package gocron

import (
	"math"
	"reflect"
	"sort"
	"strings"
	"time"
)

// Scheduler struct stores a list of Jobs and the location of time Scheduler
// Scheduler implements the sort.Interface{} for sorting Jobs, by the time of nextRun
type Scheduler struct {
	jobs []*Job
	loc  *time.Location

	running  bool
	stopChan chan struct{} // signal to stop scheduling

	time timeWrapper // wrapper around time.Time
}

// NewScheduler creates a new Scheduler
func NewScheduler(loc *time.Location) *Scheduler {
	return &Scheduler{
		jobs:     make([]*Job, 0),
		loc:      loc,
		running:  false,
		stopChan: make(chan struct{}),
		time:     &trueTime{},
	}
}

// StartBlocking starts all the pending jobs using a second-long ticker and blocks the current thread
func (s *Scheduler) StartBlocking() {
	<-s.StartAsync()
}

// StartAsync starts a goroutine that runs all the pending using a second-long ticker
func (s *Scheduler) StartAsync() chan struct{} {
	if s.running {
		return s.stopChan
	}
	s.running = true

	s.scheduleAllJobs()
	ticker := s.time.NewTicker(1 * time.Second)
	go func() {
		for {
			select {
			case <-ticker.C:
				s.RunPending()
			case <-s.stopChan:
				ticker.Stop()
				s.running = false
				return
			}
		}
	}()

	return s.stopChan
}

// Jobs returns the list of Jobs from the Scheduler
func (s *Scheduler) Jobs() []*Job {
	return s.jobs
}

// Len returns the number of Jobs in the Scheduler
func (s *Scheduler) Len() int {
	return len(s.jobs)
}

// Swap
func (s *Scheduler) Swap(i, j int) {
	s.jobs[i], s.jobs[j] = s.jobs[j], s.jobs[i]
}

func (s *Scheduler) Less(i, j int) bool {
	return s.jobs[j].nextRun.Unix() >= s.jobs[i].nextRun.Unix()
}

// ChangeLocation changes the default time location
func (s *Scheduler) ChangeLocation(newLocation *time.Location) {
	s.loc = newLocation
}

// scheduleNextRun Compute the instant when this Job should run next
func (s *Scheduler) scheduleNextRun(j *Job) {
	j.Lock()
	defer j.Unlock()
	now := s.time.Now(s.loc)

	if j.startsImmediately {
		j.nextRun = now
		j.startsImmediately = false
		return
	}

	// delta represent the time slice used to calculate the next run
	// it can be the last time ran by a job, or time.Now() if the job never ran
	var delta time.Time
	if j.neverRan() {
		if !j.nextRun.IsZero() { // scheduled for future run, wait to run at least once
			return
		}
		delta = now
	} else {
		delta = j.lastRun
	}

	switch j.unit {
	case seconds, minutes, hours:
		j.nextRun = s.rescheduleDuration(j, delta)
	case days:
		j.nextRun = s.rescheduleDay(j, delta)
	case weeks:
		j.nextRun = s.rescheduleWeek(j, delta)
	case months:
		j.nextRun = s.rescheduleMonth(j, delta)
	}
}

func (s *Scheduler) rescheduleMonth(j *Job, delta time.Time) time.Time {
	if j.neverRan() { // calculate days to j.dayOfTheMonth
		jobDay := time.Date(delta.Year(), delta.Month(), j.dayOfTheMonth, 0, 0, 0, 0, s.loc).Add(j.atTime)
		daysDifference := int(math.Abs(delta.Sub(jobDay).Hours()) / 24)
		nextRun := s.roundToMidnight(delta)
		if jobDay.Before(delta) { // shouldn't run this month; schedule for next interval minus day difference

			nextRun = nextRun.AddDate(0, int(j.interval), -daysDifference)
		} else {
			if j.interval == 1 { // every month counts current month
				nextRun = nextRun.AddDate(0, int(j.interval)-1, daysDifference)
			} else { // should run next month interval
				nextRun = nextRun.AddDate(0, int(j.interval), daysDifference)
			}
		}
		return nextRun.Add(j.atTime)
	}
	return s.roundToMidnight(delta).AddDate(0, int(j.interval), 0).Add(j.atTime)
}

