Fix compare chart date alignment

components/charts/utils/chart-data-transformers.test.ts

@@ -0,0 +1,82 @@
+import { describe, expect, it } from 'bun:test';
+import { mergeDataSeries } from './chart-data-transformers';
+
+type PricePoint = {
+  date: string;
+  price: number;
+};
+
+describe('mergeDataSeries', () => {
+  it('normalizes intraday timestamps onto the same trading day', () => {
+    const merged = mergeDataSeries<PricePoint>([
+      {
+        id: 'stock',
+        data: [
+          { date: '2026-03-10T21:00:00.000Z', price: 100 },
+          { date: '2026-03-11T21:00:00.000Z', price: 101 }
+        ]
+      },
+      {
+        id: 'sp500',
+        data: [
+          { date: '2026-03-10', price: 5000 },
+          { date: '2026-03-11', price: 5050 }
+        ]
+      }
+    ]);
+
+    expect(merged).toEqual([
+      { date: '2026-03-10', stock: 100, sp500: 5000 },
+      { date: '2026-03-11', stock: 101, sp500: 5050 }
+    ]);
+  });
+
+  it('fills a comparison series from the nearest prior trading day when dates are missing', () => {
+    const merged = mergeDataSeries<PricePoint>([
+      {
+        id: 'stock',
+        data: [
+          { date: '2026-03-10', price: 100 },
+          { date: '2026-03-11', price: 103 },
+          { date: '2026-03-12', price: 104 }
+        ]
+      },
+      {
+        id: 'sp500',
+        data: [
+          { date: '2026-03-10', price: 5000 },
+          { date: '2026-03-12', price: 5060 }
+        ]
+      }
+    ]);
+
+    expect(merged).toEqual([
+      { date: '2026-03-10', stock: 100, sp500: 5000 },
+      { date: '2026-03-11', stock: 103, sp500: 5000 },
+      { date: '2026-03-12', stock: 104, sp500: 5060 }
+    ]);
+  });
+
+  it('does not backfill dates before a series first appears', () => {
+    const merged = mergeDataSeries<PricePoint>([
+      {
+        id: 'stock',
+        data: [
+          { date: '2026-03-10', price: 100 },
+          { date: '2026-03-11', price: 103 }
+        ]
+      },
+      {
+        id: 'sp500',
+        data: [
+          { date: '2026-03-11', price: 5000 }
+        ]
+      }
+    ]);
+
+    expect(merged).toEqual([
+      { date: '2026-03-10', stock: 100 },
+      { date: '2026-03-11', stock: 103, sp500: 5000 }
+    ]);
+  });
+});