package main

import (
	"fmt"
	"time"
)

// https://yourbasic.org/golang/time-change-convert-location-timezone/
// https://sebest.github.io/post/create-a-small-docker-image-for-a-golang-binary/
// https://github.com/FKSE/docker-golang-base
// tar cfz zoneinfo.tar.gz /usr/share/zoneinfo
// git clone https://github.com/eggert/tz
// grep '^Rule' -r tz/ | cut -f8-10 | egrep -iv 'Rule|SAVE'
// egrep '\s0:30' -r tz/
func main() {
	// blacklist "", "Local"
	// UTC to TZ should always be correct
	// TZ to UTC may not be correct
	now := time.Now()
	fmt.Println("Now", now.Format(time.RFC3339))
	loc, err := time.LoadLocation("America/Phoenix")
	if nil != err {
		panic(err)
	}
	fmt.Println("Loc", now.In(loc))

	/* boundary checks */
	CheckInput([]int{2019, 11, 10,
		01, 02, 56, 0})
	CheckInput([]int{2019, 11, 10,
		01, 02, 60, 0})
	CheckInput([]int{2019, 11, 10,
		01, 60, 59, 0})
	CheckInput([]int{2019, 11, 10,
		24, 59, 59, 0})
	CheckInput([]int{2019, 11, 10,
		25, 59, 59, 0})
	CheckInput([]int{2019, 11, 10,
		23, 59, 59, 0})
	CheckInput([]int{2019, 11, 31,
		23, 0, 0, 0})

	/* funky times */
	tz := "America/Denver"
	fmt.Println("funky")
	CheckInput2([]int{2019, 3, 10,
		01, 59, 00, 0}, tz)
	CheckInput2([]int{2019, 3, 10,
		02, 00, 00, 0}, tz)
	CheckInput2([]int{2019, 3, 10,
		02, 01, 00, 0}, tz)
	CheckInput2([]int{2019, 3, 10,
		02, 59, 00, 0}, tz)
	CheckInput2([]int{2019, 3, 10,
		03, 00, 00, 0}, tz)
	CheckInput2([]int{2019, 3, 10,
		03, 01, 00, 0}, tz)
	CheckInput2([]int{2019, 11, 03,
		0, 59, 00, 0}, tz)
	CheckInput2([]int{2019, 11, 03,
		01, 59, 00, 0}, tz)
	CheckInput2([]int{2019, 11, 03,
		02, 00, 00, 0}, tz)
	CheckInput2([]int{2019, 11, 03,
		02, 01, 00, 0}, tz)
	CheckInput2([]int{2019, 11, 03,
		02, 59, 00, 0}, tz)
	CheckInput2([]int{2019, 11, 03,
		03, 00, 00, 0}, tz)
	CheckInput2([]int{2019, 11, 03,
		03, 01, 00, 0}, tz)
	CheckInput2([]int{2019, 11, 03,
		04, 01, 00, 0}, tz)
	CheckInput2([]int{2019, 11, 03,
		05, 01, 00, 0}, tz)
}

func CheckInput2(st []int, tzstr string) {
	m := time.Month(st[1])
	tz, err := time.LoadLocation(tzstr)
	if nil != err {
		fmt.Println("screwed the pooch")
		return
	}

	// Does the time exist
	t1 := time.Date(st[0], m, st[2], st[3], st[4], st[5], st[6], tz)
	if st[5] != t1.Second() {
		fmt.Println("Bad Second", st, t1)
		return
	}
	if st[4] != t1.Minute() {
		fmt.Println("Bad Minute", st, t1.Minute())
		return
	}
	if st[3] != t1.Hour() {
		fmt.Println("Bad Hour", st, t1)
		return
	}
	if st[2] != t1.Day() {
		fmt.Println("Bad Day of Month", st, t1)
		return
	}
	if st[1] != int(t1.Month()) {
		fmt.Println("Bad Month", st, t1)
		return
	}
	if st[0] != t1.Year() {
		fmt.Println("Bad Year", st, t1)
		return
	}

