package openssl

import (
	"bufio"
	"errors"
	"fmt"
	"math/big"
	"os"
	"path"
	"strings"
	"sync"
	"time"

	"git.cacert.org/cacert-gosigner/x509/revoking"
	"git.cacert.org/cacert-gosigner/x509/signing"
)

// The FileRepository stores information about signed and revoked certificates
// in an openssl index.txt compatible file.
//
// A reference for the file format can be found at
// https://pki-tutorial.readthedocs.io/en/latest/cadb.html.
type FileRepository struct {
	indexFileName string
	lock          sync.Locker
}

type indexStatus string

const (
	CertificateValid   indexStatus = "V"
	CertificateRevoked             = "R"
	CertificateExpired             = "E"
)

const opensslTimeSpec = "060102030405Z"

type indexEntry struct {
	statusFlag           indexStatus
	expiresAt            time.Time
	revokedAt            time.Time
	revocationReason     string
	serialNumber         *big.Int
	fileName             string
	certificateSubjectDN string
}

func (e *indexEntry) markRevoked(revocationTime time.Time, reason string) {
	if e.statusFlag == CertificateValid {
		e.statusFlag = CertificateRevoked
		e.revokedAt = revocationTime
		e.revocationReason = reason
	}
}

type IndexFile struct {
	entries []*indexEntry
}

func (f *IndexFile) findEntry(number *big.Int) (*indexEntry, error) {
	for _, entry := range f.entries {
		if entry.serialNumber == number {
			return entry, nil
		}
	}
	return nil, fmt.Errorf("no entry for serial number %s found", number)
}

// StoreRevocation records information about a revoked certificate.
func (r *FileRepository) StoreRevocation(revoked *revoking.CertificateRevoked) error {
	r.lock.Lock()
	defer r.lock.Unlock()

	index, err := r.loadIndex()
	if err != nil {
		return err
	}

	entry, err := index.findEntry(revoked.SerialNumber())
	if err != nil {
		return err
	}

	entry.markRevoked(revoked.RevocationTime(), revoked.Reason())
	err = r.writeIndex(index)
	return err
}

// StoreCertificate records information about a signed certificate.
func (r *FileRepository) StoreCertificate(signed *signing.CertificateSigned) error {
	r.lock.Lock()
	defer r.lock.Unlock()

	return nil
}

func (r *FileRepository) loadIndex() (*IndexFile, error) {
	f, err := os.Open(r.indexFileName)
	if err != nil {
		return nil, err
	}
	defer func() { _ = f.Close() }()

	entries := make([]*indexEntry, 0)

	indexScanner := bufio.NewScanner(f)
	for indexScanner.Scan() {
		indexEntry, err := r.newIndexEntry(indexScanner.Text())
		if err != nil {
			return nil, err
		}
		entries = append(entries, indexEntry)
	}
	if err := indexScanner.Err(); err != nil {
		return nil, err
	}

	return &IndexFile{entries: entries}, nil
}

func (r *FileRepository) writeIndex(index *IndexFile) error {
	return errors.New("not implemented")
}

func (r *FileRepository) newIndexEntry(text string) (*indexEntry, error) {
	fields := strings.Split(text, "\t")

	const expectedFieldNumber = 6
	if len(fields) != expectedFieldNumber {
		return nil, fmt.Errorf(
			"unexpected number of fields %d instead of %d",
			len(fields),
			expectedFieldNumber,
		)
	}

	expirationParsed, err := time.Parse(opensslTimeSpec, fields[1])
	if err != nil {
		return nil, err
	}

	var revocationTimeParsed time.Time
	var revocationReason string

	if fields[2] != "" {
		var timeString string
		if strings.Contains(fields[2], ",") {
			parts := strings.SplitN(fields[2], ",", 2)
			timeString = parts[0]
			revocationReason = parts[1]
		} else {
			timeString = fields[2]
		}
		revocationTimeParsed, err = time.Parse(opensslTimeSpec, timeString)
		if err != nil {
			return nil, err
		}
	}

	serialParsed := new(big.Int)
	if _, ok := serialParsed.SetString(fields[3], 16); !ok {
		return nil, fmt.Errorf("could not parse serial number %s", fields[3])
	}

	fileNameParsed := "unknown"
	if fields[4] != "" {
		_, err = os.Stat(path.Join(path.Dir(r.indexFileName), fields[4]))
		if err != nil {
			if !os.IsNotExist(err) {
				return nil, err
			}
		} else {
			fileNameParsed = fields[4]
		}
	}

	subjectDNParsed := fields[5]

	return &indexEntry{
		statusFlag:           indexStatus(fields[0]),
		expiresAt:            expirationParsed,
		revokedAt:            revocationTimeParsed,
		revocationReason:     revocationReason,
		serialNumber:         serialParsed,
		fileName:             fileNameParsed,
		certificateSubjectDN: subjectDNParsed,
	}, nil
}

func NewFileRepository(baseDirectory string) (*FileRepository, error) {
	err := os.Chdir(baseDirectory)
	if err != nil {
		return nil, err
	}
	return &FileRepository{
		indexFileName: path.Join(baseDirectory, "index.txt"),
		lock:          &sync.Mutex{},
	}, nil
}