package manager

import "sync"
import "time"
import "runtime"

//import "github.com/gin-gonic/gin"
import "github.com/rs/zerolog/log"
import "github.com/sneak/feta/toot"
import "github.com/sneak/feta/seeds"
import "github.com/sneak/feta/instance"

const hostDiscoveryParallelism = 5

// LogReportInterval defines how long between logging internal
// stats/reporting for user supervision
var LogReportInterval = time.Second * 10

// InstanceManager is the main data structure for the goroutine that manages
// the list of all known instances, fed by the locator
type InstanceManager struct {
	mu                       sync.Mutex
	instances                map[instance.Hostname]*instance.Instance
	newInstanceNotifications chan instance.Hostname
	tootDestination          chan *toot.Toot
	startup                  time.Time
	hostAdderSemaphore       chan bool
}

// New returns a new InstanceManager for use by the Process
func New() *InstanceManager {
	i := new(InstanceManager)
	i.hostAdderSemaphore = make(chan bool, hostDiscoveryParallelism)
	i.instances = make(map[instance.Hostname]*instance.Instance)
	return i
}

// SetTootDestination provides the instancemanager with a channel to the
// ingester that it can give to its instances
func (im *InstanceManager) SetTootDestination(td chan *toot.Toot) {
	im.tootDestination = td
}

func (im *InstanceManager) logCaller(msg string) {
	fpcs := make([]uintptr, 1)
	// Skip 2 levels to get the caller
	n := runtime.Callers(3, fpcs)
	if n == 0 {
		log.Debug().Msg("MSG: NO CALLER")
	}

	caller := runtime.FuncForPC(fpcs[0] - 1)
	if caller == nil {
		log.Debug().Msg("MSG CALLER WAS NIL")
	}

	// Print the file name and line number
	filename, line := caller.FileLine(fpcs[0] - 1)
	function := caller.Name()

	log.Debug().
		Str("filename", filename).
		Int("linenum", line).
		Str("function", function).
		Msg(msg)
}

func (im *InstanceManager) lock() {
	im.mu.Lock()
}

func (im *InstanceManager) unlock() {
	im.mu.Unlock()
}

// SetInstanceNotificationChannel is how the Process tells the
// InstanceManager about the channel from the InstanceLocator so that the
// InstanceLocator can provide it/us (the InstanceManager) with new
// instance.Hostnames.  We (the manager) deduplicate the list ourselves.
func (im *InstanceManager) SetInstanceNotificationChannel(via chan instance.Hostname) {
	im.lock()
	defer im.unlock()
	im.newInstanceNotifications = via
}

func (im *InstanceManager) receiveSeedInstanceHostnames() {
	for _, x := range seeds.SeedInstances {
		go func(tmp instance.Hostname) {
			im.addInstanceByHostname(tmp)
		}(instance.Hostname(x))
	}
}

// Manage is the main entrypoint of the InstanceManager, designed to be
// called once in its own goroutine.
func (im *InstanceManager) Manage() {
	log.Info().Msg("InstanceManager starting")
	go func() {
		im.receiveNewInstanceHostnames()
	}()

	im.startup = time.Now()
	x := im.startup

	go func() {
		im.receiveSeedInstanceHostnames()
	}()

	for {
		log.Info().Msg("InstanceManager tick")
		im.managerLoop()
		time.Sleep(1 * time.Second)
		if time.Now().After(x.Add(LogReportInterval)) {
			x = time.Now()
			im.logInstanceReport()
		}
	}
}

func (im *InstanceManager) managerLoop() {
	im.lock()
	il := make([]*instance.Instance, 0)
	for _, v := range im.instances {
		il = append(il, v)
	}
	im.unlock()

	// FIXME is this a bug outside of the mutex above?
	for _, v := range il {
		go func(i *instance.Instance) {
			i.Tick()
		}(v)
	}
}

func (im *InstanceManager) hostnameExists(newhn instance.Hostname) bool {
	im.lock()
	defer im.unlock()
	for k := range im.instances {
		if newhn == k {
			return true
		}
	}
	return false
}

func (im *InstanceManager) addInstanceByHostname(newhn instance.Hostname) {
	if im.hostnameExists(newhn) {
		// ignore adding new if we already know about it
		return
	}

	// this blocks on the channel size, limiting concurrency
	im.hostAdderSemaphore <- true

	i := instance.New(func(x *instance.Instance) {
		x.Hostname = string(newhn)               // set hostname
		x.SetTootDestination(im.tootDestination) // copy ingester input channel from manager to instance
	})
	// we do node detection under the adderSemaphore to avoid thundering
	// on startup
	i.DetectNodeTypeIfNecessary()

	// pop an item from the buffered channel
	<-im.hostAdderSemaphore

	// lock the map to insert
	im.lock()
	im.instances[newhn] = i
	im.unlock()

}

func (im *InstanceManager) receiveNewInstanceHostnames() {
	var newhn instance.Hostname
	for {
		newhn = <-im.newInstanceNotifications
		// receive them fast out of the channel, let the adding function lock to add
		// them one at a time, using a bunch of blocked goroutines as our
		// modification queue
		go im.addInstanceByHostname(newhn)
	}
}

func (im *InstanceManager) logInstanceReport() {
	r := im.instanceSummaryReport()

	sublogger := log.With().Logger()

	for k, v := range r {
		sublogger = sublogger.With().Uint(k, v).Logger()
	}

	sublogger.Info().
		Msg("instance report")
}

// ListInstances dumps a slice of all Instances the InstanceManager knows
// about
func (im *InstanceManager) ListInstances() []*instance.Instance {
	var out []*instance.Instance
	im.lock()
	defer im.unlock()
	for _, v := range im.instances {
		out = append(out, v)
	}
	return out
}

func (im *InstanceManager) instanceSummaryReport() map[string]uint {
	r := make(map[string]uint)
	for _, v := range im.ListInstances() {
		v.Lock()
		r[v.Status()]++
		v.Unlock()
	}
	return r
}