Merge pull request 'T-Dark letter cases implemented' (#10) from feature/tdark-cases into master

Reviewed-on: https://git.ablecorp.us:443/AbleScript/able-script/pulls/10

ablescript/src/parser.rs

@@ -596,12 +596,36 @@ impl<'source> Parser<'source> {
     }
 
     /// Perform lang -> script substitution if in T-Dark block
-    fn tdark_subst(&self, string: String) -> String {
+    fn tdark_subst(&self, mut string: String) -> String {
         if self.tdark {
-            string.replace("lang", "script")
-        } else {
-            string
+            if let Some(pos) = string.to_lowercase().find("lang") {
+                let range = pos..pos + 4;
+                let mut count_upper = 0_u8;
+                string.replace_range(
+                    range.clone(),
+                    &(string[range]
+                        .chars()
+                        .zip("scri".chars())
+                        .map(|(lc, sc)| {
+                            if lc.is_uppercase() {
+                                count_upper += 1;
+                                sc.to_ascii_uppercase()
+                            } else {
+                                sc.to_ascii_lowercase()
+                            }
+                        })
+                        .collect::<String>()
+                        + match count_upper {
+                            0 | 1 => "pt",
+                            2 if rand::random() => "Pt",
+                            2 => "pT",
+                            _ => "PT",
+                        }),
+                )
+            }
         }
+
+        string
     }
 }