package coap

import (
	"bytes"
	"encoding/binary"
	"errors"
	"fmt"
	"reflect"
	"sort"
	"strconv"
	"strings"
)

// COAPType 代表消息类型
type COAPType uint8

// MaxTokenSize 最大token size
const MaxTokenSize = 8

const (
	// CON 需要被确认的请求
	CON COAPType = 0
	// NON 不需要被确认的请求
	NON COAPType = 1
	// ACK 应答消息，接受到CON消息的响应
	ACK COAPType = 2
	// RST 复位消息，当接收者接受到的消息包含一个错误，接受者解析消息或者不再关心发送者发送的内容，那么复位消息将会被发送
	RST COAPType = 3
)

// COAPCode 请求方法的类型
type COAPCode uint8

// request codes
const (
	GET COAPCode = iota + 1
	POST
	PUT
	DELETE
)

// Response codes
const (
	Empty                   COAPCode = 0
	Created                 COAPCode = 65
	Deleted                 COAPCode = 66
	Valid                   COAPCode = 67
	Changed                 COAPCode = 68
	Content                 COAPCode = 69
	Continue                COAPCode = 95
	BadRequest              COAPCode = 128
	Unauthorized            COAPCode = 129
	BadOption               COAPCode = 130
	Forbidden               COAPCode = 131
	NotFound                COAPCode = 132
	MethodNotAllowed        COAPCode = 133
	NotAcceptable           COAPCode = 134
	RequestEntityIncomplete COAPCode = 136
	PreconditionFailed      COAPCode = 140
	RequestEntityTooLarge   COAPCode = 141
	UnsupportedMediaType    COAPCode = 143
	InternalServerError     COAPCode = 160
	NotImplemented          COAPCode = 161
	BadGateway              COAPCode = 162
	ServiceUnavailable      COAPCode = 163
	GatewayTimeout          COAPCode = 164
	ProxyingNotSupported    COAPCode = 165
)

// MediaType 请求消息的媒体类型 对应Content-Format
type MediaType uint16

// Content formats.
const (
	TextPlain MediaType = 0  // text/plain;charset=utf-8
	AppXML    MediaType = 41 // application/xml
	AppOctets MediaType = 42 // application/octet-stream
	AppExi    MediaType = 47 // application/exi
	AppJSON   MediaType = 50 // application/json
	AppCBOR   MediaType = 60 //application/cbor (RFC 7049)
)

func (c MediaType) String() string {
	switch c {
	case TextPlain:
		return "text/plain;charset=utf-8"
	case AppXML:
		return "application/xml"
	case AppOctets:
		return "application/octet-stream"
	case AppExi:
		return "application/exi"
	case AppJSON:
		return "application/json"
	case AppCBOR:
		return "application/cbor (RFC 7049)"
	}
	return "Unknown media type: 0x" + strconv.FormatInt(int64(c), 16)
}

// OptionID Option编号
type OptionID uint8

// Option IDs.
const (
	IfMatch       OptionID = 1
	URIHost       OptionID = 3
	ETag          OptionID = 4
	IfNoneMatch   OptionID = 5
	Observe       OptionID = 6
	URIPort       OptionID = 7
	LocationPath  OptionID = 8
	URIPath       OptionID = 11
	ContentFormat OptionID = 12
	MaxAge        OptionID = 14
	URIQuery      OptionID = 15
	Accept        OptionID = 17
	LocationQuery OptionID = 20
	Block2        OptionID = 23
	Block1        OptionID = 27
	Size2         OptionID = 28
	ProxyURI      OptionID = 35
	ProxyScheme   OptionID = 39
	Size1         OptionID = 60
)

