package via

import (
	"errors"
	"fmt"
)

// Channel is a VIA lighting channel. The values are QMK's id_qmk_*_channel
// constants from quantum/via.h.
type Channel uint8

const (
	ChannelBacklight Channel = 1
	ChannelRgblight  Channel = 2
	ChannelRgbMatrix Channel = 3
	ChannelAudio     Channel = 4
	ChannelLedMatrix Channel = 5
)

// AssignedChannelMax is the highest channel QMK currently assigns. The probe
// asks beyond it on purpose, see probeChannelMax.
const AssignedChannelMax = ChannelLedMatrix

// probeChannelMax is the highest channel the probe asks about. The QMK enum
// stops at 5; the extra reads cost one round trip each and let a future QMK
// that claims a higher channel be found without a code change.
const probeChannelMax = 15

// probeValueID is the brightness value ID. It is one byte and valid on every
// lighting subsystem, so one request per channel finds any kind of channel.
const probeValueID = 0x01

// Subsystem returns the QMK name of the channel's lighting subsystem. The name
// follows from the channel number, so no board file stores it and it is always
// available for a channel the keyboard has.
func (c Channel) Subsystem() string {
	switch c {
	case ChannelBacklight:
		return "backlight"
	case ChannelRgblight:
		return "rgblight"
	case ChannelRgbMatrix:
		return "rgb_matrix"
	case ChannelAudio:
		return "audio"
	case ChannelLedMatrix:
		return "led_matrix"
	default:
		return ""
	}
}

// DetectChannels asks the keyboard which lighting channels it has, in ascending
// order.
//
// The 0xFF answer is the discriminator, not the payload: QMK rejects a channel
// it does not compile in with id_unhandled, whereas an unknown value ID on a
// known channel is mirrored back with a zero payload. A read that fails for any
// other reason aborts the probe, because a channel list missing entries is
// indistinguishable from a complete one and would silently under-report.
func (p *Protocol) DetectChannels() ([]Channel, error) {
	var present []Channel
	for c := Channel(1); c <= probeChannelMax; c++ {
		if _, err := p.GetValue(c, probeValueID); err != nil {
			if errors.Is(err, errUnhandled) {
				continue
			}
			return nil, fmt.Errorf("probe channel %d: %w", c, err)
		}
		present = append(present, c)
	}
	return present, nil
}