package client

import (
	"context"
	"fmt"
	"net"
	"strconv"
	"strings"
	"time"

	"storrent/bt"
	"storrent/dht"
	"storrent/metainfo"
	"storrent/utp"
)

type state int

const (
	stopped state = iota
	downloading
	seeding
	done
	errored
)

const (
	maxPeers      = 8
	maxPending    = 5
	dialTimeout   = 30 * time.Second
	retryInterval = 30 * time.Second
	dhtTimeout    = 5 * time.Minute
	recvBufSize   = 128
)

type recv struct {
	msg *bt.Msg
	err error
	p   *bt.Peer
}

type statusReq struct {
	field string
	resp  chan string
}

type torrent struct {
	id   int
	meta *metainfo.File
	dir  string
	dht  *dht.DHT
	utp  *utp.Socket

	start    chan struct{}
	stop     chan struct{}
	seed     chan struct{}
	incoming chan *bt.Peer
	addPeer  chan *net.TCPAddr
	status   chan statusReq

	peers     *peerManager
	scheduler *pieceScheduler
	dialPool  *dialPool

	st   state
	down int64
	up   int64

	ctx    context.Context
	cancel context.CancelFunc
	recvs  chan recv
	retry  <-chan time.Time
}

func newTorrent(id int, m *metainfo.File, dir string, d *dht.DHT, utpSock *utp.Socket) *torrent {
	t := &torrent{
		id:        id,
		meta:      m,
		dir:       dir,
		dht:       d,
		utp:       utpSock,
		start:     make(chan struct{}, 1),
		stop:      make(chan struct{}, 1),
		seed:      make(chan struct{}, 1),
		incoming:  make(chan *bt.Peer),
		addPeer:   make(chan *net.TCPAddr, 8),
		status:    make(chan statusReq),
		peers:     newPeerManager(maxPeers),
		scheduler: newPieceScheduler(m, dir),
		dialPool:  newDialPool(d, utpSock, m.InfoHash),
		st:        stopped,
		recvs:     make(chan recv, recvBufSize),
	}
	return t
}

func (t *torrent) run() {
	for {
		select {
		case <-t.start:
			t.handleStart()

		case <-t.seed:
			t.handleSeed()

		case <-t.stop:
			t.handleStop()

		case <-t.retry:
			t.handleRetry()

		case d := <-t.dialPool.results:
			t.handleDialResult(d)

		case p := <-t.incoming:
			t.handleIncoming(p)

		case addr := <-t.addPeer:
			t.handleAddPeer(addr)

		case r := <-t.recvs:
			t.handleRecv(r)

		case req := <-t.status:
			req.resp <- t.handleStatus(req.field)
		}
	}
}

func (t *torrent) handleStart() {
	if t.st != stopped {
		return
	}
	t.st = downloading
	t.ctx, t.cancel = context.WithCancel(context.Background())
	t.dialPool.start(t.ctx)
}

func (t *torrent) handleSeed() {
	if t.st != stopped && t.st != done {
		return
	}
	if !t.scheduler.isComplete() {
		return
	}
	t.st = seeding
	t.ctx, t.cancel = context.WithCancel(context.Background())
	t.dialPool.start(t.ctx)
}

func (t *torrent) handleStop() {
	if !t.isActive() {
		return
	}
	t.cancel()
	t.dialPool.stop()
	t.peers.closeAll()
	t.retry = nil
	t.st = stopped
}

func (t *torrent) handleRetry() {
	t.retry = nil
	if t.isActive() {
		t.dialPool.start(t.ctx)
	}
}

func (t *torrent) handleDialResult(d dialResult) {
	if d.done {
		if t.peers.count() < maxPeers && t.isActive() {
			t.retry = time.After(retryInterval)
		}
		return
	}

	if d.peer == nil {
		return
	}

	p := d.peer
	if !t.peers.add(p) {
		p.Close()
		return
	}

	go t.recvLoop(p)
	if err := t.initPeer(p); err != nil {
		p.Close()
		t.peers.remove(p)
	}
}

func (t *torrent) handleIncoming(p *bt.Peer) {
	t.peers.addUnlimited(p)
	go t.recvLoop(p)

	if err := p.Send(&bt.Msg{Kind: bt.Bitfield, Bitfield: t.scheduler.bitfield(false)}); err != nil {
		p.Close()
		t.peers.remove(p)
		return
	}
	if err := p.Send(&bt.Msg{Kind: bt.Unchoke}); err != nil {
		p.Close()
		t.peers.remove(p)
	}
}

func (t *torrent) handleAddPeer(addr *net.TCPAddr) {
	if !t.isActive() {
		return
	}
	t.dialPool.dialSingle(t.ctx, addr)
}

