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

export function parseDate(input = new Date()) {
	if (input instanceof Date) {
		return new Date(input.getTime())
	}

	if (typeof input === 'number') {
		return new Date(input)
	}

	if (typeof input === 'string') {
		if (/^\d{4}-\d{2}-\d{2}$/.test(input)) {
			const [year, month, day] = input.split('-').map(Number)
			return new Date(year, month - 1, day)
		}

		if (/^\d{4}-\d{2}$/.test(input)) {
			const [year, month] = input.split('-').map(Number)
			return new Date(year, month - 1, 1)
		}

		return new Date(input.replace(/-/g, '/'))
	}

	return new Date()
}

export function toDateKey(input = new Date()) {
	const date = parseDate(input)
	return `${date.getFullYear()}-${pad(date.getMonth() + 1)}-${pad(date.getDate())}`
}

export function toMonthKey(input = new Date()) {
	const date = parseDate(input)
	return `${date.getFullYear()}-${pad(date.getMonth() + 1)}`
}

export function formatDateLabel(value) {
	if (!value) {
		return ''
	}

	const date = parseDate(value)
	const weekMap = ['周日', '周一', '周二', '周三', '周四', '周五', '周六']
	return `${date.getMonth() + 1}月${date.getDate()}日 ${weekMap[date.getDay()]}`
}

export function formatMonthLabel(monthKey) {
	if (!monthKey) {
		return ''
	}

	const [year, month] = monthKey.split('-')
	return `${year}年${Number(month)}月`
}

export function isSameMonth(dateValue, monthKey) {
	return toMonthKey(dateValue) === monthKey
}

export function getMonthDays(monthKey) {
	const [year, month] = monthKey.split('-').map(Number)
	return new Date(year, month, 0).getDate()
}

export function getDaysLeftInMonth(monthKey) {
	const today = new Date()
	if (toMonthKey(today) !== monthKey) {
		return getMonthDays(monthKey)
	}

	return getMonthDays(monthKey) - today.getDate() + 1
}

export function getRecentDateKeys(days, endDate = new Date()) {
	const result = []
	const end = parseDate(endDate)

	for (let index = days - 1; index >= 0; index -= 1) {
		const current = new Date(end)
		current.setDate(end.getDate() - index)
		result.push(toDateKey(current))
	}

	return result
}

export function getMonthSeries(length, endMonthKey = toMonthKey()) {
	const [year, month] = endMonthKey.split('-').map(Number)
	const cursor = new Date(year, month - 1, 1)
	const result = []

	for (let index = length - 1; index >= 0; index -= 1) {
		const current = new Date(cursor)
		current.setMonth(cursor.getMonth() - index)
		result.push(toMonthKey(current))
	}

	return result
}