Update service worker to cache requests

Author: victoreronmosele

.fvmrc

@@ -0,0 +1,4 @@
+{
+  "flutter": "3.16.9",
+  "flavors": {}
+}

web/index.html

@@ -92,7 +92,7 @@ <h1>Flutter&trade; Gradient Generator</h1>
 
       _flutter.loader.load({
         serviceWorkerSettings: {
-          serviceWorkerUrl: './self_destructing_flutter_service_worker.js'
+          serviceWorkerUrl: './service_worker.js'
         },
         onEntrypointLoaded: function (engineInitializer) {
           engineInitializer.initializeEngine(

web/self_destructing_flutter_service_worker.js

@@ -0,0 +1,37 @@
+const CACHE_VERSION = "0.0.1";
+const CACHE_NAME = `flutter_gradient_generator_${CACHE_VERSION}`;
+
+self.addEventListener("activate", (event) => {
+    event.waitUntil(
+        caches.keys().then((keys) => {
+            return Promise.all(
+                keys.map((key) => {
+                    if (key !== CACHE_NAME) {
+                        return caches.delete(key);
+                    }
+                })
+            );
+        })
+    );
+});
+
+self.addEventListener("fetch", (event) => {
+    event.respondWith(
+        caches.match(event.request).then((response) => {
+            if (response) {
+                return response;
+            }
+
+            return fetch(event.request).then((response) => {
+                if (!response.ok) {
+                    return response;
+                }
+
+                return caches.open(CACHE_NAME).then((cache) => {
+                    cache.put(event.request, response.clone());
+                    return response;
+                });
+            });
+        })
+    );
+});