feat(FN-4411): complete Step 2 — add CodeMirror language resolver

Fusion-Task-Id: FN-4411
Fusion-Task-Lineage: d90785f2-b828-4fa0-b330-ede7f3c14349

packages/dashboard/app/utils/codemirror-language.ts

@@ -0,0 +1,35 @@
+import { type Extension } from "@codemirror/state";
+import { css } from "@codemirror/lang-css";
+import { javascript } from "@codemirror/lang-javascript";
+import { json } from "@codemirror/lang-json";
+import { markdown } from "@codemirror/lang-markdown";
+
+export function resolveCodeMirrorLanguage(filePath: string | undefined): Extension | null {
+  if (!filePath) {
+    return null;
+  }
+
+  const lowerPath = filePath.toLowerCase();
+
+  if (lowerPath.endsWith(".js") || lowerPath.endsWith(".mjs") || lowerPath.endsWith(".cjs") || lowerPath.endsWith(".jsx")) {
+    return javascript({ jsx: true });
+  }
+
+  if (lowerPath.endsWith(".ts") || lowerPath.endsWith(".tsx")) {
+    return javascript({ jsx: true, typescript: true });
+  }
+
+  if (lowerPath.endsWith(".css")) {
+    return css();
+  }
+
+  if (lowerPath.endsWith(".json")) {
+    return json();
+  }
+
+  if (lowerPath.endsWith(".md") || lowerPath.endsWith(".markdown") || lowerPath.endsWith(".mdx")) {
+    return markdown();
+  }
+
+  return null;
+}