Repository: robfig/cron
Branch: master
Commit: bc59245fe10e
Files: 19
Total size: 90.5 KB

Directory structure:
gitextract_s3rbtqli/

├── .gitignore
├── .travis.yml
├── LICENSE
├── README.md
├── chain.go
├── chain_test.go
├── constantdelay.go
├── constantdelay_test.go
├── cron.go
├── cron_test.go
├── doc.go
├── go.mod
├── logger.go
├── option.go
├── option_test.go
├── parser.go
├── parser_test.go
├── spec.go
└── spec_test.go

================================================
FILE CONTENTS
================================================

================================================
FILE: .gitignore
================================================
# Compiled Object files, Static and Dynamic libs (Shared Objects)
*.o
*.a
*.so

# Folders
_obj
_test

# Architecture specific extensions/prefixes
*.[568vq]
[568vq].out

*.cgo1.go
*.cgo2.c
_cgo_defun.c
_cgo_gotypes.go
_cgo_export.*

_testmain.go

*.exe


================================================
FILE: .travis.yml
================================================
language: go


================================================
FILE: LICENSE
================================================
Copyright (C) 2012 Rob Figueiredo
All Rights Reserved.

MIT LICENSE

Permission is hereby granted, free of charge, to any person obtaining a copy of
this software and associated documentation files (the "Software"), to deal in
the Software without restriction, including without limitation the rights to
use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
the Software, and to permit persons to whom the Software is furnished to do so,
subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.


================================================
FILE: README.md
================================================
[![GoDoc](http://godoc.org/github.com/robfig/cron?status.png)](http://godoc.org/github.com/robfig/cron)
[![Build Status](https://travis-ci.org/robfig/cron.svg?branch=master)](https://travis-ci.org/robfig/cron)

# cron

Cron V3 has been released!

To download the specific tagged release, run:
```bash
go get github.com/robfig/cron/v3@v3.0.0
```
Import it in your program as:
```go
import "github.com/robfig/cron/v3"
```
It requires Go 1.11 or later due to usage of Go Modules.

Refer to the documentation here:
http://godoc.org/github.com/robfig/cron

The rest of this document describes the the advances in v3 and a list of
breaking changes for users that wish to upgrade from an earlier version.

## Upgrading to v3 (June 2019)

cron v3 is a major upgrade to the library that addresses all outstanding bugs,
feature requests, and rough edges. It is based on a merge of master which
contains various fixes to issues found over the years and the v2 branch which
contains some backwards-incompatible features like the ability to remove cron
jobs. In addition, v3 adds support for Go Modules, cleans up rough edges like
the timezone support, and fixes a number of bugs.

New features:

- Support for Go modules. Callers must now import this library as
  `github.com/robfig/cron/v3`, instead of `gopkg.in/...`

- Fixed bugs:
  - 0f01e6b parser: fix combining of Dow and Dom (#70)
  - dbf3220 adjust times when rolling the clock forward to handle non-existent midnight (#157)
  - eeecf15 spec_test.go: ensure an error is returned on 0 increment (#144)
  - 70971dc cron.Entries(): update request for snapshot to include a reply channel (#97)
  - 1cba5e6 cron: fix: removing a job causes the next scheduled job to run too late (#206)

- Standard cron spec parsing by default (first field is "minute"), with an easy
  way to opt into the seconds field (quartz-compatible). Although, note that the
  year field (optional in Quartz) is not supported.

- Extensible, key/value logging via an interface that complies with
  the https://github.com/go-logr/logr project.

- The new Chain & JobWrapper types allow you to install "interceptors" to add
  cross-cutting behavior like the following:
  - Recover any panics from jobs
  - Delay a job's execution if the previous run hasn't completed yet
  - Skip a job's execution if the previous run hasn't completed yet
  - Log each job's invocations
  - Notification when jobs are completed

It is backwards incompatible with both v1 and v2. These updates are required:

- The v1 branch accepted an optional seconds field at the beginning of the cron
  spec. This is non-standard and has led to a lot of confusion. The new default
  parser conforms to the standard as described by [the Cron wikipedia page].

  UPDATING: To retain the old behavior, construct your Cron with a custom
  parser:
```go
// Seconds field, required
cron.New(cron.WithSeconds())

// Seconds field, optional
cron.New(cron.WithParser(cron.NewParser(
	cron.SecondOptional | cron.Minute | cron.Hour | cron.Dom | cron.Month | cron.Dow | cron.Descriptor,
)))
```
- The Cron type now accepts functional options on construction rather than the
  previous ad-hoc behavior modification mechanisms (setting a field, calling a setter).

  UPDATING: Code that sets Cron.ErrorLogger or calls Cron.SetLocation must be
  updated to provide those values on construction.

- CRON_TZ is now the recommended way to specify the timezone of a single
  schedule, which is sanctioned by the specification. The legacy "TZ=" prefix
  will continue to be supported since it is unambiguous and easy to do so.

  UPDATING: No update is required.

- By default, cron will no longer recover panics in jobs that it runs.
  Recovering can be surprising (see issue #192) and seems to be at odds with
  typical behavior of libraries. Relatedly, the `cron.WithPanicLogger` option
  has been removed to accommodate the more general JobWrapper type.

  UPDATING: To opt into panic recovery and configure the panic logger:
```go
cron.New(cron.WithChain(
  cron.Recover(logger),  // or use cron.DefaultLogger
))
```
- In adding support for https://github.com/go-logr/logr, `cron.WithVerboseLogger` was
  removed, since it is duplicative with the leveled logging.

  UPDATING: Callers should use `WithLogger` and specify a logger that does not
  discard `Info` logs. For convenience, one is provided that wraps `*log.Logger`:
```go
cron.New(
  cron.WithLogger(cron.VerbosePrintfLogger(logger)))
```

### Background - Cron spec format

There are two cron spec formats in common usage:

- The "standard" cron format, described on [the Cron wikipedia page] and used by
  the cron Linux system utility.

- The cron format used by [the Quartz Scheduler], commonly used for scheduled
  jobs in Java software

[the Cron wikipedia page]: https://en.wikipedia.org/wiki/Cron
[the Quartz Scheduler]: http://www.quartz-scheduler.org/documentation/quartz-2.3.0/tutorials/tutorial-lesson-06.html

The original version of this package included an optional "seconds" field, which
made it incompatible with both of these formats. Now, the "standard" format is
the default format accepted, and the Quartz format is opt-in.


================================================
FILE: chain.go
================================================
package cron

import (
	"fmt"
	"runtime"
	"sync"
	"time"
)

// JobWrapper decorates the given Job with some behavior.
type JobWrapper func(Job) Job

// Chain is a sequence of JobWrappers that decorates submitted jobs with
// cross-cutting behaviors like logging or synchronization.
type Chain struct {
	wrappers []JobWrapper
}

// NewChain returns a Chain consisting of the given JobWrappers.
func NewChain(c ...JobWrapper) Chain {
	return Chain{c}
}

// Then decorates the given job with all JobWrappers in the chain.
//
// This:
//     NewChain(m1, m2, m3).Then(job)
// is equivalent to:
//     m1(m2(m3(job)))
func (c Chain) Then(j Job) Job {
	for i := range c.wrappers {
		j = c.wrappers[len(c.wrappers)-i-1](j)
	}
	return j
}

// Recover panics in wrapped jobs and log them with the provided logger.
func Recover(logger Logger) JobWrapper {
	return func(j Job) Job {
		return FuncJob(func() {
			defer func() {
				if r := recover(); r != nil {
					const size = 64 << 10
					buf := make([]byte, size)
					buf = buf[:runtime.Stack(buf, false)]
					err, ok := r.(error)
					if !ok {
						err = fmt.Errorf("%v", r)
					}
					logger.Error(err, "panic", "stack", "...\n"+string(buf))
				}
			}()
			j.Run()
		})
	}
}

// DelayIfStillRunning serializes jobs, delaying subsequent runs until the
// previous one is complete. Jobs running after a delay of more than a minute
// have the delay logged at Info.
func DelayIfStillRunning(logger Logger) JobWrapper {
	return func(j Job) Job {
		var mu sync.Mutex
		return FuncJob(func() {
			start := time.Now()
			mu.Lock()
			defer mu.Unlock()
			if dur := time.Since(start); dur > time.Minute {
				logger.Info("delay", "duration", dur)
			}
			j.Run()
		})
	}
}

// SkipIfStillRunning skips an invocation of the Job if a previous invocation is
// still running. It logs skips to the given logger at Info level.
func SkipIfStillRunning(logger Logger) JobWrapper {
	return func(j Job) Job {
		var ch = make(chan struct{}, 1)
		ch <- struct{}{}
		return FuncJob(func() {
			select {
			case v := <-ch:
				defer func() { ch <- v }()
				j.Run()
			default:
				logger.Info("skip")
			}
		})
	}
}


================================================
FILE: chain_test.go
================================================
package cron

import (
	"io/ioutil"
	"log"
	"reflect"
	"sync"
	"testing"
	"time"
)

func appendingJob(slice *[]int, value int) Job {
	var m sync.Mutex
	return FuncJob(func() {
		m.Lock()
		*slice = append(*slice, value)
		m.Unlock()
	})
}

func appendingWrapper(slice *[]int, value int) JobWrapper {
	return func(j Job) Job {
		return FuncJob(func() {
			appendingJob(slice, value).Run()
			j.Run()
		})
	}
}

func TestChain(t *testing.T) {
	var nums []int
	var (
		append1 = appendingWrapper(&nums, 1)
		append2 = appendingWrapper(&nums, 2)
		append3 = appendingWrapper(&nums, 3)
		append4 = appendingJob(&nums, 4)
	)
	NewChain(append1, append2, append3).Then(append4).Run()
	if !reflect.DeepEqual(nums, []int{1, 2, 3, 4}) {
		t.Error("unexpected order of calls:", nums)
	}
}

func TestChainRecover(t *testing.T) {
	panickingJob := FuncJob(func() {
		panic("panickingJob panics")
	})

	t.Run("panic exits job by default", func(t *testing.T) {
		defer func() {
			if err := recover(); err == nil {
				t.Errorf("panic expected, but none received")
			}
		}()
		NewChain().Then(panickingJob).
			Run()
	})

	t.Run("Recovering JobWrapper recovers", func(t *testing.T) {
		NewChain(Recover(PrintfLogger(log.New(ioutil.Discard, "", 0)))).
			Then(panickingJob).
			Run()
	})

	t.Run("composed with the *IfStillRunning wrappers", func(t *testing.T) {
		NewChain(Recover(PrintfLogger(log.New(ioutil.Discard, "", 0)))).
			Then(panickingJob).
			Run()
	})
}

type countJob struct {
	m       sync.Mutex
	started int
	done    int
	delay   time.Duration
}

func (j *countJob) Run() {
	j.m.Lock()
	j.started++
	j.m.Unlock()
	time.Sleep(j.delay)
	j.m.Lock()
	j.done++
	j.m.Unlock()
}

func (j *countJob) Started() int {
	defer j.m.Unlock()
	j.m.Lock()
	return j.started
}

func (j *countJob) Done() int {
	defer j.m.Unlock()
	j.m.Lock()
	return j.done
}

func TestChainDelayIfStillRunning(t *testing.T) {

	t.Run("runs immediately", func(t *testing.T) {
		var j countJob
		wrappedJob := NewChain(DelayIfStillRunning(DiscardLogger)).Then(&j)
		go wrappedJob.Run()
		time.Sleep(2 * time.Millisecond) // Give the job 2ms to complete.
		if c := j.Done(); c != 1 {
			t.Errorf("expected job run once, immediately, got %d", c)
		}
	})

	t.Run("second run immediate if first done", func(t *testing.T) {
		var j countJob
		wrappedJob := NewChain(DelayIfStillRunning(DiscardLogger)).Then(&j)
		go func() {
			go wrappedJob.Run()
			time.Sleep(time.Millisecond)
			go wrappedJob.Run()
		}()
		time.Sleep(3 * time.Millisecond) // Give both jobs 3ms to complete.
		if c := j.Done(); c != 2 {
			t.Errorf("expected job run twice, immediately, got %d", c)
		}
	})

	t.Run("second run delayed if first not done", func(t *testing.T) {
		var j countJob
		j.delay = 10 * time.Millisecond
		wrappedJob := NewChain(DelayIfStillRunning(DiscardLogger)).Then(&j)
		go func() {
			go wrappedJob.Run()
			time.Sleep(time.Millisecond)
			go wrappedJob.Run()
		}()

		// After 5ms, the first job is still in progress, and the second job was
		// run but should be waiting for it to finish.
		time.Sleep(5 * time.Millisecond)
		started, done := j.Started(), j.Done()
		if started != 1 || done != 0 {
			t.Error("expected first job started, but not finished, got", started, done)
		}

		// Verify that the second job completes.
		time.Sleep(25 * time.Millisecond)
		started, done = j.Started(), j.Done()
		if started != 2 || done != 2 {
			t.Error("expected both jobs done, got", started, done)
		}
	})