func (t *torrent) handleRecv(r recv) {
	if r.err != nil {
		r.p.Close()
		t.peers.remove(r.p)
		t.scheduler.peerDisconnected(r.p)
		if t.peers.count() < maxPeers && t.isActive() {
			t.dialPool.start(t.ctx)
		}
		return
	}

	if r.msg == nil {
		return
	}

	p := r.p
	m := r.msg

	switch m.Kind {
	case bt.Choke:
		p.Choked = true
		p.Pending = 0

	case bt.Unchoke:
		p.Choked = false

	case bt.Have:
		p.SetPiece(int(m.Index))

	case bt.Bitfield:
		p.SetPieces(m.Bitfield, t.scheduler.count())

	case bt.Piece:
		t.scheduler.put(int(m.Index), int(m.Begin), m.Block)
		p.Pending--
		t.down += int64(len(m.Block))

	case bt.Request:
		t.handleRequest(p, m)
	}

	t.sendRequests(p)
	t.checkCompletion()
}

func (t *torrent) handleRequest(p *bt.Peer, m *bt.Msg) {
	data := t.scheduler.pieceData(int(m.Index))
	if data == nil {
		return
	}
	end := int(m.Begin + m.Length)
	if end > len(data) {
		return
	}
	if err := p.Send(&bt.Msg{
		Kind:  bt.Piece,
		Index: m.Index,
		Begin: m.Begin,
		Block: data[m.Begin:end],
	}); err != nil {
		p.Close()
		return
	}
	t.up += int64(m.Length)
}

func (t *torrent) sendRequests(p *bt.Peer) {
	if p.Choked {
		return
	}
	for p.Pending < maxPending {
		req := t.scheduler.nextRequest(p)
		if req == nil {
			break
		}
		if err := p.Send(req); err != nil {
			p.Close()
			break
		}
		p.Pending++
	}
}

func (t *torrent) checkCompletion() {
	if t.st == downloading && t.scheduler.isComplete() {
		t.st = done
		t.peers.closeAll()
	}
}

func (t *torrent) initPeer(p *bt.Peer) error {
	if t.st == seeding {
		return p.Send(&bt.Msg{Kind: bt.Bitfield, Bitfield: t.scheduler.bitfield(true)})
	}
	return p.Send(&bt.Msg{Kind: bt.Interested})
}

func (t *torrent) recvLoop(p *bt.Peer) {
	for {
		msg, err := p.Recv()
		t.recvs <- recv{msg, err, p}
		if err != nil {
			return
		}
	}
}

func (t *torrent) isActive() bool {
	return t.st == downloading || t.st == seeding
}

func (t *torrent) startDownload() {
	select {
	case t.start <- struct{}{}:
	default:
	}
}

func (t *torrent) startSeed() {
	select {
	case t.seed <- struct{}{}:
	default:
	}
}

func (t *torrent) stopTorrent() {
	select {
	case t.stop <- struct{}{}:
	default:
	}
}

func (t *torrent) enqueuePeer(addr *net.TCPAddr) {
	t.addPeer <- addr
}

func (t *torrent) getStatus(field string) string {
	ch := make(chan string)
	t.status <- statusReq{field, ch}
	return <-ch
}

func (t *torrent) handleStatus(field string) string {
	switch field {
	case "name":
		return t.meta.Info.Name
	case "state":
		return t.st.String()
	case "progress":
		verified, total := t.scheduler.progress()
		if total == 0 {
			return "0"
		}
		return strconv.Itoa(verified * 100 / total)
	case "size":
		return strconv.FormatInt(t.meta.Size, 10)
	case "down":
		return strconv.FormatInt(t.down, 10)
	case "up":
		return strconv.FormatInt(t.up, 10)
	case "pieces":
		verified, total := t.scheduler.progress()
		return fmt.Sprintf("%d/%d", verified, total)
	case "peers":
		return t.formatPeers()
	}
	return ""
}

func (t *torrent) formatPeers() string {
	var buf strings.Builder
	npieces := t.scheduler.count()
	for _, p := range t.peers.all() {
		st := "unchoked"
		if p.Choked {
			st = "choked"
		}
		have := 0
		for _, h := range p.Have {
			if h {
				have++
			}
		}
		fmt.Fprintf(&buf, "%s %s %s have:%d/%d pending:%d\n",
			p.Addr, p.PeerID[:8], st, have, npieces, p.Pending)
	}
	return buf.String()
}

func (s state) String() string {
	switch s {
	case stopped:
		return "stopped"
	case downloading:
		return "downloading"
	case seeding:
		return "seeding"
	case done:
		return "done"
	case errored:
		return "error"
	}
	return "unknown"
}