/*
Copyright 2022-2023 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 (
	"context"
	"crypto"
	"crypto/ecdsa"
	"crypto/elliptic"
	"crypto/rand"
	"crypto/x509"
	"crypto/x509/pkix"
	"fmt"
	"io"
	mathRand "math/rand"
	"os"
	"sort"
	"time"

	"github.com/shamaton/msgpackgen/msgpack"
	"github.com/sirupsen/logrus"

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

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

type TestCommandGenerator struct {
	logger   *logrus.Logger
	commands chan *protocol.Command
}

func (g *TestCommandGenerator) GenerateCommands(ctx context.Context) error {
	// write some leading garbage to test signer robustness
	_, _ = io.CopyN(os.Stdout, rand.Reader, 50) //nolint:gomnd

	g.commands <- &protocol.Command{
		Announce: messages.BuildCommandAnnounce(messages.CmdHealth),
		Command:  &messages.HealthCommand{},
	}

	const (
		healthInterval  = 5 * time.Second
		crlInterval     = 15 * time.Minute
		startPause      = 3 * time.Second
		minSignInterval = 5 * time.Second
		maxSignInterval = 10 * time.Second
	)

	g.logger.Info("start generating commands")

	time.Sleep(startPause)

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

	healthTimer := time.NewTimer(healthInterval)
	crlTimer := time.NewTimer(crlInterval)
	signTimer := time.NewTimer(minSignInterval)

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

			g.logger.Info("stopped health check loop")

			_ = crlTimer.Stop()

			g.logger.Info("stopped CRL fetch loop")

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

			healthTimer.Reset(healthInterval)
		case <-crlTimer.C:
			g.commands <- &protocol.Command{
				Announce: messages.BuildCommandAnnounce(messages.CmdFetchCRL),
				Command:  &messages.FetchCRLCommand{IssuerID: "ecc_person_2022"},
			}
		case <-signTimer.C:
			g.commands <- &protocol.Command{
				Announce: messages.BuildCommandAnnounce(messages.CmdSignCertificate),
				Command: &messages.SignCertificateCommand{
					IssuerID:       "ecc_person_2022",
					ProfileName:    "person",
					CSRData:        g.generateCsr("Test Person"),
					CommonName:     "Test Person",
					EmailAddresses: []string{"test@example.org"},
					PreferredHash:  crypto.SHA256,
				},
			}

			newRandomDuration := minSignInterval + time.Duration(mathRand.Int63n(int64(maxSignInterval))) //nolint:gosec

			signTimer.Reset(newRandomDuration)
		}
	}
}

func (g *TestCommandGenerator) generateCsr(cn string) []byte {
	keyPair, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
	if err != nil {
		g.logger.WithError(err).Panic("could not generate key pair")
	}

	template := &x509.CertificateRequest{
		SignatureAlgorithm: x509.ECDSAWithSHA256,
		PublicKey:          keyPair.Public(),
		Subject:            pkix.Name{CommonName: cn},
	}

	csrBytes, err := x509.CreateCertificateRequest(rand.Reader, template, keyPair)
	if err != nil {
		g.logger.WithError(err).Panic("could not create signing request")
	}

	return csrBytes
}

type clientSimulator struct {
	clientHandler    protocol.ClientHandler
	framesIn         chan []byte
	framesOut        chan []byte
	framer           protocol.Framer
	commandGenerator *TestCommandGenerator
	logger           *logrus.Logger
}

const (
	responseAnnounceTimeout = 30 * time.Second
	responseDataTimeout     = 2 * time.Second
)

func (c *clientSimulator) Run(ctx context.Context) error {
	framerErrors := make(chan error)
	protocolErrors := make(chan error)
	generatorErrors := make(chan error)

	go func() {
		err := c.framer.ReadFrames(ctx, os.Stdin, c.framesIn)

		framerErrors <- err
	}()

	go func() {
		err := c.framer.WriteFrames(ctx, os.Stdout, c.framesOut)

		framerErrors <- err
	}()

	go func() {
		clientProtocol := protocol.NewClient(c.clientHandler, c.commandGenerator.commands, c.framesIn, c.framesOut, c.logger)

		err := clientProtocol.Handle(ctx)

		protocolErrors <- err
	}()

	go func() {
		err := c.commandGenerator.GenerateCommands(ctx)

		generatorErrors <- 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 := <-generatorErrors:
			if err != nil {
				return fmt.Errorf("error from command generator: %w", err)
			}

