/*
Copyright 2022 CAcert Inc.
SPDX-License-Identifier: Apache-2.0

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

// Package serial provides a handler for the serial connection of the signer machine.
package serial

import (
	"context"
	"errors"
	"fmt"

	"github.com/sirupsen/logrus"
	"github.com/tarm/serial"

	"git.cacert.org/cacert-gosigner/internal/config"
	"git.cacert.org/cacert-gosigner/pkg/protocol"
)

type protocolState int8

const (
	cmdAnnounce protocolState = iota
	cmdData
	handleCommand
	respond
)

var protocolStateNames = map[protocolState]string{
	cmdAnnounce:   "CMD ANNOUNCE",
	cmdData:       "CMD DATA",
	handleCommand: "RESP ANNOUNCE",
	respond:       "RESP DATA",
}

func (p protocolState) String() string {
	if name, ok := protocolStateNames[p]; ok {
		return name
	}

	return fmt.Sprintf("unknown %d", p)
}

type Handler struct {
	protocolHandler protocol.ServerHandler
	protocolState   protocolState
	framer          protocol.Framer
	config          *serial.Config
	port            *serial.Port
	logger          *logrus.Logger
	framesIn        chan []byte
	framesOut       chan []byte
}

func (h *Handler) setupConnection() error {
	s, err := serial.OpenPort(h.config)
	if err != nil {
		return fmt.Errorf("could not open serial port: %w", err)
	}

	h.port = s

	return nil
}

func (h *Handler) Close() error {
	err := h.port.Close()
	if err != nil {
		return fmt.Errorf("could not close serial port: %w", err)
	}

	return nil
}

func (h *Handler) Run(ctx context.Context) error {
	h.protocolState = cmdAnnounce
	protocolErrors, framerErrors := make(chan error), make(chan error)

	go func() {
		err := h.framer.ReadFrames(h.port, h.framesIn)

		framerErrors <- err
	}()

	go func() {
		err := h.framer.WriteFrames(h.port, h.framesOut)

		framerErrors <- err
	}()

	go func() {
		err := h.handleProtocolState()

		protocolErrors <- err
	}()

	for {
		select {
		case <-ctx.Done():
			return nil
		case err := <-framerErrors:
			if err != nil {
				return fmt.Errorf("error from framer: %w", err)
			}

			return nil
		case err := <-protocolErrors:
			if err != nil {
				return fmt.Errorf("error from protocol handler: %w", err)
			}

			return nil
		}
	}
}

var errCommandExpected = errors.New("command must not be nil")
var errResponseExpected = errors.New("response must not be nil")

func (h *Handler) handleProtocolState() error {
	var (
		command  *protocol.Command
		response *protocol.Response
		err      error
	)

	for {
		h.logger.Debugf("handling protocol state %s", h.protocolState)

		switch h.protocolState {
		case cmdAnnounce:
			command, err = h.protocolHandler.CommandAnnounce(h.framesIn)
			if err != nil {
				h.logger.WithError(err).Error("could not handle command announce")

				break
			}

			h.protocolState = cmdData
		case cmdData:
			if command == nil {
				return errCommandExpected
			}

			err = h.protocolHandler.CommandData(h.framesIn, command)
			if err != nil {
				h.logger.WithError(err).Error("could not handle command data")

				h.protocolState = cmdAnnounce

				break
			}

			h.protocolState = handleCommand
		case handleCommand:
			if command == nil {
				return errCommandExpected
			}

			response, err = h.protocolHandler.HandleCommand(command)
			if err != nil {
				h.logger.WithError(err).Error("could not handle command")

				h.protocolState = cmdAnnounce

				break
			}

			command = nil

			h.protocolState = respond
		case respond:
			if response == nil {
				return errResponseExpected
			}

			err = h.protocolHandler.Respond(response, h.framesOut)
			if err != nil {
				h.logger.WithError(err).Error("could not respond")

				h.protocolState = cmdAnnounce

				break
			}

			response = nil

			h.protocolState = cmdAnnounce
		default:
			return fmt.Errorf("unknown protocol state %s", h.protocolState)
		}
	}
}

func New(
	cfg *config.Serial,
	logger *logrus.Logger,
	protocolHandler protocol.ServerHandler,
) (*Handler, error) {
	h := &Handler{
		protocolHandler: protocolHandler,
		logger:          logger,
		framesIn:        make(chan []byte),
		framesOut:       make(chan []byte),
		framer:          protocol.NewCOBSFramer(logger),
	}
	h.config = &serial.Config{Name: cfg.Device, Baud: cfg.Baud, ReadTimeout: cfg.Timeout}

	err := h.setupConnection()
	if err != nil {
		return nil, err
	}

	return h, nil
}