Tweak timestampFromDatetimeLocal. Add new helper

lib/dateHelpers.ts

@@ -1,6 +1,9 @@
 import Long from "long";
 
-const timestampFromDatetimeLocal = (datetimeLocal: string): Long => {
+export const timestampFromDatetimeLocal = (
+  datetimeLocal: string,
+  units?: "s" | "ms" | "ns",
+): Long => {
   const [date, time] = datetimeLocal.split("T");
   const [year, month, day] = date.split("-");
   const [hours, minutes] = time.split(":");
@@ -12,7 +15,34 @@ const timestampFromDatetimeLocal = (datetimeLocal: string): Long => {
     Number(hours),
     Number(minutes),
   );
-  return Long.fromNumber(dateObj.getTime()).divide(1000);
+
+  const timestampMillis = Long.fromNumber(dateObj.getTime());
+
+  switch (units) {
+    case "s":
+      return timestampMillis.divide(1000); // seconds
+    case "ns":
+      return timestampMillis.divide(1000_000); // nanoseconds
+    default:
+      return timestampMillis; // milliseconds
+  }
 };
 
-export { timestampFromDatetimeLocal };
+// With stripped seconds and milliseconds
+export const datetimeLocalFromTimestamp = (timestamp: number): string => {
+  const minDate = new Date(timestamp);
+
+  const minMonth = minDate.getMonth() + 1; // It's 0-indexed
+  const minMonthStr = minMonth < 10 ? `0${minMonth}` : String(minMonth);
+
+  const minDay = minDate.getDate();
+  const minDayStr = minDay < 10 ? `0${minDay}` : String(minDay);
+
+  const minHours = minDate.getHours();
+  const minHoursStr = minHours < 10 ? `0${minHours}` : String(minHours);
+
+  const minMinutes = minDate.getMinutes();
+  const minMinutesStr = minMinutes < 10 ? `0${minMinutes}` : String(minMinutes);
+
+  return `${minDate.getFullYear()}-${minMonthStr}-${minDayStr}T${minHoursStr}:${minMinutesStr}`;
+};