impr(custom text): replace control character improvements (@Leonabcd123) (monkeytypegame#6909)

### Description

Made it so all \t are converted to tab characters.

### Closes

Fixes monkeytypegame#6906

---------

Co-authored-by: Miodec <[email protected]>

Author: Leonabcd123

frontend/__tests__/utils/strings.spec.ts

@@ -10,4 +10,60 @@ describe("string utils", () => {
       expect(Strings.splitIntoCharacters("t𐑩e")).toEqual(["t", "𐑩", "e"]);
     });
   });
+  describe("replaceControlCharacters", () => {
+    it.each([
+      // Basic tab conversions
+      ["\\t", "\t", "single tab"],
+      ["\\t\\t\\t", "\t\t\t", "multiple tabs"],
+      ["hello\\tworld", "hello\tworld", "tab between words"],
+      ["\\tstart", "\tstart", "tab at start"],
+      ["end\\t", "end\t", "tab at end"],
+
+      // Basic newline conversions
+      ["\\n", " \n", "single newline with space prefix"],
+      ["hello\\nworld", "hello \nworld", "newline between words with space"],
+      ["\\nstart", " \nstart", "newline at start with space"],
+      ["end\\n", "end \n", "newline at end with space"],
+
+      // Complex newline handling (after first two regexes)
+      ["a\\n", "a \n", "single char followed by newline gets space prefix"],
+      ["hello\\n", "hello \n", "word followed by newline gets space prefix"],
+
+      // Double-escaped sequences (should become single-escaped)
+      ["\\\\t", "\\t", "double-escaped tab becomes single-escaped"],
+      [
+        "\\\\n",
+        "\\ \n",
+        "double-escaped newline becomes backslash + space + newline",
+      ],
+      ["\\\\t\\\\n", "\\t\\ \n", "multiple double-escaped sequences"],
+
+      // Mixed scenarios
+      [
+        "\\t\\n\\\\t",
+        "\t \n\\t",
+        "mix of tab, newline, and double-escaped tab",
+      ],
+      [
+        "hello\\tworld\\ntest\\\\t",
+        "hello\tworld \ntest\\t",
+        "complex mixed scenario",
+      ],
+
+      // Edge cases
+      ["", "", "empty string"],
+      ["no escapes", "no escapes", "string with no escape sequences"],
+      ["\\", "\\", "single backslash"],
+      ["\\x", "\\x", "backslash with non-control character"],
+
+      // Escaped backslashes that don't precede control chars
+      ["\\\\", "\\\\", "double backslash not followed by control char"],
+      ["\\\\x", "\\\\x", "double backslash followed by non-control char"],
+    ])(
+      "should convert %s to %s (%s)",
+      (input: string, expected: string, _description: string) => {
+        expect(Strings.replaceControlCharacters(input)).toBe(expected);
+      }
+    );
+  });
 });

frontend/src/ts/modals/custom-text.ts

@@ -279,11 +279,7 @@ function cleanUpText(): string[] {
   }
 
   if (state.replaceControlCharactersEnabled) {
-    text = text.replace(/([^\\]|^)\\t/gm, "$1\t");
-    text = text.replace(/\\n/g, " \n");
-    text = text.replace(/([^\\]|^)\\n/gm, "$1\n");
-    text = text.replace(/\\\\t/gm, "\\t");
-    text = text.replace(/\\\\n/gm, "\\n");
+    text = Strings.replaceControlCharacters(text);
   }
 
   text = text.replace(/ +/gm, " ");

frontend/src/ts/utils/strings.ts

@@ -167,3 +167,20 @@ export function splitIntoCharacters(s: string): string[] {
 
   return result;
 }
+
+/**
+ * Replaces escaped control characters with their literal equivalents.
+ * Converts \t to tab characters, \n to newlines (with a space prefix),
+ * and handles double-escaped sequences (\\t, \\n) by converting them back to single escaped versions.
+ * @param textToClear The input string containing escaped control characters.
+ * @returns A new string with control characters properly converted.
+ */
+export function replaceControlCharacters(textToClear: string): string {
+  textToClear = textToClear.replace(/(?<!\\)\\t/g, "\t");
+  textToClear = textToClear.replace(/\\n/g, " \n");
+  textToClear = textToClear.replace(/([^\\]|^)\\n/gm, "$1\n");
+  textToClear = textToClear.replace(/\\\\t/gm, "\\t");
+  textToClear = textToClear.replace(/\\\\n/gm, "\\n");
+
+  return textToClear;
+}