Add PWA update indicator.

src/components/common/UpdateIndicator.tsx

@@ -0,0 +1,25 @@
+import { updateSW } from "../../main";
+import IconButton from "../ui/IconButton";
+import { ThemeContext } from "../../context/Theme";
+import { Download } from "@styled-icons/boxicons-regular";
+import { internalSubscribe } from "../../lib/eventEmitter";
+import { useContext, useEffect, useState } from "preact/hooks";
+
+var pendingUpdate = false;
+
+export default function UpdateIndicator() {
+    const [ pending, setPending ] = useState(pendingUpdate);
+
+    useEffect(() => {
+        return internalSubscribe('PWA', 'update', () => setPending(true));
+    });
+
+    if (!pending) return;
+    const theme = useContext(ThemeContext);
+
+    return (
+        <IconButton onClick={() => updateSW(true)}>
+            <Download size={22} color={theme.success} />
+        </IconButton>
+    )
+}