client: add resolveLegMode helper for endpoint-aware leg modes

client/src/components/Planner/legMode.test.ts

@@ -0,0 +1,30 @@
+import { describe, it, expect } from 'vitest';
+import { resolveLegMode } from './legMode';
+
+const P = (o?: Partial<{ leg_transport_mode: string | null; incoming_leg_transport_mode: string | null }>) =>
+  ({ isPlace: true, ...o });
+const B = () => ({ isPlace: false });
+
+describe('resolveLegMode', () => {
+  it('origin place with outgoing mode wins', () => {
+    expect(resolveLegMode(P({ leg_transport_mode: 'cycling' }), P(), 'walking')).toBe('cycling');
+  });
+  it('origin place, no override -> day default', () => {
+    expect(resolveLegMode(P(), P(), 'driving')).toBe('driving');
+  });
+  it('non-place origin -> destination incoming override', () => {
+    expect(resolveLegMode(B(), P({ incoming_leg_transport_mode: 'transit' }), 'walking')).toBe('transit');
+  });
+  it('non-place origin, no incoming override -> day default', () => {
+    expect(resolveLegMode(B(), P(), 'walking')).toBe('walking');
+  });
+  it('no place endpoint at all -> day default', () => {
+    expect(resolveLegMode(B(), B(), 'walking')).toBe('walking');
+  });
+  it('incoming is inert when origin is a place', () => {
+    expect(resolveLegMode(P(), P({ incoming_leg_transport_mode: 'transit' }), 'walking')).toBe('walking');
+  });
+  it('undefined dest falls back to day default for a non-place origin', () => {
+    expect(resolveLegMode(B(), undefined, 'walking')).toBe('walking');
+  });
+});

client/src/components/Planner/legMode.ts

@@ -0,0 +1,22 @@
+export type LegPoint = {
+  isPlace: boolean;
+  leg_transport_mode?: string | null;
+  incoming_leg_transport_mode?: string | null;
+};
+
+/**
+ * Travel mode of the leg from `origin` to `dest`. The mode is owned by the leg's
+ * place endpoint: the origin's outgoing override wins when the origin is a place;
+ * otherwise the destination's incoming override applies (only meaningful when the
+ * origin is not a place - a booking arrival or the morning hotel); otherwise the
+ * day default. The incoming value is inert whenever the origin is a place.
+ */
+export function resolveLegMode(
+  origin: LegPoint,
+  dest: LegPoint | undefined,
+  dayDefault: string,
+): string {
+  if (origin.isPlace) return origin.leg_transport_mode ?? dayDefault;
+  if (dest?.isPlace) return dest.incoming_leg_transport_mode ?? dayDefault;
+  return dayDefault;
+}