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scheduler.go
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scheduler.go
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// Package chronos is a scheduling tool for Go based on:
// https://github.com/carlescere/scheduler
package chronos
import (
"errors"
"time"
)
// Enum of scheduler kind
const (
periodicKind = iota
monthlyKind = iota
yearlyKind = iota
)
const (
Day = 24 * time.Hour
Week = 7 * Day
)
type scheduler interface {
// Returns wether there is another event scheduled and the remaining time
next() (bool, time.Duration)
}
// Auxiliar type that holds the information needed to build the scheduler
type auxiliar struct {
kind, // Enum of scheduler kind
ammount int
notInmediately bool
start,
end time.Time
unit time.Duration
}
// Accepts periods in every time unit from ns to weeks, months and years need to
// be considered separately as their length is not constant
type periodic struct {
start, // Start time
end time.Time // End time, zero value means no end
started bool // Internal flag to handle first executions
ammount time.Duration // Period
n int // Number of already executed events
}
// Constructor
func newPeriodic(start, end time.Time, ammount int, unit time.Duration, notInmediately bool) (*periodic, error) {
// Check the input is valid
if ammount == 0 || unit == 0 {
return nil, errors.New("0 is not a valid period")
}
// If no start time was assigned, use current time
if start.IsZero() {
start = time.Now()
}
// If notInmediately was called, the starting date should not be returned
// by periodic.next() call, so we add 1 to the event count to avoid it
var n int
if notInmediately {
n = 1
}
return &periodic{start: start, end: end, started: notInmediately,
ammount: time.Duration(ammount * int(unit)), n: n}, nil
}
// Auxiliar function that returns the execution time candidate
func (s *periodic) getCandidate() time.Time {
return s.start.Add(time.Duration(s.n * int(s.ammount)))
}
// Implements scheduler.next()
func (s *periodic) next() (bool, time.Duration) {
// Calculate the next iteration
next := s.getCandidate()
for next.Before(time.Now()) {
if !s.started {
break
}
s.n++
next = s.getCandidate()
}
s.n++
if !s.started {
s.started = true
}
// Check if the end date has arrived
return s.end.IsZero() || next.Before(s.end), next.Sub(time.Now())
}
// Monthly periods need to be considered separately as their length is not
// constant (28-31 days)
type monthly struct {
start, // Start time
end time.Time // End time, zero value means no end
started bool // Internal flag to handle first executions
ammount, // Ammount of months that made up a period
n int // Number of already executed events
}
// Constructor
func newMonthly(start, end time.Time, ammount int, notInmediately bool) (*monthly, error) {
// Check the input is valid
if ammount == 0 {
return nil, errors.New("0 months is not a valid period")
}
// If no start time was assigned, use current time
if start.IsZero() {
start = time.Now()
}
// If notInmediately was called, the starting date should not be returned
// by periodic.next() call, so we add 1 to the event count to avoid it
var n int
if notInmediately {
n = 1
}
return &monthly{start: start, end: end, started: notInmediately,
ammount: ammount, n: n}, nil
}
func (s *monthly) getCandidate() time.Time {
res := s.start.AddDate(0, s.n*s.ammount, 0)
if res.Day() != s.start.Day() {
res = res.AddDate(0, 0, -res.Day())
}
return res
}
// Implements scheduler.next()
func (s *monthly) next() (bool, time.Duration) {
// Calculate the next iteration
next := s.getCandidate()
for next.Before(time.Now()) {
if !s.started {
break
}
s.n++
next = s.getCandidate()
}
s.n++
if !s.started {
s.started = true
}
// Check if the end date has arrived
return s.end.IsZero() || next.Before(s.end), next.Sub(time.Now())
}
// Yearly periods need to be considered separately as
// their length is not constant (365-366 days)
type yearly struct {
start, // Start time
end time.Time // End time, zero value means no end
started bool // Internal flag to handle first executions
ammount, // Ammount of years that made up a period
n int // Number of already executed events
}
// Constructor
func newYearly(start, end time.Time, ammount int, notInmediately bool) (*yearly, error) {
// Check the input is valid
if ammount == 0 {
return nil, errors.New("0 years is not a valid period")
}
// If no start time was assigned, use current time
if start.IsZero() {
start = time.Now()
}
// If notInmediately was called, the starting date should not be returned
// by periodic.next() call, so we add 1 to the event count to avoid it
var n int
if notInmediately {
n = 1
}
return &yearly{start: start, end: end, started: notInmediately,
ammount: ammount, n: n}, nil
}
func (s *yearly) getCandidate() time.Time {
res := s.start.AddDate(s.n*s.ammount, 0, 0)
if res.Day() != s.start.Day() {
res = res.AddDate(0, 0, -res.Day())
}
return res
}
// implements scheduler.next()
func (s *yearly) next() (bool, time.Duration) {
// Calculate the next iteration
next := s.getCandidate()
for next.Before(time.Now()) {
if !s.started {
break
}
s.n++
next = s.getCandidate()
}
s.n++
if !s.started {
s.started = true
}
// Check if the end date has arrived
return s.end.IsZero() || next.Before(s.end), next.Sub(time.Now())
}