package utp

/*
#include "utp.h"
#include <stdbool.h>

struct utp_process_udp_args {
	const byte *buf;
	size_t len;
	const struct sockaddr *sa;
	socklen_t sal;
};

void process_received_messages(utp_context *ctx, struct utp_process_udp_args *args, size_t argslen)
{
	bool gotUtp = false;
	size_t i;
	for (i = 0; i < argslen; i++) {
		struct utp_process_udp_args *a = &args[i];
		//if (!a->len) continue;
		if (utp_process_udp(ctx, a->buf, a->len, a->sa, a->sal)) {
			gotUtp = true;
		}
	}
	if (gotUtp) {
		utp_issue_deferred_acks(ctx);
		utp_check_timeouts(ctx);
	}
}
*/
import "C"
import (
	"context"
	"errors"
	"net"
	"runtime/pprof"
	"time"

	"github.com/anacrolix/missinggo"
	"github.com/anacrolix/missinggo/inproc"
	"github.com/anacrolix/mmsg"
)

type Socket struct {
	pc               net.PacketConn
	ctx              *C.utp_context
	backlog          chan *Conn
	closed           bool
	conns            map[*C.utp_socket]*Conn
	nonUtpReads      chan packet
	writeDeadline    time.Time
	readDeadline     time.Time
	firewallCallback FirewallCallback
	// Whether the next accept is to be blocked.
	block bool
}

type FirewallCallback func(net.Addr) bool

var (
	_               net.PacketConn = (*Socket)(nil)
	_               net.Listener   = (*Socket)(nil)
	errSocketClosed                = errors.New("Socket closed")
)

type packet struct {
	b    []byte
	from net.Addr
}

func listenPacket(network, addr string) (pc net.PacketConn, err error) {
	if network == "inproc" {
		return inproc.ListenPacket(network, addr)
	}
	return net.ListenPacket(network, addr)
}

func NewSocket(network, addr string) (*Socket, error) {
	pc, err := listenPacket(network, addr)
	if err != nil {
		return nil, err
	}
	mu.Lock()
	defer mu.Unlock()
	ctx := C.utp_init(2)
	if ctx == nil {
		panic(ctx)
	}
	ctx.setCallbacks()
	if utpLogging {
		ctx.setOption(C.UTP_LOG_NORMAL, 1)
		ctx.setOption(C.UTP_LOG_MTU, 1)
		ctx.setOption(C.UTP_LOG_DEBUG, 1)
	}
	s := &Socket{
		pc:          pc,
		ctx:         ctx,
		backlog:     make(chan *Conn, 5),
		conns:       make(map[*C.utp_socket]*Conn),
		nonUtpReads: make(chan packet, 100),
	}
	libContextToSocket[ctx] = s
	go s.timeoutChecker()
	go s.packetReader()
	return s, nil
}

func (s *Socket) onLibSocketDestroyed(ls *C.utp_socket) {
	delete(s.conns, ls)
}

func (s *Socket) newConn(us *C.utp_socket) *Conn {
	c := &Conn{
		s:         s,
		us:        us,
		localAddr: s.pc.LocalAddr(),
	}
	c.cond.L = &mu
	s.conns[us] = c
	c.writeDeadlineTimer = time.AfterFunc(-1, c.cond.Broadcast)
	c.readDeadlineTimer = time.AfterFunc(-1, c.cond.Broadcast)
	return c
}

