import {
  buildGreetingMessage,
  buildReminderMessage,
  toWhatsAppNumber,
  whatsAppUrl,
} from "@/lib/messaging/whatsapp";
import { absoluteUrl } from "@/services/notifications/templates/shared";
import { customerAppointmentLink } from "@/services/scheduling/guest-access.service";

/**
 * The one place a WhatsApp reminder link for a booking is assembled — shared
 * by the per-appointment button and the daily reminders list so the two can
 * never word the message differently. Returns null when the customer has no
 * phone number WhatsApp could use.
 */
export function reminderWhatsAppUrl(params: {
  /** The business's own country (ISO alpha-2) — see getBusinessCountry. */
  country: string;
  businessName: string;
  timezone: string;
  customer: { firstName: string; phone: string | null; userId: string | null };
  appointment?: { id: string; startAt: Date; staffName: string; serviceNames: string };
}): string | null {
  const { customer, appointment, businessName, timezone } = params;
  const digits = toWhatsAppNumber(customer.phone, params.country);
  if (!digits) return null;

  if (!appointment) {
    return whatsAppUrl(digits, buildGreetingMessage({ customerFirstName: customer.firstName, businessName }));
  }

  return whatsAppUrl(
    digits,
    buildReminderMessage({
      customerFirstName: customer.firstName,
      businessName,
      services: appointment.serviceNames,
      staffName: appointment.staffName,
      dateLabel: appointment.startAt.toLocaleDateString("en-GB", {
        weekday: "short",
        day: "numeric",
        month: "short",
        timeZone: timezone,
      }),
      timeLabel: appointment.startAt.toLocaleTimeString("en-GB", {
        hour: "2-digit",
        minute: "2-digit",
        timeZone: timezone,
      }),
      manageUrl: absoluteUrl(customerAppointmentLink({ id: appointment.id, customer: { userId: customer.userId } })),
    }),
  );
}