}

func TestChainSkipIfStillRunning(t *testing.T) {

	t.Run("runs immediately", func(t *testing.T) {
		var j countJob
		wrappedJob := NewChain(SkipIfStillRunning(DiscardLogger)).Then(&j)
		go wrappedJob.Run()
		time.Sleep(2 * time.Millisecond) // Give the job 2ms to complete.
		if c := j.Done(); c != 1 {
			t.Errorf("expected job run once, immediately, got %d", c)
		}
	})

	t.Run("second run immediate if first done", func(t *testing.T) {
		var j countJob
		wrappedJob := NewChain(SkipIfStillRunning(DiscardLogger)).Then(&j)
		go func() {
			go wrappedJob.Run()
			time.Sleep(time.Millisecond)
			go wrappedJob.Run()
		}()
		time.Sleep(3 * time.Millisecond) // Give both jobs 3ms to complete.
		if c := j.Done(); c != 2 {
			t.Errorf("expected job run twice, immediately, got %d", c)
		}
	})

	t.Run("second run skipped if first not done", func(t *testing.T) {
		var j countJob
		j.delay = 10 * time.Millisecond
		wrappedJob := NewChain(SkipIfStillRunning(DiscardLogger)).Then(&j)
		go func() {
			go wrappedJob.Run()
			time.Sleep(time.Millisecond)
			go wrappedJob.Run()
		}()

		// After 5ms, the first job is still in progress, and the second job was
		// aleady skipped.
		time.Sleep(5 * time.Millisecond)
		started, done := j.Started(), j.Done()
		if started != 1 || done != 0 {
			t.Error("expected first job started, but not finished, got", started, done)
		}

		// Verify that the first job completes and second does not run.
		time.Sleep(25 * time.Millisecond)
		started, done = j.Started(), j.Done()
		if started != 1 || done != 1 {
			t.Error("expected second job skipped, got", started, done)
		}
	})

	t.Run("skip 10 jobs on rapid fire", func(t *testing.T) {
		var j countJob
		j.delay = 10 * time.Millisecond
		wrappedJob := NewChain(SkipIfStillRunning(DiscardLogger)).Then(&j)
		for i := 0; i < 11; i++ {
			go wrappedJob.Run()
		}
		time.Sleep(200 * time.Millisecond)
		done := j.Done()
		if done != 1 {
			t.Error("expected 1 jobs executed, 10 jobs dropped, got", done)
		}
	})

	t.Run("different jobs independent", func(t *testing.T) {
		var j1, j2 countJob
		j1.delay = 10 * time.Millisecond
		j2.delay = 10 * time.Millisecond
		chain := NewChain(SkipIfStillRunning(DiscardLogger))
		wrappedJob1 := chain.Then(&j1)
		wrappedJob2 := chain.Then(&j2)
		for i := 0; i < 11; i++ {
			go wrappedJob1.Run()
			go wrappedJob2.Run()
		}
		time.Sleep(100 * time.Millisecond)
		var (
			done1 = j1.Done()
			done2 = j2.Done()
		)
		if done1 != 1 || done2 != 1 {
			t.Error("expected both jobs executed once, got", done1, "and", done2)
		}
	})

}


================================================
FILE: constantdelay.go
================================================
package cron

import "time"

// ConstantDelaySchedule represents a simple recurring duty cycle, e.g. "Every 5 minutes".
// It does not support jobs more frequent than once a second.
type ConstantDelaySchedule struct {
	Delay time.Duration
}

// Every returns a crontab Schedule that activates once every duration.
// Delays of less than a second are not supported (will round up to 1 second).
// Any fields less than a Second are truncated.
func Every(duration time.Duration) ConstantDelaySchedule {
	if duration < time.Second {
		duration = time.Second
	}
	return ConstantDelaySchedule{
		Delay: duration - time.Duration(duration.Nanoseconds())%time.Second,
	}
}

// Next returns the next time this should be run.
// This rounds so that the next activation time will be on the second.
func (schedule ConstantDelaySchedule) Next(t time.Time) time.Time {
	return t.Add(schedule.Delay - time.Duration(t.Nanosecond())*time.Nanosecond)
}


================================================
FILE: constantdelay_test.go
================================================
package cron

import (
	"testing"
	"time"
)

func TestConstantDelayNext(t *testing.T) {
	tests := []struct {
		time     string
		delay    time.Duration
		expected string
	}{
		// Simple cases
		{"Mon Jul 9 14:45 2012", 15*time.Minute + 50*time.Nanosecond, "Mon Jul 9 15:00 2012"},
		{"Mon Jul 9 14:59 2012", 15 * time.Minute, "Mon Jul 9 15:14 2012"},
		{"Mon Jul 9 14:59:59 2012", 15 * time.Minute, "Mon Jul 9 15:14:59 2012"},

		// Wrap around hours
		{"Mon Jul 9 15:45 2012", 35 * time.Minute, "Mon Jul 9 16:20 2012"},

		// Wrap around days
		{"Mon Jul 9 23:46 2012", 14 * time.Minute, "Tue Jul 10 00:00 2012"},
		{"Mon Jul 9 23:45 2012", 35 * time.Minute, "Tue Jul 10 00:20 2012"},
		{"Mon Jul 9 23:35:51 2012", 44*time.Minute + 24*time.Second, "Tue Jul 10 00:20:15 2012"},
		{"Mon Jul 9 23:35:51 2012", 25*time.Hour + 44*time.Minute + 24*time.Second, "Thu Jul 11 01:20:15 2012"},

		// Wrap around months
		{"Mon Jul 9 23:35 2012", 91*24*time.Hour + 25*time.Minute, "Thu Oct 9 00:00 2012"},

		// Wrap around minute, hour, day, month, and year
		{"Mon Dec 31 23:59:45 2012", 15 * time.Second, "Tue Jan 1 00:00:00 2013"},

		// Round to nearest second on the delay
		{"Mon Jul 9 14:45 2012", 15*time.Minute + 50*time.Nanosecond, "Mon Jul 9 15:00 2012"},

		// Round up to 1 second if the duration is less.
		{"Mon Jul 9 14:45:00 2012", 15 * time.Millisecond, "Mon Jul 9 14:45:01 2012"},

		// Round to nearest second when calculating the next time.
		{"Mon Jul 9 14:45:00.005 2012", 15 * time.Minute, "Mon Jul 9 15:00 2012"},

		// Round to nearest second for both.
		{"Mon Jul 9 14:45:00.005 2012", 15*time.Minute + 50*time.Nanosecond, "Mon Jul 9 15:00 2012"},
	}

	for _, c := range tests {
		actual := Every(c.delay).Next(getTime(c.time))
		expected := getTime(c.expected)
		if actual != expected {
			t.Errorf("%s, \"%s\": (expected) %v != %v (actual)", c.time, c.delay, expected, actual)
		}
	}
}


================================================
FILE: cron.go
================================================
package cron

import (
	"context"
	"sort"
	"sync"
	"time"
)

// Cron keeps track of any number of entries, invoking the associated func as
// specified by the schedule. It may be started, stopped, and the entries may
// be inspected while running.
type Cron struct {
	entries   []*Entry
	chain     Chain
	stop      chan struct{}
	add       chan *Entry
	remove    chan EntryID
	snapshot  chan chan []Entry
	running   bool
	logger    Logger
	runningMu sync.Mutex
	location  *time.Location
	parser    ScheduleParser
	nextID    EntryID
	jobWaiter sync.WaitGroup
}

// ScheduleParser is an interface for schedule spec parsers that return a Schedule
type ScheduleParser interface {
	Parse(spec string) (Schedule, error)
}

// Job is an interface for submitted cron jobs.
type Job interface {
	Run()
}

// Schedule describes a job's duty cycle.
type Schedule interface {
	// Next returns the next activation time, later than the given time.
	// Next is invoked initially, and then each time the job is run.
	Next(time.Time) time.Time
}

// EntryID identifies an entry within a Cron instance
type EntryID int

// Entry consists of a schedule and the func to execute on that schedule.
type Entry struct {
	// ID is the cron-assigned ID of this entry, which may be used to look up a
	// snapshot or remove it.
	ID EntryID

	// Schedule on which this job should be run.
	Schedule Schedule

	// Next time the job will run, or the zero time if Cron has not been
	// started or this entry's schedule is unsatisfiable
	Next time.Time

	// Prev is the last time this job was run, or the zero time if never.
	Prev time.Time

	// WrappedJob is the thing to run when the Schedule is activated.
	WrappedJob Job

	// Job is the thing that was submitted to cron.
	// It is kept around so that user code that needs to get at the job later,
	// e.g. via Entries() can do so.
	Job Job
}

// Valid returns true if this is not the zero entry.
func (e Entry) Valid() bool { return e.ID != 0 }

// byTime is a wrapper for sorting the entry array by time
// (with zero time at the end).
type byTime []*Entry

func (s byTime) Len() int      { return len(s) }
func (s byTime) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
func (s byTime) Less(i, j int) bool {
	// Two zero times should return false.
	// Otherwise, zero is "greater" than any other time.
	// (To sort it at the end of the list.)
	if s[i].Next.IsZero() {
		return false
	}
	if s[j].Next.IsZero() {
		return true
	}
	return s[i].Next.Before(s[j].Next)
}

// New returns a new Cron job runner, modified by the given options.
//
// Available Settings
//
//   Time Zone
//     Description: The time zone in which schedules are interpreted
//     Default:     time.Local
//
//   Parser
//     Description: Parser converts cron spec strings into cron.Schedules.
//     Default:     Accepts this spec: https://en.wikipedia.org/wiki/Cron
//
//   Chain
//     Description: Wrap submitted jobs to customize behavior.
//     Default:     A chain that recovers panics and logs them to stderr.
//
// See "cron.With*" to modify the default behavior.
func New(opts ...Option) *Cron {
	c := &Cron{
		entries:   nil,
		chain:     NewChain(),
		add:       make(chan *Entry),
		stop:      make(chan struct{}),
		snapshot:  make(chan chan []Entry),
		remove:    make(chan EntryID),
		running:   false,
		runningMu: sync.Mutex{},
		logger:    DefaultLogger,
		location:  time.Local,
		parser:    standardParser,
	}
	for _, opt := range opts {
		opt(c)
	}
	return c
}

// FuncJob is a wrapper that turns a func() into a cron.Job
type FuncJob func()

func (f FuncJob) Run() { f() }

// AddFunc adds a func to the Cron to be run on the given schedule.
// The spec is parsed using the time zone of this Cron instance as the default.
// An opaque ID is returned that can be used to later remove it.
func (c *Cron) AddFunc(spec string, cmd func()) (EntryID, error) {
	return c.AddJob(spec, FuncJob(cmd))
}

// AddJob adds a Job to the Cron to be run on the given schedule.
// The spec is parsed using the time zone of this Cron instance as the default.
// An opaque ID is returned that can be used to later remove it.
func (c *Cron) AddJob(spec string, cmd Job) (EntryID, error) {
	schedule, err := c.parser.Parse(spec)
	if err != nil {
		return 0, err
	}
	return c.Schedule(schedule, cmd), nil
}

// Schedule adds a Job to the Cron to be run on the given schedule.
// The job is wrapped with the configured Chain.
func (c *Cron) Schedule(schedule Schedule, cmd Job) EntryID {
	c.runningMu.Lock()
	defer c.runningMu.Unlock()
	c.nextID++
	entry := &Entry{
		ID:         c.nextID,
		Schedule:   schedule,
		WrappedJob: c.chain.Then(cmd),
		Job:        cmd,
	}
	if !c.running {
		c.entries = append(c.entries, entry)
	} else {
		c.add <- entry
	}
	return entry.ID
}

// Entries returns a snapshot of the cron entries.
func (c *Cron) Entries() []Entry {
	c.runningMu.Lock()
	defer c.runningMu.Unlock()
	if c.running {
		replyChan := make(chan []Entry, 1)
		c.snapshot <- replyChan
		return <-replyChan
	}
	return c.entrySnapshot()
}

// Location gets the time zone location
func (c *Cron) Location() *time.Location {
	return c.location
}

// Entry returns a snapshot of the given entry, or nil if it couldn't be found.
func (c *Cron) Entry(id EntryID) Entry {
	for _, entry := range c.Entries() {
		if id == entry.ID {
			return entry
		}
	}
	return Entry{}
}

// Remove an entry from being run in the future.
func (c *Cron) Remove(id EntryID) {
	c.runningMu.Lock()
	defer c.runningMu.Unlock()
	if c.running {
		c.remove <- id
	} else {
		c.removeEntry(id)
	}
}

// Start the cron scheduler in its own goroutine, or no-op if already started.
func (c *Cron) Start() {
	c.runningMu.Lock()
	defer c.runningMu.Unlock()
	if c.running {
		return
	}
	c.running = true
	go c.run()
}

// Run the cron scheduler, or no-op if already running.
func (c *Cron) Run() {
	c.runningMu.Lock()
	if c.running {
		c.runningMu.Unlock()
		return
	}
	c.running = true
	c.runningMu.Unlock()
	c.run()
}

// run the scheduler.. this is private just due to the need to synchronize
// access to the 'running' state variable.
func (c *Cron) run() {
	c.logger.Info("start")

	// Figure out the next activation times for each entry.
	now := c.now()
	for _, entry := range c.entries {
		entry.Next = entry.Schedule.Next(now)
		c.logger.Info("schedule", "now", now, "entry", entry.ID, "next", entry.Next)
	}

	for {
		// Determine the next entry to run.
		sort.Sort(byTime(c.entries))

		var timer *time.Timer
		if len(c.entries) == 0 || c.entries[0].Next.IsZero() {
			// If there are no entries yet, just sleep - it still handles new entries
			// and stop requests.
			timer = time.NewTimer(100000 * time.Hour)
		} else {
			timer = time.NewTimer(c.entries[0].Next.Sub(now))
		}

		for {
			select {
			case now = <-timer.C:
				now = now.In(c.location)
				c.logger.Info("wake", "now", now)

