feat: newest message first, Raycast-style conversation sidebar (#7)

src/lib/utils.ts

@@ -29,6 +29,27 @@ export function formatRelativeTime(timestamp: number, now: number = Date.now()):
   return new Date(timestamp).toLocaleDateString(undefined, { month: "short", day: "numeric" });
 }
 
+export type RecencyGroup = "Today" | "Yesterday" | "This week" | "Older";
+
+/**
+ * Buckets a timestamp for the conversation sidebar.
+ *
+ * Raycast groups its sidebar this way, and it buys the grouping that per-row
+ * timestamps were trying to convey — without putting a timestamp on every row.
+ */
+export function recencyGroup(timestamp: number, now: number = Date.now()): RecencyGroup {
+  const startOfToday = new Date(now);
+  startOfToday.setHours(0, 0, 0, 0);
+  const start = startOfToday.getTime();
+
+  const DAY = 86_400_000;
+
+  if (timestamp >= start) return "Today";
+  if (timestamp >= start - DAY) return "Yesterday";
+  if (timestamp >= start - 7 * DAY) return "This week";
+  return "Older";
+}
+
 /** Pulls a human-readable message out of anything that can be thrown. */
 export function errorMessage(error: unknown): string {
   if (error instanceof Error) return error.message;