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

import (
	"fmt"
	"time"

	"github.com/justincpresley/go-cobs"
	"github.com/tarm/serial"

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

type Handler struct {
	protocolHandler protocol.Handler
	config          *serial.Config
	port            *serial.Port
}

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
}

const cobsDelimiter = 0x00

func (h *Handler) Run() error {
	const (
		bufferSize   = 1024 * 1024
		readInterval = 50 * time.Millisecond
	)

	errors := make(chan error)

	cobsConfig := cobs.Config{SpecialByte: cobsDelimiter, Delimiter: true, EndingSave: true}

	go func() {
		buf := make([]byte, bufferSize)

		for {
			count, err := h.port.Read(buf)
			if err != nil {
				errors <- err

				return
			}

			if count == 0 {
				time.Sleep(readInterval)

				continue
			}

			err = cobs.Verify(buf[:count], cobsConfig)
			if err != nil {
				errors <- err

				return
			}

			// perform COBS decoding
			decoded := cobs.Decode(buf[:count], cobsConfig)

			msg, err := h.protocolHandler.HandleFrame(decoded)
			if err != nil {
				errors <- err

				return
			}

			// perform COBS encoding
			encoded := cobs.Encode(msg, cobsConfig)

			_, err = h.port.Write(encoded)
			if err != nil {
				errors <- err

				return
			}
		}
	}()

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

	return nil
}

func New(cfg *config.Serial, protocolHandler protocol.Handler) (*Handler, error) {
	h := &Handler{protocolHandler: protocolHandler}
	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
}