/*
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 client

import (
	"context"
	"crypto/x509"
	"fmt"
	"math/big"
	"os"
	"path"
	"sync"
	"time"

	"github.com/balacode/go-delta"
	"github.com/sirupsen/logrus"
	"github.com/tarm/serial"

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

const CallBackBufferSize = 50

const (
	worldReadableDirPerm  = 0o755
	worldReadableFilePerm = 0o644
)

type Profile struct {
	Name   string
	UseFor string
}

type CertInfo struct {
	Name     string
	FetchCRL bool
}

type SignerInfo struct {
	SignerHealth   bool
	SignerVersion  string
	CACertificates []CertInfo
	UsableProfiles map[string][]Profile
}

type Client struct {
	port       *serial.Port
	logger     *logrus.Logger
	framer     protocol.Framer
	in         chan []byte
	out        chan []byte
	commands   chan *protocol.Command
	handler    protocol.ClientHandler
	config     *config.ClientConfig
	signerInfo *SignerInfo
	callback   chan interface{}
	sync.Mutex
	lastKnownCRLS map[string]*big.Int
}

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

	go func(f protocol.Framer) {
		framerErrors <- f.ReadFrames(ctx, c.port, c.in)
	}(c.framer)

	go func(f protocol.Framer) {
		framerErrors <- f.WriteFrames(ctx, c.port, c.out)
	}(c.framer)

	go func() {
		clientProtocol := protocol.NewClient(c.handler, c.commands, c.in, c.out, c.logger)

		protocolErrors <- clientProtocol.Handle(ctx)
	}()

	ctx, cancelCommandLoop := context.WithCancel(ctx)

	go c.commandLoop(ctx)

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

			return nil
		case err := <-framerErrors:
			cancelCommandLoop()

			if err != nil {
				return fmt.Errorf("error from framer: %w", err)
			}

			return nil
		case err := <-protocolErrors:
			cancelCommandLoop()

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

			return nil
		}
	}
}

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

	c.port = s

	err = c.port.Flush()
	if err != nil {
		c.logger.WithError(err).Warn("could not flush buffers of port: %w", err)
	}

	return nil
}

func (c *Client) Close() error {
	close(c.in)
	close(c.out)

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

	return nil
}

func (c *Client) commandLoop(ctx context.Context) {
	healthTimer := time.NewTimer(c.config.HealthStart)
	fetchCRLTimer := time.NewTimer(c.config.FetchCRLStart)

	for {
		select {
		case <-ctx.Done():
			return
		case callbackData := <-c.callback:
			err := c.handleCallback(callbackData)
			if err != nil {
				c.logger.WithError(err).Error("callback handling failed")
			}
		case <-fetchCRLTimer.C:
			for _, crlInfo := range c.buildCRLInfo() {
				var lastKnown []byte

				if crlInfo.LastKnown != nil {
					lastKnown = crlInfo.LastKnown.Bytes()
				}

				c.commands <- &protocol.Command{
					Announce: messages.BuildCommandAnnounce(messages.CmdFetchCRL),
					Command: &messages.FetchCRLCommand{
						IssuerID:    crlInfo.Name,
						LastKnownID: lastKnown,
					},
				}
			}

			fetchCRLTimer.Reset(c.config.FetchCRLInterval)
		case <-healthTimer.C:
			c.commands <- &protocol.Command{
				Announce: messages.BuildCommandAnnounce(messages.CmdHealth),
				Command:  &messages.HealthCommand{},
			}

			healthTimer.Reset(c.config.HealthInterval)
		}
	}
}

func (c *Client) handleCallback(data interface{}) error {
	switch d := data.(type) {
	case SignerInfo:
		c.updateSignerInfo(d)
	case *messages.FetchCRLResponse:
		c.updateCRL(d)
	default:
		return fmt.Errorf("unknown callback data of type %T", data)
	}

	return nil
}

func (c *Client) updateSignerInfo(signerInfo SignerInfo) {
	c.Lock()
	defer c.Unlock()

	c.logger.Debug("update signer info")

	c.signerInfo = &signerInfo
}

type CRLInfo struct {
	Name      string
	LastKnown *big.Int
}

func (c *Client) buildCRLInfo() []CRLInfo {
	c.Lock()
	defer c.Unlock()

	if c.signerInfo == nil {
		c.logger.Warn("no signer info available")

		return nil
	}

	infos := make([]CRLInfo, 0)

	for _, caInfo := range c.signerInfo.CACertificates {
		if caInfo.FetchCRL {
			lastKnown := c.lastKnownCRL(caInfo.Name)

			infos = append(infos, CRLInfo{Name: caInfo.Name, LastKnown: lastKnown})
		}
	}

	return infos
}

func (c *Client) lastKnownCRL(caName string) *big.Int {
	crlFileName := c.buildCRLFileName(caName)

