export function preferredScheduleSemester(semesters, date) {
    const items = (semesters || [])
        .filter(semester => semester?.startDate && semester?.endDate);
    const current = items.find(semester =>
        semester.startDate <= date && semester.endDate >= date
    );
    if (current) return current;

    const upcoming = items
        .filter(semester => semester.startDate > date)
        .sort((first, second) => first.startDate.localeCompare(second.startDate));
    if (upcoming.length) return upcoming[0];

    return items
        .filter(semester => semester.endDate < date)
        .sort((first, second) => second.endDate.localeCompare(first.endDate))[0] || null;
}

export function defaultSchedulePeriod(semesters, date, durationDays = 14) {
    const semester = preferredScheduleSemester(semesters, date);
    const startDate = semester && (date < semester.startDate || date > semester.endDate)
        ? semester.startDate
        : date;
    const calculatedEnd = addIsoDays(startDate, Math.max(1, durationDays) - 1);
    return {
        semester,
        startDate,
        endDate: semester && calculatedEnd > semester.endDate
            ? semester.endDate
            : calculatedEnd
    };
}

function addIsoDays(value, days) {
    const [year, month, day] = String(value).split('-').map(Number);
    const date = new Date(year, month - 1, day);
    date.setDate(date.getDate() + days);
    return [
        date.getFullYear(),
        String(date.getMonth() + 1).padStart(2, '0'),
        String(date.getDate()).padStart(2, '0')
    ].join('-');
}