Add pwa support

Tesses.YouTubeDownloader.Server/res/service_worker.js

@@ -0,0 +1,42 @@
+const assets = ["<@ASSETS@>"];
+
+const staticCacheName = "tytd-static-<@BUILD_TIME@>";
+
+self.addEventListener('install',evt => {
+    evt.waitUntil(
+        caches.open(staticCacheName).then(cache =>{
+            cache.addAll(assets);
+        })
+    );
+});
+
+self.addEventListener('activate',(evt)=>{
+    evt.waitUntil(
+        caches.keys().then(keys => {
+            return Promise.all(keys.filter(key => key !== staticCacheName).map(key => caches.delete(key)));
+        })
+    );
+});
+
+self.addEventListener('fetch', evt => {
+    const uri = new URL(evt.request.url);
+    
+    evt.respondWith(
+        
+        caches.match(evt.request).then(cacheRes=>{
+            return cacheRes || fetch(evt.request);
+        }).catch(()=>{
+            if(uri.pathname === '/queue-size')
+            {
+                return new Response('<span hx-trigger="every 5000ms" hx-target="this" hx-push-url="false" hx-indicator="none" hx-get="./queue-size"  hx-swap="outerHTML" class="badge">?</span>',{
+                    headers: { 'Content-Type': 'text/html' }
+                  });
+            }
+            if(uri.pathname === "/progress")
+            {
+                return caches.match("/offline-progress.html");
+            }
+            return caches.match('/offline.html');
+        })
+    );
+});