webtools/cmds/clocks/main.go

//go:build js

package main

import (
	"log"
	"time"

	_ "time/tzdata"
)

func main() {
	melTime, err := time.LoadLocation("Australia/Melbourne")
	if err != nil {
		log.Fatal(err)
	}

	sg, err := time.LoadLocation("Asia/Singapore")
	if err != nil {
		log.Fatal(err)
	}

	nyc, err := time.LoadLocation("America/New_York")
	if err != nil {
		log.Fatal(err)
	}

	la, err := time.LoadLocation("America/Los_Angeles")
	if err != nil {
		log.Fatal(err)
	}

	utc := time.UTC

	clocks := []clock{
		{
			name:     "UTC",
			loc:      utc,
			elements: findClockElements("utc"),
		},
		{
			name:     "Australia/Melbourne",
			loc:      melTime,
			elements: findClockElements("mel"),
		},
		{
			name:     "Asia/Singapore",
			loc:      sg,
			elements: findClockElements("sg"),
		},
		{
			name:     "America/New_York",
			loc:      nyc,
			elements: findClockElements("nyc"),
		},
		{
			name:     "America/Los_Angeles",
			loc:      la,
			elements: findClockElements("la"),
		},
	}

	updateClocks(clocks)
	go startClockUpdater(clocks)

	<-make(chan struct{})
}

func startClockUpdater(clocks []clock) {
	for range time.Tick(1 * time.Second) {
		updateClocks(clocks)
	}
}

func updateClocks(clocks []clock) {
	n := time.Now()
	for _, c := range clocks {
		updateClock(n, c)
	}
}

func updateClock(t time.Time, clk clock) {
	lt := t.In(clk.loc)
	clk.elements.locationDiv.Set("innerText", clk.name)
	clk.elements.dateDiv.Set("innerText", lt.Format("02 Jan 2006"))
	clk.elements.timeDiv.Set("innerText", lt.Format("15:04:05"))
}