package scheduler

import (
	"log"
	"strings"
	"time"

	"gitea.ceperka.net/rosti/incus-sentinel/incus"
	"github.com/robfig/cron/v3"
)

const queueLength = 100
const planReasonBackup = "backup"
const planReasonBackupVolume = "backup-volume"
const planReasonSync = "sync"
const planReasonSyncVolume = "sync-volume"

var defaultTags = []string{"sentinel"}

type schedulerPlan struct {
	Instance incus.Instance
	Volume   incus.Volume
	Reason   string // backup or sync
}

// Scheduler is the main struct that handles the scheduling of backups and syncs.
// It keeps internal queue of instances to be processed and it runs cron-like
// schedules for each instance.
type Scheduler struct {
	driver   Driver
	notifier Notifier

	planner           chan schedulerPlan   // Receives instance to be backed up and/or synced
	queueDumpRequest  chan bool            // Request to dump the queue
	queueDumpResponse chan []schedulerPlan // Response with the queue
	exit              chan bool            // Exit signal

	scheduledFootprint string // Footprint of the scheduler, used to identify if the scheduler needs to be changed
	cron               *cron.Cron
}

func NewScheduler(d Driver, n Notifier) *Scheduler {
	cron.New(cron.WithSeconds())

	s := &Scheduler{
		driver:            d,
		notifier:          n,
		planner:           make(chan schedulerPlan, 10),
		queueDumpRequest:  make(chan bool, 1),
		queueDumpResponse: make(chan []schedulerPlan, 1),
		exit:              make(chan bool),
	}

	go s.runMainLoop()

	return s
}

func (s *Scheduler) do(plan schedulerPlan, done chan schedulerPlan) {
	defer func() {
		done <- plan
	}()

	// Do the actual work
	sen := plan.Instance.Sentinel()
	var err error

	start := time.Now()

	notifyURL := ""

	switch plan.Reason {
	case planReasonBackup:
		log.Printf(".. backup of %s/%s instance started", plan.Instance.Project, plan.Instance.Name)

		err = s.driver.Backup(plan.Instance.Project, plan.Instance.Name, defaultTags)
		if err != nil {
			log.Printf(".. failed to backup %s: %s", plan.Instance.Name, err.Error())
			return
		}

		log.Printf(".. backup of %s took %s", plan.Instance.Name, time.Since(start).String())

		notifyURL = sen.BackupNotifyURL
	case planReasonSync:
		log.Printf(".. syncing of %s/%s instance started", plan.Instance.Project, plan.Instance.Name)

		err = s.driver.Sync(plan.Instance.Project, plan.Instance.Name, plan.Instance.Name+sen.SyncTargetInstanceSuffix, sen.SyncTargetRemote, sen.SyncTargetPool)
		if err != nil {
			log.Printf(".. failed to sync %s: %s", plan.Instance.Name, err.Error())
			return
		}

		log.Printf(".. sync of %s took %s", plan.Instance.Name, time.Since(start).String())

		notifyURL = sen.SyncNotifyURL
	case planReasonBackupVolume:
		log.Printf(".. backup of %s/%s/%s volume started", plan.Volume.Project, plan.Volume.Pool, plan.Volume.Name)

		sen := plan.Volume.Sentinel()
		if sen.BackupMode == "dir" {
			err = s.driver.BackupVolumeDir(plan.Volume.Project, plan.Volume.Pool, plan.Volume.Name, defaultTags)
		} else if sen.BackupMode == "native" {
			err = s.driver.BackupVolumeNative(plan.Volume.Project, plan.Volume.Pool, plan.Volume.Name, defaultTags)
		} else {
			log.Printf(".. invalid backup mode for volume %s/%s/%s: %s", plan.Volume.Project, plan.Volume.Pool, plan.Volume.Name, sen.BackupMode)
			return
		}

		if err != nil {
			log.Printf(".. failed to backup volume %s/%s/%s: %s", plan.Volume.Project, plan.Volume.Pool, plan.Volume.Name, err.Error())
			return
		}

