package signer

import (
	"bufio"
	"crypto"
	"crypto/rsa"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/pem"
	"fmt"
	"io/ioutil"
	"math/big"
	"os"
	"path"
	"strconv"
	"strings"
	"time"

	log "github.com/sirupsen/logrus"

	"git.cacert.org/cacert-gosigner/shared"
)

type RootCredentials struct {
	Name            string
	PrivateKeyFile  string
	PublicKeyFile   string
	CertificateFile string
	DatabaseFile    string
	CRLNumber       string
}

type CryptoSystem struct {
	Name             string
	Roots            map[shared.CryptoSystemRootId]*RootCredentials
	Profiles         map[shared.CertificateProfileId]string
	DigestAlgorithms map[shared.MessageDigestAlgorithmId]x509.SignatureAlgorithm
}

func (system CryptoSystem) String() string {
	return system.Name
}

func (system CryptoSystem) loadCertificate(rootId shared.CryptoSystemRootId) (*x509.Certificate, error) {
	certificateFile := system.Roots[rootId].CertificateFile
	pemBytes, err := ioutil.ReadFile(certificateFile)
	if err != nil {
		return nil, fmt.Errorf(
			"could not load certificate %s: %v",
			certificateFile,
			err,
		)
	}
	pemBlock, _ := pem.Decode(pemBytes)
	if pemBlock.Type != "CERTIFICATE" {
		log.Warnf(
			"PEM in %s is probably not a certificate. PEM block has type %s",
			certificateFile,
			pemBlock.Type,
		)
	}
	certificate, err := x509.ParseCertificate(pemBlock.Bytes)
	if err != nil {
		return nil, fmt.Errorf(
			"could no parse certificate from %s: %v",
			certificateFile,
			err,
		)
	}
	return certificate, nil
}

func (system CryptoSystem) getPrivateKey(rootId shared.CryptoSystemRootId) (crypto.Signer, error) {
	privateKeyFile := system.Roots[rootId].PrivateKeyFile
	pemBytes, err := ioutil.ReadFile(privateKeyFile)
	if err != nil {
		return nil, fmt.Errorf(
			"could not load private key %s: %v",
			privateKeyFile,
			err,
		)
	}
	pemBlock, _ := pem.Decode(pemBytes)
	if pemBlock.Type != "PRIVATE KEY" {
		log.Warnf(
			"PEM in %s is probably not a private key. PEM block has type %s",
			privateKeyFile,
			pemBlock.Type,
		)
	}
	privateKey, err := x509.ParsePKCS8PrivateKey(pemBlock.Bytes)
	if err != nil {
		return nil, fmt.Errorf(
			"could no parse private key from %s: %v",
			privateKeyFile,
			err,
		)
	}
	return privateKey.(*rsa.PrivateKey), nil
}

func (system *CryptoSystem) getNextCRLNumber(rootId shared.CryptoSystemRootId) (*big.Int, error) {
	crlNumberFile := system.Roots[rootId].CRLNumber
	_, err := os.Stat(crlNumberFile)
	if err != nil {
		log.Warnf("CRL number file %s does not exist: %v", crlNumberFile, err)
		return big.NewInt(1), nil
	}
	data, err := ioutil.ReadFile(crlNumberFile)
	if err != nil {
		return nil, fmt.Errorf("could not read CRL number file %s", crlNumberFile)
	}
	result, err := stringAsBigInt(data)
	if err != nil {
		return nil, fmt.Errorf("could not parse content of %s as CRL number: %v", crlNumberFile, err)
	}
	return result, nil
}

func (system *CryptoSystem) bumpCRLNumber(rootId shared.CryptoSystemRootId, current *big.Int) error {
	serial := current.Int64() + 1
	crlNumberFile := system.Roots[rootId].CRLNumber
	outFile, err := ioutil.TempFile(path.Dir(crlNumberFile), "*.txt")
	defer func() { _ = outFile.Close() }()

