Add timeAgo util to format elapsed time

Formats time difference as seconds, minutes, hours, or date string
for longer intervals.

apps/amethyst/lib/utils.ts

···
   let first = arr.shift()?.toUpperCase();
   return (first || "") + arr.join("");
 }
+
+export function timeAgo(date: Date) {
+  const seconds = Math.floor((new Date().getTime() - date.getTime()) / 1000);
+  let interval = Math.floor(seconds / 31536000);
+
+  // return date.toLocaleDateString("en-US");
+  if (interval > 1) {
+    const formatter = new Intl.DateTimeFormat("en-US", {
+      year: "numeric",
+      month: "short",
+      day: "numeric",
+      hour: "numeric",
+      minute: "numeric",
+    });
+    return "on " + formatter.format(date);
+  }
+  interval = Math.floor(seconds / 86400);
+  // return date without years
+  if (interval > 1) {
+    const formatter = new Intl.DateTimeFormat("en-US", {
+      month: "short",
+      day: "numeric",
+      hour: "numeric",
+      minute: "numeric",
+    });
+    return "on " + formatter.format(date);
+  }
+  interval = Math.floor(seconds / 3600);
+  if (interval > 1) {
+    return interval + " hours ago";
+  }
+  interval = Math.floor(seconds / 60);
+  if (interval > 1) {
+    return interval + " minutes ago";
+  }
+  return Math.floor(seconds) + " seconds ago";
+}