func (s *Scheduler) rescheduleWeek(j *Job, delta time.Time) time.Time {
	var days int
	if j.scheduledWeekday != nil { // weekday selected, Every().Monday(), for example
		days = s.calculateWeekdayDifference(delta, j)
	} else {
		days = int(j.interval) * 7
	}
	delta = s.roundToMidnight(delta)
	return delta.AddDate(0, 0, days).Add(j.atTime)
}

func (s *Scheduler) rescheduleDay(j *Job, delta time.Time) time.Time {
	if j.interval == 1 {
		atTime := time.Date(delta.Year(), delta.Month(), delta.Day(), 0, 0, 0, 0, s.loc).Add(j.atTime)
		if delta.Before(atTime) { // should run today
			return s.roundToMidnight(delta).Add(j.atTime)
		}
	}
	return s.roundToMidnight(delta).AddDate(0, 0, int(j.interval)).Add(j.atTime)
}

func (s *Scheduler) rescheduleDuration(j *Job, delta time.Time) time.Time {
	if j.neverRan() && j.atTime != 0 { // ugly. in order to avoid this we could prohibit setting .At() and allowing only .StartAt() when dealing with Duration types
		atTime := time.Date(delta.Year(), delta.Month(), delta.Day(), 0, 0, 0, 0, s.loc).Add(j.atTime)
		if delta.Before(atTime) || delta.Equal(atTime) {
			return s.roundToMidnight(delta).Add(j.atTime)
		}
	}

	var periodDuration time.Duration
	switch j.unit {
	case seconds:
		periodDuration = time.Duration(j.interval) * time.Second
	case minutes:
		periodDuration = time.Duration(j.interval) * time.Minute
	case hours:
		periodDuration = time.Duration(j.interval) * time.Hour
	}
	return delta.Add(periodDuration)
}

func (s *Scheduler) calculateWeekdayDifference(delta time.Time, j *Job) int {
	daysToWeekday := remainingDaysToWeekday(delta.Weekday(), *j.scheduledWeekday)

	if j.interval > 1 {
		return daysToWeekday + int(j.interval-1)*7 // minus a week since to compensate daysToWeekday
	}

	if daysToWeekday > 0 { // within the next following days, but not today
		return daysToWeekday
	}

	// following paths are on same day
	if j.atTime.Seconds() == 0 && j.neverRan() { // .At() not set, run today
		return 0
	}

	atJobTime := time.Date(delta.Year(), delta.Month(), delta.Day(), 0, 0, 0, 0, s.loc).Add(j.atTime)
	if delta.Before(atJobTime) || delta.Equal(atJobTime) { // .At() set and should run today
		return 0
	}

	return 7
}

func remainingDaysToWeekday(from time.Weekday, to time.Weekday) int {
	daysUntilScheduledDay := int(to) - int(from)
	if daysUntilScheduledDay < 0 {
		daysUntilScheduledDay += 7
	}
	return daysUntilScheduledDay
}

// roundToMidnight truncates time to midnight
func (s *Scheduler) roundToMidnight(t time.Time) time.Time {
	return time.Date(t.Year(), t.Month(), t.Day(), 0, 0, 0, 0, s.loc)
}

// Get the current runnable Jobs, which shouldRun is True
func (s *Scheduler) runnableJobs() []*Job {
	var runnableJobs []*Job
	sort.Sort(s)
	for _, job := range s.jobs {
		if s.shouldRun(job) {
			runnableJobs = append(runnableJobs, job)
		} else {
			break
		}
	}
	return runnableJobs
}

// NextRun datetime when the next Job should run.
func (s *Scheduler) NextRun() (*Job, time.Time) {
	if len(s.jobs) <= 0 {
		return nil, s.time.Now(s.loc)
	}
	sort.Sort(s)
	return s.jobs[0], s.jobs[0].nextRun
}

// Every schedules a new periodic Job with interval
func (s *Scheduler) Every(interval uint64) *Scheduler {
	job := NewJob(interval)
	s.jobs = append(s.jobs, job)
	return s
}

