package hsm

import (
	"crypto"
	"crypto/ecdsa"
	"crypto/rand"
	"crypto/rsa"
	"crypto/x509"
	"encoding/asn1"
	"encoding/pem"
	"errors"
	"fmt"
	"log"
	"math/big"
	"os"
	"syscall"
	"time"

	"git.cacert.org/cacert-gosigner/pkg/config"
	"github.com/ThalesIgnite/crypto11"
)

func GetRootCACertificate(p11Context *crypto11.Context, settings *config.Settings, caCert *config.CaCertificateEntry) (*x509.Certificate, crypto.Signer, error) {
	keyPair, err := getKeyPair(p11Context, caCert.Label, caCert.KeyInfo)
	if err != nil {
		return nil, nil, err
	}

	certFile := caCert.CertificateFileName()

	certificate, err := loadCertificate(certFile)
	if err != nil {
		return nil, nil, err
	}

	if certificate != nil && certificateMatches(certificate, keyPair) {
		return certificate, keyPair, nil
	}

	notBefore := time.Now()
	notAfter := notBefore.AddDate(settings.RootYears, 0, 0)

	subject := settings.Organization
	subject.CommonName = caCert.CommonName

	certificate, err = generateRootCACertificate(
		certFile,
		keyPair,
		&x509.Certificate{
			Subject:               subject,
			NotBefore:             notBefore,
			NotAfter:              notAfter,
			MaxPathLen:            0,
			MaxPathLenZero:        false,
			BasicConstraintsValid: true,
			KeyUsage:              x509.KeyUsageCRLSign | x509.KeyUsageCertSign,
			IsCA:                  true,
		},
	)

	if err != nil {
		return nil, nil, err
	}

	err = addCertificate(p11Context, caCert.Label, certificate)
	if err != nil {
		return nil, nil, err
	}

	return certificate, keyPair, nil
}

func GetIntermediaryCACertificate(
	p11Context *crypto11.Context,
	settings *config.Settings,
	caCert *config.CaCertificateEntry,
) (*x509.Certificate, crypto.Signer, error) {
	keyPair, err := getKeyPair(p11Context, caCert.Label, caCert.KeyInfo)
	if err != nil {
		return nil, nil, err
	}

	certFile := caCert.CertificateFileName()

	certificate, err := loadCertificate(certFile)
	if err != nil {
		return nil, nil, err
	}

	if certificate != nil && certificateMatches(certificate, keyPair) {
		return certificate, keyPair, nil
	}

	notBefore, notAfter := settings.CalculateValidity(caCert)
	subject := settings.CalculateSubject(caCert)

	certificate, err = generateIntermediaryCACertificate(
		caCert,
		keyPair.Public(),
		&x509.Certificate{
			Subject:               subject,
			NotBefore:             notBefore,
			NotAfter:              notAfter,
			MaxPathLen:            caCert.MaxPathLen,
			MaxPathLenZero:        true,
			BasicConstraintsValid: true,
			IsCA:                  true,
			KeyUsage:              x509.KeyUsageDigitalSignature | x509.KeyUsageCertSign | x509.KeyUsageCRLSign,
			ExtKeyUsage:           caCert.ExtKeyUsage,
			IssuingCertificateURL: []string{settings.BuildIssuerURL(caCert.Parent)},
			OCSPServer:            []string{settings.BuildOCSPURL(caCert.Parent)},
			CRLDistributionPoints: []string{settings.BuildCRLUrl(caCert.Parent)},
			PolicyIdentifiers: []asn1.ObjectIdentifier{
				// use policy identifiers from http://wiki.cacert.org/OidAllocation
				{1, 3, 6, 1, 4, 1, 18506, 2, 3, 1}, // 1.3.6.1.4.1.18506.2.3.1 Class3 Policy Version 1
			},
		},
	)

	if err != nil {
		return nil, nil, err
	}

	err = addCertificate(p11Context, caCert.Label, certificate)
	if err != nil {
		return nil, nil, err
	}

	return certificate, keyPair, nil
}

func generateIntermediaryCACertificate(caCert *config.CaCertificateEntry, publicKey crypto.PublicKey, template *x509.Certificate) (*x509.Certificate, error) {
	serial, err := randomSerialNumber()
	if err != nil {
		return nil, err
	}

	template.SerialNumber = serial
	template.SignatureAlgorithm, err = determineSignatureAlgorithm(caCert.Parent.KeyPair)

	if err != nil {
		return nil, err
	}

	certBytes, err := x509.CreateCertificate(
		rand.Reader,
		template,
		caCert.Parent.Certificate,
		publicKey,
		caCert.Parent.KeyPair,
	)
	if err != nil {
		return nil, fmt.Errorf("could not create intermediary CA certificate: %w", err)
	}

	certBlock := &pem.Block{
		Type:  "CERTIFICATE",
		Bytes: certBytes,
	}

	certFile := caCert.CertificateFileName()

	err = os.WriteFile(certFile, pem.EncodeToMemory(certBlock), 0o600)
	if err != nil {
		return nil, fmt.Errorf("could not write certificate to %s: %w", certFile, err)
	}

