em-dash: make trailing -s into em-dashes

macros/em-dash.lua

@@ -1,12 +1,17 @@
 script_name = "Em-dash"
 script_description = "I do not have an em-dash key on my keyboard"
 script_author = "garret"
-script_version = "2021-04-05"
-em = "—"
-function append(sub, sel)
+script_version = "2.0.0"
+
+local em = "—"
+
+local function append(sub, sel)
 	for si, li in ipairs(sel) do
 		local line = sub[li]
-		line.text = line.text..em
+		if string.sub(line.text, -1) == "-" then
+			line.text = line.text:sub(1, #line.text - 1)
+		end
+			line.text = line.text..em
 		sub[li] = line
 	end
 	aegisub.set_undo_point(script_name)