package mesh

import (
	"crypto/rand"
	"encoding/binary"
	"fmt"
	"strings"
	"unicode/utf8"

	"google.golang.org/protobuf/encoding/protowire"
)

// BuildOptions 是构建 MeshPacket 的公共选项。
type BuildOptions struct {
	FromNodeNum uint32
	ToNodeNum   uint32
	PacketID    uint32
	ChannelID   string
	GatewayID   string
	PSK         []byte
	Encrypt     bool
	ViaMQTT     bool
}

// TextBuildOptions 是构建文本消息的选项。
type TextBuildOptions struct {
	BuildOptions
	Text string
}

// NodeInfoBuildOptions 是构建节点信息广播的选项。
type NodeInfoBuildOptions struct {
	BuildOptions
	NodeID     string
	LongName   string
	ShortName  string
	HWModel    uint32
	Role       uint32
	IsLicensed bool
	PublicKey  []byte
}

// RandomPacketID 生成一个非零随机 packet id。
func RandomPacketID() uint32 {
	var buf [4]byte
	if _, err := rand.Read(buf[:]); err != nil {
		return 1
	}
	id := binary.LittleEndian.Uint32(buf[:])
	if id == 0 {
		id = 1
	}
	return id
}

// BuildTextServiceEnvelope 构建一条加密的文本消息 ServiceEnvelope。
func BuildTextServiceEnvelope(opts TextBuildOptions) ([]byte, error) {
	if opts.FromNodeNum == 0 {
		return nil, fmt.Errorf("from node number is required")
	}
	if opts.PacketID == 0 {
		return nil, fmt.Errorf("packet id is required")
	}
	if opts.ChannelID == "" {
		return nil, fmt.Errorf("channel id is required")
	}
	if opts.GatewayID == "" {
		opts.GatewayID = NodeNumToID(opts.FromNodeNum)
	}
	if opts.Text == "" {
		return nil, fmt.Errorf("text is required")
	}
	if !utf8.ValidString(opts.Text) {
		return nil, fmt.Errorf("text must be valid utf-8")
	}
	data := buildData(PortNumTextMessage, []byte(opts.Text))
	packet, err := buildMeshPacket(opts.BuildOptions, data)
	if err != nil {
		return nil, err
	}
	return buildServiceEnvelope(packet, opts.ChannelID, opts.GatewayID), nil
}

// BuildNodeInfoServiceEnvelope 构建一条节点信息广播 ServiceEnvelope。
func BuildNodeInfoServiceEnvelope(opts NodeInfoBuildOptions) ([]byte, error) {
	if opts.FromNodeNum == 0 {
		return nil, fmt.Errorf("from node number is required")
	}
	if opts.NodeID == "" {
		opts.NodeID = NodeNumToID(opts.FromNodeNum)
	}
	if opts.GatewayID == "" {
		opts.GatewayID = NodeNumToID(opts.FromNodeNum)
	}
	if opts.ChannelID == "" {
		return nil, fmt.Errorf("channel id is required")
	}
	if opts.LongName == "" {
		opts.LongName = NodeNumToID(opts.FromNodeNum)
	}
	if opts.ShortName == "" {
		opts.ShortName = strings.ToUpper(opts.LongName)
		if len(opts.ShortName) > 4 {
			opts.ShortName = opts.ShortName[:4]
		}
	}
	user := buildUser(opts)
	data := buildData(PortNumNodeInfo, user)
	packet, err := buildMeshPacket(opts.BuildOptions, data)
	if err != nil {
		return nil, err
	}
	return buildServiceEnvelope(packet, opts.ChannelID, opts.GatewayID), nil
}

func buildData(portnum uint32, payload []byte) []byte {
	var out []byte
	out = protowire.AppendTag(out, 1, protowire.VarintType)
	out = protowire.AppendVarint(out, uint64(portnum))
	out = protowire.AppendTag(out, 2, protowire.BytesType)
	out = protowire.AppendBytes(out, payload)
	return out
}

