//go:build linux

package serial

import (
	"errors"
	"fmt"
	"reflect"

	"golang.org/x/sys/unix"
)

type platformLineOperations struct{}

type platformLineSnapshot struct {
	termios      unix.Termios
	modemOutputs int
}

func (platformLineOperations) Open(path string) (lineDevice, error) {
	return openSerialDevice(path)
}

func (platformLineOperations) Snapshot(device lineDevice) (any, error) {
	termios, err := unix.IoctlGetTermios(int(device.Fd()), unix.TCGETS)
	if err != nil {
		return nil, fmt.Errorf("read serial termios snapshot: %w", err)
	}
	bits, err := unix.IoctlGetInt(int(device.Fd()), unix.TIOCMGET)
	if err != nil {
		return nil, fmt.Errorf("read serial modem-output snapshot: %w", err)
	}
	return platformLineSnapshot{
		termios:      *termios,
		modemOutputs: bits & (unix.TIOCM_DTR | unix.TIOCM_RTS),
	}, nil
}

func (platformLineOperations) Apply(device lineDevice, config LineConfig) error {
	return ApplyLineConfig(device.Fd(), config)
}

func (platformLineOperations) Read(device lineDevice, path string) (LineConfig, error) {
	return ReadLineConfig(device.Fd(), path)
}

func (platformLineOperations) Restore(device lineDevice, snapshot any) error {
	state, ok := snapshot.(platformLineSnapshot)
	if !ok {
		return errors.New("invalid serial line snapshot")
	}
	if err := unix.IoctlSetTermios(int(device.Fd()), unix.TCSETS, &state.termios); err != nil {
		return fmt.Errorf("restore serial termios: %w", err)
	}
	readback, err := unix.IoctlGetTermios(int(device.Fd()), unix.TCGETS)
	if err != nil {
		return fmt.Errorf("read restored serial termios: %w", err)
	}
	if !reflect.DeepEqual(*readback, state.termios) {
		return errors.New("restored serial termios does not match snapshot")
	}
	if err := restoreModemOutputs(int(device.Fd()), state.modemOutputs); err != nil {
		return err
	}
	return nil
}

func restoreModemOutputs(fd, outputs int) error {
	const outputMask = unix.TIOCM_DTR | unix.TIOCM_RTS
	setMask := outputs & outputMask
	clearMask := outputMask &^ outputs
	if setMask != 0 {
		if err := unix.IoctlSetPointerInt(fd, unix.TIOCMBIS, setMask); err != nil {
			return fmt.Errorf("restore serial modem outputs on: %w", err)
		}
	}
	if clearMask != 0 {
		if err := unix.IoctlSetPointerInt(fd, unix.TIOCMBIC, clearMask); err != nil {
			return fmt.Errorf("restore serial modem outputs off: %w", err)
		}
	}
	readback, err := unix.IoctlGetInt(fd, unix.TIOCMGET)
	if err != nil {
		return fmt.Errorf("read restored serial modem outputs: %w", err)
	}
	if readback&outputMask != outputs&outputMask {
		return errors.New("restored serial modem outputs do not match snapshot")
	}
	return nil
}