package cvend

import (
	"encoding/binary"
	"encoding/hex"
	"hash/crc32"
	"io"
	"log"
	"sync"

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

const Path = "/dev/ttymxc3"

var crc8table = [256]byte{
	0x00, 0x5e, 0xbc, 0xe2, 0x61, 0x3f, 0xdd, 0x83, 0xc2, 0x9c, 0x7e, 0x20, 0xa3, 0xfd, 0x1f, 0x41,
	0x9d, 0xc3, 0x21, 0x7f, 0xfc, 0xa2, 0x40, 0x1e, 0x5f, 0x01, 0xe3, 0xbd, 0x3e, 0x60, 0x82, 0xdc,
	0x23, 0x7d, 0x9f, 0xc1, 0x42, 0x1c, 0xfe, 0xa0, 0xe1, 0xbf, 0x5d, 0x03, 0x80, 0xde, 0x3c, 0x62,
	0xbe, 0xe0, 0x02, 0x5c, 0xdf, 0x81, 0x63, 0x3d, 0x7c, 0x22, 0xc0, 0x9e, 0x1d, 0x43, 0xa1, 0xff,
	0x46, 0x18, 0xfa, 0xa4, 0x27, 0x79, 0x9b, 0xc5, 0x84, 0xda, 0x38, 0x66, 0xe5, 0xbb, 0x59, 0x07,
	0xdb, 0x85, 0x67, 0x39, 0xba, 0xe4, 0x06, 0x58, 0x19, 0x47, 0xa5, 0xfb, 0x78, 0x26, 0xc4, 0x9a,
	0x65, 0x3b, 0xd9, 0x87, 0x04, 0x5a, 0xb8, 0xe6, 0xa7, 0xf9, 0x1b, 0x45, 0xc6, 0x98, 0x7a, 0x24,
	0xf8, 0xa6, 0x44, 0x1a, 0x99, 0xc7, 0x25, 0x7b, 0x3a, 0x64, 0x86, 0xd8, 0x5b, 0x05, 0xe7, 0xb9,
	0x8c, 0xd2, 0x30, 0x6e, 0xed, 0xb3, 0x51, 0x0f, 0x4e, 0x10, 0xf2, 0xac, 0x2f, 0x71, 0x93, 0xcd,
	0x11, 0x4f, 0xad, 0xf3, 0x70, 0x2e, 0xcc, 0x92, 0xd3, 0x8d, 0x6f, 0x31, 0xb2, 0xec, 0x0e, 0x50,
	0xaf, 0xf1, 0x13, 0x4d, 0xce, 0x90, 0x72, 0x2c, 0x6d, 0x33, 0xd1, 0x8f, 0x0c, 0x52, 0xb0, 0xee,
	0x32, 0x6c, 0x8e, 0xd0, 0x53, 0x0d, 0xef, 0xb1, 0xf0, 0xae, 0x4c, 0x12, 0x91, 0xcf, 0x2d, 0x73,
	0xca, 0x94, 0x76, 0x28, 0xab, 0xf5, 0x17, 0x49, 0x08, 0x56, 0xb4, 0xea, 0x69, 0x37, 0xd5, 0x8b,
	0x57, 0x09, 0xeb, 0xb5, 0x36, 0x68, 0x8a, 0xd4, 0x95, 0xcb, 0x29, 0x77, 0xf4, 0xaa, 0x48, 0x16,
	0xe9, 0xb7, 0x55, 0x0b, 0x88, 0xd6, 0x34, 0x6a, 0x2b, 0x75, 0x97, 0xc9, 0x4a, 0x14, 0xf6, 0xa8,
	0x74, 0x2a, 0xc8, 0x96, 0x15, 0x4b, 0xa9, 0xf7, 0xb6, 0xe8, 0x0a, 0x54, 0xd7, 0x89, 0x6b, 0x35,
}

func crc8(bs ...byte) (x byte) {
	for _, b := range bs {
		x = crc8table[x^b]
	}
	return
}

type IPPHandler func(byte, []byte)

type Device interface {
	io.Closer
	io.Writer
	SendIPP(ippType byte, ippData []byte) error
}

type device struct {
	fd         int
	handler    IPPHandler
	mu         sync.Mutex
	nextSeqOut byte // mu
	closed     bool // mu
}