func buildUser(opts NodeInfoBuildOptions) []byte {
	var out []byte
	out = protowire.AppendTag(out, 1, protowire.BytesType)
	out = protowire.AppendBytes(out, []byte(opts.NodeID))
	out = protowire.AppendTag(out, 2, protowire.BytesType)
	out = protowire.AppendBytes(out, []byte(opts.LongName))
	out = protowire.AppendTag(out, 3, protowire.BytesType)
	out = protowire.AppendBytes(out, []byte(opts.ShortName))
	if opts.HWModel != 0 {
		out = protowire.AppendTag(out, 5, protowire.VarintType)
		out = protowire.AppendVarint(out, uint64(opts.HWModel))
	}
	out = protowire.AppendTag(out, 6, protowire.VarintType)
	if opts.IsLicensed {
		out = protowire.AppendVarint(out, 1)
	} else {
		out = protowire.AppendVarint(out, 0)
	}
	out = protowire.AppendTag(out, 7, protowire.VarintType)
	out = protowire.AppendVarint(out, uint64(opts.Role))
	if len(opts.PublicKey) > 0 {
		out = protowire.AppendTag(out, 8, protowire.BytesType)
		out = protowire.AppendBytes(out, opts.PublicKey)
	}
	return out
}

func buildMeshPacket(opts BuildOptions, data []byte) ([]byte, error) {
	if opts.FromNodeNum == 0 {
		return nil, fmt.Errorf("from node number is required")
	}
	if opts.PacketID == 0 {
		return nil, fmt.Errorf("packet id is required")
	}
	if opts.ChannelID == "" {
		return nil, fmt.Errorf("channel id is required")
	}
	var out []byte
	out = protowire.AppendTag(out, 1, protowire.Fixed32Type)
	out = protowire.AppendFixed32(out, opts.FromNodeNum)
	out = protowire.AppendTag(out, 2, protowire.Fixed32Type)
	out = protowire.AppendFixed32(out, opts.ToNodeNum)

	if opts.Encrypt {
		if len(opts.PSK) == 0 {
			return nil, fmt.Errorf("psk is required for encrypted packet")
		}
		ciphertext, err := cryptAESCTR(opts.PSK, opts.FromNodeNum, opts.PacketID, data)
		if err != nil {
			return nil, err
		}
		out = protowire.AppendTag(out, 3, protowire.VarintType)
		out = protowire.AppendVarint(out, uint64(channelHash(opts.ChannelID, opts.PSK)))
		out = protowire.AppendTag(out, 5, protowire.BytesType)
		out = protowire.AppendBytes(out, ciphertext)
	} else {
		out = protowire.AppendTag(out, 4, protowire.BytesType)
		out = protowire.AppendBytes(out, data)
	}

	out = protowire.AppendTag(out, 6, protowire.Fixed32Type)
	out = protowire.AppendFixed32(out, opts.PacketID)
	if opts.ViaMQTT {
		out = protowire.AppendTag(out, 14, protowire.VarintType)
		out = protowire.AppendVarint(out, 1)
	}
	// hop_limit = 7（默认）
	out = protowire.AppendTag(out, 9, protowire.VarintType)
	out = protowire.AppendVarint(out, 7)
	out = protowire.AppendTag(out, 15, protowire.VarintType)
	out = protowire.AppendVarint(out, 7)
	return out, nil
}

func buildServiceEnvelope(packet []byte, channelID string, gatewayID string) []byte {
	var out []byte
	out = protowire.AppendTag(out, 1, protowire.BytesType)
	out = protowire.AppendBytes(out, packet)
	out = protowire.AppendTag(out, 2, protowire.BytesType)
	out = protowire.AppendBytes(out, []byte(channelID))
	out = protowire.AppendTag(out, 3, protowire.BytesType)
	out = protowire.AppendBytes(out, []byte(gatewayID))
	return out
}