// Packege pubsub implements publisher-subscribers model used in multi-channel streaming.
package pubsub

import (
	"github.com/nareix/joy4/av"
	"io"
	"time"
	"sync"
)

//        time
// ----------------->
// 
// V-A-V-V-A-V-V-A-V-V
// |                 |
// 0        5        10
// head             tail
// oldest          latest
// 

// One publisher and multiple subscribers thread-safe packet buffer queue.
type Queue struct {
	pkts []av.Packet
	head, tail int
	lock *sync.RWMutex
	cond *sync.Cond
	maxdur time.Duration
	streams []av.CodecData
	videoidx int
	closed bool
}

func NewQueue(streams []av.CodecData) *Queue {
	q := &Queue{}
	q.streams = streams
	q.maxdur = time.Second*10
	q.lock = &sync.RWMutex{}
	q.cond = sync.NewCond(q.lock.RLocker())
	q.videoidx = -1
	for i, stream := range streams {
		if stream.Type().IsVideo() {
			q.videoidx = i
		}
	}
	return q
}

// Set max buffered total packets duration.
func (self *Queue) SetMaxDuration(dur time.Duration) {
	self.lock.Lock()

	self.maxdur = dur
	for self.maxdur > 0 && len(self.pkts) >= 2 && self.pkts[len(self.pkts)-1].Time - self.pkts[0].Time > self.maxdur {
		self.pkts = self.pkts[1:]
		self.head++
	}

	self.lock.Unlock()
	return
}

// Currently buffered packets total duration.
func (self *Queue) Duration() (dur time.Duration) {
	self.lock.RLock()

	if len(self.pkts) >= 2 {
		dur = self.pkts[len(self.pkts)-1].Time - self.pkts[0].Time
	}

	self.lock.RUnlock()
	return
}

// After Close() called, all QueueCursor's ReadPacket will return io.EOF.
func (self *Queue) Close() (err error) {
	self.lock.Lock()

	self.closed = true
	self.cond.Broadcast()

	self.lock.Unlock()
	return
}

// Put packet into buffer, old packets will be discared.
func (self *Queue) WritePacket(pkt av.Packet) (err error) {
	self.lock.Lock()

	if self.maxdur > 0 && len(self.pkts) >= 2 && self.pkts[len(self.pkts)-1].Time - self.pkts[0].Time > self.maxdur {
		self.pkts = self.pkts[1:]
		self.head++
	}
	self.pkts = append(self.pkts, pkt)
	self.tail++
	self.cond.Broadcast()

	self.lock.Unlock()
	return
}

type QueueCursor struct {
	que *Queue
	pos int
	init func(pkts []av.Packet, videoidx int) int
}

func (self *Queue) newCursor() *QueueCursor {
	return &QueueCursor{
		que: self,
		pos: -1,
	}
}

// Create cursor position at latest packet.
func (self *Queue) Latest() *QueueCursor {
	cursor := self.newCursor()
	cursor.init = func(pkts []av.Packet, videoidx int) int {
		return len(pkts)
	}
	return cursor
}

// Create cursor position at oldest buffered packet.
func (self *Queue) Oldest() *QueueCursor {
	cursor := self.newCursor()
	cursor.init = func(pkts []av.Packet, videoidx int) int {
		return 0
	}
	return cursor
}

// Create cursor position at specific time in buffered packets.
func (self *Queue) DelayedTime(dur time.Duration) *QueueCursor {
	cursor := self.newCursor()
	cursor.init = func(pkts []av.Packet, videoidx int) int {
		i := len(self.pkts)-1
		if i > 0 {
			end := self.pkts[i]
			for i--; i >= 0; i-- {
				if end.Time - self.pkts[i].Time > dur {
					break
				}
			}
		}
		return i
	}
	return cursor
}

// Create cursor position at specific delayed GOP count in buffered packets.
func (self *Queue) DelayedGopCount(n int) *QueueCursor {
	cursor := self.newCursor()
	cursor.init = func(pkts []av.Packet, videoidx int) int {
		i := 0
		if videoidx != -1 {
			i = len(self.pkts)-1
			for gop := 0; i >= 0 && gop < n; i-- {
				if self.pkts[i].Idx == int8(self.videoidx) && self.pkts[i].IsKeyFrame {
					gop++
				}
			}
		}
		return i
	}
	return cursor
}

func (self *QueueCursor) Streams() (streams []av.CodecData, err error) {
	self.que.lock.RLock()
	streams = self.que.streams
	self.que.lock.RUnlock()
	return
}

// ReadPacket will not consume packets in Queue, it's just a cursor.
func (self *QueueCursor) ReadPacket() (pkt av.Packet, err error) {
	self.que.cond.L.Lock()
	if self.pos == -1 {
		self.pos = self.init(self.que.pkts, self.que.videoidx)+self.que.head
	}
	for {
		if self.pos - self.que.head < 0 {
			self.pos = self.que.head
		} else if self.pos - self.que.tail > 0 {
			self.pos = self.que.tail
		}
		if self.pos - self.que.head >= 0 && self.pos - self.que.tail < 0 {
			pkt = self.que.pkts[self.pos - self.que.head]
			self.pos++
			break
		}
		if self.que.closed {
			err = io.EOF
			break
		}
		self.que.cond.Wait()
	}
	self.que.cond.L.Unlock()
	return
}