// Package sensor defines the hardware seam. Everything above this interface is
// pure and testable on any machine; everything below it touches the Pi.
package sensor

import "time"

// Reading is one complete sample. A Reading only exists if every channel was
// read successfully — there is no partial Reading, because a partial sample
// cannot be reasoned about downstream.
type Reading struct {
	ACPresent bool
	Volts     float64
	SOC       float64
	At        time.Time
}

// Sensor reads the UPS. Read returns an error if any channel fails; callers
// must treat the Reading as invalid in that case.
//
// Implementations may hold OS handles open across calls. A Read that returns
// an error must leave the Sensor usable: the next Read reacquires whatever it
// needs.
type Sensor interface {
	Read() (Reading, error)
	Close() error
}