command.go

package kasa

import (
	"encoding/binary"
	"fmt"
)

// BuildCommand takes a JSON command string, encrypts it, and prepends the length header.
// The length header is 4 bytes in big-endian format containing the length of the encrypted payload.
func BuildCommand(jsonCmd string) []byte {
	// Encrypt the JSON command
	encrypted := Encrypt([]byte(jsonCmd))

	// Create the message with 4-byte length header
	msg := make([]byte, 4+len(encrypted))

	// Write the length as big-endian uint32
	binary.BigEndian.PutUint32(msg[0:4], uint32(len(encrypted)))

	// Copy the encrypted payload
	copy(msg[4:], encrypted)

	return msg
}

// BuildGetSysInfoCommand builds a command to retrieve device system information.
// This includes device name, model, hardware/software versions, and relay states.
func BuildGetSysInfoCommand() []byte {
	return BuildCommand(CmdGetSysInfo)
}

// BuildGetEnergyMeterCommand builds a command to retrieve real-time energy meter data.
// This includes voltage, current, power, and total energy consumption.
func BuildGetEnergyMeterCommand() []byte {
	return BuildCommand(CmdGetRealtimeEM)
}

// BuildGetPlugEnergyCommand builds a command to retrieve energy data for a specific plug/child.
// This is used for power strips like the HS300 that support per-plug power monitoring.
func BuildGetPlugEnergyCommand(childID string) []byte {
	cmd := fmt.Sprintf(`{"context":{"child_ids":["%s"]},"emeter":{"get_realtime":{}}}`, childID)
	return BuildCommand(cmd)
}

// BuildTurnOnCommand builds a command to turn on a device or relay.
func BuildTurnOnCommand() []byte {
	return BuildCommand(CmdTurnOn)
}

// BuildTurnOffCommand builds a command to turn off a device or relay.
func BuildTurnOffCommand() []byte {
	return BuildCommand(CmdTurnOff)
}

// BuildDiscoveryCommand builds a command for UDP device discovery.
func BuildDiscoveryCommand() []byte {
	return BuildGetSysInfoCommand()
}