package meshcore

import (
	"crypto/sha256"
	"encoding/binary"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"io"
	"strings"
)

const (
	minPacketSize  = 2
	maxPathSize    = 64
	maxPayloadSize = 184
)

type Packet struct {
	// SNR is the signal-to-noise ratio.
	SNR float64 `json:"snr"`

	// RSSI is the received signal strength indicator (in dBm).
	RSSI int8 `json:"rssi"`

	// Raw bytes (optional).
	Raw []byte `json:"raw,omitempty"`

	// RouteType is the type of route for this packet.
	RouteType RouteType `json:"route_type"`

	// PayloadType is the type of payload for this packet.
	PayloadType PayloadType `json:"payload_type"`

	// TransportCodes are set by transport route types.
	TransportCodes []uint16 `json:"transport_codes,omitempty"`

	// Path are repeater hashes.
	Path []byte `json:"path"`

	// Payload is the raw (encoded) payload.
	Payload []byte `json:"payload,omitempty"`
}

func Decode(data []byte) (Payload, error) {
	packet := new(Packet)
	if err := packet.UnmarshalBytes(data); err != nil {
		return nil, err
	}
	return packet.Decode()
}

func (packet *Packet) Decode() (Payload, error) {
	var payload Payload
	switch packet.PayloadType {
	case TypeRequest:
		payload = &Request{Raw: packet}
	case TypeResponse:
		payload = &Response{Raw: packet}
	case TypeText:
		payload = &Text{Raw: packet}
	case TypeAck:
		payload = &Acknowledgement{Raw: packet}
	case TypeAdvert:
		payload = &Advert{Raw: packet}
	case TypeGroupText:
		payload = &GroupText{Raw: packet}
	case TypeGroupData:
		payload = &GroupData{Raw: packet}
	case TypeAnonRequest:
		payload = &AnonymousRequest{Raw: packet}
	case TypePath:
		payload = &Path{Raw: packet}
	case TypeTrace:
		payload = &Trace{Raw: packet}
	case TypeMultipart:
		payload = &Multipart{Raw: packet}
	case TypeControl:
		payload = &Control{Raw: packet}
	case TypeRawCustom:
		payload = &RawCustom{Raw: packet}
	default:
		return nil, fmt.Errorf("meshcore: invalid payload type %#02x", packet.PayloadType)
	}

	if err := payload.Unmarshal(packet.Payload); err != nil {
		return nil, err
	}

	return payload, nil
}

func (packet *Packet) String() string {
	s := []string{
		packet.RouteType.String(),
		packet.PayloadType.String(),
	}
	if len(packet.TransportCodes) == 2 {
		s = append(s, fmt.Sprintf("%02X%02X", packet.TransportCodes[0], packet.TransportCodes[1]))
	}
	if len(packet.Path) > 0 {
		s = append(s, formatPath(packet.Path))
	} else {
		s = append(s, "direct")
	}
	return strings.Join(s, " ")
}

func (packet *Packet) MarshalBytes() []byte {
	var (
		data   [1 + 4 + 1 + maxPathSize + maxPayloadSize]byte
		offset int
	)
	data[offset] = byte(packet.RouteType&0x03) | byte((packet.PayloadType&0x0f)<<2)
	offset += 1

	if packet.RouteType.HasTransportCodes() {
		binary.LittleEndian.PutUint16(data[offset:], packet.TransportCodes[0])
		offset += 2
		binary.LittleEndian.PutUint16(data[offset:], packet.TransportCodes[1])
		offset += 2
	}

	data[offset] = byte(len(packet.Path))
	offset += 1
	offset += copy(data[offset:], packet.Path)
	offset += copy(data[offset:], packet.Payload)
	return data[:offset]
}

func (packet *Packet) UnmarshalBytes(data []byte) error {
	if len(data) < minPacketSize {
		return io.ErrUnexpectedEOF
	}

	packet.Raw = make([]byte, len(data))
	copy(packet.Raw, data)

	packet.RouteType = RouteType(data[0] & 0x03)
	packet.PayloadType = PayloadType((data[0] >> 2) & 0x0f)
	offset := 1