				// Run every entry whose next time was less than now
				for _, e := range c.entries {
					if e.Next.After(now) || e.Next.IsZero() {
						break
					}
					c.startJob(e.WrappedJob)
					e.Prev = e.Next
					e.Next = e.Schedule.Next(now)
					c.logger.Info("run", "now", now, "entry", e.ID, "next", e.Next)
				}

			case newEntry := <-c.add:
				timer.Stop()
				now = c.now()
				newEntry.Next = newEntry.Schedule.Next(now)
				c.entries = append(c.entries, newEntry)
				c.logger.Info("added", "now", now, "entry", newEntry.ID, "next", newEntry.Next)

			case replyChan := <-c.snapshot:
				replyChan <- c.entrySnapshot()
				continue

			case <-c.stop:
				timer.Stop()
				c.logger.Info("stop")
				return

			case id := <-c.remove:
				timer.Stop()
				now = c.now()
				c.removeEntry(id)
				c.logger.Info("removed", "entry", id)
			}

			break
		}
	}
}

// startJob runs the given job in a new goroutine.
func (c *Cron) startJob(j Job) {
	c.jobWaiter.Add(1)
	go func() {
		defer c.jobWaiter.Done()
		j.Run()
	}()
}

// now returns current time in c location
func (c *Cron) now() time.Time {
	return time.Now().In(c.location)
}

// Stop stops the cron scheduler if it is running; otherwise it does nothing.
// A context is returned so the caller can wait for running jobs to complete.
func (c *Cron) Stop() context.Context {
	c.runningMu.Lock()
	defer c.runningMu.Unlock()
	if c.running {
		c.stop <- struct{}{}
		c.running = false
	}
	ctx, cancel := context.WithCancel(context.Background())
	go func() {
		c.jobWaiter.Wait()
		cancel()
	}()
	return ctx
}

// entrySnapshot returns a copy of the current cron entry list.
func (c *Cron) entrySnapshot() []Entry {
	var entries = make([]Entry, len(c.entries))
	for i, e := range c.entries {
		entries[i] = *e
	}
	return entries
}

func (c *Cron) removeEntry(id EntryID) {
	var entries []*Entry
	for _, e := range c.entries {
		if e.ID != id {
			entries = append(entries, e)
		}
	}
	c.entries = entries
}


================================================
FILE: cron_test.go
================================================
package cron

import (
	"bytes"
	"fmt"
	"log"
	"strings"
	"sync"
	"sync/atomic"
	"testing"
	"time"
)

// Many tests schedule a job for every second, and then wait at most a second
// for it to run.  This amount is just slightly larger than 1 second to
// compensate for a few milliseconds of runtime.
const OneSecond = 1*time.Second + 50*time.Millisecond

type syncWriter struct {
	wr bytes.Buffer
	m  sync.Mutex
}

func (sw *syncWriter) Write(data []byte) (n int, err error) {
	sw.m.Lock()
	n, err = sw.wr.Write(data)
	sw.m.Unlock()
	return
}

func (sw *syncWriter) String() string {
	sw.m.Lock()
	defer sw.m.Unlock()
	return sw.wr.String()
}

func newBufLogger(sw *syncWriter) Logger {
	return PrintfLogger(log.New(sw, "", log.LstdFlags))
}

func TestFuncPanicRecovery(t *testing.T) {
	var buf syncWriter
	cron := New(WithParser(secondParser),
		WithChain(Recover(newBufLogger(&buf))))
	cron.Start()
	defer cron.Stop()
	cron.AddFunc("* * * * * ?", func() {
		panic("YOLO")
	})

	select {
	case <-time.After(OneSecond):
		if !strings.Contains(buf.String(), "YOLO") {
			t.Error("expected a panic to be logged, got none")
		}
		return
	}
}

type DummyJob struct{}

func (d DummyJob) Run() {
	panic("YOLO")
}

func TestJobPanicRecovery(t *testing.T) {
	var job DummyJob

	var buf syncWriter
	cron := New(WithParser(secondParser),
		WithChain(Recover(newBufLogger(&buf))))
	cron.Start()
	defer cron.Stop()
	cron.AddJob("* * * * * ?", job)

	select {
	case <-time.After(OneSecond):
		if !strings.Contains(buf.String(), "YOLO") {
			t.Error("expected a panic to be logged, got none")
		}
		return
	}
}

// Start and stop cron with no entries.
func TestNoEntries(t *testing.T) {
	cron := newWithSeconds()
	cron.Start()

	select {
	case <-time.After(OneSecond):
		t.Fatal("expected cron will be stopped immediately")
	case <-stop(cron):
	}
}

// Start, stop, then add an entry. Verify entry doesn't run.
func TestStopCausesJobsToNotRun(t *testing.T) {
	wg := &sync.WaitGroup{}
	wg.Add(1)

	cron := newWithSeconds()
	cron.Start()
	cron.Stop()
	cron.AddFunc("* * * * * ?", func() { wg.Done() })

	select {
	case <-time.After(OneSecond):
		// No job ran!
	case <-wait(wg):
		t.Fatal("expected stopped cron does not run any job")
	}
}

// Add a job, start cron, expect it runs.
func TestAddBeforeRunning(t *testing.T) {
	wg := &sync.WaitGroup{}
	wg.Add(1)

	cron := newWithSeconds()
	cron.AddFunc("* * * * * ?", func() { wg.Done() })
	cron.Start()
	defer cron.Stop()

	// Give cron 2 seconds to run our job (which is always activated).
	select {
	case <-time.After(OneSecond):
		t.Fatal("expected job runs")
	case <-wait(wg):
	}
}

// Start cron, add a job, expect it runs.
func TestAddWhileRunning(t *testing.T) {
	wg := &sync.WaitGroup{}
	wg.Add(1)

	cron := newWithSeconds()
	cron.Start()
	defer cron.Stop()
	cron.AddFunc("* * * * * ?", func() { wg.Done() })

	select {
	case <-time.After(OneSecond):
		t.Fatal("expected job runs")
	case <-wait(wg):
	}
}

// Test for #34. Adding a job after calling start results in multiple job invocations
func TestAddWhileRunningWithDelay(t *testing.T) {
	cron := newWithSeconds()
	cron.Start()
	defer cron.Stop()
	time.Sleep(5 * time.Second)
	var calls int64
	cron.AddFunc("* * * * * *", func() { atomic.AddInt64(&calls, 1) })

	<-time.After(OneSecond)
	if atomic.LoadInt64(&calls) != 1 {
		t.Errorf("called %d times, expected 1\n", calls)
	}
}

// Add a job, remove a job, start cron, expect nothing runs.
func TestRemoveBeforeRunning(t *testing.T) {
	wg := &sync.WaitGroup{}
	wg.Add(1)

	cron := newWithSeconds()
	id, _ := cron.AddFunc("* * * * * ?", func() { wg.Done() })
	cron.Remove(id)
	cron.Start()
	defer cron.Stop()

	select {
	case <-time.After(OneSecond):
		// Success, shouldn't run
	case <-wait(wg):
		t.FailNow()
	}
}

// Start cron, add a job, remove it, expect it doesn't run.
func TestRemoveWhileRunning(t *testing.T) {
	wg := &sync.WaitGroup{}
	wg.Add(1)

	cron := newWithSeconds()
	cron.Start()
	defer cron.Stop()
	id, _ := cron.AddFunc("* * * * * ?", func() { wg.Done() })
	cron.Remove(id)

	select {
	case <-time.After(OneSecond):
	case <-wait(wg):
		t.FailNow()
	}
}

// Test timing with Entries.
func TestSnapshotEntries(t *testing.T) {
	wg := &sync.WaitGroup{}
	wg.Add(1)

	cron := New()
	cron.AddFunc("@every 2s", func() { wg.Done() })
	cron.Start()
	defer cron.Stop()

	// Cron should fire in 2 seconds. After 1 second, call Entries.
	select {
	case <-time.After(OneSecond):
		cron.Entries()
	}

	// Even though Entries was called, the cron should fire at the 2 second mark.
	select {
	case <-time.After(OneSecond):
		t.Error("expected job runs at 2 second mark")
	case <-wait(wg):
	}
}

// Test that the entries are correctly sorted.
// Add a bunch of long-in-the-future entries, and an immediate entry, and ensure
// that the immediate entry runs immediately.
// Also: Test that multiple jobs run in the same instant.
func TestMultipleEntries(t *testing.T) {
	wg := &sync.WaitGroup{}
	wg.Add(2)

	cron := newWithSeconds()
	cron.AddFunc("0 0 0 1 1 ?", func() {})
	cron.AddFunc("* * * * * ?", func() { wg.Done() })
	id1, _ := cron.AddFunc("* * * * * ?", func() { t.Fatal() })
	id2, _ := cron.AddFunc("* * * * * ?", func() { t.Fatal() })
	cron.AddFunc("0 0 0 31 12 ?", func() {})
	cron.AddFunc("* * * * * ?", func() { wg.Done() })

	cron.Remove(id1)
	cron.Start()
	cron.Remove(id2)
	defer cron.Stop()

	select {
	case <-time.After(OneSecond):
		t.Error("expected job run in proper order")
	case <-wait(wg):
	}
}

// Test running the same job twice.
func TestRunningJobTwice(t *testing.T) {
	wg := &sync.WaitGroup{}
	wg.Add(2)

	cron := newWithSeconds()
	cron.AddFunc("0 0 0 1 1 ?", func() {})
	cron.AddFunc("0 0 0 31 12 ?", func() {})
	cron.AddFunc("* * * * * ?", func() { wg.Done() })

	cron.Start()
	defer cron.Stop()

	select {
	case <-time.After(2 * OneSecond):
		t.Error("expected job fires 2 times")
	case <-wait(wg):
	}
}

func TestRunningMultipleSchedules(t *testing.T) {
	wg := &sync.WaitGroup{}
	wg.Add(2)

	cron := newWithSeconds()
	cron.AddFunc("0 0 0 1 1 ?", func() {})
	cron.AddFunc("0 0 0 31 12 ?", func() {})
	cron.AddFunc("* * * * * ?", func() { wg.Done() })
	cron.Schedule(Every(time.Minute), FuncJob(func() {}))
	cron.Schedule(Every(time.Second), FuncJob(func() { wg.Done() }))
	cron.Schedule(Every(time.Hour), FuncJob(func() {}))

	cron.Start()
	defer cron.Stop()

	select {
	case <-time.After(2 * OneSecond):
		t.Error("expected job fires 2 times")
	case <-wait(wg):
	}
}

// Test that the cron is run in the local time zone (as opposed to UTC).
func TestLocalTimezone(t *testing.T) {
	wg := &sync.WaitGroup{}
	wg.Add(2)

	now := time.Now()
	// FIX: Issue #205
	// This calculation doesn't work in seconds 58 or 59.
	// Take the easy way out and sleep.
	if now.Second() >= 58 {
		time.Sleep(2 * time.Second)
		now = time.Now()
	}
	spec := fmt.Sprintf("%d,%d %d %d %d %d ?",
		now.Second()+1, now.Second()+2, now.Minute(), now.Hour(), now.Day(), now.Month())

	cron := newWithSeconds()
	cron.AddFunc(spec, func() { wg.Done() })
	cron.Start()
	defer cron.Stop()

	select {
	case <-time.After(OneSecond * 2):
		t.Error("expected job fires 2 times")
	case <-wait(wg):
	}
}

// Test that the cron is run in the given time zone (as opposed to local).
func TestNonLocalTimezone(t *testing.T) {
	wg := &sync.WaitGroup{}
	wg.Add(2)

	loc, err := time.LoadLocation("Atlantic/Cape_Verde")
	if err != nil {
		fmt.Printf("Failed to load time zone Atlantic/Cape_Verde: %+v", err)
		t.Fail()
	}

	now := time.Now().In(loc)
	// FIX: Issue #205
	// This calculation doesn't work in seconds 58 or 59.
	// Take the easy way out and sleep.
	if now.Second() >= 58 {
		time.Sleep(2 * time.Second)
		now = time.Now().In(loc)
	}
	spec := fmt.Sprintf("%d,%d %d %d %d %d ?",
		now.Second()+1, now.Second()+2, now.Minute(), now.Hour(), now.Day(), now.Month())

	cron := New(WithLocation(loc), WithParser(secondParser))
	cron.AddFunc(spec, func() { wg.Done() })
	cron.Start()
	defer cron.Stop()

	select {
	case <-time.After(OneSecond * 2):
		t.Error("expected job fires 2 times")
	case <-wait(wg):
	}
}

// Test that calling stop before start silently returns without
// blocking the stop channel.
func TestStopWithoutStart(t *testing.T) {
	cron := New()
	cron.Stop()
}

type testJob struct {
	wg   *sync.WaitGroup
	name string
}

func (t testJob) Run() {
	t.wg.Done()
}

// Test that adding an invalid job spec returns an error
func TestInvalidJobSpec(t *testing.T) {
	cron := New()
	_, err := cron.AddJob("this will not parse", nil)
	if err == nil {
		t.Errorf("expected an error with invalid spec, got nil")
	}
}

// Test blocking run method behaves as Start()
func TestBlockingRun(t *testing.T) {
	wg := &sync.WaitGroup{}
	wg.Add(1)

	cron := newWithSeconds()
	cron.AddFunc("* * * * * ?", func() { wg.Done() })

	var unblockChan = make(chan struct{})

	go func() {
		cron.Run()
		close(unblockChan)
	}()
	defer cron.Stop()

	select {
	case <-time.After(OneSecond):
		t.Error("expected job fires")
	case <-unblockChan:
		t.Error("expected that Run() blocks")
	case <-wait(wg):
	}
}

