package can

import (
	"encoding/binary"
	"errors"
	"io"
	"net"
	"time"
	"unsafe"

	"golang.org/x/sys/unix"
)

const bufferSize = 100

type CanFrame struct {
	CanId   uint32
	Payload *[]uint8
	Date    *time.Time
}

// NewCan New returns a new CAN bus socket.
func NewCan() (*Socket, error) {
	fd, err := unix.Socket(unix.AF_CAN, unix.SOCK_RAW, unix.CAN_RAW)
	if err != nil {
		return nil, err
	}

	return &Socket{dev: device{fd}}, nil
}

// Socket is a high-level representation of a CANBus socket.
type Socket struct {
	iface *net.Interface
	addr  *unix.SockaddrCAN
	dev   device
}

// Close closes the CAN bus socket.
func (sck *Socket) Close() error {
	return unix.Close(sck.dev.fd)
}

func (sck *Socket) Bind(addr string, filter []unix.CanFilter) error {
	iface, err := net.InterfaceByName(addr)
	if err != nil {
		return err
	}

	sck.iface = iface
	sck.addr = &unix.SockaddrCAN{Ifindex: sck.iface.Index}

	//add filter
	if filter != nil {
		unix.SetsockoptCanRawFilter(sck.dev.fd, unix.SOL_CAN_RAW, unix.CAN_RAW_FILTER, filter)
	}

	return unix.Bind(sck.dev.fd, sck.addr)
}

// Receive receives data from the CAN socket.
// id is the CAN_frame id the data was originated from.
func (sck *Socket) Receive() (id uint32, data *[]byte, err error) {
	var buf [frameSize]byte
	n, err := io.ReadFull(sck.dev, buf[:])
	if err != nil {
		return id, data, err
	}

	if n != len(buf) {
		return id, data, io.ErrUnexpectedEOF
	}

	id = binary.LittleEndian.Uint32(buf[:4])
	//TODO make correct switch betwin EFF and SFF
	id &= unix.CAN_EFF_MASK
	payload := make([]byte, buf[4])
	copy(payload, buf[8:])
	return id, &payload, nil
}

type device struct {
	fd int
}

func (d device) Read(data []byte) (int, error) {
	return unix.Read(d.fd, data)
}

func (d device) Write(data []byte) (int, error) {
	return unix.Write(d.fd, data)
}

const frameSize = unsafe.Sizeof(canframe{})

// frame is a can_frame.
type canframe struct {
	ID   uint32
	Len  byte
	_    [3]byte
	Data [8]byte
}

func StartCan(canbus string, filter []unix.CanFilter) (<-chan *CanFrame, error) {

	if socket, err := NewCan(); err == nil {

		if cerr := socket.Bind(canbus, filter); cerr == nil {

			canevents := make(chan *CanFrame, bufferSize)

			go func() {
				defer close(canevents)
				defer socket.Close()

				for { //TODO implement stop
					if id, data, serr := socket.Receive(); serr == nil {
						var now = time.Now()
						canevents <- &CanFrame{
							Date:    &now,
							CanId:   id,
							Payload: data,
						}
					}
				}
			}()

			return canevents, nil
		}
	}
	return nil, errors.New("can't bind can socket")
}