		log.Printf(".. backup of volume %s/%s/%s took %s", plan.Volume.Project, plan.Volume.Pool, plan.Volume.Name, time.Since(start).String())

		notifyURL = sen.BackupNotifyURL
	case planReasonSyncVolume:
		log.Printf(".. syncing of %s/%s/%s volume started", plan.Volume.Project, plan.Volume.Pool, plan.Volume.Name)

		sen := plan.Volume.Sentinel()
		targetPool := plan.Volume.Pool
		if sen.SyncTargetPool != "" {
			targetPool = sen.SyncTargetPool
		}

		err = s.driver.SyncVolume(plan.Volume.Project, plan.Volume.Pool, plan.Volume.Name, sen.SyncTargetRemote, targetPool, plan.Volume.Name+sen.SyncTargetVolumeSuffix)
		if err != nil {
			log.Printf(".. failed to sync volume %s/%s/%s: %s", plan.Volume.Project, plan.Volume.Pool, plan.Volume.Name, err.Error())
			return
		}

		log.Printf(".. sync of volume %s/%s/%s took %s", plan.Volume.Project, plan.Volume.Pool, plan.Volume.Name, time.Since(start).String())

		notifyURL = sen.SyncNotifyURL
	}

	if notifyURL != "" && s.notifier != nil {
		err = s.notifier.Notify(notifyURL)
		if err != nil {
			log.Printf(".. failed to notify %s: %s", notifyURL, err.Error())
		} else {
			log.Printf(".. notification sent to %s", notifyURL)
		}
	} else if notifyURL != "" && s.notifier == nil {
		log.Println("Warning: No notifier configured, skipping notification")
	}
}

// Loop that does the heavy-lifting
func (s *Scheduler) runMainLoop() error {
	inProgress := false
	done := make(chan schedulerPlan)
	instancesToProcess := []schedulerPlan{}

	queue := make(chan schedulerPlan, queueLength)
	queuedInstances := make(map[string]schedulerPlan)

	ticker := time.NewTicker(2 * time.Second)
	defer ticker.Stop()

	lastQueueLog := 0

	for {
		select {
		// New instance to plan
		case newPlan := <-s.planner:
			if len(queue) >= queueLength {
				log.Printf("Queue full (%d)), dropping plan for %s of %s", len(queue), newPlan.Reason, newPlan.Instance.Name)
				continue
			}

			// Check if instance is already planned
			_, found := queuedInstances[newPlan.Reason+":"+newPlan.Instance.Name]

			if !found {
				queue <- newPlan
				queuedInstances[newPlan.Reason+":"+newPlan.Instance.Name] = newPlan
			}
		// Instance is done, remove it from the tracker
		case plan := <-done:
			delete(queuedInstances, plan.Reason+":"+plan.Instance.Name)
			inProgress = false
		// Dump the queue
		case <-s.queueDumpRequest:
			response := []schedulerPlan{}
			copy(response, instancesToProcess)
			s.queueDumpResponse <- response
		case <-s.exit:
			if inProgress {
				log.Println("Waiting for the current instance to finish ..")
				<-done
			}
			return nil
		// Check the queue and start processing
		case <-ticker.C:
			if !inProgress && len(queue) > 0 {
				inProgress = true
				go s.do(<-queue, done)
			}

			if len(queue) > 0 && lastQueueLog != len(queue) {
				log.Printf("Queue length: %d", len(queue))
			} else if len(queue) == 0 && lastQueueLog != 0 {
				log.Println("Queue empty")
			}

			lastQueueLog = len(queue)
		}
	}
}

func (s *Scheduler) Close() {
	s.exit <- true
}

func (s *Scheduler) Run() error {
	lastQueueDump := ""

	log.Println("Starting scheduler ..")
	for {
		s.refresh()

