[Glitch] fix: support KaiOS arrow navigation on public pages

Port 1e232e455c to glitch-soc

Signed-off-by: Thibaut Girka <thib@sitedethib.com>

app/javascript/flavours/glitch/packs/public.js

@@ -1,5 +1,6 @@
 import loadPolyfills from 'flavours/glitch/util/load_polyfills';
 import ready from 'flavours/glitch/util/ready';
+import loadKeyboardExtensions from 'flavours/glitch/util/load_keyboard_extensions';
 
 function main() {
   const IntlMessageFormat = require('intl-messageformat').default;
@@ -118,6 +119,9 @@ function main() {
   });
 }
 
-loadPolyfills().then(main).catch(error => {
-  console.error(error);
-});
+loadPolyfills()
+  .then(main)
+  .then(loadKeyboardExtensions)
+  .catch(error => {
+    console.error(error);
+  });

app/javascript/flavours/glitch/packs/settings.js

@@ -1,5 +1,6 @@
 import loadPolyfills from 'flavours/glitch/util/load_polyfills';
 import ready from 'flavours/glitch/util/ready';
+import loadKeyboardExtensions from 'flavours/glitch/util/load_keyboard_extensions';
 
 function main() {
   const { delegate } = require('rails-ujs');
@@ -15,6 +16,9 @@ function main() {
   });
 }
 
-loadPolyfills().then(main).catch(error => {
-  console.error(error);
-});
+loadPolyfills()
+  .then(main)
+  .then(loadKeyboardExtensions)
+  .catch(error => {
+    console.error(error);
+  });

app/javascript/flavours/glitch/util/load_keyboard_extensions.js

@@ -0,0 +1,16 @@
+// On KaiOS, we may not be able to use a mouse cursor or navigate using Tab-based focus, so we install
+// special left/right focus navigation keyboard listeners, at least on public pages (i.e. so folks
+// can at least log in using KaiOS devices).
+
+function importArrowKeyNavigation() {
+  return import(/* webpackChunkName: "arrow-key-navigation" */ 'arrow-key-navigation');
+}
+
+export default function loadKeyboardExtensions() {
+  if (/KAIOS/.test(navigator.userAgent)) {
+    return importArrowKeyNavigation().then(arrowKeyNav => {
+      arrowKeyNav.register();
+    });
+  }
+  return Promise.resolve();
+}