Added a link from each opportunity to its latest Find a Tender notice

Opportunities from Find a Tender have a link icon before their title.
Clicking it fetches the opportunity with its releases (the list leaves
them out) and opens its newest release's notice,
www.find-tender.service.gov.uk/notice/<release_id>, in a new tab. The
tab is opened on the click and pointed at the notice when the request
returns, so it isn't blocked as a popup; if the request fails, or there
are no releases, it's closed and a toast says why. Opportunities from
other sources have no link for now, but keep its space so the titles
line up.

The icon is lucide-solid's, added for it at 1.52.0.

web/src/lib/opportunities.test.ts

@@ -1,6 +1,12 @@
 import { expect, test } from 'vitest';
 
-import { mergeOpportunities } from './opportunities';
+import type { OpportunityRelease } from '@/types/Opportunities';
+import {
+  findATenderNoticeUrl,
+  isFromFindATender,
+  latestRelease,
+  mergeOpportunities,
+} from './opportunities';
 import { testOpportunity } from './testOpportunity';
 
 test('replaces opportunities in place and adds new ones at the end', () => {
@@ -16,3 +22,38 @@ test('replaces opportunities in place and adds new ones at the end', () => {
   ]);
   expect(list[0]?.title).toBe('Opportunity a');
 });
+
+const release = (releaseId: string, releaseDate: string): OpportunityRelease => ({
+  uuid: 'a',
+  release_id: releaseId,
+  release_date: releaseDate,
+  release_tags: null,
+  data: '{}',
+});
+
+test('only Find a Tender opportunities are from Find a Tender', () => {
+  expect(isFromFindATender(testOpportunity('a'))).toBe(true);
+  expect(isFromFindATender(testOpportunity('a', { source: 'FTSMock' }))).toBe(false);
+});
+
+test('the latest release is the newest, wherever it is in the list', () => {
+  const opportunity = testOpportunity('a', {
+    releases: [
+      release('001-2026', '2026-10-01T09:00:00Z'),
+      release('003-2026', '2026-10-09T19:21:17+01:00'),
+      release('002-2026', '2026-10-05T12:00:00Z'),
+    ],
+  });
+  expect(latestRelease(opportunity)?.release_id).toBe('003-2026');
+});
+
+test('an opportunity without releases has no latest release', () => {
+  expect(latestRelease(testOpportunity('a', { releases: null }))).toBeUndefined();
+  expect(latestRelease(testOpportunity('a', { releases: [] }))).toBeUndefined();
+});
+
+test('a notice’s URL is its release ID on Find a Tender', () => {
+  expect(findATenderNoticeUrl('095868-2026')).toBe(
+    'https://www.find-tender.service.gov.uk/notice/095868-2026',
+  );
+});

web/src/lib/opportunities.ts

@@ -1,4 +1,4 @@
-import type { Opportunity } from '@/types/Opportunities';
+import type { Opportunity, OpportunityRelease } from '@/types/Opportunities';
 
 /**
  * The opportunities with changed merged in: each replaces the opportunity
@@ -12,3 +12,27 @@ export function mergeOpportunities(
   for (const opportunity of changed) byUuid.set(opportunity.uuid, opportunity);
   return [...byUuid.values()];
 }
+
+/** The source the backend gives opportunities fetched from Find a Tender. */
+const FIND_A_TENDER_SOURCE = 'FindATender';
+
+/** Whether the opportunity was fetched from Find a Tender, so its releases are notices there. */
+export function isFromFindATender(opportunity: Opportunity): boolean {
+  return opportunity.source === FIND_A_TENDER_SOURCE;
+}
+
+/** The opportunity's newest release, or undefined if it has none. */
+export function latestRelease(opportunity: Opportunity): OpportunityRelease | undefined {
+  let latest: OpportunityRelease | undefined;
+  for (const release of opportunity.releases ?? []) {
+    if (!latest || Date.parse(release.release_date) > Date.parse(latest.release_date)) {
+      latest = release;
+    }
+  }
+  return latest;
+}
+
+/** The page of a Find a Tender notice; a Find a Tender release's ID is its notice's. */
+export function findATenderNoticeUrl(releaseId: string): string {
+  return `https://www.find-tender.service.gov.uk/notice/${encodeURIComponent(releaseId)}`;
+}