Extract explicit CodeQL bundle URL classification

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

src/codeql-bundle.ts

@@ -0,0 +1,33 @@
+import { BuiltInLanguage, parseBuiltInLanguage } from "./languages";
+
+/** Describes the contents and location of a downloadable CodeQL bundle. */
+export type CodeQLBundle =
+  | { kind: "combined"; url: string }
+  | {
+      kind: "per-language";
+      url: string;
+      language: BuiltInLanguage;
+      /** Only set when the Action selected the bundle, allowing a same-version fallback. */
+      combinedBundleURL?: string;
+    };
+
+const PER_LANGUAGE_BUNDLE_NAME =
+  /^codeql-bundle-(.+)-(?:linux64|osx64|win64)\.tar\.(?:gz|zst)$/;
+
+/** Classifies an explicit tools URL without changing it or adding a fallback. */
+export function getCodeQLBundleFromUrl(url: string): CodeQLBundle {
+  let assetName: string;
+  try {
+    const pathname = new URL(url).pathname;
+    // URL-encoded names must not bypass the toolcache safeguard.
+    assetName = decodeURIComponent(pathname.split("/").pop() ?? "");
+  } catch {
+    return { kind: "combined", url };
+  }
+
+  const match = assetName.match(PER_LANGUAGE_BUNDLE_NAME);
+  const language = match ? parseBuiltInLanguage(match[1]) : undefined;
+  return language === undefined
+    ? { kind: "combined", url }
+    : { kind: "per-language", url, language };
+}