Tick at specific times everyday

tick_at_time.go

package main

import (
	"errors"
	"strconv"
	"strings"
	"time"
)

var (
	ErrTimeFormat = errors.New("time format error")
)

// Runs everyday at a specified time
// at examples: "10:30", "15:22"
func NewTickAtTime(at string) (<-chan time.Time, error) {
	hour, min, err := formatTime(at)
	if err != nil {
		return nil, err
	}

	tickChan := make(chan time.Time)
	// save atTime start as duration from midnight
	atTime := time.Duration(hour)*time.Hour + time.Duration(min)*time.Minute
	now := time.Now()

	firstTickAt := getDate(now).Add(atTime)
	if firstTickAt.Before(now) {
		firstTickAt = firstTickAt.Add(time.Hour * 24)
	}

	time.AfterFunc(time.Until(firstTickAt), func() {
		tickChan <- time.Now()
		// Use NewTicker and return it if you need to stop the ticker eventually.
		for tick := range time.Tick(time.Hour * 24) {
			tickChan <- tick
		}
	})

	return tickChan, nil
}

func getDate(t time.Time) time.Time {
	return time.Date(t.Year(), t.Month(), t.Day(), 0, 0, 0, 0, nil)
}

func formatTime(t string) (hour, min int, err error) {
	ts := strings.Split(t, ":")
	if len(ts) != 2 {
		return 0, 0, ErrTimeFormat
	}

	if hour, err = strconv.Atoi(ts[0]); err != nil {
		return 0, 0, err
	}
	if min, err = strconv.Atoi(ts[1]); err != nil {
		return 0, 0, err
	}

	if hour < 0 || hour > 23 || min < 0 || min > 59 {
		return 0, 0, ErrTimeFormat
	}

	return hour, min, nil
}