refactor(perimeters): share getSnapshotDetail without this

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/layers/perimeters/source.js

@@ -8,18 +8,12 @@ const msg = (text) => text;
 export function createWfigsPerimeterSource({
   fetchImpl = (...args) => globalThis.fetch(...args),
 } = {}) {
-  return {
-    /** The perimeter rows (see getSnapshotDetail for staleness). */
-    async getSnapshot(options = {}) {
-      return (await this.getSnapshotDetail(options)).rows;
-    },
-
   /**
    * The rows with how fresh they are: the proxy answers from its last
    * snapshot, marked stale, while WFIGS is unreachable.
    * @returns {Promise<{rows: object[], stale: boolean, fetchedAt: number|null}>}
    */
-    async getSnapshotDetail({ signal } = {}) {
+  async function getSnapshotDetail({ signal } = {}) {
     signal?.throwIfAborted();
     const response = await fetchImpl('/api/fire-perimeters', { signal });
     if (!response.ok) throw new Error(`WFIGS HTTP ${response.status}`);
@@ -34,10 +28,15 @@ export function createWfigsPerimeterSource({
     return {
       rows: payload.rows,
       stale: payload.stale === true,
-        fetchedAt: Number.isFinite(payload.fetchedAt)
+      fetchedAt: Number.isFinite(payload.fetchedAt) ? payload.fetchedAt : null,
-          ? payload.fetchedAt
-          : null,
     };
+  }
+
+  return {
+    /** The perimeter rows (see getSnapshotDetail for staleness). */
+    async getSnapshot(options = {}) {
+      return (await getSnapshotDetail(options)).rows;
     },
+    getSnapshotDetail,
   };
 }

src/layers/perimeters/source.test.mjs

@@ -172,3 +172,10 @@ test('the snapshot detail carries the proxy staleness and fetch time', async ()
   });
   assert.deepEqual(await source.getSnapshot(), []);
 });
+
+test('getSnapshot works when taken off its source object', async () => {
+  const { getSnapshot } = createWfigsPerimeterSource({
+    fetchImpl: async () => Response.json({ rows: [] }),
+  });
+  assert.deepEqual(await getSnapshot(), []);
+});