func Open(path string, handler IPPHandler) (Device, error) {
	var d device
	d.handler = handler
	var err error
	d.fd, err = unix.Open(path, unix.O_RDWR|unix.O_NOCTTY, 0)
	if err != nil {
		return nil, err
	}
	var termios *unix.Termios
	termios, err = unix.IoctlGetTermios(d.fd, unix.TCGETS)
	if err != nil {
		return nil, err
	}
	termios.Iflag &^= unix.IGNBRK | unix.BRKINT | unix.PARMRK | unix.ISTRIP | unix.INLCR | unix.IGNCR | unix.ICRNL | unix.IXON
	termios.Oflag &^= unix.OPOST
	termios.Lflag &^= unix.ECHO | unix.ECHONL | unix.ICANON | unix.ISIG | unix.IEXTEN
	termios.Cflag &^= unix.CBAUD | unix.CSIZE | unix.PARENB | unix.CSTOPB
	termios.Cflag |= unix.B115200 | unix.CS8 | unix.CREAD | unix.CLOCAL
	err = unix.IoctlSetTermios(d.fd, unix.TCSETS, termios)
	if err != nil {
		return nil, err
	}
	go d.readTask()
	return &d, nil
}

func (d *device) readTask() {
	var bs [1 << 16]byte
	var offset int
	for {
		n, err := unix.Read(d.fd, bs[offset:])
		if err != nil {
			d.mu.Lock()
			closed := d.closed
			d.mu.Unlock()
			if closed {
				break
			}
			panic(err)
		}
		nRead := d.handleMsg(bs[:offset+n])
		offset = copy(bs[:], bs[nRead:offset+n])
	}
}

func (d *device) handleMsg(bs []byte) (nRead int) {
	expectedLen := 1
	if len(bs) < expectedLen {
		log.Printf("skipping empty message")
		return
	}
	msgType := bs[0]
	if msgType != 0xbc {
		log.Printf("skipping non-IPP message %s", hex.EncodeToString(bs))
		nRead = len(bs)
		return
	}
	expectedLen += 6
	if len(bs) < expectedLen {
		log.Printf("skipping truncated IPP message %s", hex.EncodeToString(bs))
		return
	}
	_ = bs[1] // seq
	_ = bs[2] // unknown
	ippType := bs[3]
	ippLen := int(bs[4])<<8 + int(bs[5])
	hdrCRC := bs[6]
	expectedHdrCRC := crc8(bs[0:6]...)
	if hdrCRC != expectedHdrCRC {
		log.Printf("skipping IPP message %02x, expected crc8 %02x got %02x", ippType, expectedHdrCRC, hdrCRC)
		return
	}
	expectedLen += ippLen
	hasMsgCRC := ippType&0x80 != 0
	if hasMsgCRC {
		expectedLen += 4
	}
	if len(bs) < expectedLen {
		log.Printf("skipping truncated IPP message %s", hex.EncodeToString(bs))
		return
	}
	nRead = expectedLen
	ippData := bs[7 : 7+ippLen]
	if hasMsgCRC {
		msgCRC := bs[7+ippLen : 7+ippLen+4]
		expectedMsgCRC := ^crc32.ChecksumIEEE(ippData)
		actualMsgCRC := binary.LittleEndian.Uint32(msgCRC)
		if actualMsgCRC != expectedMsgCRC {
			log.Printf("skipping IPP message %02x, expected crc32 %08x got %08x", expectedMsgCRC, actualMsgCRC)
			return
		}
	}
	if d.handler != nil {
		d.handler(ippType, ippData)
	}
	return
}

func (d *device) Close() error {
	d.mu.Lock()
	defer d.mu.Unlock()
	d.closed = true
	return unix.Close(d.fd)
}

func (d *device) Write(bs []byte) (int, error) {
	log.Printf("send %s", hex.EncodeToString(bs))
	return unix.Write(d.fd, bs)
}

func (d *device) SendIPP(ippType byte, ippData []byte) error {
	d.mu.Lock()
	d.nextSeqOut++
	if d.nextSeqOut == 0 {
		d.nextSeqOut++
	}
	seq := d.nextSeqOut
	d.mu.Unlock()
	ippLen := len(ippData)
	ippHdr := []byte{0xbc, seq, 0, ippType, byte(ippLen >> 8), byte(ippLen), 0}
	ippHdr[6] = crc8(ippHdr[:6]...)
	var msgCRC []byte
	if ippType&0x80 != 0 {
		msgCRC = make([]byte, 4)
		binary.LittleEndian.PutUint32(msgCRC, ^crc32.ChecksumIEEE(ippData))
	}
	log.Printf("send %s%s%s", hex.EncodeToString(ippHdr), hex.EncodeToString(ippData), hex.EncodeToString(msgCRC))
	if _, err := unix.Writev(d.fd, [][]byte{ippHdr, ippData, msgCRC}); err != nil {
		return err
	}
	return nil
}