// Test that double-running is a no-op
func TestStartNoop(t *testing.T) {
	var tickChan = make(chan struct{}, 2)

	cron := newWithSeconds()
	cron.AddFunc("* * * * * ?", func() {
		tickChan <- struct{}{}
	})

	cron.Start()
	defer cron.Stop()

	// Wait for the first firing to ensure the runner is going
	<-tickChan

	cron.Start()

	<-tickChan

	// Fail if this job fires again in a short period, indicating a double-run
	select {
	case <-time.After(time.Millisecond):
	case <-tickChan:
		t.Error("expected job fires exactly twice")
	}
}

// Simple test using Runnables.
func TestJob(t *testing.T) {
	wg := &sync.WaitGroup{}
	wg.Add(1)

	cron := newWithSeconds()
	cron.AddJob("0 0 0 30 Feb ?", testJob{wg, "job0"})
	cron.AddJob("0 0 0 1 1 ?", testJob{wg, "job1"})
	job2, _ := cron.AddJob("* * * * * ?", testJob{wg, "job2"})
	cron.AddJob("1 0 0 1 1 ?", testJob{wg, "job3"})
	cron.Schedule(Every(5*time.Second+5*time.Nanosecond), testJob{wg, "job4"})
	job5 := cron.Schedule(Every(5*time.Minute), testJob{wg, "job5"})

	// Test getting an Entry pre-Start.
	if actualName := cron.Entry(job2).Job.(testJob).name; actualName != "job2" {
		t.Error("wrong job retrieved:", actualName)
	}
	if actualName := cron.Entry(job5).Job.(testJob).name; actualName != "job5" {
		t.Error("wrong job retrieved:", actualName)
	}

	cron.Start()
	defer cron.Stop()

	select {
	case <-time.After(OneSecond):
		t.FailNow()
	case <-wait(wg):
	}

	// Ensure the entries are in the right order.
	expecteds := []string{"job2", "job4", "job5", "job1", "job3", "job0"}

	var actuals []string
	for _, entry := range cron.Entries() {
		actuals = append(actuals, entry.Job.(testJob).name)
	}

	for i, expected := range expecteds {
		if actuals[i] != expected {
			t.Fatalf("Jobs not in the right order.  (expected) %s != %s (actual)", expecteds, actuals)
		}
	}

	// Test getting Entries.
	if actualName := cron.Entry(job2).Job.(testJob).name; actualName != "job2" {
		t.Error("wrong job retrieved:", actualName)
	}
	if actualName := cron.Entry(job5).Job.(testJob).name; actualName != "job5" {
		t.Error("wrong job retrieved:", actualName)
	}
}

// Issue #206
// Ensure that the next run of a job after removing an entry is accurate.
func TestScheduleAfterRemoval(t *testing.T) {
	var wg1 sync.WaitGroup
	var wg2 sync.WaitGroup
	wg1.Add(1)
	wg2.Add(1)

	// The first time this job is run, set a timer and remove the other job
	// 750ms later. Correct behavior would be to still run the job again in
	// 250ms, but the bug would cause it to run instead 1s later.

	var calls int
	var mu sync.Mutex

	cron := newWithSeconds()
	hourJob := cron.Schedule(Every(time.Hour), FuncJob(func() {}))
	cron.Schedule(Every(time.Second), FuncJob(func() {
		mu.Lock()
		defer mu.Unlock()
		switch calls {
		case 0:
			wg1.Done()
			calls++
		case 1:
			time.Sleep(750 * time.Millisecond)
			cron.Remove(hourJob)
			calls++
		case 2:
			calls++
			wg2.Done()
		case 3:
			panic("unexpected 3rd call")
		}
	}))

	cron.Start()
	defer cron.Stop()

	// the first run might be any length of time 0 - 1s, since the schedule
	// rounds to the second. wait for the first run to true up.
	wg1.Wait()

	select {
	case <-time.After(2 * OneSecond):
		t.Error("expected job fires 2 times")
	case <-wait(&wg2):
	}
}

type ZeroSchedule struct{}

func (*ZeroSchedule) Next(time.Time) time.Time {
	return time.Time{}
}

// Tests that job without time does not run
func TestJobWithZeroTimeDoesNotRun(t *testing.T) {
	cron := newWithSeconds()
	var calls int64
	cron.AddFunc("* * * * * *", func() { atomic.AddInt64(&calls, 1) })
	cron.Schedule(new(ZeroSchedule), FuncJob(func() { t.Error("expected zero task will not run") }))
	cron.Start()
	defer cron.Stop()
	<-time.After(OneSecond)
	if atomic.LoadInt64(&calls) != 1 {
		t.Errorf("called %d times, expected 1\n", calls)
	}
}

func TestStopAndWait(t *testing.T) {
	t.Run("nothing running, returns immediately", func(t *testing.T) {
		cron := newWithSeconds()
		cron.Start()
		ctx := cron.Stop()
		select {
		case <-ctx.Done():
		case <-time.After(time.Millisecond):
			t.Error("context was not done immediately")
		}
	})

	t.Run("repeated calls to Stop", func(t *testing.T) {
		cron := newWithSeconds()
		cron.Start()
		_ = cron.Stop()
		time.Sleep(time.Millisecond)
		ctx := cron.Stop()
		select {
		case <-ctx.Done():
		case <-time.After(time.Millisecond):
			t.Error("context was not done immediately")
		}
	})

	t.Run("a couple fast jobs added, still returns immediately", func(t *testing.T) {
		cron := newWithSeconds()
		cron.AddFunc("* * * * * *", func() {})
		cron.Start()
		cron.AddFunc("* * * * * *", func() {})
		cron.AddFunc("* * * * * *", func() {})
		cron.AddFunc("* * * * * *", func() {})
		time.Sleep(time.Second)
		ctx := cron.Stop()
		select {
		case <-ctx.Done():
		case <-time.After(time.Millisecond):
			t.Error("context was not done immediately")
		}
	})

	t.Run("a couple fast jobs and a slow job added, waits for slow job", func(t *testing.T) {
		cron := newWithSeconds()
		cron.AddFunc("* * * * * *", func() {})
		cron.Start()
		cron.AddFunc("* * * * * *", func() { time.Sleep(2 * time.Second) })
		cron.AddFunc("* * * * * *", func() {})
		time.Sleep(time.Second)

		ctx := cron.Stop()

		// Verify that it is not done for at least 750ms
		select {
		case <-ctx.Done():
			t.Error("context was done too quickly immediately")
		case <-time.After(750 * time.Millisecond):
			// expected, because the job sleeping for 1 second is still running
		}

		// Verify that it IS done in the next 500ms (giving 250ms buffer)
		select {
		case <-ctx.Done():
			// expected
		case <-time.After(1500 * time.Millisecond):
			t.Error("context not done after job should have completed")
		}
	})

	t.Run("repeated calls to stop, waiting for completion and after", func(t *testing.T) {
		cron := newWithSeconds()
		cron.AddFunc("* * * * * *", func() {})
		cron.AddFunc("* * * * * *", func() { time.Sleep(2 * time.Second) })
		cron.Start()
		cron.AddFunc("* * * * * *", func() {})
		time.Sleep(time.Second)
		ctx := cron.Stop()
		ctx2 := cron.Stop()

		// Verify that it is not done for at least 1500ms
		select {
		case <-ctx.Done():
			t.Error("context was done too quickly immediately")
		case <-ctx2.Done():
			t.Error("context2 was done too quickly immediately")
		case <-time.After(1500 * time.Millisecond):
			// expected, because the job sleeping for 2 seconds is still running
		}

		// Verify that it IS done in the next 1s (giving 500ms buffer)
		select {
		case <-ctx.Done():
			// expected
		case <-time.After(time.Second):
			t.Error("context not done after job should have completed")
		}

		// Verify that ctx2 is also done.
		select {
		case <-ctx2.Done():
			// expected
		case <-time.After(time.Millisecond):
			t.Error("context2 not done even though context1 is")
		}

		// Verify that a new context retrieved from stop is immediately done.
		ctx3 := cron.Stop()
		select {
		case <-ctx3.Done():
			// expected
		case <-time.After(time.Millisecond):
			t.Error("context not done even when cron Stop is completed")
		}

	})
}

func TestMultiThreadedStartAndStop(t *testing.T) {
	cron := New()
	go cron.Run()
	time.Sleep(2 * time.Millisecond)
	cron.Stop()
}

func wait(wg *sync.WaitGroup) chan bool {
	ch := make(chan bool)
	go func() {
		wg.Wait()
		ch <- true
	}()
	return ch
}

func stop(cron *Cron) chan bool {
	ch := make(chan bool)
	go func() {
		cron.Stop()
		ch <- true
	}()
	return ch
}

// newWithSeconds returns a Cron with the seconds field enabled.
func newWithSeconds() *Cron {
	return New(WithParser(secondParser), WithChain())
}


================================================
FILE: doc.go
================================================
/*
Package cron implements a cron spec parser and job runner.

Installation

To download the specific tagged release, run:

	go get github.com/robfig/cron/v3@v3.0.0

Import it in your program as:

	import "github.com/robfig/cron/v3"

It requires Go 1.11 or later due to usage of Go Modules.

Usage

Callers may register Funcs to be invoked on a given schedule.  Cron will run
them in their own goroutines.

	c := cron.New()
	c.AddFunc("30 * * * *", func() { fmt.Println("Every hour on the half hour") })
	c.AddFunc("30 3-6,20-23 * * *", func() { fmt.Println(".. in the range 3-6am, 8-11pm") })
	c.AddFunc("CRON_TZ=Asia/Tokyo 30 04 * * *", func() { fmt.Println("Runs at 04:30 Tokyo time every day") })
	c.AddFunc("@hourly",      func() { fmt.Println("Every hour, starting an hour from now") })
	c.AddFunc("@every 1h30m", func() { fmt.Println("Every hour thirty, starting an hour thirty from now") })
	c.Start()
	..
	// Funcs are invoked in their own goroutine, asynchronously.
	...
	// Funcs may also be added to a running Cron
	c.AddFunc("@daily", func() { fmt.Println("Every day") })
	..
	// Inspect the cron job entries' next and previous run times.
	inspect(c.Entries())
	..
	c.Stop()  // Stop the scheduler (does not stop any jobs already running).

CRON Expression Format

A cron expression represents a set of times, using 5 space-separated fields.

	Field name   | Mandatory? | Allowed values  | Allowed special characters
	----------   | ---------- | --------------  | --------------------------
	Minutes      | Yes        | 0-59            | * / , -
	Hours        | Yes        | 0-23            | * / , -
	Day of month | Yes        | 1-31            | * / , - ?
	Month        | Yes        | 1-12 or JAN-DEC | * / , -
	Day of week  | Yes        | 0-6 or SUN-SAT  | * / , - ?

Month and Day-of-week field values are case insensitive.  "SUN", "Sun", and
"sun" are equally accepted.

The specific interpretation of the format is based on the Cron Wikipedia page:
https://en.wikipedia.org/wiki/Cron

Alternative Formats

Alternative Cron expression formats support other fields like seconds. You can
implement that by creating a custom Parser as follows.

	cron.New(
		cron.WithParser(
			cron.NewParser(
				cron.SecondOptional | cron.Minute | cron.Hour | cron.Dom | cron.Month | cron.Dow | cron.Descriptor)))

Since adding Seconds is the most common modification to the standard cron spec,
cron provides a builtin function to do that, which is equivalent to the custom
parser you saw earlier, except that its seconds field is REQUIRED:

	cron.New(cron.WithSeconds())

That emulates Quartz, the most popular alternative Cron schedule format:
http://www.quartz-scheduler.org/documentation/quartz-2.x/tutorials/crontrigger.html

Special Characters

Asterisk ( * )

The asterisk indicates that the cron expression will match for all values of the
field; e.g., using an asterisk in the 5th field (month) would indicate every
month.

Slash ( / )

Slashes are used to describe increments of ranges. For example 3-59/15 in the
1st field (minutes) would indicate the 3rd minute of the hour and every 15
minutes thereafter. The form "*\/..." is equivalent to the form "first-last/...",
that is, an increment over the largest possible range of the field.  The form
"N/..." is accepted as meaning "N-MAX/...", that is, starting at N, use the
increment until the end of that specific range.  It does not wrap around.

Comma ( , )

Commas are used to separate items of a list. For example, using "MON,WED,FRI" in
the 5th field (day of week) would mean Mondays, Wednesdays and Fridays.

Hyphen ( - )

Hyphens are used to define ranges. For example, 9-17 would indicate every
hour between 9am and 5pm inclusive.

Question mark ( ? )

Question mark may be used instead of '*' for leaving either day-of-month or
day-of-week blank.

Predefined schedules

You may use one of several pre-defined schedules in place of a cron expression.

	Entry                  | Description                                | Equivalent To
	-----                  | -----------                                | -------------
	@yearly (or @annually) | Run once a year, midnight, Jan. 1st        | 0 0 1 1 *
	@monthly               | Run once a month, midnight, first of month | 0 0 1 * *
	@weekly                | Run once a week, midnight between Sat/Sun  | 0 0 * * 0
	@daily (or @midnight)  | Run once a day, midnight                   | 0 0 * * *
	@hourly                | Run once an hour, beginning of hour        | 0 * * * *

Intervals

You may also schedule a job to execute at fixed intervals, starting at the time it's added
or cron is run. This is supported by formatting the cron spec like this:

    @every <duration>

where "duration" is a string accepted by time.ParseDuration
(http://golang.org/pkg/time/#ParseDuration).

For example, "@every 1h30m10s" would indicate a schedule that activates after
1 hour, 30 minutes, 10 seconds, and then every interval after that.