	// Does the time exist twice?
	// (if I change the time in UTC, do I still get the same time)
	// Note: Some timezones change by half or quarter hour
	//       However, it seems that DST always changes by one or two whole hours
	// Oh, and then there's Luthuania...
	// Rule	LH	2008	max	-	Oct	Sun>=1	2:00	0:30	-
	//
	// https://en.wikipedia.org/wiki/Daylight_saving_time_by_country
	// https://en.wikipedia.org/wiki/Winter_time_(clock_lag)
	// https://en.wikipedia.org/wiki/Summer_time_in_Europe
	// https://en.wikipedia.org/wiki/Daylight_saving_time_in_the_Americas
	// If I change the time iadd or subtract time in UTC, do I see the same difference in TZ?
	u1 := t1.UTC()
	// A better way to do this would probably be to parse the timezone database, but... yeah...
	for _, n := range []int{ /*-120, -60,*/ 30, 60, 120} {
		t2 := time.Date(st[0], m, st[2], st[3], st[4]+n, st[5], st[6], tz)
		u2 := t2.UTC()
		if u1.Equal(u2) {
			fmt.Println("Ambiguous Time")
			fmt.Printf("%s, %s, %+d\n", t1, u1, n)
			fmt.Printf("%s, %s, %+d\n", t2, u2, n)
			return
		}
	}
	//ta :=
}

func CheckInput(st []int) {
	m := time.Month(st[1])
	t1 := time.Date(st[0], m, st[2], st[3], st[4], st[5], st[6], time.UTC)
	if st[5] != t1.Second() {
		fmt.Println("Bad Second", st)
		return
	}
	if st[4] != t1.Minute() {
		fmt.Println("Bad Minute", st, t1.Minute())
		return
	}
	if st[3] != t1.Hour() {
		fmt.Println("Bad Hour", st)
		return
	}
	if st[2] != t1.Day() {
		fmt.Println("Bad Day of Month", st)
		return
	}
	if st[1] != int(t1.Month()) {
		fmt.Println("Bad Month", st)
		return
	}
	if st[0] != t1.Year() {
		fmt.Println("Bad Year", st)
		return
	}
}

/*

//////
////// 9:01 twice
//////

var d = new Date("3/10/2019, 01:59:00");
console.log("tzUTC:" + tzUTC(d, 'America/Denver'));
// tzUTC:Sun, 10 Mar 2019 08:59:00 GMT

var d = new Date("3/10/2019, 02:01:00");
console.log("tzUTC:" + tzUTC(d, 'America/Denver'));
// tzUTC:Sun, 10 Mar 2019 09:01:00 GMT

var d = new Date("3/10/2019, 02:59:00");
console.log("tzUTC:" + tzUTC(d, 'America/Denver'));
// tzUTC:Sun, 10 Mar 2019 09:59:00 GMT

var d = new Date("3/10/2019, 03:01:00");
console.log("tzUTC:" + tzUTC(d, 'America/Denver'));
// tzUTC:Sun, 10 Mar 2019 09:01:00 GMT

//////
////// 8:01 never
//////

var d = new Date("11/03/2019, 01:59:00");
console.log("tzUTC:" + tzUTC(d, 'America/Denver'));
// tzUTC:Sun, 03 Nov 2019 07:59:00 GMT

var d = new Date("11/03/2019, 02:01:00");
console.log("tzUTC:" + tzUTC(d, 'America/Denver'));
// tzUTC:Sun, 03 Nov 2019 09:01:00 GMT

var d = new Date("11/03/2019, 02:59:00");
console.log("tzUTC:" + tzUTC(d, 'America/Denver'));
// tzUTC:Sun, 03 Nov 2019 09:59:00 GMT

var d = new Date("11/03/2019, 03:01:00");
console.log("tzUTC:" + tzUTC(d, 'America/Denver'));
tzUTC:Sun, 03 Nov 2019 10:01:00 GMT

*/