Port Angular's closest-flight auto-select + scroll-into-view behavior

Angular's route/departure/arrival search result list picks a 'current
flight' on load and auto-expands + scrolls it into view — the flight
whose dep/arr time is closest to 'now' for today's searches, or the
first/last flight when the search is for a future/past day. React was
always rendering the list scrolled to the top, so on today's route
search the user sees flights from 00:30 onwards instead of landing on
whatever is departing right now.

- Add features/online-board/closestFlight.ts with a React-flavored port
  of find-closest-flight.ts (plus a today-guard that reuses the same
  'yyyymmdd' shape the URL parser produces).
- FlightList takes an optional initialCurrentFlightId, attaches a ref
  to each card, and scrollIntoView's it on mount / list change.
- FlightCard takes an initialExpanded prop and seeds its useState so
  the selected flight lands expanded, matching the Angular 'expanded:
  true' assignment after setCurrentFlight.
- OnlineBoardSearchPage computes the id via findClosestFlightId using
  the current params (type + date) and forwards it to FlightList.

src/features/online-board/closestFlight.ts

@@ -0,0 +1,97 @@
+/**
+ * Ported from Angular's find-closest-flight utility. Picks the flight
+ * whose departure (or arrival, for arrival-view) time is closest to
+ * "now" on today's searches, or the first/last flight for future/past
+ * days. The result gets auto-expanded and scrolled into view on the
+ * search results card, matching Angular behavior.
+ *
+ * @module
+ */
+
+import type { ISimpleFlight, IFlightLeg } from "./types.js";
+
+function firstLeg(flight: ISimpleFlight): IFlightLeg {
+  return flight.routeType === "Direct" ? flight.leg : flight.legs[0]!;
+}
+
+function lastLeg(flight: ISimpleFlight): IFlightLeg {
+  return flight.routeType === "Direct"
+    ? flight.leg
+    : flight.legs[flight.legs.length - 1]!;
+}
+
+function pickTime(flight: ISimpleFlight, isArrival: boolean): string | null {
+  const leg = isArrival ? lastLeg(flight) : firstLeg(flight);
+  const times = isArrival ? leg.arrival.times : leg.departure.times;
+  const dep = (times as { scheduledDeparture?: { local?: string } }).scheduledDeparture;
+  const arr = (times as { scheduledArrival?: { local?: string } }).scheduledArrival;
+  const actualOff = (times as { actualBlockOff?: { local?: string } }).actualBlockOff;
+  const actualOn = (times as { actualBlockOn?: { local?: string } }).actualBlockOn;
+  const latest =
+    (times as { latestDeparture?: { local?: string }; latestArrival?: { local?: string } })
+      [isArrival ? "latestArrival" : "latestDeparture"];
+  if (isArrival) return actualOn?.local ?? latest?.local ?? arr?.local ?? null;
+  return actualOff?.local ?? latest?.local ?? dep?.local ?? null;
+}
+
+function parseTimeMs(iso: string | null): number | null {
+  if (!iso) return null;
+  const ms = Date.parse(iso);
+  return Number.isNaN(ms) ? null : ms;
+}
+
+/**
+ * Returns `true` when `yyyymmdd` (e.g. '20260419') refers to today's
+ * calendar day in the browser's local time.
+ */
+function isTodayYyyymmdd(yyyymmdd: string, now: Date = new Date()): boolean {
+  if (yyyymmdd.length !== 8) return false;
+  const todayYyyymmdd =
+    String(now.getFullYear()) +
+    String(now.getMonth() + 1).padStart(2, "0") +
+    String(now.getDate()).padStart(2, "0");
+  return yyyymmdd === todayYyyymmdd;
+}
+
+export interface ClosestOptions {
+  /** 'yyyyMMdd' — the search date */
+  searchDate: string;
+  /** `true` when the list is an arrival view (use arrival times) */
+  isArrival: boolean;
+  /** Override current time for deterministic tests. */
+  now?: Date;
+}
+
+/**
+ * @returns the id of the flight whose time is closest to `now`, or the
+ * boundary flight when the search is not for today. Returns `null`
+ * when the list is empty.
+ */
+export function findClosestFlightId(
+  flights: ISimpleFlight[],
+  opts: ClosestOptions,
+): string | null {
+  if (!flights.length) return null;
+  const now = opts.now ?? new Date();
+  const nowMs = now.getTime();
+
+  if (!isTodayYyyymmdd(opts.searchDate, now)) {
+    // For future days, show the first flight; for past days, the last.
+    const firstMs = parseTimeMs(pickTime(flights[0]!, opts.isArrival));
+    if (firstMs !== null && nowMs < firstMs) return flights[0]!.id;
+    return flights[flights.length - 1]!.id;
+  }
+
+  let best: string | null = flights[0]?.id ?? null;
+  let bestAbsDiff = Number.POSITIVE_INFINITY;
+  for (const f of flights) {
+    const ms = parseTimeMs(pickTime(f, opts.isArrival));
+    if (ms === null) continue;
+    const abs = Math.abs(ms - nowMs);
+    if (abs < bestAbsDiff) {
+      bestAbsDiff = abs;
+      best = f.id;
+    }
+  }
+  return best;
+}

src/features/online-board/components/OnlineBoardSearchPage.tsx

@@ -17,6 +17,7 @@ import { useCallback, useEffect } from "react";
 import { useNavigate, useParams } from "@modern-js/runtime/router";
 import { useTranslation } from "@/i18n/provider.js";
 import { FlightList } from "@/ui/flights/FlightList.js";
+import { findClosestFlightId } from "../closestFlight.js";
 import { PageLayout } from "@/ui/layout/PageLayout.js";
 import { PageTabs } from "@/ui/layout/PageTabs.js";
 import { SearchHistory } from "@/ui/layout/SearchHistory.js";
@@ -331,6 +332,18 @@ export const OnlineBoardSearchPage: FC<OnlineBoardSearchPageProps> = ({
   // Use live flights when connected, otherwise fetched flights
   const displayFlights = connectionStatus === "live" ? liveFlights : flights;
 
+  // Port of Angular's findClosestFlight — on today's search, picks the
+  // flight with the smallest abs time-diff from 'now' (expands + scrolls
+  // it on mount). For future/past days, picks the first/last.
+  const initialCurrentFlightId = (() => {
+    if (!displayFlights.length || !params.date) return null;
+    const isArrival = params.type === "arrival";
+    return findClosestFlightId(displayFlights, {
+      searchDate: params.date,
+      isArrival,
+    });
+  })();
+
   // JSON-LD for search results (rendered once we have flights)
   const searchDescription = `Online board ${params.type} search results`;
   const jsonLd = displayFlights.length > 0
@@ -442,6 +455,7 @@ export const OnlineBoardSearchPage: FC<OnlineBoardSearchPageProps> = ({
               flights={displayFlights}
               loading={loading}
               onFlightClick={handleFlightClick}
+              initialCurrentFlightId={initialCurrentFlightId}
             />
           </section>
         )}