/**
 * Human readable elapsed or remaining time (example: 3 minutes ago)
 * @author https://github.com/victornpb
 * @see https://stackoverflow.com/a/67338038/938822
 */
export function ago(
	/** A Date object, timestamp or string parsable with Date.parse() */
	date: string | number | Date,
	/** A Date object, timestamp or string parsable with Date.parse() */
	nowDate: string | number | Date = Date.now(),
	/** A Intl formater */
	rft: Intl.RelativeTimeFormat = new Intl.RelativeTimeFormat(undefined, { numeric: 'auto' })
): string {
	const SECOND = 1000
	const MINUTE = 60 * SECOND
	const HOUR = 60 * MINUTE
	const DAY = 24 * HOUR
	const WEEK = 7 * DAY
	const MONTH = 30 * DAY
	const YEAR = 365 * DAY
	const intervals = [
		{ ge: YEAR, divisor: YEAR, unit: 'year' },
		{ ge: MONTH, divisor: MONTH, unit: 'month' },
		{ ge: WEEK, divisor: WEEK, unit: 'week' },
		{ ge: DAY, divisor: DAY, unit: 'day' },
		{ ge: HOUR, divisor: HOUR, unit: 'hour' },
		{ ge: MINUTE, divisor: MINUTE, unit: 'minute' },
		{ ge: 30 * SECOND, divisor: SECOND, unit: 'seconds' },
		{ ge: 0, divisor: 1, text: 'just now' },
	]
	const now = typeof nowDate === 'object' ? nowDate.getTime() : new Date(nowDate).getTime()
	const diff = now - (typeof date === 'object' ? date : new Date(date)).getTime()
	const diffAbs = Math.abs(diff)
	for (const interval of intervals) {
		if (diffAbs >= interval.ge) {
			const x = Math.round(Math.abs(diff) / interval.divisor)
			const isFuture = diff < 0
			if (
				typeof navigator !== 'undefined' &&
				(navigator.language === 'zh-CN' || navigator.language === 'zh')
			) {
				return chs_format(x, isFuture, interval.unit as Unit)
			}
			return interval.unit ? rft.format(isFuture ? x : -x, interval.unit as Unit) : interval.text
		}
	}
}

type Unit =
	| 'second'
	| 'seconds'
	| 'minute'
	| 'minutes'
	| 'hour'
	| 'hours'
	| 'day'
	| 'days'
	| 'week'
	| 'weeks'
	| 'month'
	| 'months'
	| 'year'
	| 'years'

type ChsUnit = '秒' | '分' | '小时' | '天' | '周' | '月' | '年'

/**
 * Convert unit to chinese unit
 * @param unit
 * @returns {ChsUnit}
 */
function convertUnitToChsUnit(unit: Unit): ChsUnit {
	switch (unit) {
		case 'second':
		case 'seconds':
			return '秒'
		case 'minute':
		case 'minutes':
			return '分'
		case 'hour':
		case 'hours':
			return '小时'
		case 'day':
		case 'days':
			return '天'
		case 'week':
		case 'weeks':
			return '周'
		case 'month':
		case 'months':
			return '月'
		case 'year':
		case 'years':
			return '年'
	}
}

/**
 * The default converter provided by js does not conform to Chinese typography.
 * @param value date value
 * @param isFuture
 * @param unit
 * @returns {string}
 */
function chs_format(value: number, isFuture: boolean, unit: Unit): string {
	const chsUnit = convertUnitToChsUnit(unit)
	let quantifier = ''
	switch (chsUnit) {
		case '月':
		case '小时':
			quantifier = '个'
	}
	return `${value} ${quantifier}${chsUnit}${isFuture ? '后' : '前'}`
}