import { CalendarEvent } from "@calchat/shared";

// German date/time formatting helpers
export const formatDate = (d: Date) => d.toLocaleDateString("de-DE");
export const formatTime = (d: Date) =>
  d.toLocaleTimeString("de-DE", { hour: "2-digit", minute: "2-digit" });
export const formatDateTime = (d: Date) =>
  `${formatDate(d)} ${d.toLocaleTimeString("de-DE")}`;

/**
 * Format a list of events for display in the system prompt.
 * Output is in German with date/time formatting.
 */
export function formatExistingEvents(events: CalendarEvent[]): string {
  if (events.length === 0) {
    return "Keine Termine vorhanden.";
  }

  return events
    .map((e) => {
      const start = new Date(e.startTime);
      const end = new Date(e.endTime);
      const timeStr = `${formatTime(start)} - ${formatTime(end)}`;
      const recurring = e.isRecurring ? " (wiederkehrend)" : "";
      const desc = e.description ? ` | ${e.description}` : "";
      return `- ${e.title} (ID: ${e.id}) | ${formatDate(start)} ${timeStr}${recurring}${desc}`;
    })
    .join("\n");
}