package via

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

// Vial's protocol. This is a QMK fork that keeps VIA's command set unchanged and
// hangs its own commands off a prefix byte, and it replaces the rgb_matrix
// lighting handler with one of its own. The numbers below are read from
// vial-kb/vial-qmk, branch `vial`:
//
//	quantum/via.h      enum via_command_id  -> id_vial_prefix
//	quantum/vial.h     enum                -> vial_get_keyboard_id, VIAL_PROTOCOL_VERSION
//	quantum/vialrgb.h  enum                -> vialrgb_get_info, vialrgb_get_supported
//
// None of this has been run against Vial firmware. It is written from that
// source and tested against a scripted keyboard, which is what makes it
// reviewable rather than what makes it right.
const (
	// vialPrefix is Vial's command prefix. VIA's own commands are 0x01 to 0x13 and
	// untouched; this is where Vial's begin.
	vialPrefix = 0xFE

	// vialGetKeyboardID is the one command worth sending to find out whether a
	// keyboard speaks Vial at all. It answers with the protocol version and
	// nothing else, so it cannot be mistaken for state.
	vialGetKeyboardID = 0x00
)

// VialRGB's commands, from quantum/vialrgb.h. They are not behind vialPrefix:
// VialRGB answers the ordinary VIA lighting command 0x08 and carries its own
// command in the channel byte, so a request for the supported effect IDs is a
// custom get with a channel of 0x42. That is in vialrgb_get_value, which reads
// `uint8_t cmd = data[1]` and switches on it.
const (
	lightingGet         = 0x08
	vialrgbGetInfo      = 0x40
	vialrgbGetSupported = 0x42
)

// vialrgbMaxPayload is how many bytes of a report the supported-ID list may
// fill. The report is 32 bytes, the command byte and Vial's command byte take
// two, and the list starts in the third.
const vialrgbMaxPayload = 32 - 2

// VialVersion asks whether the keyboard speaks Vial and, if it does, for its
// protocol version.
//
// The answer is a discriminator rather than a guess because the two firmwares
// differ in what they do with a command they do not know. Stock QMK's
// raw_hid_receive ends its switch with
//
//	default: { *command_id = id_unhandled; }
//
// so an unknown command comes back as 0xFF. Vial's default case does not set that
// marker — it defers to the keyboard instead — and its keyboard-ID handler fills
// bytes 1 to 4 with the version. So 0xFF in byte 0 is a keyboard that is not
// Vial, and a version that is not zero is one that is. A keyboard implementing
// raw_hid_receive_kb for 0xFE would defeat this, which is the one case the
// source cannot rule out.
func (p *Protocol) VialVersion() (uint32, bool, error) {
	report := make([]byte, 32)
	report[0] = vialPrefix
	report[1] = vialGetKeyboardID

	if _, err := p.handle.SendReport(0x00, report); err != nil {
		return 0, false, err
	}
	buf, err := p.readPrefixed(vialPrefix)
	if err != nil {
		if errors.Is(err, errUnhandled) {
			// Stock QMK marking a command it does not know is the ordinary
			// answer for a keyboard that is not Vial, not a failure.
			return 0, false, nil
		}
		return 0, false, err
	}
	// Vial's handlers take msg = &data[1], so the version lands in bytes 1 to 4.
	version := binary.LittleEndian.Uint32(buf[1:5])
	if version == 0 {
		// Byte 0 came back as the prefix and the rest as nothing, which is what a
		// keyboard that echoes the request looks like. A Vial version is never 0.
		return 0, false, nil
	}
	return version, true, nil
}

