/*
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 crlcertdb

import (
	"context"
	"crypto/x509"
	"fmt"
	"io/ioutil"
	"math/big"
	"path/filepath"

	"git.cacert.org/cacert-goocsp/pkg/filewatcher"
	"git.cacert.org/cacert-goocsp/pkg/ocsp"
	"git.cacert.org/cacert-goocsp/pkg/ocspsource"
	"github.com/fsnotify/fsnotify"
	"github.com/sirupsen/logrus"
)

type CRLCertDB struct {
	crlPath string
	content map[string]*ocsp.Response
}

func NewCertDB(ctx context.Context, crlPath string) (*CRLCertDB, error) {
	absFile, err := filepath.Abs(crlPath)
	if err != nil {
		return nil, fmt.Errorf("cold not determine absolute file name of %s: %w", crlPath, err)
	}

	certDb := &CRLCertDB{crlPath: absFile, content: make(map[string]*ocsp.Response)}

	err = certDb.update()
	if err != nil {
		return nil, err
	}

	go func(ctx context.Context) {
		watcherCtx, cancel := context.WithCancel(ctx)
		filewatcher.Watch(watcherCtx, certDb.crlPath, certDb.watchCRLFile)

		<-ctx.Done()
		cancel()
	}(ctx)

	return certDb, nil
}

func (d *CRLCertDB) update() error {
	crlBytes, err := ioutil.ReadFile(d.crlPath)
	if err != nil {
		return fmt.Errorf("could not read CRL from %s: %w", d.crlPath, err)
	}

	crl, err := x509.ParseCRL(crlBytes)
	if err != nil {
		return fmt.Errorf("could not parse CRL from %s: %w", d.crlPath, err)
	}

	var update *ocspsource.CertificateUpdate

	for _, entry := range crl.TBSCertList.RevokedCertificates {
		update = &ocspsource.CertificateUpdate{
			Serial:           entry.SerialNumber,
			Status:           ocsp.Revoked,
			RevokedAt:        entry.RevocationTime,
			RevocationReason: ocsp.Unspecified,
		}

		d.UpdateCertificate(update)
	}

	logrus.Infof(
		"parsed CRL '%s', found information for %d certificates",
		d.crlPath,
		len(crl.TBSCertList.RevokedCertificates),
	)

	return nil
}

func (d *CRLCertDB) UpdateCertificate(update *ocspsource.CertificateUpdate) {
	d.content[update.Serial.Text(16)] = &ocsp.Response{
		Status:           update.Status,
		SerialNumber:     update.Serial,
		RevokedAt:        update.RevokedAt,
		RevocationReason: update.RevocationReason,
	}
}

func (d *CRLCertDB) LookupResponseTemplate(number *big.Int) *ocsp.Response {
	serial := number.Text(16)
	if response, ok := d.content[serial]; ok {
		return response
	}

	logrus.Debugf("received request for certificate %s that is not in our data source", serial)

	// RFC https://datatracker.ietf.org/doc/html/rfc6960#section-2.2 states that certificates we cannot answer for
	// should be marked as good.
	response := &ocsp.Response{
		Status:       ocsp.Good,
		SerialNumber: number,
	}

	return response
}

func (d *CRLCertDB) watchCRLFile(watcher *fsnotify.Watcher) {
	for {
		select {
		case event, ok := <-watcher.Events:
			if !ok {
				return
			}

			if event.Op&fsnotify.Write == fsnotify.Write {
				if event.Name == d.crlPath {
					logrus.Infof("modified: %s", event.Name)

					err := d.update()
					if err != nil {
						logrus.Error(err)
					}
				}
			}
		case err, ok := <-watcher.Errors:
			if !ok {
				return
			}

			logrus.Errorf("error from watcher: %w", err)
		}
	}
}