Move left pane entirely to React

ts/util/timer.ts

@@ -0,0 +1,23 @@
+import { padStart } from 'lodash';
+
+export function getIncrement(length: number): number {
+  if (length < 0) {
+    return 1000;
+  }
+
+  return Math.ceil(length / 12);
+}
+
+export function getTimerBucket(expiration: number, length: number): string {
+  const delta = expiration - Date.now();
+  if (delta < 0) {
+    return '00';
+  }
+  if (delta > length) {
+    return '60';
+  }
+
+  const bucket = Math.round(delta / length * 12);
+
+  return padStart(String(bucket * 5), 2, '0');
+}