package gtq

import (
	"gopkg.in/yaml.v2"
	"sync"
	"time"
)

// Counter is an incrementing statistical value, with a Start time for rate
// calculation.
type Counter struct {
	Start time.Time
	Value uint64
}

// Stat for a queue priority level, grouped into timeslice buckets.
type Stat struct {
	timeSlices   []Counter
	currentSlice int
	window       time.Duration
	mutex        sync.Mutex
}

// NewStat initializes and returns a new Stat. window determines
// the size of the rolling statistics timeframe that is captured,
// which in turn determines how finely grained stats collection and task
// scheduling can be. window defaults to 1 second.
func NewStat(window time.Duration) (s *Stat) {
	s = &Stat{window: window}
	if s.window == 0 {
		s.window = time.Second
	}
	// default to 10 timeslice buckets, maybe make configurable later.
	s.timeSlices = make([]Counter, 10)
	return s
}

// Add increments the specified counter by the amount in val. window specifies
func (s *Stat) Add(val uint64) {
	s.mutex.Lock()
	defer s.mutex.Unlock()
	// roll over to next timeslice if slice duration has been exceeded.
	sliceLength := s.window / time.Duration(len(s.timeSlices))
	now := time.Now()
	elapsed := now.Sub(s.timeSlices[s.currentSlice].Start)
	if elapsed > sliceLength {
		s.currentSlice++
		s.currentSlice = s.currentSlice % len(s.timeSlices)
		s.timeSlices[s.currentSlice].Start = now
		s.timeSlices[s.currentSlice].Value = val
	}
	s.timeSlices[s.currentSlice].Value += val
}

// Total returns the current rolling total for this Stat.
func (s *Stat) Total() (t uint64) {
	for _, slice := range s.timeSlices {
		t += slice.Value
	}
	return t
}

// Start returns the start time for this statistics window.
func (s *Stat) Start() (start time.Time) {
	for i := s.currentSlice; i < 10; i++ {
		if s.timeSlices[i%10].Start.After(time.Time{}) {
			return s.timeSlices[i%10].Start
		}
	}
	return start
}

// Duration returns the size of the current statistics window in this Stat.
// This will fluctuate between 90-100% of the window size set when the state
// was created, as internal buckets roll over.
func (s *Stat) Duration() time.Duration {
	return time.Now().Sub(s.Start())
}

// Rate returns the flow rate of this counter, which is the current rolling
// value / the current statistics duration.
func (s *Stat) Rate() (r float64) {
	return float64(s.Total()) / (float64(s.Duration()) / float64(time.Second))
}

// QueueStats is a report of formatted Stat data about a specific priority
// queue captured at a point in time.
type QueueStats struct {
	Start time.Time
	time.Duration
	Count uint64
	Rate  float64
}

func (qs *QueueStats) String() string {
	b, _ := yaml.Marshal(qs)
	return string(b)
}

// Stats returns the current time usage statistics for all active task
// priority levels.
func (tq *TaskQueue) Stats() (stats map[uint]*QueueStats) {
	stats = make(map[uint]*QueueStats)
	tq.mutex.Lock()
	defer tq.mutex.Unlock()
	tq.queues.Range(func(prio, q interface{}) bool {
		stat := q.(*Queue).Done
		qs := &QueueStats{
			Start:    stat.Start(),
			Duration: stat.Duration(),
			Count:    stat.Total(),
			Rate:     stat.Rate(),
		}
		stats[prio.(uint)] = qs
		return true
	})
	return stats
}