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

			return nil
		}
	}
}

type ClientHandler struct {
	logger   *logrus.Logger
	commands chan *protocol.Command
	caList   []string
}

func (c *ClientHandler) Send(ctx context.Context, command *protocol.Command, out chan<- []byte) error {
	var (
		frame []byte
		err   error
	)

	frame, err = msgpack.Marshal(command.Announce)
	if err != nil {
		return fmt.Errorf("could not marshal command annoucement: %w", err)
	}

	c.logger.WithField("announcement", command.Announce).Info("write command announcement")

	c.logger.Trace("writing command announcement")

	select {
	case <-ctx.Done():
		return nil
	case out <- frame:
		break
	}

	frame, err = msgpack.Marshal(command.Command)
	if err != nil {
		return fmt.Errorf("could not marshal command data: %w", err)
	}

	c.logger.WithField("command", command.Command).Info("write command data")

	select {
	case <-ctx.Done():
		return nil
	case out <- frame:
		break
	}

	return nil
}

func (c *ClientHandler) ResponseAnnounce(ctx context.Context, in <-chan []byte) (*protocol.Response, error) {
	response := &protocol.Response{}

	var announce messages.ResponseAnnounce

	select {
	case <-ctx.Done():
		return nil, nil
	case frame := <-in:
		if err := msgpack.Unmarshal(frame, &announce); err != nil {
			return nil, fmt.Errorf("could not unmarshal response announcement: %w", err)
		}

		response.Announce = &announce

		c.logger.WithField("announcement", response.Announce).Debug("received response announcement")

		return response, nil
	case <-time.After(responseAnnounceTimeout):
		return nil, protocol.ErrResponseAnnounceTimeoutExpired
	}
}

func (c *ClientHandler) ResponseData(ctx context.Context, in <-chan []byte, response *protocol.Response) error {
	select {
	case <-ctx.Done():
		return nil
	case frame := <-in:
		switch response.Announce.Code {
		case messages.RespHealth:
			var resp messages.HealthResponse
			if err := msgpack.Unmarshal(frame, &resp); err != nil {
				return fmt.Errorf("could not unmarshal health response data: %w", err)
			}

			c.updateCAs(ctx, c.commands, resp.Info)

			response.Response = &resp
		case messages.RespCAInfo:
			var resp messages.CAInfoResponse
			if err := msgpack.Unmarshal(frame, &resp); err != nil {
				return fmt.Errorf("could not unmarshal CA info response data: %w", err)
			}

			certificate, err := x509.ParseCertificate(resp.Certificate)
			if err != nil {
				return fmt.Errorf("could not parse certificate data: %w", err)
			}

			c.logger.Infof(
				"certificate for %s: subject=%s, issuer=%s, serial=0x%x, valid from %s to %s",
				resp.Name,
				certificate.Subject,
				certificate.Issuer,
				certificate.SerialNumber,
				certificate.NotBefore,
				certificate.NotAfter)

			response.Response = &resp
		case messages.RespFetchCRL:
			var resp messages.FetchCRLResponse
			if err := msgpack.Unmarshal(frame, &resp); err != nil {
				return fmt.Errorf("could not unmarshal fetch CRL response data: %w", err)
			}

			response.Response = &resp
		case messages.RespSignCertificate:
			var resp messages.SignCertificateResponse
			if err := msgpack.Unmarshal(frame, &resp); err != nil {
				return fmt.Errorf("could not unmarshal sign certificate response data: %w", err)
			}

			response.Response = &resp
		default:
			return fmt.Errorf("unhandled response code %s", response.Announce.Code)
		}
	case <-time.After(responseDataTimeout):
		return protocol.ErrResponseDataTimeoutExpired
	}

	return nil
}

func (c *ClientHandler) HandleResponse(_ context.Context, response *protocol.Response) error {
	c.logger.WithField("response", response.Announce).Info("handled response")
	c.logger.WithField("response", response).Debug("full response")

	return nil
}

func (c *ClientHandler) updateCAs(ctx context.Context, out chan *protocol.Command, info []*messages.HealthInfo) {
	caList := make([]string, 0)

	for _, i := range info {
		if i.Source == "HSM" {
			c.logger.Debugf("info from HSM: %s", i)

			for caName := range i.MoreInfo {
				caList = append(caList, caName)
			}
		}
	}

	sort.Strings(caList)

	if len(caList) != len(c.caList) {
		c.caList = caList

		for _, ca := range c.caList {
			select {
			case <-ctx.Done():
				return
			case out <- &protocol.Command{
				Announce: messages.BuildCommandAnnounce(messages.CmdCAInfo),
				Command:  &messages.CAInfoCommand{Name: ca},
			}:
				continue
			}
		}
	}
}

func newClientHandler(logger *logrus.Logger, commands chan *protocol.Command) *ClientHandler {
	return &ClientHandler{logger: logger, commands: commands}
}

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

	messages.RegisterGeneratedResolver()

	cobsFramer, err := protocol.NewCOBSFramer(logger)
	if err != nil {
		logger.WithError(err).Fatal("could not create COBS framer")
	}

	commandBufferSize := 50

	commandCh := make(chan *protocol.Command, commandBufferSize)

	sim := &clientSimulator{
		commandGenerator: &TestCommandGenerator{
			logger:   logger,
			commands: commandCh,
		},
		logger:        logger,
		framesIn:      make(chan []byte),
		framesOut:     make(chan []byte),
		framer:        cobsFramer,
		clientHandler: newClientHandler(logger, commandCh),
	}

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