// Option value format (RFC7252 section 3.2)
type valueFormat uint8

const (
	valueUnknown valueFormat = iota
	valueEmpty
	valueOpaque
	valueUint
	valueString
)

type optionDef struct {
	valueFormat valueFormat
	minLen      int
	maxLen      int
}

var coapOptionDefs = map[OptionID]optionDef{
	IfMatch:       optionDef{valueFormat: valueOpaque, minLen: 0, maxLen: 8},
	URIHost:       optionDef{valueFormat: valueString, minLen: 1, maxLen: 255},
	ETag:          optionDef{valueFormat: valueOpaque, minLen: 1, maxLen: 8},
	IfNoneMatch:   optionDef{valueFormat: valueEmpty, minLen: 0, maxLen: 0},
	Observe:       optionDef{valueFormat: valueUint, minLen: 0, maxLen: 3},
	URIPort:       optionDef{valueFormat: valueUint, minLen: 0, maxLen: 2},
	LocationPath:  optionDef{valueFormat: valueString, minLen: 0, maxLen: 255},
	URIPath:       optionDef{valueFormat: valueString, minLen: 0, maxLen: 255},
	ContentFormat: optionDef{valueFormat: valueUint, minLen: 0, maxLen: 2},
	MaxAge:        optionDef{valueFormat: valueUint, minLen: 0, maxLen: 4},
	URIQuery:      optionDef{valueFormat: valueString, minLen: 0, maxLen: 255},
	Accept:        optionDef{valueFormat: valueUint, minLen: 0, maxLen: 2},
	LocationQuery: optionDef{valueFormat: valueString, minLen: 0, maxLen: 255},
	Block2:        optionDef{valueFormat: valueUint, minLen: 0, maxLen: 3},
	Block1:        optionDef{valueFormat: valueUint, minLen: 0, maxLen: 3},
	Size2:         optionDef{valueFormat: valueUint, minLen: 0, maxLen: 4},
	ProxyURI:      optionDef{valueFormat: valueString, minLen: 1, maxLen: 1034},
	ProxyScheme:   optionDef{valueFormat: valueString, minLen: 1, maxLen: 255},
	Size1:         optionDef{valueFormat: valueUint, minLen: 0, maxLen: 4},
}

type option struct {
	ID    OptionID
	Value interface{}
}

func encodeInt(v uint32) []byte {
	switch {
	case v == 0:
		return nil
	case v < 256:
		return []byte{byte(v)}
	case v < 65536:
		rv := []byte{0, 0}
		binary.BigEndian.PutUint16(rv, uint16(v))
		return rv
	case v < 16777216:
		rv := []byte{0, 0, 0, 0}
		binary.BigEndian.PutUint32(rv, uint32(v))
		return rv[1:]
	default:
		rv := []byte{0, 0, 0, 0}
		binary.BigEndian.PutUint32(rv, uint32(v))
		return rv
	}
}

func decodeInt(b []byte) uint32 {
	tmp := []byte{0, 0, 0, 0}
	copy(tmp[4-len(b):], b)
	return binary.BigEndian.Uint32(tmp)
}

func (o option) toBytes() []byte {
	var v uint32

	switch i := o.Value.(type) {
	case string:
		return []byte(i)
	case []byte:
		return i
	case MediaType:
		v = uint32(i)
	case int:
		v = uint32(i)
	case int32:
		v = uint32(i)
	case uint:
		v = uint32(i)
	case uint32:
		v = i
	default:
		panic(fmt.Errorf("invalid type for option %x: %T (%v)",
			o.ID, o.Value, o.Value))
	}

	return encodeInt(v)
}

type options []option

func (o options) Len() int {
	return len(o)
}

func (o options) Less(i, j int) bool {
	if o[i].ID == o[j].ID {
		return i < j
	}
	return o[i].ID < o[j].ID
}

func (o options) Swap(i, j int) {
	o[i], o[j] = o[j], o[i]
}

func (o options) Remove(oid OptionID) options {
	idx := 0
	for i := 0; i < len(o); i++ {
		if o[i].ID != oid {
			o[idx] = o[i]
			idx++
		}
	}
	return o[:idx]
}

const (
	extoptByteCode   = 13
	extoptByteAddend = 13
	extoptWordCode   = 14
	extoptWordAddend = 269
	extoptError      = 15
)

// Message interface
type Message interface {
	Encode() ([]byte, error)
	Decode(data []byte) error
	Option(opid OptionID) interface{}
	Path() []string
	PathString() string
	SetPath([]string)
	SetPathString(s string)
	AddOption(opid OptionID, val interface{})
	RemoveOption(opid OptionID)
	IsConfirmable() bool
	OptionStrings(opid OptionID) []string
	GetMessageID() uint16
	GetToken() []byte
	GetCode() COAPCode
	GetPayload() []byte
}

