feat: reject token if it's not valid

src/libs/changeStringCase.ts

@@ -0,0 +1,34 @@
+export enum Case {
+  camelCase,
+  snake_case,
+}
+
+export function changeStringCase<T>(
+  str: string,
+  currentCase: Case,
+  newCase: Case,
+): string {
+  if (currentCase === newCase) {
+    return str;
+  }
+
+  const currentSeparator = currentCase === Case.snake_case ? "_" : /(?=[A-Z])/;
+  const words = str.split(currentSeparator);
+
+  return words
+    .map((word, index) => {
+      switch (newCase) {
+        case Case.camelCase:
+          if (index === 0) {
+            return word.toLowerCase();
+          }
+
+          return word[0].toUpperCase() + word.slice(1).toLowerCase();
+        case Case.snake_case:
+          return word.toLowerCase();
+        default:
+          throw new Error("Unknown case");
+      }
+    })
+    .join(newCase === Case.snake_case ? "_" : "");
+}