const maxNumBuffers = 16

func (s *Socket) packetReader() {
	mc := mmsg.NewConn(s.pc)
	// Increasing the messages increases the memory use, but also means we can
	// reduces utp_issue_deferred_acks and syscalls which should improve
	// efficiency. On the flip side, not all OSs implement batched reads.
	ms := make([]mmsg.Message, func() int {
		if mc.Err() == nil {
			return maxNumBuffers
		} else {
			return 1
		}
	}())
	for i := range ms {
		// The IPv4 UDP limit is allegedly about 64 KiB, and this message has
		// been seen on receiving on Windows with just 0x1000: wsarecvfrom: A
		// message sent on a datagram socket was larger than the internal
		// message buffer or some other network limit, or the buffer used to
		// receive a datagram into was smaller than the datagram itself.
		ms[i].Buffers = [][]byte{make([]byte, 0x10000)}
	}
	// Some crap OSs like Windoze will raise errors in Reads that don't
	// actually mean we should stop.
	consecutiveErrors := 0
	for {
		// In C, all the reads are processed and when it threatens to block,
		// we're supposed to call utp_issue_deferred_acks.
		n, err := mc.RecvMsgs(ms)
		if n == 1 {
			singleMsgRecvs.Add(1)
		}
		if n > 1 {
			multiMsgRecvs.Add(1)
		}
		if err != nil {
			mu.Lock()
			closed := s.closed
			mu.Unlock()
			if closed {
				// We don't care.
				return
			}
			// See https://github.com/anacrolix/torrent/issues/83. If we get
			// an endless stream of errors (such as the PacketConn being
			// Closed outside of our control, this work around may need to be
			// reconsidered.
			Logger.Printf("ignoring socket read error: %s", err)
			consecutiveErrors++
			if consecutiveErrors >= 100 {
				Logger.Print("too many consecutive errors, closing socket")
				s.Close()
				return
			}
			continue
		}
		consecutiveErrors = 0
		expMap.Add("successful mmsg receive calls", 1)
		expMap.Add("received messages", int64(n))
		s.processReceivedMessages(ms[:n])
	}
}

func (s *Socket) processReceivedMessages(ms []mmsg.Message) {
	mu.Lock()
	defer mu.Unlock()
	if s.closed {
		return
	}
	if processPacketsInC {
		var args [maxNumBuffers]C.struct_utp_process_udp_args
		for i, m := range ms {
			a := &args[i]
			a.buf = (*C.byte)(&m.Buffers[0][0])
			a.len = C.size_t(m.N)
			a.sa, a.sal = netAddrToLibSockaddr(m.Addr)
		}
		C.process_received_messages(s.ctx, &args[0], C.size_t(len(ms)))
	} else {
		gotUtp := false
		for _, m := range ms {
			gotUtp = s.processReceivedMessage(m.Buffers[0][:m.N], m.Addr) || gotUtp
		}
		if gotUtp && !s.closed {
			s.afterReceivingUtpMessages()
		}
	}
}

func (s *Socket) afterReceivingUtpMessages() {
	pprof.Do(context.Background(), pprof.Labels("go-libutp", "afterReceivingUtpMessages"), func(context.Context) {
		C.utp_issue_deferred_acks(s.ctx)
		// TODO: When is this done in C?
		C.utp_check_timeouts(s.ctx)
	})
}

func (s *Socket) processReceivedMessage(b []byte, addr net.Addr) (utp bool) {
	if s.utpProcessUdp(b, addr) {
		socketUtpPacketsReceived.Add(1)
		return true
	} else {
		s.onReadNonUtp(b, addr)
		return false
	}
}

// Process packet batches entirely from C, reducing CGO overhead. Currently
// requires GODEBUG=cgocheck=0.
const processPacketsInC = false

// Wraps libutp's utp_process_udp, returning relevant information.
func (s *Socket) utpProcessUdp(b []byte, addr net.Addr) (utp bool) {
	sa, sal := netAddrToLibSockaddr(addr)
	if len(b) == 0 {
		// The implementation of utp_process_udp rejects null buffers, and
		// anything smaller than the UTP header size. It's also prone to
		// assert on those, which we don't want to trigger.
		return false
	}
	if missinggo.AddrPort(addr) == 0 {
		return false
	}
	mu.Unlock()
	block := func() bool {
		if s.firewallCallback == nil {
			return false
		}
		return s.firewallCallback(addr)
	}()
	mu.Lock()
	s.block = block
	if s.closed {
		return false
	}
	ret := C.utp_process_udp(s.ctx, (*C.byte)(&b[0]), C.size_t(len(b)), sa, sal)
	switch ret {
	case 1:
		return true
	case 0:
		return false
	default:
		panic(ret)
	}
}

func (s *Socket) timeoutChecker() {
	for {
		mu.Lock()
		if s.closed {
			mu.Unlock()
			return
		}
		// C.utp_issue_deferred_acks(s.ctx)
		C.utp_check_timeouts(s.ctx)
		mu.Unlock()
		time.Sleep(500 * time.Millisecond)
	}
}

func (s *Socket) Close() error {
	mu.Lock()
	defer mu.Unlock()
	return s.closeLocked()
}