	_, err := os.Stat(crlFileName)
	if err != nil {
		c.logger.WithField("crl", crlFileName).Debug("CRL file does not exist")

		delete(c.lastKnownCRLS, caName)

		return nil
	}

	lastKnown, ok := c.lastKnownCRLS[caName]
	if !ok {
		derData, err := os.ReadFile(crlFileName)
		if err != nil {
			c.logger.WithError(err).WithField("crl", crlFileName).Error("could not read CRL data")

			return nil
		}

		crl, err := x509.ParseRevocationList(derData)
		if err != nil {
			c.logger.WithError(err).WithField("crl", crlFileName).Error("could not parse CRL data")

			return nil
		}

		lastKnown = crl.Number

		c.lastKnownCRLS[caName] = lastKnown
	}

	return lastKnown
}

func (c *Client) buildCRLFileName(caName string) string {
	return path.Join(c.config.CRLDirectory, fmt.Sprintf("%s.crl", caName))
}

func (c *Client) updateCRL(d *messages.FetchCRLResponse) {
	var (
		der       []byte
		crlNumber *big.Int
	)

	if d.UnChanged {
		c.logger.WithField("issuer", d.IssuerID).Debug("CRL did not change")

		return
	}

	if !d.IsDelta {
		der = d.CRLData

		list, err := x509.ParseRevocationList(der)
		if err != nil {
			c.logger.WithError(err).Error("CRL from signer could not be parsed")

			return
		}

		crlNumber = list.Number
	} else {
		crlFileName := c.buildCRLFileName(d.IssuerID)

		der, err := c.patchCRL(crlFileName, d.CRLData)
		if err != nil {
			c.logger.WithError(err).Error("CRL patching failed")

			delete(c.lastKnownCRLS, d.IssuerID)

			return
		}

		list, err := x509.ParseRevocationList(der)
		if err != nil {
			c.logger.WithError(err).Error("could not parse patched CRL")

			delete(c.lastKnownCRLS, d.IssuerID)

			return
		}

		crlNumber = list.Number
	}

	if err := c.writeCRL(d.IssuerID, der); err != nil {
		c.logger.WithError(err).Error("could not store CRL")

		delete(c.lastKnownCRLS, d.IssuerID)

		return
	}

	c.lastKnownCRLS[d.IssuerID] = crlNumber
}

func (c *Client) writeCRL(caName string, crlBytes []byte) error {
	if err := os.MkdirAll(c.config.CRLDirectory, worldReadableDirPerm); err != nil {
		return fmt.Errorf("could not create CRL directory %s: %w", c.config.CRLDirectory, err)
	}

	if err := os.WriteFile(c.buildCRLFileName(caName), crlBytes, worldReadableFilePerm); err != nil {
		c.logger.WithError(err).Error("could not write CRL file")
	}

	return nil
}

func (c *Client) patchCRL(crlFileName string, diff []byte) ([]byte, error) {
	original, err := os.ReadFile(crlFileName)
	if err != nil {
		return nil, fmt.Errorf("could not read existing CRL %s: %w", crlFileName, err)
	}

	patch, err := delta.Load(diff)
	if err != nil {
		return nil, fmt.Errorf("could not parse CRL delta: %w", err)
	}

	der, err := patch.Apply(original)
	if err != nil {
		return nil, fmt.Errorf("could not apply CRL delta: %w", err)
	}

	return der, nil
}

func New(
	cfg *config.ClientConfig,
	logger *logrus.Logger,
	handler protocol.ClientHandler,
	commands chan *protocol.Command,
	callback chan interface{},
) (*Client, error) {
	cobsFramer, err := protocol.NewCOBSFramer(logger)
	if err != nil {
		return nil, fmt.Errorf("could not create COBS framer: %w", err)
	}

	client := &Client{
		logger:        logger,
		framer:        cobsFramer,
		in:            make(chan []byte),
		out:           make(chan []byte),
		commands:      commands,
		handler:       handler,
		config:        cfg,
		callback:      callback,
		lastKnownCRLS: make(map[string]*big.Int),
	}

	err = client.setupConnection(&serial.Config{
		Name:        cfg.Serial.Device,
		Baud:        cfg.Serial.Baud,
		ReadTimeout: cfg.Serial.Timeout,
	})
	if err != nil {
		return nil, err
	}

	return client, nil
}