Add deterministic daily weather brief

lib/server-forecast.ts

@@ -0,0 +1,52 @@
+import { mergeForecastSources } from "@/lib/forecast-merge";
+import type { RawImgwForecastResponse, RawWeatherForecast } from "@/types/forecast";
+
+const OPEN_METEO_FORECAST_URL = "https://api.open-meteo.com/v1/forecast";
+const IMGW_FORECAST_URL = "https://meteo.imgw.pl/api/v1/forecast/fcapi";
+// This browser token is published by the official meteo.imgw.pl frontend.
+const IMGW_FORECAST_TOKEN = "p4DXKjsYadfBV21TYrDk";
+const OPEN_METEO_TIMEOUT_MS = 12_000;
+const IMGW_TIMEOUT_MS = 5_000;
+
+export function parseForecastCoordinate(value: string | null, min: number, max: number) {
+  if (!value?.trim()) return null;
+  const coordinate = Number(value);
+  return Number.isFinite(coordinate) && coordinate >= min && coordinate <= max ? coordinate : null;
+}
+
+async function readImgwPayload(response: Response | null) {
+  if (!response?.ok) return null;
+  try {
+    return await response.json() as RawImgwForecastResponse;
+  } catch {
+    return null;
+  }
+}
+
+export async function fetchServerForecast(latitude: number, longitude: number) {
+  const openMeteoParams = new URLSearchParams({
+    latitude: String(latitude),
+    longitude: String(longitude),
+    hourly: "temperature_2m,apparent_temperature,precipitation_probability,precipitation,weather_code,wind_speed_10m",
+    daily: "weather_code,temperature_2m_max,temperature_2m_min,precipitation_probability_max,precipitation_sum,sunrise,sunset",
+    timezone: "Europe/Warsaw",
+    forecast_days: "7",
+    wind_speed_unit: "ms",
+  });
+  const imgwParams = new URLSearchParams({
+    token: IMGW_FORECAST_TOKEN,
+    lat: String(latitude),
+    lon: String(longitude),
+    m: "alaro",
+  });
+
+  const [openMeteoResponse, imgwResponse] = await Promise.all([
+    fetch(`${OPEN_METEO_FORECAST_URL}?${openMeteoParams}`, { next: { revalidate: 900 }, signal: AbortSignal.timeout(OPEN_METEO_TIMEOUT_MS) }),
+    fetch(`${IMGW_FORECAST_URL}?${imgwParams}`, { next: { revalidate: 900 }, signal: AbortSignal.timeout(IMGW_TIMEOUT_MS) }).catch(() => null),
+  ]);
+  if (!openMeteoResponse.ok) throw new Error("Forecast service is unavailable.");
+
+  const openMeteoPayload = await openMeteoResponse.json() as RawWeatherForecast;
+  const imgwPayload = await readImgwPayload(imgwResponse);
+  return mergeForecastSources(openMeteoPayload, imgwPayload);
+}