/*
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"
	"fmt"
	"sync"

	"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
	respAnnounce
	respData
)

var validTransitions = map[protocolState]protocolState{
	cmdAnnounce:  cmdData,
	cmdData:      respAnnounce,
	respAnnounce: respData,
	respData:     cmdAnnounce,
}

var protocolStateNames = map[protocolState]string{
	cmdAnnounce:  "CMD ANNOUNCE",
	cmdData:      "CMD DATA",
	respAnnounce: "RESP ANNOUNCE",
	respData:     "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.Handler
	protocolState   protocolState
	framer          protocol.Framer
	config          *serial.Config
	port            *serial.Port
	logger          *logrus.Logger
	lock            sync.Mutex
	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
	errors := make(chan error)

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

		errors <- err
	}()

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

		errors <- err
	}()

	for {
		select {
		case <-ctx.Done():
			return nil

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

			return nil

		default:
			if err := h.handleProtocolState(); err != nil {
				return err
			}
		}
	}
}

func (h *Handler) nextState() error {
	next, ok := validTransitions[h.protocolState]
	if !ok {
		return fmt.Errorf("illegal protocol state %s", h.protocolState)
	}

	h.protocolState = next

	return nil
}

func (h *Handler) handleProtocolState() error {
	h.logger.Tracef("handling protocol state %s", h.protocolState)

	h.lock.Lock()
	defer h.lock.Unlock()

	switch h.protocolState {
	case cmdAnnounce:
		if err := h.handleCmdAnnounce(); err != nil {
			return err
		}
	case cmdData:
		if err := h.handleCmdData(); err != nil {
			return err
		}
	case respAnnounce:
		if err := h.handleRespAnnounce(); err != nil {
			return err
		}
	case respData:
		if err := h.handleRespData(); err != nil {
			return err
		}
	default:
		return fmt.Errorf("unknown protocol state %s", h.protocolState)
	}

	return nil
}

func (h *Handler) handleCmdAnnounce() error {
	h.logger.Trace("waiting for command announce")

	frame := <-h.framesIn

	if frame == nil {
		return nil
	}

	if err := h.protocolHandler.HandleCommandAnnounce(frame); err != nil {
		return fmt.Errorf("command announce handling failed: %w", err)
	}

	if err := h.nextState(); err != nil {
		return err
	}

	return nil
}

func (h *Handler) handleCmdData() error {
	h.logger.Trace("waiting for command data")

	frame := <-h.framesIn

	if frame == nil {
		return nil
	}

	if err := h.protocolHandler.HandleCommand(frame); err != nil {
		return fmt.Errorf("command handler failed: %w", err)
	}

	if err := h.nextState(); err != nil {
		return err
	}

	return nil
}

func (h *Handler) handleRespAnnounce() error {
	frame, err := h.protocolHandler.ResponseAnnounce()
	if err != nil {
		return fmt.Errorf("could not get response announcement: %w", err)
	}

	h.framesOut <- frame

	if err := h.nextState(); err != nil {
		return err
	}

	return nil
}

func (h *Handler) handleRespData() error {
	frame, err := h.protocolHandler.ResponseData()
	if err != nil {
		return fmt.Errorf("could not get response data: %w", err)
	}

	h.framesOut <- frame

	if err := h.nextState(); err != nil {
		return err
	}

	return nil
}

func New(cfg *config.Serial, logger *logrus.Logger, protocolHandler protocol.Handler) (*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
}