// RunPending runs all the Jobs that are scheduled to run.
func (s *Scheduler) RunPending() {
	for _, job := range s.runnableJobs() {
		s.runAndReschedule(job) // we should handle this error somehow
	}
}

func (s *Scheduler) runAndReschedule(job *Job) error {
	if err := s.run(job); err != nil {
		return err
	}
	s.scheduleNextRun(job)
	return nil
}

func (s *Scheduler) run(job *Job) error {
	job.lastRun = s.time.Now(s.loc)
	go job.run()

	return nil
}

// RunAll run all Jobs regardless if they are scheduled to run or not
func (s *Scheduler) RunAll() {
	s.RunAllWithDelay(0)
}

// RunAllWithDelay runs all Jobs with delay seconds
func (s *Scheduler) RunAllWithDelay(d int) {
	for _, job := range s.jobs {
		err := s.run(job)
		if err != nil {
			continue
		}
		s.time.Sleep(time.Duration(d) * time.Second)
	}
}

// Remove specific Job j by function
func (s *Scheduler) Remove(j interface{}) {
	s.removeByCondition(func(someJob *Job) bool {
		return someJob.jobFunc == getFunctionName(j)
	})
}

// RemoveByReference removes specific Job j by reference
func (s *Scheduler) RemoveByReference(j *Job) {
	s.removeByCondition(func(someJob *Job) bool {
		return someJob == j
	})
}

func (s *Scheduler) removeByCondition(shouldRemove func(*Job) bool) {
	retainedJobs := make([]*Job, 0)
	for _, job := range s.jobs {
		if !shouldRemove(job) {
			retainedJobs = append(retainedJobs, job)
		}
	}
	s.jobs = retainedJobs
}

// RemoveJobByTag will Remove Jobs by Tag
func (s *Scheduler) RemoveJobByTag(tag string) error {
	jobindex, err := s.findJobsIndexByTag(tag)
	if err != nil {
		return err
	}
	// Remove job if jobindex is valid
	s.jobs = removeAtIndex(s.jobs, jobindex)
	return nil
}

// Find first job index by given string
func (s *Scheduler) findJobsIndexByTag(tag string) (int, error) {
	for i, job := range s.jobs {
		if strings.Contains(strings.Join(job.Tags(), " "), tag) {
			return i, nil
		}
	}
	return -1, ErrJobNotFoundWithTag
}

func removeAtIndex(jobs []*Job, i int) []*Job {
	if i == len(jobs)-1 {
		return jobs[:i]
	}
	jobs = append(jobs[:i], jobs[i+1:]...)
	return jobs
}

// Scheduled checks if specific Job j was already added
func (s *Scheduler) Scheduled(j interface{}) bool {
	for _, job := range s.jobs {
		if job.jobFunc == getFunctionName(j) {
			return true
		}
	}
	return false
}

// Clear clear all Jobs from this scheduler
func (s *Scheduler) Clear() {
	s.jobs = make([]*Job, 0)
}

// Stop stops the scheduler. This is a no-op if the scheduler is already stopped .
func (s *Scheduler) Stop() {
	if s.running {
		s.stopScheduler()
	}
}

func (s *Scheduler) stopScheduler() {
	s.stopChan <- struct{}{}
}

// Do specifies the jobFunc that should be called every time the Job runs
func (s *Scheduler) Do(jobFun interface{}, params ...interface{}) (*Job, error) {
	j := s.getCurrentJob()
	if j.err != nil {
		return nil, j.err
	}

	typ := reflect.TypeOf(jobFun)
	if typ.Kind() != reflect.Func {
		return nil, ErrNotAFunction
	}

	fname := getFunctionName(jobFun)
	j.funcs[fname] = jobFun
	j.fparams[fname] = params
	j.jobFunc = fname

	// we should not schedule if not running since we cant foresee how long it will take for the scheduler to start
	if s.running {
		s.scheduleNextRun(j)
	}

	return j, nil
}

// At schedules the Job at a specific time of day in the form "HH:MM:SS" or "HH:MM"
func (s *Scheduler) At(t string) *Scheduler {
	j := s.getCurrentJob()
	hour, min, sec, err := parseTime(t)
	if err != nil {
		j.err = ErrTimeFormat
		return s
	}
	// save atTime start as duration from midnight
	j.atTime = time.Duration(hour)*time.Hour + time.Duration(min)*time.Minute + time.Duration(sec)*time.Second
	return s
}