func (s *Socket) closeLocked() error {
	if s.closed {
		return nil
	}
	// Calling this deletes the pointer. It must not be referred to after
	// this.
	C.utp_destroy(s.ctx)
	s.ctx = nil
	s.pc.Close()
	close(s.backlog)
	close(s.nonUtpReads)
	s.closed = true
	return nil
}

func (s *Socket) Addr() net.Addr {
	return s.pc.LocalAddr()
}

func (s *Socket) LocalAddr() net.Addr {
	return s.pc.LocalAddr()
}

func (s *Socket) Accept() (net.Conn, error) {
	nc, ok := <-s.backlog
	if !ok {
		return nil, errors.New("closed")
	}
	return nc, nil
}

func (s *Socket) Dial(addr string) (net.Conn, error) {
	return s.DialTimeout(addr, 0)
}

func (s *Socket) DialTimeout(addr string, timeout time.Duration) (net.Conn, error) {
	ctx := context.Background()
	if timeout != 0 {
		var cancel context.CancelFunc
		ctx, cancel = context.WithTimeout(ctx, timeout)
		defer cancel()
	}
	return s.DialContext(ctx, "", addr)
}

func (s *Socket) resolveAddr(network, addr string) (net.Addr, error) {
	if network == "" {
		network = s.Addr().Network()
	}
	return resolveAddr(network, addr)
}

func resolveAddr(network, addr string) (net.Addr, error) {
	switch network {
	case "inproc":
		return inproc.ResolveAddr(network, addr)
	default:
		return net.ResolveUDPAddr(network, addr)
	}
}

// Passing an empty network will use the network of the Socket's listener.
func (s *Socket) DialContext(ctx context.Context, network, addr string) (net.Conn, error) {
	c, err := s.NewConn()
	if err != nil {
		return nil, err
	}
	err = c.Connect(ctx, network, addr)
	if err != nil {
		c.Close()
		return nil, err
	}
	return c, nil
}

func (s *Socket) NewConn() (*Conn, error) {
	mu.Lock()
	defer mu.Unlock()
	if s.closed {
		return nil, errors.New("socket closed")
	}
	return s.newConn(C.utp_create_socket(s.ctx)), nil
}

func (s *Socket) pushBacklog(c *Conn) {
	select {
	case s.backlog <- c:
	default:
		c.close()
	}
}

func (s *Socket) ReadFrom(b []byte) (n int, addr net.Addr, err error) {
	p, ok := <-s.nonUtpReads
	if !ok {
		err = errors.New("closed")
		return
	}
	n = copy(b, p.b)
	addr = p.from
	return
}

func (s *Socket) onReadNonUtp(b []byte, from net.Addr) {
	if s.closed {
		return
	}
	socketNonUtpPacketsReceived.Add(1)
	select {
	case s.nonUtpReads <- packet{append([]byte(nil), b...), from}:
	default:
		// log.Printf("dropped non utp packet: no room in buffer")
		nonUtpPacketsDropped.Add(1)
	}
}

func (s *Socket) SetReadDeadline(t time.Time) error {
	panic("not implemented")
}

func (s *Socket) SetWriteDeadline(t time.Time) error {
	panic("not implemented")
}

func (s *Socket) SetDeadline(t time.Time) error {
	panic("not implemented")
}

func (s *Socket) WriteTo(b []byte, addr net.Addr) (int, error) {
	return s.pc.WriteTo(b, addr)
}

func (s *Socket) ReadBufferLen() int {
	mu.Lock()
	defer mu.Unlock()
	return int(C.utp_context_get_option(s.ctx, C.UTP_RCVBUF))
}

func (s *Socket) WriteBufferLen() int {
	mu.Lock()
	defer mu.Unlock()
	return int(C.utp_context_get_option(s.ctx, C.UTP_SNDBUF))
}

func (s *Socket) SetWriteBufferLen(len int) {
	mu.Lock()
	defer mu.Unlock()
	i := C.utp_context_set_option(s.ctx, C.UTP_SNDBUF, C.int(len))
	if i != 0 {
		panic(i)
	}
}

func (s *Socket) SetOption(opt Option, val int) int {
	mu.Lock()
	defer mu.Unlock()
	return int(C.utp_context_set_option(s.ctx, opt, C.int(val)))
}

func (s *Socket) SetFirewallCallback(f FirewallCallback) {
	mu.Lock()
	s.firewallCallback = f
	mu.Unlock()
}