refresh stale data (#156)

app/actions/data.ts

@@ -29,6 +29,9 @@ import { signInSchema } from '@/lib/zod';
 import { auth } from '@/auth';
 import _ from 'lodash';
 import { getCurrentUser, getCurrentUserId } from '@/lib/server-helpers'
+import stableStringify from 'json-stable-stringify';
+import { prepareDataForHashing, generateCryptoHash } from '@/lib/utils';
+
 
 import { PermissionError } from '@/lib/exceptions'
 
@@ -123,6 +126,33 @@ async function saveData<T>(type: DataType, data: T): Promise<void> {
   }
 }
 
+/**
+ * Calculates the server's global freshness token based on all core data files.
+ * This is an expensive operation as it reads all data files.
+ */
+async function calculateServerFreshnessToken(): Promise<string> {
+  try {
+    const settings = await loadSettings();
+    const habits = await loadHabitsData();
+    const coins = await loadCoinsData();
+    const wishlist = await loadWishlistData();
+    const users = await loadUsersData();
+
+    const dataString = prepareDataForHashing(
+      settings,
+      habits,
+      coins,
+      wishlist,
+      users
+    );
+    const serverToken = await generateCryptoHash(dataString);
+    return serverToken;
+  } catch (error) {
+    console.error("Error calculating server freshness token:", error);
+    throw error;
+  }
+}
+
 // Wishlist specific functions
 export async function loadWishlistData(): Promise<WishlistData> {
   const user = await getCurrentUser()
@@ -595,3 +625,24 @@ export async function loadServerSettings(): Promise<ServerSettings> {
     isDemo: !!process.env.DEMO,
   }
 }
+
+/**
+ * Checks if the client's data is fresh by comparing its token with the server's token.
+ * @param clientToken The freshness token calculated by the client.
+ * @returns A promise that resolves to an object { isFresh: boolean }.
+ */
+export async function checkDataFreshness(clientToken: string): Promise<{ isFresh: boolean }> {
+  try {
+    const serverToken = await calculateServerFreshnessToken();
+    const isFresh = clientToken === serverToken;
+    if (!isFresh) {
+      console.log(`Data freshness check: Stale. Client token: ${clientToken}, Server token: ${serverToken}`);
+    }
+    return { isFresh };
+  } catch (error) {
+    console.error("Error in checkDataFreshness:", error);
+    // If server fails to determine its token, assume client might be stale to be safe,
+    // or handle error reporting differently.
+    return { isFresh: false };
+  }
+}