	if packet.RouteType.HasTransportCodes() {
		if len(data) < minPacketSize+4 {
			return io.ErrUnexpectedEOF
		}

		packet.TransportCodes = []uint16{
			binary.LittleEndian.Uint16(data[offset+0:]),
			binary.LittleEndian.Uint16(data[offset+2:]),
		}
		offset += 4
	} else {
		packet.TransportCodes = nil
	}

	pathLength := int(data[offset])
	offset += 1
	if pathLength > maxPathSize {
		return fmt.Errorf("meshcore: path length %d exceeds maximum of %d", pathLength, maxPathSize)
	} else if pathLength > len(data[offset:]) {
		return io.ErrUnexpectedEOF
	}
	packet.Path = make([]byte, pathLength)
	offset += copy(packet.Path, data[offset:])

	payloadLength := len(data[offset:])
	if payloadLength > maxPayloadSize {
		return fmt.Errorf("meshcore: payload length %d exceeds maximum of %d", payloadLength, maxPayloadSize)
	}
	packet.Payload = make([]byte, payloadLength)
	copy(packet.Payload, data[offset:])

	return nil
}

func (packet *Packet) Hash() []byte {
	h := sha256.New()
	h.Write([]byte{byte(packet.PayloadType)})
	if packet.PayloadType == TypeTrace {
		h.Write(packet.Path)
	}
	h.Write(packet.Payload)
	return h.Sum(nil)[:8]
}

func (packet *Packet) MarshalJSON() ([]byte, error) {
	return json.Marshal(struct {
		SNR            float64     `json:"snr"`
		RSSI           int8        `json:"rssi"`
		RouteType      RouteType   `json:"route_type"`
		PayloadType    PayloadType `json:"payload_type"`
		TransportCodes []uint16    `json:"transport_codes,omitempty"`
		Path           string      `json:"path"`
		Payload        string      `json:"payload,omitempty"`
		Hash           string      `json:"hash"`
	}{
		packet.SNR,
		packet.RSSI,
		packet.RouteType,
		packet.PayloadType,
		packet.TransportCodes,
		hex.EncodeToString(packet.Path),
		hex.EncodeToString(packet.Payload),
		hex.EncodeToString(packet.Hash()),
	})
}

type RouteType byte

// Route types.
const (
	TransportFlood RouteType = iota
	Flood
	Direct
	TransportDirect
)

// HasTransportCodes indicates if this route type has transport codes in the packet.
func (rt RouteType) HasTransportCodes() bool {
	return rt == TransportFlood || rt == TransportDirect
}

// IsDirect is a direct routing type.
func (rt RouteType) IsDirect() bool {
	return rt == Direct || rt == TransportDirect
}

// IsFlood is a flood routing type.
func (rt RouteType) IsFlood() bool {
	return rt == Flood || rt == TransportFlood
}

func (rt RouteType) String() string {
	switch rt {
	case TransportFlood:
		return "F[T]"
	case Flood:
		return "F"
	case Direct:
		return "D"
	case TransportDirect:
		return "D[T]"
	default:
		return "?"
	}
}

type PayloadType byte

// Payload types.
const (
	TypeRequest PayloadType = iota
	TypeResponse
	TypeText
	TypeAck
	TypeAdvert
	TypeGroupText
	TypeGroupData
	TypeAnonRequest
	TypePath
	TypeTrace
	TypeMultipart
	TypeControl
	_ // reserved
	_ // reserved
	_ // reserved
	TypeRawCustom
)

func (pt PayloadType) String() string {
	switch pt {
	case TypeRequest:
		return "request"
	case TypeResponse:
		return "response"
	case TypeText:
		return "text"
	case TypeAck:
		return "ack"
	case TypeAdvert:
		return "advert"
	case TypeGroupText:
		return "group text"
	case TypeGroupData:
		return "group data"
	case TypeAnonRequest:
		return "anon request"
	case TypePath:
		return "path"
	case TypeTrace:
		return "trace"
	case TypeMultipart:
		return "multipart"
	case TypeControl:
		return "control"
	case TypeRawCustom:
		return "raw custom"
	default:
		return fmt.Sprintf("invalid %02x", byte(pt))
	}
}