// SetTag will add tag when creating a job
func (s *Scheduler) SetTag(t []string) *Scheduler {
	job := s.getCurrentJob()
	job.tags = t
	return s
}

// StartAt schedules the next run of the Job
func (s *Scheduler) StartAt(t time.Time) *Scheduler {
	s.getCurrentJob().nextRun = t
	return s
}

// StartImmediately sets the Jobs next run as soon as the scheduler starts
func (s *Scheduler) StartImmediately() *Scheduler {
	job := s.getCurrentJob()
	job.startsImmediately = true
	return s
}

// shouldRun returns true if the Job should be run now
func (s *Scheduler) shouldRun(j *Job) bool {
	return j.shouldRun() && s.time.Now(s.loc).Unix() >= j.nextRun.Unix()
}

// setUnit sets the unit type
func (s *Scheduler) setUnit(unit timeUnit) {
	currentJob := s.getCurrentJob()
	currentJob.unit = unit
}

// Second sets the unit with seconds
func (s *Scheduler) Second() *Scheduler {
	return s.Seconds()
}

// Seconds sets the unit with seconds
func (s *Scheduler) Seconds() *Scheduler {
	s.setUnit(seconds)
	return s
}

// Minute sets the unit with minutes
func (s *Scheduler) Minute() *Scheduler {
	return s.Minutes()
}

// Minutes sets the unit with minutes
func (s *Scheduler) Minutes() *Scheduler {
	s.setUnit(minutes)
	return s
}

// Hour sets the unit with hours
func (s *Scheduler) Hour() *Scheduler {
	return s.Hours()
}

// Hours sets the unit with hours
func (s *Scheduler) Hours() *Scheduler {
	s.setUnit(hours)
	return s
}

// Day sets the unit with days
func (s *Scheduler) Day() *Scheduler {
	s.setUnit(days)
	return s
}

// Days set the unit with days
func (s *Scheduler) Days() *Scheduler {
	s.setUnit(days)
	return s
}

// Week sets the unit with weeks
func (s *Scheduler) Week() *Scheduler {
	s.setUnit(weeks)
	return s
}

// Weeks sets the unit with weeks
func (s *Scheduler) Weeks() *Scheduler {
	s.setUnit(weeks)
	return s
}

// Month sets the unit with months
func (s *Scheduler) Month(dayOfTheMonth int) *Scheduler {
	return s.Months(dayOfTheMonth)
}

// Months sets the unit with months
func (s *Scheduler) Months(dayOfTheMonth int) *Scheduler {
	s.getCurrentJob().dayOfTheMonth = dayOfTheMonth
	s.setUnit(months)
	return s
}

// NOTE: If the dayOfTheMonth for the above two functions is
// more than the number of days in that month, the extra day(s)
// spill over to the next month. Similarly, if it's less than 0,
// it will go back to the month before

// Weekday sets the start with a specific weekday weekday
func (s *Scheduler) Weekday(startDay time.Weekday) *Scheduler {
	s.getCurrentJob().scheduledWeekday = &startDay
	s.setUnit(weeks)
	return s
}

// Monday sets the start day as Monday
func (s *Scheduler) Monday() *Scheduler {
	return s.Weekday(time.Monday)
}

// Tuesday sets the start day as Tuesday
func (s *Scheduler) Tuesday() *Scheduler {
	return s.Weekday(time.Tuesday)
}

// Wednesday sets the start day as Wednesday
func (s *Scheduler) Wednesday() *Scheduler {
	return s.Weekday(time.Wednesday)
}

// Thursday sets the start day as Thursday
func (s *Scheduler) Thursday() *Scheduler {
	return s.Weekday(time.Thursday)
}

// Friday sets the start day as Friday
func (s *Scheduler) Friday() *Scheduler {
	return s.Weekday(time.Friday)
}

// Saturday sets the start day as Saturday
func (s *Scheduler) Saturday() *Scheduler {
	return s.Weekday(time.Saturday)
}

// Sunday sets the start day as Sunday
func (s *Scheduler) Sunday() *Scheduler {
	return s.Weekday(time.Sunday)
}

func (s *Scheduler) getCurrentJob() *Job {
	return s.jobs[len(s.jobs)-1]
}

func (s *Scheduler) scheduleAllJobs() {
	for _, j := range s.jobs {
		s.scheduleNextRun(j)
	}
}