Note: The interval does not take the job runtime into account.  For example,
if a job takes 3 minutes to run, and it is scheduled to run every 5 minutes,
it will have only 2 minutes of idle time between each run.

Time zones

By default, all interpretation and scheduling is done in the machine's local
time zone (time.Local). You can specify a different time zone on construction:

      cron.New(
          cron.WithLocation(time.UTC))

Individual cron schedules may also override the time zone they are to be
interpreted in by providing an additional space-separated field at the beginning
of the cron spec, of the form "CRON_TZ=Asia/Tokyo".

For example:

	# Runs at 6am in time.Local
	cron.New().AddFunc("0 6 * * ?", ...)

	# Runs at 6am in America/New_York
	nyc, _ := time.LoadLocation("America/New_York")
	c := cron.New(cron.WithLocation(nyc))
	c.AddFunc("0 6 * * ?", ...)

	# Runs at 6am in Asia/Tokyo
	cron.New().AddFunc("CRON_TZ=Asia/Tokyo 0 6 * * ?", ...)

	# Runs at 6am in Asia/Tokyo
	c := cron.New(cron.WithLocation(nyc))
	c.SetLocation("America/New_York")
	c.AddFunc("CRON_TZ=Asia/Tokyo 0 6 * * ?", ...)

The prefix "TZ=(TIME ZONE)" is also supported for legacy compatibility.

Be aware that jobs scheduled during daylight-savings leap-ahead transitions will
not be run!

Job Wrappers

A Cron runner may be configured with a chain of job wrappers to add
cross-cutting functionality to all submitted jobs. For example, they may be used
to achieve the following effects:

  - Recover any panics from jobs (activated by default)
  - Delay a job's execution if the previous run hasn't completed yet
  - Skip a job's execution if the previous run hasn't completed yet
  - Log each job's invocations

Install wrappers for all jobs added to a cron using the `cron.WithChain` option:

	cron.New(cron.WithChain(
		cron.SkipIfStillRunning(logger),
	))

Install wrappers for individual jobs by explicitly wrapping them:

	job = cron.NewChain(
		cron.SkipIfStillRunning(logger),
	).Then(job)

Thread safety

Since the Cron service runs concurrently with the calling code, some amount of
care must be taken to ensure proper synchronization.

All cron methods are designed to be correctly synchronized as long as the caller
ensures that invocations have a clear happens-before ordering between them.

Logging

Cron defines a Logger interface that is a subset of the one defined in
github.com/go-logr/logr. It has two logging levels (Info and Error), and
parameters are key/value pairs. This makes it possible for cron logging to plug
into structured logging systems. An adapter, [Verbose]PrintfLogger, is provided
to wrap the standard library *log.Logger.

For additional insight into Cron operations, verbose logging may be activated
which will record job runs, scheduling decisions, and added or removed jobs.
Activate it with a one-off logger as follows:

	cron.New(
		cron.WithLogger(
			cron.VerbosePrintfLogger(log.New(os.Stdout, "cron: ", log.LstdFlags))))


Implementation

Cron entries are stored in an array, sorted by their next activation time.  Cron
sleeps until the next job is due to be run.

Upon waking:
 - it runs each entry that is active on that second
 - it calculates the next run times for the jobs that were run
 - it re-sorts the array of entries by next activation time.
 - it goes to sleep until the soonest job.
*/
package cron


================================================
FILE: go.mod
================================================
module github.com/robfig/cron/v3

go 1.12


================================================
FILE: logger.go
================================================
package cron

import (
	"io/ioutil"
	"log"
	"os"
	"strings"
	"time"
)

// DefaultLogger is used by Cron if none is specified.
var DefaultLogger Logger = PrintfLogger(log.New(os.Stdout, "cron: ", log.LstdFlags))

// DiscardLogger can be used by callers to discard all log messages.
var DiscardLogger Logger = PrintfLogger(log.New(ioutil.Discard, "", 0))

// Logger is the interface used in this package for logging, so that any backend
// can be plugged in. It is a subset of the github.com/go-logr/logr interface.
type Logger interface {
	// Info logs routine messages about cron's operation.
	Info(msg string, keysAndValues ...interface{})
	// Error logs an error condition.
	Error(err error, msg string, keysAndValues ...interface{})
}

// PrintfLogger wraps a Printf-based logger (such as the standard library "log")
// into an implementation of the Logger interface which logs errors only.
func PrintfLogger(l interface{ Printf(string, ...interface{}) }) Logger {
	return printfLogger{l, false}
}

// VerbosePrintfLogger wraps a Printf-based logger (such as the standard library
// "log") into an implementation of the Logger interface which logs everything.
func VerbosePrintfLogger(l interface{ Printf(string, ...interface{}) }) Logger {
	return printfLogger{l, true}
}

type printfLogger struct {
	logger  interface{ Printf(string, ...interface{}) }
	logInfo bool
}

func (pl printfLogger) Info(msg string, keysAndValues ...interface{}) {
	if pl.logInfo {
		keysAndValues = formatTimes(keysAndValues)
		pl.logger.Printf(
			formatString(len(keysAndValues)),
			append([]interface{}{msg}, keysAndValues...)...)
	}
}

func (pl printfLogger) Error(err error, msg string, keysAndValues ...interface{}) {
	keysAndValues = formatTimes(keysAndValues)
	pl.logger.Printf(
		formatString(len(keysAndValues)+2),
		append([]interface{}{msg, "error", err}, keysAndValues...)...)
}

// formatString returns a logfmt-like format string for the number of
// key/values.
func formatString(numKeysAndValues int) string {
	var sb strings.Builder
	sb.WriteString("%s")
	if numKeysAndValues > 0 {
		sb.WriteString(", ")
	}
	for i := 0; i < numKeysAndValues/2; i++ {
		if i > 0 {
			sb.WriteString(", ")
		}
		sb.WriteString("%v=%v")
	}
	return sb.String()
}

// formatTimes formats any time.Time values as RFC3339.
func formatTimes(keysAndValues []interface{}) []interface{} {
	var formattedArgs []interface{}
	for _, arg := range keysAndValues {
		if t, ok := arg.(time.Time); ok {
			arg = t.Format(time.RFC3339)
		}
		formattedArgs = append(formattedArgs, arg)
	}
	return formattedArgs
}


================================================
FILE: option.go
================================================
package cron

import (
	"time"
)

// Option represents a modification to the default behavior of a Cron.
type Option func(*Cron)

// WithLocation overrides the timezone of the cron instance.
func WithLocation(loc *time.Location) Option {
	return func(c *Cron) {
		c.location = loc
	}
}

// WithSeconds overrides the parser used for interpreting job schedules to
// include a seconds field as the first one.
func WithSeconds() Option {
	return WithParser(NewParser(
		Second | Minute | Hour | Dom | Month | Dow | Descriptor,
	))
}

// WithParser overrides the parser used for interpreting job schedules.
func WithParser(p ScheduleParser) Option {
	return func(c *Cron) {
		c.parser = p
	}
}

// WithChain specifies Job wrappers to apply to all jobs added to this cron.
// Refer to the Chain* functions in this package for provided wrappers.
func WithChain(wrappers ...JobWrapper) Option {
	return func(c *Cron) {
		c.chain = NewChain(wrappers...)
	}
}

// WithLogger uses the provided logger.
func WithLogger(logger Logger) Option {
	return func(c *Cron) {
		c.logger = logger
	}
}


================================================
FILE: option_test.go
================================================
package cron

import (
	"log"
	"strings"
	"testing"
	"time"
)

func TestWithLocation(t *testing.T) {
	c := New(WithLocation(time.UTC))
	if c.location != time.UTC {
		t.Errorf("expected UTC, got %v", c.location)
	}
}

func TestWithParser(t *testing.T) {
	var parser = NewParser(Dow)
	c := New(WithParser(parser))
	if c.parser != parser {
		t.Error("expected provided parser")
	}
}

func TestWithVerboseLogger(t *testing.T) {
	var buf syncWriter
	var logger = log.New(&buf, "", log.LstdFlags)
	c := New(WithLogger(VerbosePrintfLogger(logger)))
	if c.logger.(printfLogger).logger != logger {
		t.Error("expected provided logger")
	}

	c.AddFunc("@every 1s", func() {})
	c.Start()
	time.Sleep(OneSecond)
	c.Stop()
	out := buf.String()
	if !strings.Contains(out, "schedule,") ||
		!strings.Contains(out, "run,") {
		t.Error("expected to see some actions, got:", out)
	}
}


================================================
FILE: parser.go
================================================
package cron

import (
	"fmt"
	"math"
	"strconv"
	"strings"
	"time"
)

// Configuration options for creating a parser. Most options specify which
// fields should be included, while others enable features. If a field is not
// included the parser will assume a default value. These options do not change
// the order fields are parse in.
type ParseOption int

const (
	Second         ParseOption = 1 << iota // Seconds field, default 0
	SecondOptional                         // Optional seconds field, default 0
	Minute                                 // Minutes field, default 0
	Hour                                   // Hours field, default 0
	Dom                                    // Day of month field, default *
	Month                                  // Month field, default *
	Dow                                    // Day of week field, default *
	DowOptional                            // Optional day of week field, default *
	Descriptor                             // Allow descriptors such as @monthly, @weekly, etc.
)

var places = []ParseOption{
	Second,
	Minute,
	Hour,
	Dom,
	Month,
	Dow,
}

var defaults = []string{
	"0",
	"0",
	"0",
	"*",
	"*",
	"*",
}

// A custom Parser that can be configured.
type Parser struct {
	options ParseOption
}

// NewParser creates a Parser with custom options.
//
// It panics if more than one Optional is given, since it would be impossible to
// correctly infer which optional is provided or missing in general.
//
// Examples
//
//  // Standard parser without descriptors
//  specParser := NewParser(Minute | Hour | Dom | Month | Dow)
//  sched, err := specParser.Parse("0 0 15 */3 *")
//
//  // Same as above, just excludes time fields
//  specParser := NewParser(Dom | Month | Dow)
//  sched, err := specParser.Parse("15 */3 *")
//
//  // Same as above, just makes Dow optional
//  specParser := NewParser(Dom | Month | DowOptional)
//  sched, err := specParser.Parse("15 */3")
//
func NewParser(options ParseOption) Parser {
	optionals := 0
	if options&DowOptional > 0 {
		optionals++
	}
	if options&SecondOptional > 0 {
		optionals++
	}
	if optionals > 1 {
		panic("multiple optionals may not be configured")
	}
	return Parser{options}
}

// Parse returns a new crontab schedule representing the given spec.
// It returns a descriptive error if the spec is not valid.
// It accepts crontab specs and features configured by NewParser.
func (p Parser) Parse(spec string) (Schedule, error) {
	if len(spec) == 0 {
		return nil, fmt.Errorf("empty spec string")
	}

	// Extract timezone if present
	var loc = time.Local
	if strings.HasPrefix(spec, "TZ=") || strings.HasPrefix(spec, "CRON_TZ=") {
		var err error
		i := strings.Index(spec, " ")
		eq := strings.Index(spec, "=")
		if loc, err = time.LoadLocation(spec[eq+1 : i]); err != nil {
			return nil, fmt.Errorf("provided bad location %s: %v", spec[eq+1:i], err)
		}
		spec = strings.TrimSpace(spec[i:])
	}

	// Handle named schedules (descriptors), if configured
	if strings.HasPrefix(spec, "@") {
		if p.options&Descriptor == 0 {
			return nil, fmt.Errorf("parser does not accept descriptors: %v", spec)
		}
		return parseDescriptor(spec, loc)
	}

	// Split on whitespace.
	fields := strings.Fields(spec)

	// Validate & fill in any omitted or optional fields
	var err error
	fields, err = normalizeFields(fields, p.options)
	if err != nil {
		return nil, err
	}

	field := func(field string, r bounds) uint64 {
		if err != nil {
			return 0
		}
		var bits uint64
		bits, err = getField(field, r)
		return bits
	}

	var (
		second     = field(fields[0], seconds)
		minute     = field(fields[1], minutes)
		hour       = field(fields[2], hours)
		dayofmonth = field(fields[3], dom)
		month      = field(fields[4], months)
		dayofweek  = field(fields[5], dow)
	)
	if err != nil {
		return nil, err
	}

	return &SpecSchedule{
		Second:   second,
		Minute:   minute,
		Hour:     hour,
		Dom:      dayofmonth,
		Month:    month,
		Dow:      dayofweek,
		Location: loc,
	}, nil
}

// normalizeFields takes a subset set of the time fields and returns the full set
// with defaults (zeroes) populated for unset fields.
//
// As part of performing this function, it also validates that the provided
// fields are compatible with the configured options.
func normalizeFields(fields []string, options ParseOption) ([]string, error) {
	// Validate optionals & add their field to options
	optionals := 0
	if options&SecondOptional > 0 {
		options |= Second
		optionals++
	}
	if options&DowOptional > 0 {
		options |= Dow
		optionals++
	}
	if optionals > 1 {
		return nil, fmt.Errorf("multiple optionals may not be configured")
	}

	// Figure out how many fields we need
	max := 0
	for _, place := range places {
		if options&place > 0 {
			max++
		}
	}
	min := max - optionals

	// Validate number of fields
	if count := len(fields); count < min || count > max {
		if min == max {
			return nil, fmt.Errorf("expected exactly %d fields, found %d: %s", min, count, fields)
		}
		return nil, fmt.Errorf("expected %d to %d fields, found %d: %s", min, max, count, fields)
	}

	// Populate the optional field if not provided
	if min < max && len(fields) == min {
		switch {
		case options&DowOptional > 0:
			fields = append(fields, defaults[5]) // TODO: improve access to default
		case options&SecondOptional > 0:
			fields = append([]string{defaults[0]}, fields...)
		default:
			return nil, fmt.Errorf("unknown optional field")
		}
	}

