refactor: separate transit sources and request service

src/layers/transit/index.js

@@ -1,3 +1,4 @@
+import { createTransitSource } from './source.js';
 import { createTrails } from './trails.js';
 import { createState } from './state.js';
 import { createHeight } from './height.js';
@@ -23,15 +24,26 @@ import { TRANSIT_POLL_MS } from './policy.js';
  * @param {{services: object}} options
  * @returns {object} The data-layer module the manager registers.
  */
-export function createTransitLayer({ services }) {
+export function createTransitLayer({
+  services,
+  source = createTransitSource(),
+}) {
   if (!services?.overlays || !services?.render || !services?.sprites) {
     throw new TypeError(
       'A transit layer needs overlay, render and sprite services',
     );
   }
+  if (
+    typeof source?.requestSnapshot !== 'function' ||
+    typeof source?.getHistory !== 'function'
+  ) {
+    throw new TypeError(
+      'A transit source needs snapshot and history operations',
+    );
+  }
   const state = createState({ services });
   const parts = {};
-  const context = { state, services, parts };
+  const context = { state, services, parts, source };
   parts.trails = createTrails(context);
   parts.height = createHeight(context);
   parts.selection = createSelection(context);

src/layers/transit/ingestion.js

@@ -46,7 +46,7 @@ export const ORDER_REJECTS_BEFORE_RESET = 3;
  * @param {object} context
  * @returns {object}
  */
-export function createIngestion({ state, services, parts }) {
+export function createIngestion({ state, services, parts, source }) {
   const { governorRequestRender } = services.render;
   const { registerDynamicCredit, transitFeedCredit } = services.credits;
 
@@ -436,13 +436,9 @@ export function createIngestion({ state, services, parts }) {
     status.loading = status.count === 0;
     const promise = (async () => {
       try {
-        const response = await fetch(
-          `/api/transit/vehicles/${encodeURIComponent(feed.id)}`,
-          {
-            signal: controller.signal,
-            headers: { Accept: 'application/json' },
-          },
-        );
+        const response = await source.requestSnapshot(feed.id, {
+          signal: controller.signal,
+        });
         if (!response.ok) {
           // The proxy says when it will next try the operator; carrying that
           // through means the row can offer a time instead of just a shrug.

src/layers/transit/lifecycle.test.mjs

@@ -150,6 +150,7 @@ function groundStub(floorAt) {
 function harness(
   t,
   {
+    source,
     altitude = 4_000,
     floorAt = () => 12,
     at = BOSTON,
@@ -263,6 +264,7 @@ function harness(
   /** Every call the floor cycle makes to the rendered-mesh sampler. */
   const meshCalls = [];
   const layer = createTransitLayer({
+    source,
     services: {
       ground,
       mesh: {
@@ -3639,3 +3641,35 @@ test('moving and stationary transit stay adjacent above CCTV and Bikeshare durin
     assert.equal(entry.marker.id, entry.key);
   }
 });
+
+test('transit polls the supplied source and cancels it when disabled', async (t) => {
+  const calls = [];
+  const source = {
+    async requestSnapshot(feedId, { signal }) {
+      calls.push({ feedId, signal });
+      return Response.json(
+        snapshot(
+          feedId,
+          'MBTA',
+          [vehicle('injected', 42.36, -71.06, reported())],
+          { fetchedAt: Date.now() },
+        ),
+      );
+    },
+    async getHistory() {
+      throw new Error('No selected vehicle');
+    },
+  };
+  const app = harness(t, { source });
+  globalThis.fetch = () => {
+    throw new Error('Unexpected global fetch');
+  };
+  app.layer.enable(app.viewer);
+  await app.layer.update();
+  assert.ok(calls.some(({ feedId }) => feedId === 'mbta'));
+  assert.ok(app.vehicles().some((entry) => entry.record.id === 'injected'));
+  const before = calls.length;
+  app.layer.disable(app.viewer);
+  await app.layer.update();
+  assert.equal(calls.length, before);
+});

src/layers/transit/source.js

@@ -0,0 +1,22 @@
+import { fetchTransitHistory } from '../../sources/transitHistory.js';
+
+/** Request transit snapshots through caller-owned transport. */
+export function createTransitSource({
+  fetchImpl = (...args) => fetch(...args),
+} = {}) {
+  return {
+    getHistory(feedId, vehicleId, { signal } = {}) {
+      signal?.throwIfAborted();
+      return fetchTransitHistory(feedId, vehicleId, signal, fetchImpl);
+    },
+    requestSnapshot(feedId, { signal } = {}) {
+      signal?.throwIfAborted();
+      if (typeof feedId !== 'string' || !feedId || feedId.length > 160)
+        throw new TypeError('A transit feed identifier is required');
+      return fetchImpl(`/api/transit/vehicles/${encodeURIComponent(feedId)}`, {
+        signal,
+        headers: { Accept: 'application/json' },
+      });
+    },
+  };
+}

src/layers/transit/trails.js

@@ -1,4 +1,3 @@
-import { fetchTransitHistory } from '../../data/transitProxy.js';
 import { getRegisteredTransitFeed } from '../../data/transitFeeds.js';
 import * as Cesium from 'cesium';
 import {
@@ -23,7 +22,7 @@ export const TRAIL_VERTEX_LIMIT = 2048;
 const STEP_M = 25;
 
 /** Shared prepared paths. Floors are aligned to work with Google 3D tiles. */
-export function createTrails({ state, services, parts }) {
+export function createTrails({ state, services, parts, source }) {
   let historyRequest = null;
   let requestCount = 0,
     abortCount = 0;
@@ -233,7 +232,10 @@ export function createTrails({ state, services, parts }) {
       const controller = new AbortController();
       historyRequest = controller;
       requestCount++;
-      fetchTransitHistory(entry.feedId, entry.record.id, controller.signal)
+      source
+        .getHistory(entry.feedId, entry.record.id, {
+          signal: controller.signal,
+        })
         .then((payload) => {
           if (
             controller.signal.aborted ||