// BaseMessage COAP 消息体
type BaseMessage struct {
	Type      COAPType
	Code      COAPCode
	MessageID uint16
	Token     []byte
	Payload   []byte
	Opts      options
}

// GetToken get token
func (m *BaseMessage) GetToken() []byte {
	return m.Token
}

// GetMessageID get message id
func (m *BaseMessage) GetMessageID() uint16 {
	return m.MessageID
}

// GetCode get code
func (m *BaseMessage) GetCode() COAPCode {
	return m.Code
}

// Encode 消息打包
func (m *BaseMessage) Encode() ([]byte, error) {
	tmpbuf := []byte{0, 0}
	binary.BigEndian.PutUint16(tmpbuf, m.MessageID)
	buf := bytes.Buffer{}
	buf.Write([]byte{
		(1 << 6) | (uint8(m.Type) << 4) | uint8(0xf&len(m.Token)),
		byte(m.Code),
		tmpbuf[0], tmpbuf[1],
	})
	buf.Write(m.Token)
	extendOpt := func(opt int) (int, int) {
		ext := 0
		if opt >= extoptByteAddend {
			if opt >= extoptWordAddend {
				ext = opt - extoptWordAddend
				opt = extoptWordCode
			} else {
				ext = opt - extoptByteAddend
				opt = extoptByteCode
			}
		}
		return opt, ext
	}

	writeOptHeader := func(delta, length int) {
		d, dx := extendOpt(delta)
		l, lx := extendOpt(length)

		buf.WriteByte(byte(d<<4) | byte(l))

		tmp := []byte{0, 0}
		writeExt := func(opt, ext int) {
			switch opt {
			case extoptByteCode:
				buf.WriteByte(byte(ext))
			case extoptWordCode:
				binary.BigEndian.PutUint16(tmp, uint16(ext))
				buf.Write(tmp)
			}
		}

		writeExt(d, dx)
		writeExt(l, lx)
	}

	sort.Stable(&m.Opts)

	prev := 0

	for _, o := range m.Opts {
		b := o.toBytes()
		writeOptHeader(int(o.ID)-prev, len(b))
		buf.Write(b)
		prev = int(o.ID)
	}

	if len(m.Payload) > 0 {
		buf.Write([]byte{0xff})
	}

	buf.Write(m.Payload)

	return buf.Bytes(), nil
}

// Decode 消息解包
func (m *BaseMessage) Decode(data []byte) error {
	if len(data) < 4 {
		return errors.New("short packet")
	}

	if data[0]>>6 != 1 {
		return errors.New("invalid version")
	}

	m.Type = COAPType((data[0] >> 4) & 0x3)
	tokenLen := int(data[0] & 0xf)
	if tokenLen > 8 {
		return ErrInvalidTokenLen
	}

	m.Code = COAPCode(data[1])
	m.MessageID = binary.BigEndian.Uint16(data[2:4])

	if tokenLen > 0 {
		m.Token = make([]byte, tokenLen)
	}
	if len(data) < 4+tokenLen {
		return errors.New("truncated")
	}
	copy(m.Token, data[4:4+tokenLen])
	b := data[4+tokenLen:]
	prev := 0

	parseExtOpt := func(opt int) (int, error) {
		switch opt {
		case extoptByteCode:
			if len(b) < 1 {
				return -1, errors.New("truncated")
			}
			opt = int(b[0]) + extoptByteAddend
			b = b[1:]
		case extoptWordCode:
			if len(b) < 2 {
				return -1, errors.New("truncated")
			}
			opt = int(binary.BigEndian.Uint16(b[:2])) + extoptWordAddend
			b = b[2:]
		}
		return opt, nil
	}

	for len(b) > 0 {
		if b[0] == 0xff {
			b = b[1:]
			break
		}

		delta := int(b[0] >> 4)
		length := int(b[0] & 0x0f)

