const isOvernight = (shift) => shift.end_time <= shift.start_time

const nextDay = (dateStr) => {
    const date = new Date(`${dateStr}T00:00:00`)
    date.setDate(date.getDate() + 1)
    return date.toISOString().slice(0, 10)
}

const extendPastMidnight = (time) => {
    const [hours, minutes] = time.split(':')
    return `${parseInt(hours, 10) + 24}:${minutes}`
}

export function buildShiftEvent(shift, overrides = {}) {
    const base = {
        id: String(shift.id),
        extendedProps: { shift },
        ...overrides,
    }

    if (shift.date_raw) {
        const endDate = isOvernight(shift) ? nextDay(shift.date_raw) : shift.date_raw
        return {
            ...base,
            start: `${shift.date_raw}T${shift.start_time}`,
            end: `${endDate}T${shift.end_time}`,
        }
    }

    return {
        ...base,
        daysOfWeek: [shift.day_index],
        startTime: shift.start_time,
        endTime: isOvernight(shift) ? extendPastMidnight(shift.end_time) : shift.end_time,
    }
}

const WEEKDAY_NAMES = {
    6: 'شنبه',
    0: 'یکشنبه',
    1: 'دوشنبه',
    2: 'سه‌شنبه',
    3: 'چهارشنبه',
    4: 'پنج‌شنبه',
    5: 'جمعه',
}

export function weekdayName(dayIndex) {
    return WEEKDAY_NAMES[dayIndex] ?? null
}

export function formatJalaliDay(date) {
    return new Intl.DateTimeFormat('fa-IR', { day: 'numeric', month: 'short' }).format(date)
}

export function formatJalaliRange(start, end) {
    const formatter = new Intl.DateTimeFormat('fa-IR', { day: 'numeric', month: 'long', year: 'numeric' })
    const inclusiveEnd = new Date(end.getTime() - 1)
    return `${formatter.format(start)} تا ${formatter.format(inclusiveEnd)}`
}