import type { Context } from "../index.js"

const units = {
	year: 24 * 60 * 60 * 1000 * 365,
	month: 24 * 60 * 60 * 1000 * 365 / 12,
	day: 24 * 60 * 60 * 1000,
	hour: 60 * 60 * 1000,
	minute: 60 * 1000,
	second: 1000
} as const

const rtf = new Intl.RelativeTimeFormat('en', { numeric: 'auto' })

export function RelativeTime({ timestamp }: Context): { relativeTime: string | null } {
	const elapsed = timestamp.getTime() - new Date().getTime()

	for (const u in units)
		if (Math.abs(elapsed) > units[u as keyof typeof units] || u == 'second')
			return {
				relativeTime: rtf.format(Math.round(elapsed / units[u as keyof typeof units]), u as keyof typeof units)
			}

	return { relativeTime: null }
}