Extract reverse-lookup scan to core/relationships (one shared impl)

src/core/relationships.test.ts

@@ -0,0 +1,41 @@
+import { describe, expect, test } from 'vitest';
+import { datasetUsageCounts, snippetsReferencingDataset } from './relationships';
+
+/** A minimal snippet-like record — the helpers only read `datasetRefs`. */
+const snip = (id: string, datasetRefs: string[]) => ({ id, datasetRefs });
+
+describe('snippetsReferencingDataset', () => {
+  const snippets = [
+    snip('a', ['Sales']),
+    snip('b', ['SALES', 'Regions']),
+    snip('c', ['Other']),
+    snip('d', []),
+  ];
+
+  test('matches case-insensitively and preserves the input records', () => {
+    expect(snippetsReferencingDataset(snippets, 'sales').map((s) => s.id)).toEqual(['a', 'b']);
+    // The matched element is the same object that was passed in (no remapping).
+    expect(snippetsReferencingDataset(snippets, 'sales')[0]).toBe(snippets[0]);
+  });
+
+  test('returns an empty array when nothing references the name', () => {
+    expect(snippetsReferencingDataset(snippets, 'Nonexistent')).toEqual([]);
+  });
+});
+
+describe('datasetUsageCounts', () => {
+  test('counts every reference, keyed by lower-cased name, in one pass', () => {
+    const counts = datasetUsageCounts([
+      snip('a', ['Sales']),
+      snip('b', ['SALES', 'Regions']),
+      snip('c', ['regions']),
+    ]);
+    expect(counts.get('sales')).toBe(2);
+    expect(counts.get('regions')).toBe(2);
+    expect(counts.get('other')).toBeUndefined();
+  });
+
+  test('is empty for a library with no references', () => {
+    expect(datasetUsageCounts([snip('a', []), snip('b', [])]).size).toBe(0);
+  });
+});