package core

/*
#cgo CFLAGS: -I./c/include
#include "lwip/udp.h"
*/
import "C"
import (
	"errors"
	"fmt"
	"net"
	"sync"
	"unsafe"
)

type udpConnState uint

const (
	udpNewConn udpConnState = iota
	udpConnecting
	udpConnected
	udpClosed
)

type udpPacket struct {
	data []byte
	addr *net.UDPAddr
}

type udpConn struct {
	sync.Mutex

	pcb       *C.struct_udp_pcb
	handler   UDPConnHandler
	localAddr *net.UDPAddr
	localIP   C.ip_addr_t
	localPort C.u16_t
	state     udpConnState
	pending   chan *udpPacket
}

func newUDPConn(pcb *C.struct_udp_pcb, handler UDPConnHandler, localIP C.ip_addr_t, localPort C.u16_t, localAddr, remoteAddr *net.UDPAddr) (UDPConn, error) {
	conn := &udpConn{
		handler:   handler,
		pcb:       pcb,
		localAddr: localAddr,
		localIP:   localIP,
		localPort: localPort,
		state:     udpNewConn,
		pending:   make(chan *udpPacket, 1), // For DNS request payload.
	}

	conn.Lock()
	conn.state = udpConnecting
	conn.Unlock()
	go func() {
		err := handler.Connect(conn, remoteAddr)
		if err != nil {
			conn.Close()
		} else {
			conn.Lock()
			conn.state = udpConnected
			conn.Unlock()
			// Once connected, send all pending data.
		DrainPending:
			for {
				select {
				case pkt := <-conn.pending:
					err := conn.handler.ReceiveTo(conn, pkt.data, pkt.addr)
					if err != nil {
						break DrainPending
					}
					continue DrainPending
				default:
					break DrainPending
				}
			}
		}
	}()

	return conn, nil
}

func (conn *udpConn) LocalAddr() *net.UDPAddr {
	return conn.localAddr
}

func (conn *udpConn) checkState() error {
	conn.Lock()
	defer conn.Unlock()

	switch conn.state {
	case udpClosed:
		return errors.New("connection closed")
	case udpConnected:
		return nil
	case udpNewConn, udpConnecting:
		return errors.New("not connected")
	}
	return nil
}

func (conn *udpConn) isConnecting() bool {
	conn.Lock()
	defer conn.Unlock()
	return conn.state == udpConnecting
}

func (conn *udpConn) ReceiveTo(data []byte, addr *net.UDPAddr) error {
	if conn.isConnecting() {
		pkt := &udpPacket{data: append([]byte(nil), data...), addr: addr}
		select {
		// Data will be dropped if pending is full.
		case conn.pending <- pkt:
			return nil
		default:
		}
	}
	if err := conn.checkState(); err != nil {
		return err
	}
	err := conn.handler.ReceiveTo(conn, data, addr)
	if err != nil {
		return errors.New(fmt.Sprintf("write proxy failed: %v", err))
	}
	return nil
}

func (conn *udpConn) WriteFrom(data []byte, addr *net.UDPAddr) (int, error) {
	if err := conn.checkState(); err != nil {
		return 0, err
	}
	// FIXME any memory leaks?
	cremoteIP := C.struct_ip_addr{}
	if err := ipAddrATON(addr.IP.String(), &cremoteIP); err != nil {
		return 0, err
	}
	buf := C.pbuf_alloc_reference(unsafe.Pointer(&data[0]), C.u16_t(len(data)), C.PBUF_ROM)
	defer C.pbuf_free(buf)
	C.udp_sendto(conn.pcb, buf, &conn.localIP, conn.localPort, &cremoteIP, C.u16_t(addr.Port))
	return len(data), nil
}

func (conn *udpConn) Close() error {
	connId := udpConnId{
		src: conn.LocalAddr().String(),
	}
	conn.Lock()
	conn.state = udpClosed
	conn.Unlock()
	udpConns.Delete(connId)
	return nil
}