")
D <- c("X", NA, "X", NA)

TableA <- data.frame(A,B,C,D)
TableB <- data.frame(c(1,2,3,4,5,6,7))

I am trying to make like the result to look like this:

A	B	C	D
foo	bar	foo	1
foo	bar	foo	2
foo	bar	foo	3
foo	bar	foo	4
foo	bar	foo	5
foo	bar	foo	6
foo	bar	foo	7
foo bar	foo	foo	X
foo bar	bar bar	foo	1
foo bar	bar bar	foo	2
foo bar	bar bar	foo	3
foo bar	bar bar	foo	4
foo bar	bar bar	foo	5
foo bar	bar bar	foo	6
foo bar	bar bar	foo	7
bar	foo	bar	X

I have tried following this example Add values to dataframe when condition met in R however the logic used doesn't quite seem to fit my scenario.

Any help or tips would be greatly appreciated