import angular from 'angular'
import _ from 'lodash'
import { DateTime } from 'luxon'

angular.module('app').factory('dateTimeZoneFactory', function dateTimeZoneFactory() {

	const timeZones = [
		{ value: -12, zone: 'IDLW - Internation Date Line West', display: 'IDLW' },
		{ value: -11, zone: 'SST - Samoa Standard Time', display: 'SST' },
		{ value: -10, zone: 'HST - Hawaiian Standard Time', display: 'HST' },
		{ value: -9, zone: 'AKST - Alaska Standard Time', display: 'AKST' },
		{ value: -8, zone: 'PT - Pacific Time', display: 'PT' },
		{ value: -7, zone: 'MT - Mountain Time', display: 'MT' },
		{ value: -6, zone: 'CT - Central Time', display: 'CT' },
		{ value: -5, zone: 'ET - Eastern Time', display: 'ET' },
		{ value: -4, zone: 'AST - Atlantic Standard Time', display: 'AST' },
		{ value: -3.5, zone: 'NST - Newfoundland Standard Time', display: 'NST' },
		{ value: -3, zone: 'BRA - Brazil Standard Time', display: 'BRA' },
		{ value: -2, zone: 'FDT - Fernando de Noronha Standard Time (Brazil)', display: 'FDT' },
		{ value: -1, zone: 'CVT - Cape Verde Time', display: 'CVT' },
		{ value: 0, zone: 'GMT - Greenwich Mean Time', display: 'GMT' },
		{ value: 1, zone: 'CET - Central Europe Time (Madrid, Paris)', display: 'CET' },
		{ value: 2, zone: 'EET - Eastern European Time (South Africa)', display: 'EET' },
		{ value: 3, zone: 'EAT - East Africa Time', display: 'EAT' },
		{ value: 3.5, zone: 'IRST - Iran Standard Time', display: 'IRST' },
		{ value: 4, zone: 'MSK - Moscow Time', display: 'MSK' },
		{ value: 4.5, zone: 'AFT - Afghanistan Time', display: 'AFT' },
		{ value: 5, zone: 'PKT - Pakistan Standard Time', display: 'PKT' },
		{ value: 5.5, zone: 'IST - India Standard Time', display: 'IST' },
		{ value: 5.75, zone: 'NPT - Nepal Time', display: 'NPT' },
		{ value: 6, zone: 'BST - Bangladesh Standard Time', display: 'BST' },
		{ value: 7, zone: 'ICT - Indochina Time (Bangkok, Hanoi)', display: 'ICT' },
		{ value: 8, zone: 'HKT - China Standard Time (Beijing, Hong Kong)', display: 'HKT' },
		{ value: 9, zone: 'JST - Japan Standard Time', display: 'JST' },
		{ value: 9.5, zone: 'ACST - Australian Central Standard Time', display: 'ACST' },
		{ value: 10, zone: 'AEST - Australian Eastern Standard Time', display: 'AEST' },
		{ value: 11, zone: 'SBT - Solomon Islands Time', display: 'SBT' },
		{ value: 12, zone: 'NZST - New Zealand Standard Time', display: 'NZST' }
	]

	// using string validate on the datepicker gives us more control with luxon's parsing
	const validDateFormats = [
		// Full month name formats (MMMM)
		'd-MMMM-yyyy',
		'd-MM-yyyy',
		'd-M-yyyy',
		'MMMM-d-yyyy',
		'MM-d-yyyy',
		'M-d-yyyy',
		'd/MMMM/yyyy',
		'd/MM/yyyy',
		'd/M/yyyy',
		'MMMM/d/yyyy',
		'MM/d/yyyy',
		'M/d/yyyy',
		'd.MMMM.yyyy',
		'd.MM.yyyy',
		'd.M.yyyy',
		'MMMM.d.yyyy',
		'MM.d.yyyy',
		'M.d.yyyy',
		'd-MMMM-yy',
		'd-MM-yy',
		'd-M-yy',
		'MMMM-d-yy',
		'MM-d-yy',
		'M-d-yy',
		'd/MMMM/yy',
		'd/MM/yy',
		'd/M/yy',
		'MMMM/d/yy',
		'MM/d/yy',
		'M/d/yy',
		'd.MMMM.yy',
		'd.MM.yy',
		'd.M.yy',
		'MMMM.d.yy',
		'MM.d.yy',
		'M.d.yy',
		// Abbreviated month name formats (MMM)
		'd-MMM-yyyy',
		'MMM-d-yyyy',
		'd/MMM/yyyy',
		'MMM/d/yyyy',
		'd.MMM.yyyy',
		'MMM.d.yyyy',
		'd-MMM-yy',
		'MMM-d-yy',
		'd/MMM/yy',
		'MMM/d/yy',
		'd.MMM.yy',
		'MMM.d.yy'
		]


	return {

		timeZones,

		validDateFormats,

		getTimeZone(dateTime) {

			if (dateTime && dateTime.isValid) {

				// Get the timezone offset in hours and adjust the sign
				let zoneOffset = dateTime.offset / 60

				// consider a shift for DST
				// create a fresh DateTime to check if DST is in effect
				const isDST = DateTime.fromISO(dateTime.toISO()).isInDST

				// at this point zoneOffset is our true offset from UTC 0
				// so for example if we are UTC -6 AND we are DST, then our dateTime is really "Mountain Time" which is -7
				// during the winter but is -6 during DST -- if we want to consistently show the label 'MST' for this date
				// we need to select -7 although the offset is -6 (or subtracting 1 from our actual utc output)
				zoneOffset = (isDST) ? zoneOffset - 1 : zoneOffset

				// NOTE: The above DST adjustment is somewhat arbitrary.
				// isDST() cannot be globally accurate as it works purely off a date and an offset.
				// No actual timezone information is used except for assumptions made from the users current locale.
				// Recommendation to switch to luxon's timezone handling in the future.

				return this.getTimeZoneByOffset(zoneOffset)
			}

			return null
		},

		getTimeZoneByOffset(offset) {

			return _.find(timeZones, { value: offset })
		}
	}
})