export const WEEK_LENGTH_DAYS = 7;

export function startOfWeek(date) {
    const copy = new Date(date.getFullYear(), date.getMonth(), date.getDate());
    const day = copy.getDay() || 7;
    copy.setDate(copy.getDate() - day + 1);
    return copy;
}

export function parseIsoDate(value) {
    const [year, month, day] = String(value || '').split('-').map(Number);
    return year && month && day ? new Date(year, month - 1, day) : new Date();
}

export function addDays(date, days) {
    const copy = new Date(date);
    copy.setDate(copy.getDate() + days);
    return copy;
}

export function toIsoDate(date) {
    return `${date.getFullYear()}-${String(date.getMonth() + 1).padStart(2, '0')}-${String(date.getDate()).padStart(2, '0')}`;
}

export function formatDate(date) {
    return date.toLocaleDateString('ru-RU', { day: '2-digit', month: '2-digit', year: 'numeric' });
}

export function formatIsoDate(value) {
    const [year, month, day] = String(value || '').split('-');
    return year && month && day ? `${day}.${month}.${year}` : '—';
}

export function dayName(date) {
    const value = date.toLocaleDateString('ru-RU', { weekday: 'long' });
    return value.charAt(0).toUpperCase() + value.slice(1);
}

export function trimTime(value) {
    return String(value || '').slice(0, 5);
}

export function weekDates(weekStart) {
    return Array.from({ length: WEEK_LENGTH_DAYS }, (_, index) => addDays(weekStart, index));
}

export function weekEndIso(weekStart) {
    return toIsoDate(addDays(weekStart, WEEK_LENGTH_DAYS - 1));
}

export function formatWeekLabel(weekStart) {
    return `${formatDate(weekStart)} - ${formatDate(addDays(weekStart, WEEK_LENGTH_DAYS - 1))}`;
}