feat: turn layers on in links to an area

open_in_gods_eye_view accepts layers and writes them with the app's own
share-link layer codec, so the link opens with those layers on. Layer
names are limited to the registered layer ids.

src/tools/queries/share.js

@@ -1,5 +1,10 @@
 /** A link that opens God's Eye View on an area. */
 
+import {
+  REGISTERED_LAYER_IDS,
+  createDefaultLayerState,
+  encodeLayerStateParams,
+} from '../../data/layerState.js';
 import { defineTool, ToolError } from '../catalog.js';
 import { AREA_SCHEMA, areaCenter, areaRadiusKm, resolveArea } from '../area.js';
 
@@ -12,10 +17,19 @@ export const openInGodsEyeView = defineTool({
   name: 'open_in_gods_eye_view',
   title: "Open in God's Eye View",
   description:
-    "A link that opens God's Eye View looking straight down on an area.",
+    "A link that opens God's Eye View looking straight down on an area, " +
+    'optionally with chosen data layers turned on.',
   inputSchema: {
     type: 'object',
-    properties: { area: AREA_SCHEMA },
+    properties: {
+      area: AREA_SCHEMA,
+      layers: {
+        type: 'array',
+        maxItems: REGISTERED_LAYER_IDS.length,
+        items: { type: 'string', enum: [...REGISTERED_LAYER_IDS] },
+        description: 'Layers to turn on, such as "flights" or "earthquakes".',
+      },
+    },
     required: ['area'],
     additionalProperties: false,
   },
@@ -38,18 +52,26 @@ export const openInGodsEyeView = defineTool({
         ),
       ),
     );
-    // The share-link camera fields; the app restores its defaults for the rest.
-    base.hash = new URLSearchParams({
+    // The share-link camera and layer fields; the app restores its defaults
+    // for everything else.
+    const params = new URLSearchParams({
       v: '2',
       lat: center.lat.toFixed(4),
       lon: center.lon.toFixed(4),
       alt: String(altitude),
       heading: '0',
       pitch: '-90',
-    }).toString();
+    });
+    const layers = [...new Set(args.layers || [])];
+    if (layers.length)
+      encodeLayerStateParams(params, {
+        ...createDefaultLayerState(),
+        enabledLayerIds: layers,
+      });
+    base.hash = params.toString();
     return {
       summary: `Open ${area.label} in God's Eye View: ${base.href}`,
-      data: { url: base.href, center, altitude_m: altitude },
+      data: { url: base.href, center, altitude_m: altitude, layers },
     };
   },
 });

src/tools/queries/share.test.mjs

@@ -53,3 +53,28 @@ test('altitude is bounded for tiny and planet-sized areas', async () => {
     (error) => error.code === 'unavailable',
   );
 });
+
+test('links turn on the requested layers with the app share-link codec', async () => {
+  const { decodeLayerStateParams } = await import('../../data/layerState.js');
+  const catalog = composeCatalog({
+    tools: coreTools,
+    services: { app: { baseUrl: 'http://localhost:4173/' } },
+  });
+  const result = await catalog.call('open_in_gods_eye_view', {
+    area: { lat: 30.27, lon: -97.74, radius_km: 10 },
+    layers: ['earthquakes', 'flights', 'flights'],
+  });
+  assert.deepEqual(result.data.layers, ['earthquakes', 'flights']);
+  const params = new URLSearchParams(new URL(result.data.url).hash.slice(1));
+  assert.deepEqual(decodeLayerStateParams(params).enabledLayerIds.sort(), [
+    'earthquakes',
+    'flights',
+  ]);
+  await assert.rejects(
+    catalog.call('open_in_gods_eye_view', {
+      area: { lat: 0, lon: 0, radius_km: 1 },
+      layers: ['not-a-layer'],
+    }),
+    /must be one of/,
+  );
+});