// VialEffectIDs returns the effect IDs the keyboard's rgb_matrix channel has
// compiled in, as Vial numbers.
//
// It does not report effect 0. get_supported fills the report with the IDs
// strictly greater than the cursor, and the first request asks from 0, so "off"
// is implied rather than listed. A caller that wants to set 0 writes 0; nothing
// here tells it that 0 exists.
//
// It is worth asking for where it answers, for two reasons. It does not write to
// the keyboard, where reading the range by clamping does. And it is the firmware
// reporting what it has, where the clamp is the firmware's answer to a question
// it was not asked.
//
// Three things bound the answer. The list is a run of u16 with 0xFF padding, and
// 0xFFFF is padding rather than an ID. The IDs ascend, and a list that does not
// is not one this firmware produced. And the whole list is fetched in pages,
// because get_supported fills one report at a time from a cursor.
func (p *Protocol) VialEffectIDs() ([]uint16, error) {
	var ids []uint16
	cursor := uint16(0)
	// Each page must advance the cursor or the loop would never end. One page per
	// ten IDs is generous for a firmware whose largest list is under fifty, and a
	// keyboard that needs more is not one this can make sense of.
	for page := 0; page < 32; page++ {
		batch, err := p.vialSupportedPage(cursor)
		if err != nil {
			return nil, err
		}
		if len(batch) == 0 {
			break
		}
		ids = append(ids, batch...)
		if batch[len(batch)-1] <= cursor {
			return nil, fmt.Errorf("vialrgb effect list did not advance past %d", cursor)
		}
		cursor = batch[len(batch)-1]
	}
	return ascending(ids), nil
}

// vialSupportedPage asks for the effect IDs above a cursor and reads the run of
// u16 the firmware wrote into the payload.
func (p *Protocol) vialSupportedPage(cursor uint16) ([]uint16, error) {
	report := make([]byte, 32)
	report[0] = lightingGet
	report[1] = vialrgbGetSupported
	binary.LittleEndian.PutUint16(report[2:4], cursor)

	if _, err := p.handle.SendReport(0x00, report); err != nil {
		return nil, err
	}
	// The list starts at byte 2, where the request's cursor was: get_supported
	// overwrites the cursor with the first ID it found, so those bytes are data
	// and not an echo of what was sent.
	buf, err := p.readPrefixed(lightingGet)
	if err != nil {
		return nil, err
	}
	payload := buf[2 : 2+vialrgbMaxPayload]

	var out []uint16
	for i := 0; i+1 < len(payload); i += 2 {
		id := binary.LittleEndian.Uint16(payload[i : i+2])
		if id == 0xFFFF || id == 0 {
			// get_supported pads the rest of the report with 0xFF, so 0xFFFF is
			// padding and not an effect. Zero stops it as well: the list holds the
			// IDs strictly greater than a cursor that starts at 0, so a 0 in it is
			// never an effect. That is what keeps a report that is zero-filled
			// rather than 0xFF-filled from running on through fifteen zeros.
			break
		}
		out = append(out, id)
	}
	return out, nil
}

// ascending reports whether the IDs came out in order. A list that did not is not
// this firmware's, and returning it would put a name on a number the firmware
// never said was there.
func ascending(ids []uint16) []uint16 {
	for i := 1; i < len(ids); i++ {
		if ids[i] <= ids[i-1] {
			return nil
		}
	}
	return ids
}

// readPrefixed reads the report from a command that does not answer in VIA's
// shape. readResponse checks the echoed channel and value ID, and Vial's handlers
// fill their payload from byte 1 or byte 2 without echoing either — one of them
// carries its own command in the channel byte — so those checks would reject a
// correct answer. The command byte is the one thing both firmwares leave in
// place, and 0xFF is how either says it does not handle the command.
func (p *Protocol) readPrefixed(command byte) ([]byte, error) {
	buf := make([]byte, 32)
	n, err := p.handle.Read(buf)
	if err != nil {
		return nil, fmt.Errorf("read response: %w", err)
	}
	if n != len(buf) {
		return nil, fmt.Errorf("short response: got %d bytes, want 32", n)
	}
	if buf[0] == byte(Unhandled) {
		return nil, errUnhandled
	}
	if buf[0] != command {
		return nil, fmt.Errorf("unexpected response command: 0x%02x, want 0x%02x", buf[0], command)
	}
	return buf, nil
}