[refactor] preparation for PR adressing #638 (#644)

Co-authored-by: Camille Moussu <cmoussu@linagora.com>

src/features/Events/utils/formatDateToICal.ts

@@ -0,0 +1,37 @@
+import moment from "moment-timezone";
+
+export function formatDateToICal(
+  date: Date,
+  allday: boolean,
+  timezone?: string
+) {
+  const pad = (n: number) => n.toString().padStart(2, "0");
+
+  if (allday) {
+    const year = date.getUTCFullYear();
+    const month = pad(date.getUTCMonth() + 1);
+    const day = pad(date.getUTCDate());
+    return `${year}-${month}-${day}`;
+  }
+
+  if (timezone) {
+    if (!moment.tz.zone(timezone)) {
+      console.warn(
+        `[formatDateToICal] Unrecognized timezone: "${timezone}", falling back to UTC`
+      );
+    } else {
+      const momentDate = moment.utc(date).tz(timezone);
+      if (momentDate.isValid()) {
+        return momentDate.format("YYYY-MM-DDTHH:mm:ss");
+      }
+    }
+  }
+
+  const year = date.getUTCFullYear();
+  const month = pad(date.getUTCMonth() + 1);
+  const day = pad(date.getUTCDate());
+  const hours = pad(date.getUTCHours());
+  const minutes = pad(date.getUTCMinutes());
+  const seconds = pad(date.getUTCSeconds());
+  return `${year}-${month}-${day}T${hours}:${minutes}:${seconds}Z`;
+}