merge: integrate ECMWF IFS PR #464 with bounded model switching

server/providers/wind/gfs.js

@@ -88,3 +88,34 @@ export async function fetchRange({
     throw new Error('invalid range length');
   return buffer;
 }
+
+import { GFS_BUCKET, gfsObjectKey, selectLatestGfsCycle, nearestGfsStep } from './catalog.js';
+import { decodeWindGribMessage } from './decode.js';
+import { resampleWindGrid } from './grid.js';
+
+/** Fetch and decode the GFS 10 m wind field valid closest to now. */
+export async function fetchGfsWind({ fetchImpl = fetch, now = () => Date.now(), targetDx = 1, decodeImpl = decodeWindGribMessage, signal } = {}) {
+  const nowMs = now();
+  const cycle = selectLatestGfsCycle(nowMs);
+  const runMs = Date.UTC(
+    Number(cycle.date.slice(0, 4)),
+    Number(cycle.date.slice(4, 6)) - 1,
+    Number(cycle.date.slice(6, 8)),
+    cycle.hour,
+  );
+  // Pick the forecast step whose valid time is closest to now, so the layer
+  // shows the freshest field the cycle offers instead of the analysis.
+  const forecastHour = nearestGfsStep((nowMs - runMs) / 3600_000);
+  const base = `https://${GFS_BUCKET}.s3.amazonaws.com/${gfsObjectKey({ ...cycle, forecastHour })}`;
+  const index = await fetchText({ url: `${base}.idx`, fetchImpl, signal });
+  const ranges = windMessageRanges(parseGfsIdx(index.toString()));
+  const [uBuffer, vBuffer] = await Promise.all([
+    fetchRange({ url: base, ...ranges.u, fetchImpl, signal }),
+    fetchRange({ url: base, ...ranges.v, fetchImpl, signal }),
+  ]);
+  const [u, v] = await Promise.all([decodeImpl(uBuffer), decodeImpl(vBuffer)]);
+  const grid = resampleWindGrid({ u: u.values, v: v.values, ni: u.ni, nj: u.nj, lo1: u.lo1, la1: u.la1, di: u.di, dj: u.dj, dx: targetDx, dy: targetDx });
+  const runIso = new Date(runMs).toISOString();
+  const validIso = new Date(runMs + forecastHour * 3600_000).toISOString();
+  return { cycle: { ...cycle, forecastHour, runIso, validIso }, level: '10 m above ground', units: 'm/s', grid };
+}