feat: enhance caching mechanism with pending document cache support

Author: LadyBluenotes

src/utils/cache.server.ts

@@ -1,8 +1,8 @@
-import { LRUCache } from 'lru-cache'
+import { LRUCache } from "lru-cache";
 
 declare global {
   // @ts-expect-error - globalThis.docCache is set in the server entrypoint
-  var docCache: LRUCache<string, unknown>
+  var docCache: LRUCache<string, unknown>;
 }
 
 const docCache =
@@ -11,23 +11,40 @@ const docCache =
   (globalThis.docCache = new LRUCache<string, unknown>({
     max: 300,
     // ttl: 1,
-    ttl: process.env.NODE_ENV === 'production' ? 1 : 1000000,
-  }))
+    ttl: process.env.NODE_ENV === "production" ? 1 : 1000000,
+  }));
+
+const pendingDocCache = new Map<string, Promise<unknown>>();
 
 export async function fetchCached<T>(opts: {
-  fn: () => Promise<T>
-  key: string
-  ttl: number
+  fn: () => Promise<T>;
+  key: string;
+  ttl: number;
 }): Promise<T> {
   if (docCache.has(opts.key)) {
-    return docCache.get(opts.key) as T
+    return docCache.get(opts.key) as T;
   }
 
-  const result = await opts.fn()
+  const pending = pendingDocCache.get(opts.key);
+
+  if (pending) {
+    return pending as Promise<T>;
+  }
+
+  const resultPromise = opts
+    .fn()
+    .then((result) => {
+      docCache.set(opts.key, result, {
+        ttl: opts.ttl,
+      });
+
+      return result;
+    })
+    .finally(() => {
+      pendingDocCache.delete(opts.key);
+    });
 
-  docCache.set(opts.key, result, {
-    ttl: opts.ttl,
-  })
+  pendingDocCache.set(opts.key, resultPromise);
 
-  return result
+  return resultPromise;
 }