	// Populate all fields not part of options with their defaults
	n := 0
	expandedFields := make([]string, len(places))
	copy(expandedFields, defaults)
	for i, place := range places {
		if options&place > 0 {
			expandedFields[i] = fields[n]
			n++
		}
	}
	return expandedFields, nil
}

var standardParser = NewParser(
	Minute | Hour | Dom | Month | Dow | Descriptor,
)

// ParseStandard returns a new crontab schedule representing the given
// standardSpec (https://en.wikipedia.org/wiki/Cron). It requires 5 entries
// representing: minute, hour, day of month, month and day of week, in that
// order. It returns a descriptive error if the spec is not valid.
//
// It accepts
//   - Standard crontab specs, e.g. "* * * * ?"
//   - Descriptors, e.g. "@midnight", "@every 1h30m"
func ParseStandard(standardSpec string) (Schedule, error) {
	return standardParser.Parse(standardSpec)
}

// getField returns an Int with the bits set representing all of the times that
// the field represents or error parsing field value.  A "field" is a comma-separated
// list of "ranges".
func getField(field string, r bounds) (uint64, error) {
	var bits uint64
	ranges := strings.FieldsFunc(field, func(r rune) bool { return r == ',' })
	for _, expr := range ranges {
		bit, err := getRange(expr, r)
		if err != nil {
			return bits, err
		}
		bits |= bit
	}
	return bits, nil
}

// getRange returns the bits indicated by the given expression:
//   number | number "-" number [ "/" number ]
// or error parsing range.
func getRange(expr string, r bounds) (uint64, error) {
	var (
		start, end, step uint
		rangeAndStep     = strings.Split(expr, "/")
		lowAndHigh       = strings.Split(rangeAndStep[0], "-")
		singleDigit      = len(lowAndHigh) == 1
		err              error
	)

	var extra uint64
	if lowAndHigh[0] == "*" || lowAndHigh[0] == "?" {
		start = r.min
		end = r.max
		extra = starBit
	} else {
		start, err = parseIntOrName(lowAndHigh[0], r.names)
		if err != nil {
			return 0, err
		}
		switch len(lowAndHigh) {
		case 1:
			end = start
		case 2:
			end, err = parseIntOrName(lowAndHigh[1], r.names)
			if err != nil {
				return 0, err
			}
		default:
			return 0, fmt.Errorf("too many hyphens: %s", expr)
		}
	}

	switch len(rangeAndStep) {
	case 1:
		step = 1
	case 2:
		step, err = mustParseInt(rangeAndStep[1])
		if err != nil {
			return 0, err
		}

		// Special handling: "N/step" means "N-max/step".
		if singleDigit {
			end = r.max
		}
		if step > 1 {
			extra = 0
		}
	default:
		return 0, fmt.Errorf("too many slashes: %s", expr)
	}

	if start < r.min {
		return 0, fmt.Errorf("beginning of range (%d) below minimum (%d): %s", start, r.min, expr)
	}
	if end > r.max {
		return 0, fmt.Errorf("end of range (%d) above maximum (%d): %s", end, r.max, expr)
	}
	if start > end {
		return 0, fmt.Errorf("beginning of range (%d) beyond end of range (%d): %s", start, end, expr)
	}
	if step == 0 {
		return 0, fmt.Errorf("step of range should be a positive number: %s", expr)
	}

	return getBits(start, end, step) | extra, nil
}

// parseIntOrName returns the (possibly-named) integer contained in expr.
func parseIntOrName(expr string, names map[string]uint) (uint, error) {
	if names != nil {
		if namedInt, ok := names[strings.ToLower(expr)]; ok {
			return namedInt, nil
		}
	}
	return mustParseInt(expr)
}

// mustParseInt parses the given expression as an int or returns an error.
func mustParseInt(expr string) (uint, error) {
	num, err := strconv.Atoi(expr)
	if err != nil {
		return 0, fmt.Errorf("failed to parse int from %s: %s", expr, err)
	}
	if num < 0 {
		return 0, fmt.Errorf("negative number (%d) not allowed: %s", num, expr)
	}

	return uint(num), nil
}

// getBits sets all bits in the range [min, max], modulo the given step size.
func getBits(min, max, step uint) uint64 {
	var bits uint64

	// If step is 1, use shifts.
	if step == 1 {
		return ^(math.MaxUint64 << (max + 1)) & (math.MaxUint64 << min)
	}

	// Else, use a simple loop.
	for i := min; i <= max; i += step {
		bits |= 1 << i
	}
	return bits
}

// all returns all bits within the given bounds.  (plus the star bit)
func all(r bounds) uint64 {
	return getBits(r.min, r.max, 1) | starBit
}

// parseDescriptor returns a predefined schedule for the expression, or error if none matches.
func parseDescriptor(descriptor string, loc *time.Location) (Schedule, error) {
	switch descriptor {
	case "@yearly", "@annually":
		return &SpecSchedule{
			Second:   1 << seconds.min,
			Minute:   1 << minutes.min,
			Hour:     1 << hours.min,
			Dom:      1 << dom.min,
			Month:    1 << months.min,
			Dow:      all(dow),
			Location: loc,
		}, nil

	case "@monthly":
		return &SpecSchedule{
			Second:   1 << seconds.min,
			Minute:   1 << minutes.min,
			Hour:     1 << hours.min,
			Dom:      1 << dom.min,
			Month:    all(months),
			Dow:      all(dow),
			Location: loc,
		}, nil

	case "@weekly":
		return &SpecSchedule{
			Second:   1 << seconds.min,
			Minute:   1 << minutes.min,
			Hour:     1 << hours.min,
			Dom:      all(dom),
			Month:    all(months),
			Dow:      1 << dow.min,
			Location: loc,
		}, nil

	case "@daily", "@midnight":
		return &SpecSchedule{
			Second:   1 << seconds.min,
			Minute:   1 << minutes.min,
			Hour:     1 << hours.min,
			Dom:      all(dom),
			Month:    all(months),
			Dow:      all(dow),
			Location: loc,
		}, nil

	case "@hourly":
		return &SpecSchedule{
			Second:   1 << seconds.min,
			Minute:   1 << minutes.min,
			Hour:     all(hours),
			Dom:      all(dom),
			Month:    all(months),
			Dow:      all(dow),
			Location: loc,
		}, nil

	}

	const every = "@every "
	if strings.HasPrefix(descriptor, every) {
		duration, err := time.ParseDuration(descriptor[len(every):])
		if err != nil {
			return nil, fmt.Errorf("failed to parse duration %s: %s", descriptor, err)
		}
		return Every(duration), nil
	}

	return nil, fmt.Errorf("unrecognized descriptor: %s", descriptor)
}


================================================
FILE: parser_test.go
================================================
package cron

import (
	"reflect"
	"strings"
	"testing"
	"time"
)

var secondParser = NewParser(Second | Minute | Hour | Dom | Month | DowOptional | Descriptor)

func TestRange(t *testing.T) {
	zero := uint64(0)
	ranges := []struct {
		expr     string
		min, max uint
		expected uint64
		err      string
	}{
		{"5", 0, 7, 1 << 5, ""},
		{"0", 0, 7, 1 << 0, ""},
		{"7", 0, 7, 1 << 7, ""},

		{"5-5", 0, 7, 1 << 5, ""},
		{"5-6", 0, 7, 1<<5 | 1<<6, ""},
		{"5-7", 0, 7, 1<<5 | 1<<6 | 1<<7, ""},

		{"5-6/2", 0, 7, 1 << 5, ""},
		{"5-7/2", 0, 7, 1<<5 | 1<<7, ""},
		{"5-7/1", 0, 7, 1<<5 | 1<<6 | 1<<7, ""},

		{"*", 1, 3, 1<<1 | 1<<2 | 1<<3 | starBit, ""},
		{"*/2", 1, 3, 1<<1 | 1<<3, ""},

		{"5--5", 0, 0, zero, "too many hyphens"},
		{"jan-x", 0, 0, zero, "failed to parse int from"},
		{"2-x", 1, 5, zero, "failed to parse int from"},
		{"*/-12", 0, 0, zero, "negative number"},
		{"*//2", 0, 0, zero, "too many slashes"},
		{"1", 3, 5, zero, "below minimum"},
		{"6", 3, 5, zero, "above maximum"},
		{"5-3", 3, 5, zero, "beyond end of range"},
		{"*/0", 0, 0, zero, "should be a positive number"},
	}

	for _, c := range ranges {
		actual, err := getRange(c.expr, bounds{c.min, c.max, nil})
		if len(c.err) != 0 && (err == nil || !strings.Contains(err.Error(), c.err)) {
			t.Errorf("%s => expected %v, got %v", c.expr, c.err, err)
		}
		if len(c.err) == 0 && err != nil {
			t.Errorf("%s => unexpected error %v", c.expr, err)
		}
		if actual != c.expected {
			t.Errorf("%s => expected %d, got %d", c.expr, c.expected, actual)
		}
	}
}

func TestField(t *testing.T) {
	fields := []struct {
		expr     string
		min, max uint
		expected uint64
	}{
		{"5", 1, 7, 1 << 5},
		{"5,6", 1, 7, 1<<5 | 1<<6},
		{"5,6,7", 1, 7, 1<<5 | 1<<6 | 1<<7},
		{"1,5-7/2,3", 1, 7, 1<<1 | 1<<5 | 1<<7 | 1<<3},
	}

	for _, c := range fields {
		actual, _ := getField(c.expr, bounds{c.min, c.max, nil})
		if actual != c.expected {
			t.Errorf("%s => expected %d, got %d", c.expr, c.expected, actual)
		}
	}
}

func TestAll(t *testing.T) {
	allBits := []struct {
		r        bounds
		expected uint64
	}{
		{minutes, 0xfffffffffffffff}, // 0-59: 60 ones
		{hours, 0xffffff},            // 0-23: 24 ones
		{dom, 0xfffffffe},            // 1-31: 31 ones, 1 zero
		{months, 0x1ffe},             // 1-12: 12 ones, 1 zero
		{dow, 0x7f},                  // 0-6: 7 ones
	}

	for _, c := range allBits {
		actual := all(c.r) // all() adds the starBit, so compensate for that..
		if c.expected|starBit != actual {
			t.Errorf("%d-%d/%d => expected %b, got %b",
				c.r.min, c.r.max, 1, c.expected|starBit, actual)
		}
	}
}

func TestBits(t *testing.T) {
	bits := []struct {
		min, max, step uint
		expected       uint64
	}{
		{0, 0, 1, 0x1},
		{1, 1, 1, 0x2},
		{1, 5, 2, 0x2a}, // 101010
		{1, 4, 2, 0xa},  // 1010
	}

	for _, c := range bits {
		actual := getBits(c.min, c.max, c.step)
		if c.expected != actual {
			t.Errorf("%d-%d/%d => expected %b, got %b",
				c.min, c.max, c.step, c.expected, actual)
		}
	}
}

func TestParseScheduleErrors(t *testing.T) {
	var tests = []struct{ expr, err string }{
		{"* 5 j * * *", "failed to parse int from"},
		{"@every Xm", "failed to parse duration"},
		{"@unrecognized", "unrecognized descriptor"},
		{"* * * *", "expected 5 to 6 fields"},
		{"", "empty spec string"},
	}
	for _, c := range tests {
		actual, err := secondParser.Parse(c.expr)
		if err == nil || !strings.Contains(err.Error(), c.err) {
			t.Errorf("%s => expected %v, got %v", c.expr, c.err, err)
		}
		if actual != nil {
			t.Errorf("expected nil schedule on error, got %v", actual)
		}
	}
}

func TestParseSchedule(t *testing.T) {
	tokyo, _ := time.LoadLocation("Asia/Tokyo")
	entries := []struct {
		parser   Parser
		expr     string
		expected Schedule
	}{
		{secondParser, "0 5 * * * *", every5min(time.Local)},
		{standardParser, "5 * * * *", every5min(time.Local)},
		{secondParser, "CRON_TZ=UTC  0 5 * * * *", every5min(time.UTC)},
		{standardParser, "CRON_TZ=UTC  5 * * * *", every5min(time.UTC)},
		{secondParser, "CRON_TZ=Asia/Tokyo 0 5 * * * *", every5min(tokyo)},
		{secondParser, "@every 5m", ConstantDelaySchedule{5 * time.Minute}},
		{secondParser, "@midnight", midnight(time.Local)},
		{secondParser, "TZ=UTC  @midnight", midnight(time.UTC)},
		{secondParser, "TZ=Asia/Tokyo @midnight", midnight(tokyo)},
		{secondParser, "@yearly", annual(time.Local)},
		{secondParser, "@annually", annual(time.Local)},
		{
			parser: secondParser,
			expr:   "* 5 * * * *",
			expected: &SpecSchedule{
				Second:   all(seconds),
				Minute:   1 << 5,
				Hour:     all(hours),
				Dom:      all(dom),
				Month:    all(months),
				Dow:      all(dow),
				Location: time.Local,
			},
		},
	}

	for _, c := range entries {
		actual, err := c.parser.Parse(c.expr)
		if err != nil {
			t.Errorf("%s => unexpected error %v", c.expr, err)
		}
		if !reflect.DeepEqual(actual, c.expected) {
			t.Errorf("%s => expected %b, got %b", c.expr, c.expected, actual)
		}
	}
}

