gistfile1.go

// http://play.golang.org/p/i5L__nrXyA
package main

import (
	"fmt"
	"log"
	"time"
)

// change this to your local time zone name.
const LOCAL_TZ = "America/Anchorage"

// if this is running on appengine, or on a system
// that can't load a tz database, also change this
// to match the utc offset for the tz name above
const LOCAL_OFFSET = -9

// change this to show more or fewer checkpoints
const SHOW_CHECKPOINTS = 100

// labels, don't mess with them
const (
	CHECKPOINT  = "checkpoint"
	CYCLE       = "cycle"
	TIME_FORMAT = "02-Jan-2006 15:04 MST"
)

var (
	// reference dates
	REF_CHECKPOINT = time.Date(2014, time.March, 3, 22, 0, 0, 0, time.UTC)
	REF_CYCLE      = REF_CHECKPOINT.Add(time.Hour * 85)
)

func main() {
	location, err := time.LoadLocation(LOCAL_TZ)
	if true || err != nil {
		log.Printf("couldn't load timezone " + LOCAL_TZ + "\n")
		location = time.FixedZone("local", LOCAL_OFFSET*60*60)
	}

	fmt.Printf("reference checkpoint (utc):   %v\n",
		REF_CHECKPOINT.Format(TIME_FORMAT))
	fmt.Printf("reference checkpoint (local): %v\n",
		REF_CHECKPOINT.In(location).Format(TIME_FORMAT))
	fmt.Printf("reference cycle (utc):        %v\n",
		REF_CYCLE.Format(TIME_FORMAT))
	fmt.Printf("reference cycle (local):      %v\n\n",
		REF_CYCLE.In(location).Format(TIME_FORMAT))

	var (
		checkpoint = REF_CHECKPOINT
		label      string
		now        = time.Now()
		offset     time.Duration
	)

	for i := 0; i < SHOW_CHECKPOINTS; {
		checkpoint = checkpoint.Add(5 * time.Hour)
		if checkpoint.Before(now) {
			continue
		}
		label = CHECKPOINT
		offset = checkpoint.Sub(REF_CYCLE)
		if offset.Hours() == 0 || int(offset.Hours())%125 == 0 {
			label = CYCLE
		}

		fmt.Printf("%10s (utc, local): %v, %v\n",
			label,
			checkpoint.Format(TIME_FORMAT),
			checkpoint.In(location).Format(TIME_FORMAT),
		)
		i += 1
	}
}