Update loadData function. (#1180)

Fix #1175.
We add retries when we fetch data.
We checks that fetched json is valid and it is not empty.
Reduce calls for the same urls.

Author: nikoshell

src/utils/dataLoader.ts

@@ -1,22 +1,90 @@
-export async function loadData(apiUrl: any) {
+// Define a more specific response type or use generics
+type DataResponse = unknown;
+
+const dataCache: Record<string, DataResponse> = {};
+const inFlightCache: Record<string, Promise<DataResponse>> = {};
+
+export async function loadData(
+  apiUrl: string,
+  maxRetries = 3,
+  retryDelay = 1000
+): Promise<DataResponse> {
   if (!apiUrl) {
-    console.warn(`No API URL provided`);
-    return {};
+    throw new Error(`No API URL provided`);
   }
 
-  try {
-    console.log(`Fetching data from: ${apiUrl}`);
-    const response = await fetch(apiUrl);
+  if (dataCache[apiUrl]) {
+    console.log(`✅ Cache hit for: ${apiUrl}`);
+    return dataCache[apiUrl];
+  }
+
+  if (inFlightCache[apiUrl]) {
+    console.log(`⏳ Waiting for in-flight fetch of: ${apiUrl}`);
+    return inFlightCache[apiUrl];
+  }
+
+  const fetchPromise = (async () => {
+    let lastError: Error | null = null;
+
+    for (let attempt = 1; attempt <= maxRetries; attempt++) {
+      try {
+        console.log(`📡 Fetching data from: ${apiUrl} (Attempt ${attempt})`);
+        const response = await fetch(apiUrl);
 
-    if (!response.ok) {
-      throw new Error(
-        `Failed to fetch data: ${response.status} ${response.statusText}`
-      );
+        if (!response.ok) {
+          throw new Error(
+            `Fetch failed: ${response.status} ${response.statusText}`
+          );
+        }
+
+        const data = await response.json();
+
+        if (
+          data == null ||
+          (typeof data === "object" &&
+            !Array.isArray(data) &&
+            Object.keys(data).length === 0)
+        ) {
+          throw new Error(`Received empty or invalid JSON`);
+        }
+
+        if (Array.isArray(data)) {
+          console.log(`📦 Received JSON array with ${data.length} items`);
+        } else if (typeof data === "object") {
+          console.log(
+            `📦 Received JSON object with ${Object.keys(data).length} keys`
+          );
+        }
+
+        // Store in final cache
+        dataCache[apiUrl] = data;
+        return data;
+      } catch (error) {
+        lastError = error instanceof Error ? error : new Error(String(error));
+        console.error(`❌ Attempt ${attempt} failed:`, error);
+
+        if (attempt < maxRetries) {
+          await new Promise((res) => setTimeout(res, retryDelay));
+        } else {
+          throw new Error(
+            `Failed to load data from ${apiUrl} after ${maxRetries} attempts: ${lastError.message}`,
+            { cause: lastError }
+          );
+        }
+      }
     }
 
-    return await response.json();
-  } catch (error) {
-    console.error(`Error loading data:`, error);
-    return {};
+    // This ensures TypeScript knows we always return something or throw
+    throw new Error(`Unexpected execution path in loadData for ${apiUrl}`);
+  })();
+
+  // Store the in-flight promise
+  inFlightCache[apiUrl] = fetchPromise;
+
+  try {
+    return await fetchPromise;
+  } finally {
+    // Remove from in-flight cache once done
+    delete inFlightCache[apiUrl];
   }
 }