func TestOptionalSecondSchedule(t *testing.T) {
	parser := NewParser(SecondOptional | Minute | Hour | Dom | Month | Dow | Descriptor)
	entries := []struct {
		expr     string
		expected Schedule
	}{
		{"0 5 * * * *", every5min(time.Local)},
		{"5 5 * * * *", every5min5s(time.Local)},
		{"5 * * * *", every5min(time.Local)},
	}

	for _, c := range entries {
		actual, err := parser.Parse(c.expr)
		if err != nil {
			t.Errorf("%s => unexpected error %v", c.expr, err)
		}
		if !reflect.DeepEqual(actual, c.expected) {
			t.Errorf("%s => expected %b, got %b", c.expr, c.expected, actual)
		}
	}
}

func TestNormalizeFields(t *testing.T) {
	tests := []struct {
		name     string
		input    []string
		options  ParseOption
		expected []string
	}{
		{
			"AllFields_NoOptional",
			[]string{"0", "5", "*", "*", "*", "*"},
			Second | Minute | Hour | Dom | Month | Dow | Descriptor,
			[]string{"0", "5", "*", "*", "*", "*"},
		},
		{
			"AllFields_SecondOptional_Provided",
			[]string{"0", "5", "*", "*", "*", "*"},
			SecondOptional | Minute | Hour | Dom | Month | Dow | Descriptor,
			[]string{"0", "5", "*", "*", "*", "*"},
		},
		{
			"AllFields_SecondOptional_NotProvided",
			[]string{"5", "*", "*", "*", "*"},
			SecondOptional | Minute | Hour | Dom | Month | Dow | Descriptor,
			[]string{"0", "5", "*", "*", "*", "*"},
		},
		{
			"SubsetFields_NoOptional",
			[]string{"5", "15", "*"},
			Hour | Dom | Month,
			[]string{"0", "0", "5", "15", "*", "*"},
		},
		{
			"SubsetFields_DowOptional_Provided",
			[]string{"5", "15", "*", "4"},
			Hour | Dom | Month | DowOptional,
			[]string{"0", "0", "5", "15", "*", "4"},
		},
		{
			"SubsetFields_DowOptional_NotProvided",
			[]string{"5", "15", "*"},
			Hour | Dom | Month | DowOptional,
			[]string{"0", "0", "5", "15", "*", "*"},
		},
		{
			"SubsetFields_SecondOptional_NotProvided",
			[]string{"5", "15", "*"},
			SecondOptional | Hour | Dom | Month,
			[]string{"0", "0", "5", "15", "*", "*"},
		},
	}

	for _, test := range tests {
		t.Run(test.name, func(t *testing.T) {
			actual, err := normalizeFields(test.input, test.options)
			if err != nil {
				t.Errorf("unexpected error: %v", err)
			}
			if !reflect.DeepEqual(actual, test.expected) {
				t.Errorf("expected %v, got %v", test.expected, actual)
			}
		})
	}
}

func TestNormalizeFields_Errors(t *testing.T) {
	tests := []struct {
		name    string
		input   []string
		options ParseOption
		err     string
	}{
		{
			"TwoOptionals",
			[]string{"0", "5", "*", "*", "*", "*"},
			SecondOptional | Minute | Hour | Dom | Month | DowOptional,
			"",
		},
		{
			"TooManyFields",
			[]string{"0", "5", "*", "*"},
			SecondOptional | Minute | Hour,
			"",
		},
		{
			"NoFields",
			[]string{},
			SecondOptional | Minute | Hour,
			"",
		},
		{
			"TooFewFields",
			[]string{"*"},
			SecondOptional | Minute | Hour,
			"",
		},
	}
	for _, test := range tests {
		t.Run(test.name, func(t *testing.T) {
			actual, err := normalizeFields(test.input, test.options)
			if err == nil {
				t.Errorf("expected an error, got none. results: %v", actual)
			}
			if !strings.Contains(err.Error(), test.err) {
				t.Errorf("expected error %q, got %q", test.err, err.Error())
			}
		})
	}
}

func TestStandardSpecSchedule(t *testing.T) {
	entries := []struct {
		expr     string
		expected Schedule
		err      string
	}{
		{
			expr:     "5 * * * *",
			expected: &SpecSchedule{1 << seconds.min, 1 << 5, all(hours), all(dom), all(months), all(dow), time.Local},
		},
		{
			expr:     "@every 5m",
			expected: ConstantDelaySchedule{time.Duration(5) * time.Minute},
		},
		{
			expr: "5 j * * *",
			err:  "failed to parse int from",
		},
		{
			expr: "* * * *",
			err:  "expected exactly 5 fields",
		},
	}

	for _, c := range entries {
		actual, err := ParseStandard(c.expr)
		if len(c.err) != 0 && (err == nil || !strings.Contains(err.Error(), c.err)) {
			t.Errorf("%s => expected %v, got %v", c.expr, c.err, err)
		}
		if len(c.err) == 0 && err != nil {
			t.Errorf("%s => unexpected error %v", c.expr, err)
		}
		if !reflect.DeepEqual(actual, c.expected) {
			t.Errorf("%s => expected %b, got %b", c.expr, c.expected, actual)
		}
	}
}

func TestNoDescriptorParser(t *testing.T) {
	parser := NewParser(Minute | Hour)
	_, err := parser.Parse("@every 1m")
	if err == nil {
		t.Error("expected an error, got none")
	}
}

func every5min(loc *time.Location) *SpecSchedule {
	return &SpecSchedule{1 << 0, 1 << 5, all(hours), all(dom), all(months), all(dow), loc}
}

func every5min5s(loc *time.Location) *SpecSchedule {
	return &SpecSchedule{1 << 5, 1 << 5, all(hours), all(dom), all(months), all(dow), loc}
}

func midnight(loc *time.Location) *SpecSchedule {
	return &SpecSchedule{1, 1, 1, all(dom), all(months), all(dow), loc}
}

func annual(loc *time.Location) *SpecSchedule {
	return &SpecSchedule{
		Second:   1 << seconds.min,
		Minute:   1 << minutes.min,
		Hour:     1 << hours.min,
		Dom:      1 << dom.min,
		Month:    1 << months.min,
		Dow:      all(dow),
		Location: loc,
	}
}


================================================
FILE: spec.go
================================================
package cron

import "time"

// SpecSchedule specifies a duty cycle (to the second granularity), based on a
// traditional crontab specification. It is computed initially and stored as bit sets.
type SpecSchedule struct {
	Second, Minute, Hour, Dom, Month, Dow uint64

	// Override location for this schedule.
	Location *time.Location
}

// bounds provides a range of acceptable values (plus a map of name to value).
type bounds struct {
	min, max uint
	names    map[string]uint
}

// The bounds for each field.
var (
	seconds = bounds{0, 59, nil}
	minutes = bounds{0, 59, nil}
	hours   = bounds{0, 23, nil}
	dom     = bounds{1, 31, nil}
	months  = bounds{1, 12, map[string]uint{
		"jan": 1,
		"feb": 2,
		"mar": 3,
		"apr": 4,
		"may": 5,
		"jun": 6,
		"jul": 7,
		"aug": 8,
		"sep": 9,
		"oct": 10,
		"nov": 11,
		"dec": 12,
	}}
	dow = bounds{0, 6, map[string]uint{
		"sun": 0,
		"mon": 1,
		"tue": 2,
		"wed": 3,
		"thu": 4,
		"fri": 5,
		"sat": 6,
	}}
)

const (
	// Set the top bit if a star was included in the expression.
	starBit = 1 << 63
)

// Next returns the next time this schedule is activated, greater than the given
// time.  If no time can be found to satisfy the schedule, return the zero time.
func (s *SpecSchedule) Next(t time.Time) time.Time {
	// General approach
	//
	// For Month, Day, Hour, Minute, Second:
	// Check if the time value matches.  If yes, continue to the next field.
	// If the field doesn't match the schedule, then increment the field until it matches.
	// While incrementing the field, a wrap-around brings it back to the beginning
	// of the field list (since it is necessary to re-verify previous field
	// values)

	// Convert the given time into the schedule's timezone, if one is specified.
	// Save the original timezone so we can convert back after we find a time.
	// Note that schedules without a time zone specified (time.Local) are treated
	// as local to the time provided.
	origLocation := t.Location()
	loc := s.Location
	if loc == time.Local {
		loc = t.Location()
	}
	if s.Location != time.Local {
		t = t.In(s.Location)
	}

	// Start at the earliest possible time (the upcoming second).
	t = t.Add(1*time.Second - time.Duration(t.Nanosecond())*time.Nanosecond)

	// This flag indicates whether a field has been incremented.
	added := false

	// If no time is found within five years, return zero.
	yearLimit := t.Year() + 5

WRAP:
	if t.Year() > yearLimit {
		return time.Time{}
	}

	// Find the first applicable month.
	// If it's this month, then do nothing.
	for 1<<uint(t.Month())&s.Month == 0 {
		// If we have to add a month, reset the other parts to 0.
		if !added {
			added = true
			// Otherwise, set the date at the beginning (since the current time is irrelevant).
			t = time.Date(t.Year(), t.Month(), 1, 0, 0, 0, 0, loc)
		}
		t = t.AddDate(0, 1, 0)

		// Wrapped around.
		if t.Month() == time.January {
			goto WRAP
		}
	}

	// Now get a day in that month.
	//
	// NOTE: This causes issues for daylight savings regimes where midnight does
	// not exist.  For example: Sao Paulo has DST that transforms midnight on
	// 11/3 into 1am. Handle that by noticing when the Hour ends up != 0.
	for !dayMatches(s, t) {
		if !added {
			added = true
			t = time.Date(t.Year(), t.Month(), t.Day(), 0, 0, 0, 0, loc)
		}
		t = t.AddDate(0, 0, 1)
		// Notice if the hour is no longer midnight due to DST.
		// Add an hour if it's 23, subtract an hour if it's 1.
		if t.Hour() != 0 {
			if t.Hour() > 12 {
				t = t.Add(time.Duration(24-t.Hour()) * time.Hour)
			} else {
				t = t.Add(time.Duration(-t.Hour()) * time.Hour)
			}
		}

		if t.Day() == 1 {
			goto WRAP
		}
	}

	for 1<<uint(t.Hour())&s.Hour == 0 {
		if !added {
			added = true
			t = time.Date(t.Year(), t.Month(), t.Day(), t.Hour(), 0, 0, 0, loc)
		}
		t = t.Add(1 * time.Hour)

		if t.Hour() == 0 {
			goto WRAP
		}
	}

	for 1<<uint(t.Minute())&s.Minute == 0 {
		if !added {
			added = true
			t = t.Truncate(time.Minute)
		}
		t = t.Add(1 * time.Minute)

		if t.Minute() == 0 {
			goto WRAP
		}
	}

	for 1<<uint(t.Second())&s.Second == 0 {
		if !added {
			added = true
			t = t.Truncate(time.Second)
		}
		t = t.Add(1 * time.Second)

		if t.Second() == 0 {
			goto WRAP
		}
	}

	return t.In(origLocation)
}

// dayMatches returns true if the schedule's day-of-week and day-of-month
// restrictions are satisfied by the given time.
func dayMatches(s *SpecSchedule, t time.Time) bool {
	var (
		domMatch bool = 1<<uint(t.Day())&s.Dom > 0
		dowMatch bool = 1<<uint(t.Weekday())&s.Dow > 0
	)
	if s.Dom&starBit > 0 || s.Dow&starBit > 0 {
		return domMatch && dowMatch
	}
	return domMatch || dowMatch
}


================================================
FILE: spec_test.go
================================================
package cron

import (
	"strings"
	"testing"
	"time"
)

func TestActivation(t *testing.T) {
	tests := []struct {
		time, spec string
		expected   bool
	}{
		// Every fifteen minutes.
		{"Mon Jul 9 15:00 2012", "0/15 * * * *", true},
		{"Mon Jul 9 15:45 2012", "0/15 * * * *", true},
		{"Mon Jul 9 15:40 2012", "0/15 * * * *", false},

		// Every fifteen minutes, starting at 5 minutes.
		{"Mon Jul 9 15:05 2012", "5/15 * * * *", true},
		{"Mon Jul 9 15:20 2012", "5/15 * * * *", true},
		{"Mon Jul 9 15:50 2012", "5/15 * * * *", true},

		// Named months
		{"Sun Jul 15 15:00 2012", "0/15 * * Jul *", true},
		{"Sun Jul 15 15:00 2012", "0/15 * * Jun *", false},

		// Everything set.
		{"Sun Jul 15 08:30 2012", "30 08 ? Jul Sun", true},
		{"Sun Jul 15 08:30 2012", "30 08 15 Jul ?", true},
		{"Mon Jul 16 08:30 2012", "30 08 ? Jul Sun", false},
		{"Mon Jul 16 08:30 2012", "30 08 15 Jul ?", false},

		// Predefined schedules
		{"Mon Jul 9 15:00 2012", "@hourly", true},
		{"Mon Jul 9 15:04 2012", "@hourly", false},
		{"Mon Jul 9 15:00 2012", "@daily", false},
		{"Mon Jul 9 00:00 2012", "@daily", true},
		{"Mon Jul 9 00:00 2012", "@weekly", false},
		{"Sun Jul 8 00:00 2012", "@weekly", true},
		{"Sun Jul 8 01:00 2012", "@weekly", false},
		{"Sun Jul 8 00:00 2012", "@monthly", false},
		{"Sun Jul 1 00:00 2012", "@monthly", true},

