From 449568e3a2eb0d3c1ed0200180be1385ba9b6636 Mon Sep 17 00:00:00 2001
From: k00b <k00b@stacker.news>
Date: Tue, 8 Oct 2024 17:58:15 -0500
Subject: [PATCH] don't let pending cache to build up

---
 lib/fetch.js | 53 ++++++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 47 insertions(+), 6 deletions(-)

diff --git a/lib/fetch.js b/lib/fetch.js
index c4267df5..55b6671e 100644
--- a/lib/fetch.js
+++ b/lib/fetch.js
@@ -38,33 +38,74 @@ class LRUCache {
 
 export function cachedFetcher (fetcher, { maxSize = 100, cacheExpiry, forceRefreshThreshold, keyGenerator }) {
   const cache = new LRUCache(maxSize)
+  console.log(`[CACHE] Initializing cache: maxSize=${maxSize}, cacheExpiry=${cacheExpiry}, forceRefreshThreshold=${forceRefreshThreshold}`)
+
+  if (!keyGenerator) {
+    throw new Error('keyGenerator is required')
+  }
+
+  let totalFetches = 0
+  let cacheMisses = 0
+  let cacheHits = 0
+  let backgroundRefreshes = 0
+
+  setInterval(() => {
+    console.log(`[CACHE] Stats: total=${totalFetches}, hits=${cacheHits}, misses=${cacheMisses}, backgroundRefreshes=${backgroundRefreshes}, cacheSize=${cache.cache.size}`)
+  }, 60000) // Log stats every minute
 
   return async function cachedFetch (...args) {
-    const key = keyGenerator ? keyGenerator(...args) : JSON.stringify(args)
+    const key = keyGenerator(...args)
     const now = Date.now()
+    totalFetches++
 
     async function fetchAndCache () {
+      console.log(`[CACHE] Fetching data for key: ${key}`)
       const result = await fetcher(...args)
       cache.set(key, { data: result, createdAt: now })
+      console.log(`[CACHE] Data fetched and cached for key: ${key}`)
       return result
     }
 
     const cached = cache.get(key)
 
     if (cached) {
+      if (cached.pendingPromise) {
+        console.log(`[CACHE] Waiting for pending promise for key: ${key}`)
+        return await cached.pendingPromise
+      }
+
       const age = now - cached.createdAt
 
       if (cacheExpiry === 0 || age < cacheExpiry) {
+        cacheHits++
+        console.log(`[CACHE] Cache hit for key: ${key}, age: ${age}ms`)
         return cached.data
       } else if (forceRefreshThreshold === 0 || age < forceRefreshThreshold) {
-        fetchAndCache().catch(console.error)
+        backgroundRefreshes++
+        console.log(`[CACHE] Background refresh for key: ${key}, age: ${age}ms`)
+        cached.pendingPromise = fetchAndCache()
+        cached.pendingPromise.finally(() => {
+          console.log(`[CACHE] Background refresh completed for key: ${key}`)
+          delete cached.pendingPromise
+        })
         return cached.data
       }
-    } else if (forceRefreshThreshold === 0) {
-      fetchAndCache().catch(console.error)
-      return null
     }
 
-    return await fetchAndCache()
+    cacheMisses++
+    console.log(`[CACHE] Cache miss for key: ${key}`)
+    const entry = { createdAt: now, pendingPromise: fetchAndCache() }
+    cache.set(key, entry)
+    try {
+      entry.data = await entry.pendingPromise
+      return entry.data
+    } catch (error) {
+      console.error(`[CACHE] Error fetching data for key: ${key}`, error)
+      cache.delete(key)
+      throw error
+    } finally {
+      console.log(`[CACHE] Fetch completed for key: ${key}`)
+      delete entry.pendingPromise
+    }
   }
 }