'use strict'

const {DateTime, IANAZone} = require('luxon')

const timezones = new WeakMap()

// todo: change to `(profile) => (date, time) => {}`
const parseDateTime = (profile, date, time, tzOffset = null, timestamp = false) => {
	const pDate = [date.substr(-8, 4), date.substr(-4, 2), date.substr(-2, 2)]
	if (!pDate[0] || !pDate[1] || !pDate[2]) {
		throw new Error('invalid date format: ' + date)
	}

	const pTime = [time.substr(-6, 2), time.substr(-4, 2), time.substr(-2, 2)]
	if (!pTime[0] || !pTime[1] || !pTime[2]) {
		throw new Error('invalid time format: ' + time)
	}

	const daysOffset = time.length > 6 ? parseInt(time.slice(0, -6)) : 0

	let timezone
	if (timezones.has(profile)) timezone = timezones.get(profile)
	else {
		timezone = new IANAZone(profile.timezone)
		timezones.set(profile, timezone)
	}

	if (tzOffset !== null) {
		// We don't know the timezone, but only the *timezone offset*, which is why we
		// can't use Luxon to process the offset.
		const isoOffset = ('0' + (tzOffset / 60 | 0)).slice(-2) + ('0' + (tzOffset % 60)).slice(-2)
		const isoStr = pDate.join('-') + 'T' + pTime.join(':') + '+' + isoOffset
		return timestamp ? +new Date(isoStr) : isoStr
	} else {
		let dt = DateTime.fromISO(pDate.join('-') + 'T' + pTime.join(':'), {
			locale: profile.locale,
			zone: timezone
		})
		if (daysOffset > 0) dt = dt.plus({days: daysOffset})
		return timestamp ? dt.toMillis() : dt.toISO()
	}
}

module.exports = parseDateTime