		// Test interaction of DOW and DOM.
		// If both are restricted, then only one needs to match.
		{"Sun Jul 15 00:00 2012", "* * 1,15 * Sun", true},
		{"Fri Jun 15 00:00 2012", "* * 1,15 * Sun", true},
		{"Wed Aug 1 00:00 2012", "* * 1,15 * Sun", true},
		{"Sun Jul 15 00:00 2012", "* * */10 * Sun", true}, // verifies #70

		// However, if one has a star, then both need to match.
		{"Sun Jul 15 00:00 2012", "* * * * Mon", false},
		{"Mon Jul 9 00:00 2012", "* * 1,15 * *", false},
		{"Sun Jul 15 00:00 2012", "* * 1,15 * *", true},
		{"Sun Jul 15 00:00 2012", "* * */2 * Sun", true},
	}

	for _, test := range tests {
		sched, err := ParseStandard(test.spec)
		if err != nil {
			t.Error(err)
			continue
		}
		actual := sched.Next(getTime(test.time).Add(-1 * time.Second))
		expected := getTime(test.time)
		if test.expected && expected != actual || !test.expected && expected == actual {
			t.Errorf("Fail evaluating %s on %s: (expected) %s != %s (actual)",
				test.spec, test.time, expected, actual)
		}
	}
}

func TestNext(t *testing.T) {
	runs := []struct {
		time, spec string
		expected   string
	}{
		// Simple cases
		{"Mon Jul 9 14:45 2012", "0 0/15 * * * *", "Mon Jul 9 15:00 2012"},
		{"Mon Jul 9 14:59 2012", "0 0/15 * * * *", "Mon Jul 9 15:00 2012"},
		{"Mon Jul 9 14:59:59 2012", "0 0/15 * * * *", "Mon Jul 9 15:00 2012"},

		// Wrap around hours
		{"Mon Jul 9 15:45 2012", "0 20-35/15 * * * *", "Mon Jul 9 16:20 2012"},

		// Wrap around days
		{"Mon Jul 9 23:46 2012", "0 */15 * * * *", "Tue Jul 10 00:00 2012"},
		{"Mon Jul 9 23:45 2012", "0 20-35/15 * * * *", "Tue Jul 10 00:20 2012"},
		{"Mon Jul 9 23:35:51 2012", "15/35 20-35/15 * * * *", "Tue Jul 10 00:20:15 2012"},
		{"Mon Jul 9 23:35:51 2012", "15/35 20-35/15 1/2 * * *", "Tue Jul 10 01:20:15 2012"},
		{"Mon Jul 9 23:35:51 2012", "15/35 20-35/15 10-12 * * *", "Tue Jul 10 10:20:15 2012"},

		{"Mon Jul 9 23:35:51 2012", "15/35 20-35/15 1/2 */2 * *", "Thu Jul 11 01:20:15 2012"},
		{"Mon Jul 9 23:35:51 2012", "15/35 20-35/15 * 9-20 * *", "Wed Jul 10 00:20:15 2012"},
		{"Mon Jul 9 23:35:51 2012", "15/35 20-35/15 * 9-20 Jul *", "Wed Jul 10 00:20:15 2012"},

		// Wrap around months
		{"Mon Jul 9 23:35 2012", "0 0 0 9 Apr-Oct ?", "Thu Aug 9 00:00 2012"},
		{"Mon Jul 9 23:35 2012", "0 0 0 */5 Apr,Aug,Oct Mon", "Tue Aug 1 00:00 2012"},
		{"Mon Jul 9 23:35 2012", "0 0 0 */5 Oct Mon", "Mon Oct 1 00:00 2012"},

		// Wrap around years
		{"Mon Jul 9 23:35 2012", "0 0 0 * Feb Mon", "Mon Feb 4 00:00 2013"},
		{"Mon Jul 9 23:35 2012", "0 0 0 * Feb Mon/2", "Fri Feb 1 00:00 2013"},

		// Wrap around minute, hour, day, month, and year
		{"Mon Dec 31 23:59:45 2012", "0 * * * * *", "Tue Jan 1 00:00:00 2013"},

		// Leap year
		{"Mon Jul 9 23:35 2012", "0 0 0 29 Feb ?", "Mon Feb 29 00:00 2016"},

		// Daylight savings time 2am EST (-5) -> 3am EDT (-4)
		{"2012-03-11T00:00:00-0500", "TZ=America/New_York 0 30 2 11 Mar ?", "2013-03-11T02:30:00-0400"},

		// hourly job
		{"2012-03-11T00:00:00-0500", "TZ=America/New_York 0 0 * * * ?", "2012-03-11T01:00:00-0500"},
		{"2012-03-11T01:00:00-0500", "TZ=America/New_York 0 0 * * * ?", "2012-03-11T03:00:00-0400"},
		{"2012-03-11T03:00:00-0400", "TZ=America/New_York 0 0 * * * ?", "2012-03-11T04:00:00-0400"},
		{"2012-03-11T04:00:00-0400", "TZ=America/New_York 0 0 * * * ?", "2012-03-11T05:00:00-0400"},

		// hourly job using CRON_TZ
		{"2012-03-11T00:00:00-0500", "CRON_TZ=America/New_York 0 0 * * * ?", "2012-03-11T01:00:00-0500"},
		{"2012-03-11T01:00:00-0500", "CRON_TZ=America/New_York 0 0 * * * ?", "2012-03-11T03:00:00-0400"},
		{"2012-03-11T03:00:00-0400", "CRON_TZ=America/New_York 0 0 * * * ?", "2012-03-11T04:00:00-0400"},
		{"2012-03-11T04:00:00-0400", "CRON_TZ=America/New_York 0 0 * * * ?", "2012-03-11T05:00:00-0400"},

		// 1am nightly job
		{"2012-03-11T00:00:00-0500", "TZ=America/New_York 0 0 1 * * ?", "2012-03-11T01:00:00-0500"},
		{"2012-03-11T01:00:00-0500", "TZ=America/New_York 0 0 1 * * ?", "2012-03-12T01:00:00-0400"},

		// 2am nightly job (skipped)
		{"2012-03-11T00:00:00-0500", "TZ=America/New_York 0 0 2 * * ?", "2012-03-12T02:00:00-0400"},

		// Daylight savings time 2am EDT (-4) => 1am EST (-5)
		{"2012-11-04T00:00:00-0400", "TZ=America/New_York 0 30 2 04 Nov ?", "2012-11-04T02:30:00-0500"},
		{"2012-11-04T01:45:00-0400", "TZ=America/New_York 0 30 1 04 Nov ?", "2012-11-04T01:30:00-0500"},

		// hourly job
		{"2012-11-04T00:00:00-0400", "TZ=America/New_York 0 0 * * * ?", "2012-11-04T01:00:00-0400"},
		{"2012-11-04T01:00:00-0400", "TZ=America/New_York 0 0 * * * ?", "2012-11-04T01:00:00-0500"},
		{"2012-11-04T01:00:00-0500", "TZ=America/New_York 0 0 * * * ?", "2012-11-04T02:00:00-0500"},

		// 1am nightly job (runs twice)
		{"2012-11-04T00:00:00-0400", "TZ=America/New_York 0 0 1 * * ?", "2012-11-04T01:00:00-0400"},
		{"2012-11-04T01:00:00-0400", "TZ=America/New_York 0 0 1 * * ?", "2012-11-04T01:00:00-0500"},
		{"2012-11-04T01:00:00-0500", "TZ=America/New_York 0 0 1 * * ?", "2012-11-05T01:00:00-0500"},

		// 2am nightly job
		{"2012-11-04T00:00:00-0400", "TZ=America/New_York 0 0 2 * * ?", "2012-11-04T02:00:00-0500"},
		{"2012-11-04T02:00:00-0500", "TZ=America/New_York 0 0 2 * * ?", "2012-11-05T02:00:00-0500"},

		// 3am nightly job
		{"2012-11-04T00:00:00-0400", "TZ=America/New_York 0 0 3 * * ?", "2012-11-04T03:00:00-0500"},
		{"2012-11-04T03:00:00-0500", "TZ=America/New_York 0 0 3 * * ?", "2012-11-05T03:00:00-0500"},

		// hourly job
		{"TZ=America/New_York 2012-11-04T00:00:00-0400", "0 0 * * * ?", "2012-11-04T01:00:00-0400"},
		{"TZ=America/New_York 2012-11-04T01:00:00-0400", "0 0 * * * ?", "2012-11-04T01:00:00-0500"},
		{"TZ=America/New_York 2012-11-04T01:00:00-0500", "0 0 * * * ?", "2012-11-04T02:00:00-0500"},

		// 1am nightly job (runs twice)
		{"TZ=America/New_York 2012-11-04T00:00:00-0400", "0 0 1 * * ?", "2012-11-04T01:00:00-0400"},
		{"TZ=America/New_York 2012-11-04T01:00:00-0400", "0 0 1 * * ?", "2012-11-04T01:00:00-0500"},
		{"TZ=America/New_York 2012-11-04T01:00:00-0500", "0 0 1 * * ?", "2012-11-05T01:00:00-0500"},

		// 2am nightly job
		{"TZ=America/New_York 2012-11-04T00:00:00-0400", "0 0 2 * * ?", "2012-11-04T02:00:00-0500"},
		{"TZ=America/New_York 2012-11-04T02:00:00-0500", "0 0 2 * * ?", "2012-11-05T02:00:00-0500"},

		// 3am nightly job
		{"TZ=America/New_York 2012-11-04T00:00:00-0400", "0 0 3 * * ?", "2012-11-04T03:00:00-0500"},
		{"TZ=America/New_York 2012-11-04T03:00:00-0500", "0 0 3 * * ?", "2012-11-05T03:00:00-0500"},

		// Unsatisfiable
		{"Mon Jul 9 23:35 2012", "0 0 0 30 Feb ?", ""},
		{"Mon Jul 9 23:35 2012", "0 0 0 31 Apr ?", ""},

		// Monthly job
		{"TZ=America/New_York 2012-11-04T00:00:00-0400", "0 0 3 3 * ?", "2012-12-03T03:00:00-0500"},

		// Test the scenario of DST resulting in midnight not being a valid time.
		// https://github.com/robfig/cron/issues/157
		{"2018-10-17T05:00:00-0400", "TZ=America/Sao_Paulo 0 0 9 10 * ?", "2018-11-10T06:00:00-0500"},
		{"2018-02-14T05:00:00-0500", "TZ=America/Sao_Paulo 0 0 9 22 * ?", "2018-02-22T07:00:00-0500"},
	}

	for _, c := range runs {
		sched, err := secondParser.Parse(c.spec)
		if err != nil {
			t.Error(err)
			continue
		}
		actual := sched.Next(getTime(c.time))
		expected := getTime(c.expected)
		if !actual.Equal(expected) {
			t.Errorf("%s, \"%s\": (expected) %v != %v (actual)", c.time, c.spec, expected, actual)
		}
	}
}

func TestErrors(t *testing.T) {
	invalidSpecs := []string{
		"xyz",
		"60 0 * * *",
		"0 60 * * *",
		"0 0 * * XYZ",
	}
	for _, spec := range invalidSpecs {
		_, err := ParseStandard(spec)
		if err == nil {
			t.Error("expected an error parsing: ", spec)
		}
	}
}

func getTime(value string) time.Time {
	if value == "" {
		return time.Time{}
	}

	var location = time.Local
	if strings.HasPrefix(value, "TZ=") {
		parts := strings.Fields(value)
		loc, err := time.LoadLocation(parts[0][len("TZ="):])
		if err != nil {
			panic("could not parse location:" + err.Error())
		}
		location = loc
		value = parts[1]
	}

	var layouts = []string{
		"Mon Jan 2 15:04 2006",
		"Mon Jan 2 15:04:05 2006",
	}
	for _, layout := range layouts {
		if t, err := time.ParseInLocation(layout, value, location); err == nil {
			return t
		}
	}
	if t, err := time.ParseInLocation("2006-01-02T15:04:05-0700", value, location); err == nil {
		return t
	}
	panic("could not parse time value " + value)
}

func TestNextWithTz(t *testing.T) {
	runs := []struct {
		time, spec string
		expected   string
	}{
		// Failing tests
		{"2016-01-03T13:09:03+0530", "14 14 * * *", "2016-01-03T14:14:00+0530"},
		{"2016-01-03T04:09:03+0530", "14 14 * * ?", "2016-01-03T14:14:00+0530"},

		// Passing tests
		{"2016-01-03T14:09:03+0530", "14 14 * * *", "2016-01-03T14:14:00+0530"},
		{"2016-01-03T14:00:00+0530", "14 14 * * ?", "2016-01-03T14:14:00+0530"},
	}
	for _, c := range runs {
		sched, err := ParseStandard(c.spec)
		if err != nil {
			t.Error(err)
			continue
		}
		actual := sched.Next(getTimeTZ(c.time))
		expected := getTimeTZ(c.expected)
		if !actual.Equal(expected) {
			t.Errorf("%s, \"%s\": (expected) %v != %v (actual)", c.time, c.spec, expected, actual)
		}
	}
}

func getTimeTZ(value string) time.Time {
	if value == "" {
		return time.Time{}
	}
	t, err := time.Parse("Mon Jan 2 15:04 2006", value)
	if err != nil {
		t, err = time.Parse("Mon Jan 2 15:04:05 2006", value)
		if err != nil {
			t, err = time.Parse("2006-01-02T15:04:05-0700", value)
			if err != nil {
				panic(err)
			}
		}
	}

	return t
}

// https://github.com/robfig/cron/issues/144
func TestSlash0NoHang(t *testing.T) {
	schedule := "TZ=America/New_York 15/0 * * * *"
	_, err := ParseStandard(schedule)
	if err == nil {
		t.Error("expected an error on 0 increment")
	}
}