/*
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.
*/

// client simulator

package main

import (
	"bytes"
	"context"
	"fmt"
	"os"
	"sync"
	"time"

	"github.com/justincpresley/go-cobs"
	"github.com/shamaton/msgpackgen/msgpack"
	"github.com/sirupsen/logrus"

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

	"git.cacert.org/cacert-gosigner/pkg/messages"
)

const cobsDelimiter = 0x00

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

func main() {
	logger := logrus.New()
	logger.SetOutput(os.Stderr)
	logger.SetLevel(logrus.InfoLevel)

	sim := &clientSimulator{
		logger: logger,
	}

	err := sim.Run()
	if err != nil {
		logger.WithError(err).Error("simulator returned an error")
	}
}

type clientSimulator struct {
	logger    *logrus.Logger
	commands  chan *protocol.Command
	responses chan [][]byte
}

func (c *clientSimulator) writeTestCommands(ctx context.Context) error {
	messages.RegisterGeneratedResolver()

	const healthInterval = 10 * time.Second

	time.Sleep(healthInterval)

	c.commands <- &protocol.Command{
		Announce: messages.BuildCommandAnnounce(messages.CmdFetchCRL),
		Command:  &messages.FetchCRLCommand{IssuerID: "sub-ecc_person_2022"},
	}

	timer := time.NewTimer(healthInterval)

	for {
		select {
		case <-ctx.Done():
			_ = timer.Stop()

			c.logger.Info("stopping health check loop")

			return nil
		case <-timer.C:
			c.commands <- &protocol.Command{
				Announce: messages.BuildCommandAnnounce(messages.CmdHealth),
				Command:  &messages.HealthCommand{},
			}
		}

		timer.Reset(healthInterval)
	}
}

func (c *clientSimulator) handleInput(ctx context.Context) error {
	const (
		bufferSize   = 1024 * 1024
		readInterval = 50 * time.Millisecond
	)

	buf := make([]byte, bufferSize)

	type protocolState int8

	const (
		stAnn protocolState = iota
		stResp
	)

	state := stAnn

	var announce []byte

reading:
	for {
		select {
		case <-ctx.Done():
			return nil
		default:
			count, err := os.Stdin.Read(buf)
			if err != nil {
				return fmt.Errorf("reading input failed: %w", err)
			}

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

				continue
			}

			data := buf[:count]

			for _, frame := range bytes.SplitAfter(data, []byte{cobsConfig.SpecialByte}) {
				if len(frame) == 0 {
					continue reading
				}

				err = cobs.Verify(frame, cobsConfig)
				if err != nil {
					return fmt.Errorf("frame verification failed: %w", err)
				}

				if state == stAnn {
					announce = cobs.Decode(frame, cobsConfig)

					state = stResp
				} else {
					c.responses <- [][]byte{announce, cobs.Decode(frame, cobsConfig)}

					state = stAnn
				}
			}
		}
	}
}

func (c *clientSimulator) handleCommands(ctx context.Context) error {
	for {
		select {
		case command := <-c.commands:
			if err := writeCommandAnnouncement(command); err != nil {
				return err
			}

			if err := writeCommand(command); err != nil {
				return err
			}

			respData := <-c.responses

			c.logger.WithField("respdata", respData).Trace("read response data")

			response := &protocol.Response{}

			if err := msgpack.Unmarshal(respData[0], &response.Announce); err != nil {
				return fmt.Errorf("could not unmarshal response announcement: %w", err)
			}

			if err := c.handleResponse(response, respData[1]); err != nil {
				return err
			}

		case <-ctx.Done():
			return nil
		}
	}
}

func (c *clientSimulator) handleResponse(response *protocol.Response, respBytes []byte) error {
	switch response.Announce.Code {
	case messages.RespHealth:
		data := messages.HealthResponse{}

		if err := msgpack.Unmarshal(respBytes, &data); err != nil {
			return fmt.Errorf("could not unmarshal health data: %w", err)
		}

		c.logger.WithField(
			"announce",
			response.Announce,
		).WithField(
			"data",
			&data,
		).Infof("received response")
	case messages.RespFetchCRL:
		data := messages.FetchCRLResponse{}

		if err := msgpack.Unmarshal(respBytes, &data); err != nil {
			return fmt.Errorf("could not unmarshal fetch CRL data: %w", err)
		}

		c.logger.WithField(
			"announce",
			response.Announce,
		).WithField(
			"data",
			&data,
		).Infof("received response")
	case messages.RespError:
		data := messages.ErrorResponse{}

		if err := msgpack.Unmarshal(respBytes, &data); err != nil {
			return fmt.Errorf("could not unmarshal error data: %w", err)
		}

		c.logger.WithField(
			"announce",
			response.Announce,
		).WithField(
			"data",
			&data,
		).Infof("received response")
	default:
		if err := msgpack.Unmarshal(respBytes, &response.Response); err != nil {
			return fmt.Errorf("could not unmarshal response: %w", err)
		}

		c.logger.WithField("response", response).Infof("received response")
	}

	return nil
}

func writeCommandAnnouncement(command *protocol.Command) error {
	cmdAnnounceBytes, err := msgpack.Marshal(&command.Announce)
	if err != nil {
		return fmt.Errorf("could not marshal command announcement bytes: %w", err)
	}

	if _, err = os.Stdout.Write(cobs.Encode(cmdAnnounceBytes, cobsConfig)); err != nil {
		return fmt.Errorf("command announcement write failed: %w", err)
	}

	return nil
}

func writeCommand(command *protocol.Command) error {
	cmdBytes, err := msgpack.Marshal(&command.Command)
	if err != nil {
		return fmt.Errorf("could not marshal command bytes: %w", err)
	}

	if _, err = os.Stdout.Write(cobs.Encode(cmdBytes, cobsConfig)); err != nil {
		return fmt.Errorf("command write failed: %w", err)
	}

	return nil
}

func (c *clientSimulator) Run() error {
	ctx, cancel := context.WithCancel(context.Background())

	c.commands = make(chan *protocol.Command)
	c.responses = make(chan [][]byte)

	wg := sync.WaitGroup{}
	wg.Add(2)

	go func() {
		if err := c.handleInput(ctx); err != nil {
			c.logger.WithError(err).Error("input handling failed")
		}

		cancel()

		wg.Done()
	}()

	go func() {
		if err := c.handleCommands(ctx); err != nil {
			c.logger.WithError(err).Error("command handling failed")
		}

		cancel()

		wg.Done()
	}()

	var result error

	if err := c.writeTestCommands(ctx); err != nil {
		c.logger.WithError(err).Error("test commands failed")
	}

	cancel()
	wg.Wait()

	return result
}