import { locale, t } from '@/i18n'

const MONTHS = ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec']
const MINUTE_MS = 60 * 1000
const HOUR_MS = 60 * MINUTE_MS
const ISO_DAY = /^(\d{4})-(\d{2})-(\d{2})$/

export interface DayGroup<T> {
	key: string
	label: string
	items: T[]
}

function pad(value: number) {
	return String(value).padStart(2, '0')
}

function monthShort(date: Date, timeZone?: 'UTC') {
	if (locale.value === 'fr') {
		return new Intl.DateTimeFormat('fr', {
			month: 'short',
			timeZone,
		}).format(date)
	}
	return MONTHS[timeZone ? date.getUTCMonth() : date.getMonth()]
}

export function formatAbsoluteDay(date: Date, timeZone?: 'UTC') {
	const day = timeZone ? date.getUTCDate() : date.getDate()
	const year = timeZone ? date.getUTCFullYear() : date.getFullYear()
	return `${day} ${monthShort(date, timeZone)} ${year}`
}

function clock(date: Date, withSeconds: boolean, utc: boolean) {
	const hours = utc ? date.getUTCHours() : date.getHours()
	const minutes = utc ? date.getUTCMinutes() : date.getMinutes()
	const seconds = utc ? date.getUTCSeconds() : date.getSeconds()
	const base = `${pad(hours)}:${pad(minutes)}`
	return withSeconds ? `${base}:${pad(seconds)}` : base
}

export function localDayKey(date: Date) {
	return `${date.getFullYear()}-${pad(date.getMonth() + 1)}-${pad(date.getDate())}`
}

function startOfDay(date: Date) {
	return new Date(date.getFullYear(), date.getMonth(), date.getDate())
}

export function dayLabel(iso: string, now: Date = new Date()) {
	const date = new Date(iso)
	const today = startOfDay(now)
	const yesterday = new Date(today.getFullYear(), today.getMonth(), today.getDate() - 1)
	const key = localDayKey(date)
	if (key === localDayKey(today)) return t('Today')
	if (key === localDayKey(yesterday)) return t('Yesterday')
	return formatAbsoluteDay(date)
}

export function whenLabel(iso: string, now: Date = new Date()) {
	const date = new Date(iso)
	if (localDayKey(date) !== localDayKey(now)) return clock(date, false, false)
	const elapsed = Math.max(0, now.getTime() - date.getTime())
	if (elapsed < HOUR_MS) {
		return t('{0} min ago', [Math.max(1, Math.floor(elapsed / MINUTE_MS))])
	}
	return t('{0} h ago', [Math.floor(elapsed / HOUR_MS)])
}

export function recentWhenLabel(iso: string, now: Date = new Date()) {
	const date = new Date(iso)
	const key = localDayKey(date)
	if (key === localDayKey(now)) return whenLabel(iso, now)
	const today = startOfDay(now)
	const yesterday = new Date(today.getFullYear(), today.getMonth(), today.getDate() - 1)
	if (key === localDayKey(yesterday)) return `${t('Yesterday')}, ${clock(date, false, false)}`
	return localDayTime(iso)
}

export function localDayTime(iso: string) {
	const date = new Date(iso)
	return `${formatAbsoluteDay(date)}, ${clock(date, false, false)}`
}

export function fullLocalTime(iso: string) {
	const date = new Date(iso)
	return `${formatAbsoluteDay(date)}, ${clock(date, true, false)}`
}

export function fullUtcTime(iso: string) {
	const date = new Date(iso)
	return `${formatAbsoluteDay(date, 'UTC')}, ${clock(date, true, true)}`
}

export function groupByDay<T extends { created_at: string }>(
	items: T[],
	now: Date = new Date(),
): DayGroup<T>[] {
	const groups: DayGroup<T>[] = []
	for (const item of items) {
		const key = localDayKey(new Date(item.created_at))
		const last = groups[groups.length - 1]
		if (last && last.key === key) {
			last.items.push(item)
			continue
		}
		groups.push({
			key,
			label: dayLabel(item.created_at, now),
			items: [item],
		})
	}
	return groups
}

function parseIsoDay(value: string) {
	const match = ISO_DAY.exec(value)
	if (!match) return null
	return new Date(Number(match[1]), Number(match[2]) - 1, Number(match[3]), 12)
}

export function formatDateRange(from: string, to: string) {
	const start = parseIsoDay(from)
	const end = parseIsoDay(to)
	if (!start || !end) return ''
	const sameYear = start.getFullYear() === end.getFullYear()
	const sameMonth = sameYear && start.getMonth() === end.getMonth()
	if (sameMonth && start.getDate() === end.getDate()) return formatAbsoluteDay(end)
	if (sameMonth) return `${start.getDate()} – ${formatAbsoluteDay(end)}`
	if (sameYear) return `${start.getDate()} ${monthShort(start)} – ${formatAbsoluteDay(end)}`
	return `${formatAbsoluteDay(start)} – ${formatAbsoluteDay(end)}`
}