From 92c35339f32cf99dbaa9954b2144842dafc156e6 Mon Sep 17 00:00:00 2001
From: Varun Patil <varunpatil@ucla.edu>
Date: Wed, 7 Dec 2022 22:06:27 -0800
Subject: [PATCH] sw: add expiration to preview

---
 src/service-worker-custom.ts | 36 ++++++++++++++++++++++++++++++++----
 1 file changed, 32 insertions(+), 4 deletions(-)

diff --git a/src/service-worker-custom.ts b/src/service-worker-custom.ts
index f6f7110f..45e8b52d 100644
--- a/src/service-worker-custom.ts
+++ b/src/service-worker-custom.ts
@@ -1,5 +1,7 @@
 import { registerRoute } from "workbox-routing";
+import { CacheExpiration } from "workbox-expiration";
 
+// Queue of requests to fetch preview images
 interface FetchPreviewObject {
   url: URL;
   fileid: number;
@@ -8,11 +10,20 @@ interface FetchPreviewObject {
 }
 let fetchPreviewQueue: FetchPreviewObject[] = [];
 
+// Cache for preview images
+const cacheName = "images";
 let imageCache: Cache;
 (async () => {
-  imageCache = await caches.open("images");
+  imageCache = await caches.open(cacheName);
 })();
 
+// Expiration for cache
+const expirationManager = new CacheExpiration(cacheName, {
+  maxAgeSeconds: 3600 * 24 * 7, // days
+  maxEntries: 20000, // 20k images
+});
+
+// Start fetching with multipreview
 let fetchPreviewTimer: any;
 async function flushPreviewQueue() {
   if (fetchPreviewQueue.length === 0) return;
@@ -21,6 +32,13 @@ async function flushPreviewQueue() {
   const fetchPreviewQueueCopy = fetchPreviewQueue;
   fetchPreviewQueue = [];
 
+  // Check if only one request
+  if (fetchPreviewQueueCopy.length === 1) {
+    const p = fetchPreviewQueueCopy[0];
+    return p.callback(await fetch(p.url));
+  }
+
+  // Create aggregated request body
   const files = fetchPreviewQueueCopy.map((p) => ({
     fileid: p.fileid,
     x: Number(p.url.searchParams.get("x")),
@@ -41,11 +59,13 @@ async function flushPreviewQueue() {
     url.searchParams.delete("a");
     url.searchParams.delete("c");
 
+    // Fetch multipreview
     const res = await fetch(url, {
       method: "POST",
       body: JSON.stringify(files),
     });
 
+    // Get blob
     if (res.status !== 200) throw new Error("Error fetching multi-preview");
     const blob = await res.blob();
 
@@ -85,7 +105,7 @@ async function flushPreviewQueue() {
         });
     }
   } catch (e) {
-    console.error(e);
+    console.error("Multipreview error", e);
   }
 
   // Initiate callbacks for failed requests
@@ -99,9 +119,10 @@ async function flushPreviewQueue() {
   });
 }
 
+// Intercept preview requests
 registerRoute(
   /^.*\/apps\/memories\/api\/image\/preview\/.*/,
-  async ({ url }) => {
+  async ({ url, request }) => {
     // Check if in cache
     const cache = await imageCache?.match(url);
     if (cache) return cache;
@@ -122,13 +143,20 @@ registerRoute(
       }
     });
 
+    // Fallback to single request
     if (res.status !== 200) {
       res = await fetch(url);
     }
 
     // Cache response
     if (res.status === 200) {
-      imageCache?.put(url, res.clone());
+      imageCache?.put(request, res.clone());
+      expirationManager.updateTimestamp(request.url);
+    }
+
+    // Run expiration once in every 20 requests
+    if (Math.random() < 0.05) {
+      expirationManager.expireEntries();
     }
 
     return res;