		// Print the list of instances in the queue
		s.queueDumpRequest <- true
		plans := <-s.queueDumpResponse
		if len(plans) > 0 {
			output := []string{}
			for _, plan := range plans {
				output = append(output, plan.Reason+":"+plan.Instance.Name)
			}

			outputString := strings.Join(output, ", ")
			if lastQueueDump != outputString {
				log.Println("Queue:", outputString)
				lastQueueDump = outputString
			}
		}

		time.Sleep(15 * time.Second)
	}
}

// Footprint is something like a hash of current config that is used to determine if the scheduler needs to be refreshed
func (s *Scheduler) footprint(is []incus.Instance, vols []incus.Volume) string {
	footprint := ""
	for _, inst := range is {
		sen := inst.Sentinel()
		footprint += inst.Project + inst.Name + sen.BackupSchedule + sen.SyncSchedule
	}

	for _, vol := range vols {
		sen := vol.Sentinel()
		footprint += vol.Project + vol.Name + vol.Pool + sen.BackupSchedule + sen.SyncSchedule
	}

	return footprint
}

// Checks if the scheduler needs to be refreshed and does it if needed
func (s *Scheduler) refresh() error {
	instances, err := s.driver.GetInstances("")
	if err != nil {
		return err
	}

	vols, err := s.driver.GetVolumes("")
	if err != nil {
		return err
	}

	err = s.setupInstanceSchedules(instances, vols)
	if err != nil {
		return err
	}

	return nil
}

// Refresh cron like schedulers for all instances
func (s *Scheduler) setupInstanceSchedules(is []incus.Instance, vols []incus.Volume) error {
	if s.scheduledFootprint == s.footprint(is, vols) {
		return nil
	}

	log.Println("Refreshing scheduler ..")

	if s.cron != nil {
		for _, e := range s.cron.Entries() {
			s.cron.Remove(e.ID)
		}
		s.cron.Stop()
	}

	s.cron = cron.New()

	// Instances
	for _, inst := range is {
		sen := inst.Sentinel()
		if sen.Backup {
			log.Println(".. adding backup schedule for", inst.Project, inst.Name, sen.BackupSchedule)
			_, err := s.cron.AddFunc(sen.BackupSchedule, func() {
				log.Printf(".. placing backup of %s/%s into the queue", inst.Project, inst.Name)
				s.planner <- schedulerPlan{Instance: inst, Reason: planReasonBackup}
			})
			if err != nil {
				return err
			}
		}

		if sen.Sync {
			log.Println(".. adding sync schedule for", inst.Project, inst.Name, sen.SyncSchedule)
			_, err := s.cron.AddFunc(sen.SyncSchedule, func() {
				log.Printf(".. placing sync of %s/%s into the queue", inst.Project, inst.Name)
				s.planner <- schedulerPlan{Instance: inst, Reason: planReasonSync}
			})
			if err != nil {
				return err
			}
		}
	}

	// Volumes
	for _, vol := range vols {
		sen := vol.Sentinel()
		if sen.Backup {
			log.Println(".. adding backup schedule for", vol.Project, vol.Pool, vol.Name, sen.BackupSchedule)
			_, err := s.cron.AddFunc(sen.BackupSchedule, func() {
				log.Printf(".. placing volume backup of %s/%s/%s into the queue", vol.Project, vol.Pool, vol.Name)
				s.planner <- schedulerPlan{Volume: vol, Reason: planReasonBackupVolume}
			})
			if err != nil {
				return err
			}
		}

		if sen.Sync {
			log.Println(".. adding sync schedule for", vol.Project, vol.Pool, vol.Name, sen.SyncSchedule)
			_, err := s.cron.AddFunc(sen.SyncSchedule, func() {
				log.Printf(".. placing volume sync of %s/%s/%s into the queue", vol.Project, vol.Pool, vol.Name)
				s.planner <- schedulerPlan{Volume: vol, Reason: planReasonSyncVolume}
			})
			if err != nil {
				return err
			}
		}
	}

	s.scheduledFootprint = s.footprint(is, vols)
	s.cron.Start()

	return nil
}