// Package sensor reads Tasmota ENERGY.Power measurements in watts.
package sensor

import (
	"encoding/json"
	"errors"
	"fmt"
)

// ParsePower accepts numeric ENERGY.Power, including zero. Missing, null, or
// malformed measurements return an error so callers can preserve the last value.
func ParsePower(payload []byte) (float64, error) {
	var message struct {
		Energy *struct {
			Power *float64 `json:"Power"`
		} `json:"ENERGY"`
	}
	if err := json.Unmarshal(payload, &message); err != nil {
		return 0, fmt.Errorf("decode sensor payload: %w", err)
	}
	if message.Energy == nil || message.Energy.Power == nil {
		return 0, errors.New("sensor payload has no numeric ENERGY.Power")
	}
	return *message.Energy.Power, nil
}