import type { Appointment } from "fhir/r4";

/**
 * How long a visit is, from what the appointment itself records: `minutesDuration`, else end minus start.
 * Undefined when it records neither, and never inferred from the service, which may have changed since.
 * A zero `minutesDuration` counts as unrecorded because one write path stores 0 for "not given".
 */
export const appointmentLengthMinutes = (
  appointment: Pick<Appointment, "minutesDuration" | "start" | "end">,
): number | undefined => {
  const { minutesDuration, start, end } = appointment;
  if (typeof minutesDuration === "number" && minutesDuration > 0) return minutesDuration;
  if (!start || !end) return undefined;
  const minutes = Math.round((Date.parse(end) - Date.parse(start)) / 60_000);
  return Number.isFinite(minutes) && minutes > 0 ? minutes : undefined;
};

const plural = (count: number, unit: string) => `${count} ${unit}${count === 1 ? "" : "s"}`;

/** Spelled out as the deck writes it: "20 minutes", "1 hour", "1 hour 30 minutes". */
export const formatAppointmentLength = (minutes: number): string => {
  const hours = Math.floor(minutes / 60);
  const rest = minutes % 60;
  if (hours === 0) return plural(rest, "minute");
  return rest === 0 ? plural(hours, "hour") : `${plural(hours, "hour")} ${plural(rest, "minute")}`;
};

/** A time line with the visit's length after it, or the time alone when the length is unknown. */
export const withAppointmentLength = (
  timeLabel: string,
  appointment: Pick<Appointment, "minutesDuration" | "start" | "end">,
): string => {
  const minutes = appointmentLengthMinutes(appointment);
  return minutes === undefined ? timeLabel : `${timeLabel} · ${formatAppointmentLength(minutes)}`;
};