Auswahlfeld Termin: Formular-Selektor Workaround

import setIsoDay from 'date-fns/set_iso_day';
import addWeeks from 'date-fns/add_weeks';
import setHours from 'date-fns/set_hours';
import addHours from 'date-fns/add_hours';
import setMinutes from 'date-fns/set_minutes';
import compareDesc from 'date-fns/compare_desc';

/**
 * Time slot string
 *
 * example: '4-08:00/11:00'
 * format: {weekDay}-{timeStart}/{timeEnd}
 * format date-fns: E-HH:mm/HH:mm
 * format PHP 5.1: N-H:i/H:i
 * weekDay: 1=monday, 7=saturday
 */
export const TIME_SLOT_REGEX = /^([1-7])[-](0[0-9]|1[0-9]|2[0-3])[:]([0-5][0-9])[/](0[0-9]|1[0-9]|2[0-3])[:]([0-5][0-9])$/;

export function parseTimeSlot(timeSlotString) {
  if (TIME_SLOT_REGEX.test(timeSlotString)) {
    const [
      ,
      day,
      startHours,
      startMinutes,
      endHours,
      endMinutes,
    ] = TIME_SLOT_REGEX.exec(timeSlotString);

    return {
      day: Number(day),
      startHours: Number(startHours),
      startMinutes: Number(startMinutes),
      endHours: Number(endHours),
      endMinutes: Number(endMinutes),
    };
  }

  return null;
}

export function getAppointment({ timeSlot, weekOffset, bookDate }) {
  const startDate = addWeeks(
    setIsoDay(
      setHours(
        setMinutes(bookDate, timeSlot.startMinutes),
        timeSlot.startHours,
      ),
      timeSlot.day,
    ),
    weekOffset,
  );

  const endDate = addWeeks(
    setIsoDay(
      setHours(
        setMinutes(bookDate, timeSlot.endMinutes),
        timeSlot.endHours,
      ),
      timeSlot.day,
    ),
    weekOffset,
  );

  return {
    startDate,
    endDate,
  };
}

function getNextAppointments(params, weekOffset = 0, prevAppointments = []) {
  const {
    timeSlots,
    count,
    hoursAhead,
    bookDate,
  } = params;

  const appointments = [...prevAppointments];

  const timeSlotCount = timeSlots.length;
  const aheadBookDate = addHours(bookDate, hoursAhead);

  for (let i = 0; i < timeSlotCount; i += 1) {
    const timeSlot = timeSlots[i];

    const appointment = getAppointment({
      timeSlot,
      weekOffset,
      bookDate,
    });

    const isAppointmentAvailable = compareDesc(aheadBookDate, appointment.startDate) >= 0;

    if (isAppointmentAvailable) {
      appointments.push(appointment);
    }

    if (appointments.length >= count) {
      break;
    }
  }

  /**
   * Repeat search in the next week only if:
   *
   * (1) we have not found the required number of appointments
   * AND
   * (2) we have not reached the recursion limit (two weeks with empty results)
   */
  if (appointments.length < count && weekOffset <= count) {
    return getNextAppointments(params, weekOffset + 1, appointments);
  }

  return appointments;
}

export default function getAppointments(
  {
    timeSlotStrings,
    count,
    hoursAhead,
  },
  bookDate = new Date(),
) {
  const timeSlots = timeSlotStrings.reduce(
    (prevTimeSlots, timeSlotString) => {
      const timeSlot = parseTimeSlot(timeSlotString);

      if (!timeSlot) {
        return prevTimeSlots;
      }

      return [
        ...prevTimeSlots,
        timeSlot,
      ];
    },
    [],
  );

  if (!timeSlots.length) {
    return null;
  }

  return getNextAppointments({
    timeSlots,
    count,
    hoursAhead,
    bookDate,
  });
}