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

	return certificate, nil
}

func addCertificate(p11Context *crypto11.Context, label string, certificate *x509.Certificate) error {
	objectId, err := randomObjectId()
	if err != nil {
		return err
	}

	err = p11Context.ImportCertificateWithLabel(objectId, []byte(label), certificate)
	if err != nil {
		return fmt.Errorf("could not import certificate into token: %w", err)
	}

	return nil
}

func getKeyPair(p11Context *crypto11.Context, label string, keyInfo *config.PrivateKeyInfo) (crypto.Signer, error) {
	keyPair, err := p11Context.FindKeyPair(nil, []byte(label))
	if err != nil {
		return nil, fmt.Errorf("could not find requested key pair: %w", err)
	}

	if keyPair != nil {
		return keyPair, nil
	}

	switch keyInfo.Algorithm {
	case x509.RSA:
		keyPair, err = generateRSAKeyPair(p11Context, label, keyInfo)
		if err != nil {
			return nil, fmt.Errorf("could not generate RSA key pair: %w", err)
		}
	case x509.ECDSA:
		keyPair, err = generateECDSAKeyPair(p11Context, label, keyInfo)
		if err != nil {
			return nil, fmt.Errorf("could not generate ECDSA key pair: %w", err)
		}
	default:
		return nil, fmt.Errorf("could not generate private key with label %s with unsupported key algorithm %s", label, keyInfo.Algorithm)
	}

	return keyPair, nil
}

func generateECDSAKeyPair(p11Context *crypto11.Context, label string, keyInfo *config.PrivateKeyInfo) (crypto11.Signer, error) {
	newObjectId, err := randomObjectId()
	if err != nil {
		return nil, err
	}

	return p11Context.GenerateECDSAKeyPairWithLabel(newObjectId, []byte(label), keyInfo.EccCurve)
}

func generateRSAKeyPair(p11Context *crypto11.Context, label string, keyInfo *config.PrivateKeyInfo) (crypto11.Signer, error) {
	newObjectId, err := randomObjectId()
	if err != nil {
		return nil, err
	}

	return p11Context.GenerateRSAKeyPairWithLabel(newObjectId, []byte(label), keyInfo.RSABits)
}

func randomObjectId() ([]byte, error) {
	result := make([]byte, 20)
	_, err := rand.Read(result)
	if err != nil {
		return nil, fmt.Errorf("could not create new random object id: %w", err)
	}
	return result, nil
}

func generateRootCACertificate(certFile string, keyPair crypto.Signer, template *x509.Certificate) (*x509.Certificate, error) {
	serial, err := randomSerialNumber()
	if err != nil {
		return nil, err
	}

	template.SerialNumber = serial
	template.SignatureAlgorithm, err = determineSignatureAlgorithm(keyPair)

	if err != nil {
		return nil, err
	}

	certBytes, err := x509.CreateCertificate(
		rand.Reader,
		template,
		template,
		keyPair.Public(),
		keyPair,
	)
	if err != nil {
		return nil, fmt.Errorf("could not create root certificate: %w", err)
	}

	certBlock := &pem.Block{
		Type:  "CERTIFICATE",
		Bytes: certBytes,
	}

	err = os.WriteFile(certFile, pem.EncodeToMemory(certBlock), 0o600)
	if err != nil {
		return nil, fmt.Errorf("could not write certificate to %s: %w", certFile, err)
	}

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

	return certificate, nil
}

func determineSignatureAlgorithm(keyPair crypto.Signer) (x509.SignatureAlgorithm, error) {
	switch keyPair.Public().(type) {
	case *ecdsa.PublicKey:
		return x509.ECDSAWithSHA256, nil
	case *rsa.PublicKey:
		return x509.SHA256WithRSA, nil
	default:
		return x509.UnknownSignatureAlgorithm,
			fmt.Errorf("could not determine signature algorithm for key of type %T", keyPair)
	}
}

func certificateMatches(certificate *x509.Certificate, key crypto.Signer) bool {
	switch v := certificate.PublicKey.(type) {
	case *ecdsa.PublicKey:
		if pub, ok := key.Public().(*ecdsa.PublicKey); ok {
			if v.Equal(pub) {
				return true
			}
		}
	case *rsa.PublicKey:
		if pub, ok := key.Public().(*rsa.PublicKey); ok {
			if v.Equal(pub) {
				return true
			}
		}
	default:
		log.Printf("unsupported public key %v", v)
	}

	log.Printf(
		"public key from certificate does not match private key: %s != %s",
		certificate.PublicKey,
		key.Public(),
	)
	return false
}

func loadCertificate(certFile string) (*x509.Certificate, error) {
	certFileInfo, err := os.Stat(certFile)
	if err != nil {
		if errors.Is(err, syscall.ENOENT) {
			return nil, nil
		}
		return nil, fmt.Errorf("could not get info for %s: %w", certFile, err)
	}

	if !certFileInfo.Mode().IsRegular() {
		return nil, fmt.Errorf("certificate file %s is not a regular file", certFile)
	}

	certData, err := os.ReadFile(certFile)
	if err != nil {
		return nil, fmt.Errorf("could not read %s: %w", certFile, err)
	}

	pemData, _ := pem.Decode(certData)
	if pemData == nil {
		return nil, fmt.Errorf("no PEM data in %s", certFile)
	}

	if pemData.Type != "CERTIFICATE" {
		return nil, fmt.Errorf("no certificate found in %s", certFile)
	}

	certificate, err := x509.ParseCertificate(pemData.Bytes)
	if err != nil {
		return nil, fmt.Errorf("could not parse certificate from %s: %w", certFile, err)
	}

	return certificate, nil
}

func randomSerialNumber() (*big.Int, error) {
	serialNumberLimit := new(big.Int).Lsh(big.NewInt(1), 128)
	serialNumber, err := rand.Int(rand.Reader, serialNumberLimit)
	if err != nil {
		return nil, fmt.Errorf("could not generate serial number: %w", err)
	}
	return serialNumber, nil
}