perf: Parallelize external API calls in weather route to reduce latency

backend/routes/weather.js

@@ -18,27 +18,32 @@ router.get("/", async (req, res) => {
       lang: language,
     };
 
+    let currentResponse, forecastResponse, airResponse;
+
     if (lat && lon) {
-      params.lat = lat;
+      // 1. Parallel fetch for all 3 endpoints if coordinates are available
-      params.lon = lon;
+      [currentResponse, forecastResponse, airResponse] = await Promise.all([
+        axios.get(`${baseUrl}/weather`, { params: { ...params, lat, lon } }),
+        axios.get(`${baseUrl}/forecast`, { params: { ...params, lat, lon } }),
+        axios.get(`${baseUrl}/air_pollution`, { params: { lat, lon, appid: apiKey } }),
+      ]);
     } else {
+      // 2. Sequential fallback if only city name is provided
       params.q = q || city;
+      currentResponse = await axios.get(`${baseUrl}/weather`, { params });
+      const { coord } = currentResponse.data;
+
+      [forecastResponse, airResponse] = await Promise.all([
+        axios.get(`${baseUrl}/forecast`, {
+          params: { ...params, lat: coord.lat, lon: coord.lon },
+        }),
+        axios.get(`${baseUrl}/air_pollution`, {
+          params: { lat: coord.lat, lon: coord.lon, appid: apiKey },
+        }),
+      ]);
     }
 
-    // 1. Fetch Current Weather (to get lat/lon and timezone)
-    const currentResponse = await axios.get(`${baseUrl}/weather`, { params });
     const currentData = currentResponse.data;
-    const { coord } = currentData;
-
-    // 2. Fetch Forecast (for daily min/max) & Air Quality
-    const [forecastResponse, airResponse] = await Promise.all([
-      axios.get(`${baseUrl}/forecast`, {
-        params: { ...params, lat: coord.lat, lon: coord.lon },
-      }),
-      axios.get(`${baseUrl}/air_pollution`, {
-        params: { lat: coord.lat, lon: coord.lon, appid: apiKey },
-      }),
-    ]);
 
     // 3. Process Forecast for Today's Min/Max (Seoul Time: UTC+9)
     // OpenWeatherMap returns timestamps in UTC.