	_, err = outFile.WriteString(fmt.Sprintf(
		"%s\n",
		strings.ToUpper(strconv.FormatInt(serial, 16)),
	))
	if err != nil {
		return fmt.Errorf("could not write new CRL number %d to %s: %v", serial, outFile.Name(), err)
	}

	if err = outFile.Close(); err != nil {
		return fmt.Errorf("could not close temporary file %s: %v", outFile.Name(), err)
	}
	if err = os.Rename(crlNumberFile, fmt.Sprintf("%s.old", crlNumberFile)); err != nil {
		return fmt.Errorf("could not rename %s to %s.old: %v", crlNumberFile, crlNumberFile, err)
	}
	if err = os.Rename(outFile.Name(), crlNumberFile); err != nil {
		return fmt.Errorf("could not rename %s to %s: %v", outFile.Name(), crlNumberFile, err)
	}
	return nil
}

func stringAsBigInt(data []byte) (*big.Int, error) {
	dataString := strings.TrimSpace(string(data))
	parseInt, err := strconv.ParseInt(dataString, 16, 64)
	if err != nil {
		return nil, fmt.Errorf("could not parse %s as big int: %v", dataString, err)
	}
	return big.NewInt(parseInt), nil
}

func (system *CryptoSystem) loadRevokedCertificatesFromDatabase(rootId shared.CryptoSystemRootId) ([]pkix.RevokedCertificate, error) {
	databaseFile := system.Roots[rootId].DatabaseFile
	_, err := os.Stat(databaseFile)
	if err != nil {
		log.Warnf("openssl certificate database file %s does not exist: %v", databaseFile, err)
		return []pkix.RevokedCertificate{}, nil
	}
	file, err := os.Open(databaseFile)
	if err != nil {
		return nil, fmt.Errorf("could not open openssl certificate database file %s: %v", databaseFile, err)
	}
	defer func() { _ = file.Close() }()

	result := make([]pkix.RevokedCertificate, 0)
	scanner := bufio.NewScanner(file)
	for scanner.Scan() {
		line := strings.Split(scanner.Text(), "\t")
		if line[0] == "R" {
			serialNumber, err := stringAsBigInt([]byte(line[3]))
			if err != nil {
				return nil, fmt.Errorf("could not parse serial number %s as big int: %v", line[3], err)
			}
			revokeTs, err := strconv.ParseInt(line[2][:len(line[2])-1], 10, 64)
			result = append(result, pkix.RevokedCertificate{
				SerialNumber:   serialNumber,
				RevocationTime: time.Unix(revokeTs, 0),
				Extensions:     nil,
			})
		}
	}
	return result, nil
}

func (system *CryptoSystem) recordRevocation(rootId shared.CryptoSystemRootId, certificate *x509.Certificate) (*pkix.RevokedCertificate, error) {
	databaseFile := system.Roots[rootId].DatabaseFile
	_, err := os.Stat(databaseFile)
	if err != nil {
		return nil, fmt.Errorf("openssl certificate database file %s does not exist: %v", databaseFile, err)
	}
	inFile, err := os.Open(databaseFile)
	if err != nil {
		return nil, fmt.Errorf("could not open openssl certificate database file %s: %v", databaseFile, err)
	}
	defer func() { _ = inFile.Close() }()

	outFile, err := ioutil.TempFile(path.Dir(databaseFile), "*.txt")
	defer func() { _ = outFile.Close() }()

	scanner := bufio.NewScanner(inFile)
	writer := bufio.NewWriter(outFile)

	found := false
	revocationTime := time.Now()

	for scanner.Scan() {
		line := scanner.Text()
		parts := strings.Split(line, "\t")
		serialNumber, err := stringAsBigInt([]byte(parts[3]))
		if err != nil {
			return nil, fmt.Errorf("could not parse serial number %s as big int: %v", parts[3], err)
		}
		if serialNumber == certificate.SerialNumber {
			line = strings.Join(
				[]string{"R", parts[1], strconv.FormatInt(revocationTime.Unix(), 10) + "Z", parts[3], parts[4]},
				"\t",
			)
			found = true
		}
		if _, err = writer.WriteString(fmt.Sprintf("%s\n", line)); err != nil {
			return nil, fmt.Errorf("could not write '%s' to %s: %v", line, outFile.Name(), err)
		}
	}

	if err = outFile.Close(); err != nil {
		return nil, fmt.Errorf("could not close temporary file %s: %v", outFile.Name(), err)
	}
	if err = inFile.Close(); err != nil {
		return nil, fmt.Errorf("could not close %s: %v", databaseFile, err)
	}

	if err = os.Rename(databaseFile, fmt.Sprintf("%s.old", databaseFile)); err != nil {
		return nil, fmt.Errorf("could not rename %s to %s.old: %v", databaseFile, databaseFile, err)
	}

	if err = os.Rename(outFile.Name(), databaseFile); err != nil {
		return nil, fmt.Errorf("could not rename temporary file %s to %s: %v", outFile.Name(), databaseFile, err)
	}

	if !found {
		log.Warnf("entry not found in database")
	}

	return &pkix.RevokedCertificate{
		SerialNumber:   certificate.SerialNumber,
		RevocationTime: revocationTime,
	}, nil
}