// Package plugctl provides an API for controlling Kasa smart home switches.
package plugctl

import (
	"bytes"
	"encoding/binary"
	"encoding/json"
	"fmt"
	"io"
	"net"
)

const (
	reqTurnOn     = `{"system":{"set_relay_state":{"state":1}}}`
	reqTurnOff    = `{"system":{"set_relay_state":{"state":0}}}`
	reqGetSysinfo = `{"system":{"get_sysinfo":null}}`
	reqGetEMeter  = `{"emeter":{"get_realtime":null}}`
)

// Plug provides an API for a single Kasa smart home plug or switch.
type Plug struct {
	Addr string
}

func (p *Plug) roundTrip(req string) (*response, error) {
	conn, err := net.Dial("tcp", p.Addr)
	if err != nil {
		return nil, fmt.Errorf("dialing plug: %w", err)
	}
	defer conn.Close()

	lp := []byte{0, 0, 0, 0}
	binary.BigEndian.PutUint32(lp, uint32(len(req)))

	// Start by writing length
	if _, err := conn.Write(lp); err != nil {
		return nil, fmt.Errorf("writing length: %w", err)
	}
	// Rest of the message is encrypted
	enc := newEncrypter(conn)
	if _, err := enc.Write([]byte(req)); err != nil {
		return nil, fmt.Errorf("writing message: %w", err)
	}

	// Read length of response
	if _, err := io.ReadFull(conn, lp); err != nil {
		return nil, fmt.Errorf("reading length: %w", err)
	}
	rlen := binary.BigEndian.Uint32(lp)

	// Read the encrypted response
	buf := make([]byte, rlen)
	if _, err := io.ReadFull(conn, buf); err != nil {
		return nil, fmt.Errorf("reading response: %w", err)
	}

	// Decrypt and parse the response
	var resp *response
	dec := json.NewDecoder(newDecrypter(bytes.NewReader(buf)))
	if err := dec.Decode(&resp); err != nil {
		return nil, fmt.Errorf("reading message: %w", err)
	}

	return resp, nil
}

// Implements TP Link's weaksauce encryption.
// Do NOT use for actually important secrets.
type decryptReader struct {
	r io.Reader
	c byte
}

func newDecrypter(r io.Reader) *decryptReader {
	return &decryptReader{
		r: r,
		c: 0xab,
	}
}

func (d *decryptReader) Read(b []byte) (int, error) {
	n, err := d.r.Read(b)
	for i, x := range b {
		b[i] = d.c ^ x
		d.c = x
	}
	return n, err
}

// Implements TP Link's weaksauce encryption.
// Do NOT use for actually important secrets.
type encryptWriter struct {
	w io.Writer
	c byte
}

func newEncrypter(w io.Writer) *encryptWriter {
	return &encryptWriter{
		w: w,
		c: 0xab,
	}
}

func (e *encryptWriter) Write(b []byte) (int, error) {
	eb := make([]byte, len(b))
	for i, x := range b {
		e.c ^= x
		eb[i] = e.c
	}
	return e.w.Write(eb)
}

/*
	"sw_ver": "1.0.3 Build 210506 Rel.105435",
	"hw_ver": "1.0",
	"model": "KP105(AU)",
	"deviceId": "8006CF0E89296D2A5BFBDE11C844BB2B1E2D2B7C",
	"oemId": "EAB15315847573797920EFE7E9000562",
	"hwId": "120EF751A1A4F170831E6C1F57D97B38",
	"rssi": -58,
	"longitude_i": 1473005,
	"latitude_i": -428429,
	"alias": "Car charger",
	"status": "new",
	"mic_type": "IOT.SMARTPLUGSWITCH",
	"feature": "TIM",
	"mac": "00:5F:67:01:A5:50",
	"updating": 0,
	"led_off": 0,
	"obd_src": "tplink",
	"relay_state": 0,
	"on_time": 0,
	"active_mode": "schedule",
	"icon_hash": "",
	"dev_name": "Smart Wi-Fi Plug",
	"next_action": {
		"type": -1
	},
	"ntc_state": 0,
	"err_code": 0
*/

type response struct {
	System *systemMsg `json:"system,omitempty"`
	EMeter *eMeterMsg `json:"emeter,omitempty"`
}

type eMeterMsg struct {
	GetRealtime *getRealtimeMsg `json:"get_realtime"`
}

type getRealtimeMsg struct{}

type systemMsg struct {
	GetSysInfo    *getSysInfoMsg    `json:"get_sysinfo"`
	SetRelayState *setRelayStateMsg `json:"set_relay_state,omitempty"`
}

type getSysInfoMsg struct {
	SWVer      string `json:"sw_ver,omitempty"`      // e.g. "1.0.3 Build 210506 Rel.105435",
	HWVer      string `json:"hw_ver,omitempty"`      // e.g. "1.0",
	Model      string `json:"model,omitempty"`       // e.g. "KP105(AU)",
	DeviceID   string `json:"deviceId,omitempty"`    // e.g. "8006CF0E89296D2A5BFBDE11C844BB2B1E2D2B7C",
	OEMID      string `json:"oemId,omitempty"`       // e.g. "EAB15315847573797920EFE7E9000562",
	HWID       string `json:"hwId,omitempty"`        // e.g. "120EF751A1A4F170831E6C1F57D97B38",
	RSSI       int    `json:"rssi,omitempty"`        // e.g. -58,
	LongitudeI int    `json:"longitude_i,omitempty"` // e.g. 1473005,
	LatitudeI  int    `json:"latitude_i,omitempty"`  // e.g. -428429,
	Alias      string `json:"alias,omitempty"`       // e.g. "Car charger",
	Status     string `json:"status,omitempty"`      // e.g. "new",
	MICType    string `json:"mic_type,omitempty"`    // e.g. "IOT.SMARTPLUGSWITCH",
	Feature    string `json:"feature,omitempty"`     // e.g. "TIM",
	MAC        string `json:"mac,omitempty"`         // e.g. "00:5F:67:01:A5:50",
	Updating   int    `json:"updating,omitempty"`    // e.g. 0,
	LEDOff     int    `json:"led_off,omitempty"`     // e.g. 0,
	OBDSrc     string `json:"obd_src,omitempty"`     // e.g. "tplink",
	RelayState int    `json:"relay_state,omitempty"` // e.g. 0,
	OnTime     int    `json:"on_time,omitempty"`     // e.g. 0,
	ActiveMode string `json:"active_mode,omitempty"` // e.g. "schedule",
	IconHash   string `json:"icon_hash,omitempty"`   // e.g. "",
	DevName    string `json:"dev_name,omitempty"`    // e.g. "Smart Wi-Fi Plug",
	NextAction struct {
		Type int `json:"type,omitempty"`
	} `json:"next_action,omitempty"` // e.g. {"type": -1},
	NTCState int `json:"ntc_state,omitempty"` // e.g. 0,
	ErrCode  int `json:"err_code,omitempty"`  // e.g. 0
}

type setRelayStateMsg struct {
	ErrCode int `json:"err_code,omitempty"`
	State   int `json:"state,omitempty"`
}