		if delta == extoptError || length == extoptError {
			return errors.New("unexpected extended option marker")
		}

		b = b[1:]

		delta, err := parseExtOpt(delta)
		if err != nil {
			return err
		}
		length, err = parseExtOpt(length)
		if err != nil {
			return err
		}

		if len(b) < length {
			return errors.New("truncated")
		}

		oid := OptionID(prev + delta)
		opval := parseOptionValue(oid, b[:length])
		b = b[length:]
		prev = int(oid)

		if opval != nil {
			m.Opts = append(m.Opts, option{ID: oid, Value: opval})
		}
	}
	m.Payload = b
	return nil
}

// IsConfirmable 如果是CON类型的消息类型，返回true
func (m *BaseMessage) IsConfirmable() bool {
	return m.Type == CON
}

// GetPayload get payload
func (m *BaseMessage) GetPayload() []byte {
	return m.Payload
}

// Option get option by id
func (m *BaseMessage) Option(o OptionID) interface{} {
	for _, v := range m.Opts {
		if o == v.ID {
			return v.Value
		}
	}
	return nil
}

// Options 获取所的option value
func (m *BaseMessage) Options(o OptionID) []interface{} {
	var rv []interface{}

	for _, v := range m.Opts {
		if o == v.ID {
			rv = append(rv, v.Value)
		}
	}

	return rv
}

// OptionStrings get option strings by id
func (m *BaseMessage) OptionStrings(o OptionID) []string {
	var rv []string
	for _, o := range m.Options(o) {
		rv = append(rv, o.(string))
	}
	return rv
}

// Path 获取URIPath
func (m *BaseMessage) Path() []string {
	return m.OptionStrings(URIPath)
}

// PathString gets a path as a / separated string.
func (m *BaseMessage) PathString() string {
	return strings.Join(m.Path(), "/")
}

// SetPathString sets a path by a / separated string.
func (m *BaseMessage) SetPathString(s string) {
	switch s {
	case "", "/":
		//root path is not set as option
		return
	default:
		if s[0] == '/' {
			s = s[1:]
		}
		m.SetPath(strings.Split(s, "/"))
	}
}

//RemoveOption remove a given opid
func (m *BaseMessage) RemoveOption(opID OptionID) {
	m.Opts = m.Opts.Remove(opID)
}

// AddOption ``
func (m *BaseMessage) AddOption(opID OptionID, val interface{}) {
	iv := reflect.ValueOf(val)
	if (iv.Kind() == reflect.Slice || iv.Kind() == reflect.Array) &&
		iv.Type().Elem().Kind() == reflect.String {
		for i := 0; i < iv.Len(); i++ {
			m.Opts = append(m.Opts, option{opID, iv.Index(i).Interface()})
		}
		return
	}
	m.Opts = append(m.Opts, option{opID, val})
}

// SetPath ``
func (m *BaseMessage) SetPath(s []string) {
	m.SetOption(URIPath, s)
}

// SetOption sets an option, discarding any previous value
func (m *BaseMessage) SetOption(opID OptionID, val interface{}) {
	m.RemoveOption(opID)
	m.AddOption(opID, val)
}
func parseOptionValue(optionID OptionID, valueBuf []byte) interface{} {
	def := coapOptionDefs[optionID]
	if def.valueFormat == valueUnknown {
		// Skip unrecognized options (RFC7252 section 5.4.1)
		return nil
	}
	if len(valueBuf) < def.minLen || len(valueBuf) > def.maxLen {
		// Skip options with illegal value length (RFC7252 section 5.4.3)
		return nil
	}
	switch def.valueFormat {
	case valueUint:
		intValue := decodeInt(valueBuf)
		if optionID == ContentFormat || optionID == Accept {
			return MediaType(intValue)
		}
		return intValue

	case valueString:
		return string(valueBuf)
	case valueOpaque, valueEmpty:
		return valueBuf
	}
	// Skip unrecognized options (should never be reached)
	return nil
}

// ParseMessage parse []byte to message
func ParseMessage(data []byte) (Message, error) {
	rv := &BaseMessage{}
	return rv, rv.Decode(data)
}