package tls

import (
	"crypto/tls"
	"crypto/x509"
	"errors"
	"fmt"
	"os"
	"strings"

	"github.com/rs/zerolog/log"
	"github.com/traefik/traefik/v3/pkg/types"
)

var (
	// MinVersion Map of allowed TLS minimum versions.
	MinVersion = map[string]uint16{
		`VersionTLS10`: tls.VersionTLS10,
		`VersionTLS11`: tls.VersionTLS11,
		`VersionTLS12`: tls.VersionTLS12,
		`VersionTLS13`: tls.VersionTLS13,
	}

	// MaxVersion Map of allowed TLS maximum versions.
	MaxVersion = map[string]uint16{
		`VersionTLS10`: tls.VersionTLS10,
		`VersionTLS11`: tls.VersionTLS11,
		`VersionTLS12`: tls.VersionTLS12,
		`VersionTLS13`: tls.VersionTLS13,
	}

	// CurveIDs is a Map of TLS elliptic curves from crypto/tls
	// Available CurveIDs defined at https://godoc.org/crypto/tls#CurveID,
	// also allowing rfc names defined at https://tools.ietf.org/html/rfc8446#section-4.2.7
	CurveIDs = map[string]tls.CurveID{
		`secp256r1`:      tls.CurveP256,
		`CurveP256`:      tls.CurveP256,
		`secp384r1`:      tls.CurveP384,
		`CurveP384`:      tls.CurveP384,
		`secp521r1`:      tls.CurveP521,
		`CurveP521`:      tls.CurveP521,
		`x25519`:         tls.X25519,
		`X25519`:         tls.X25519,
		`x25519mlkem768`: tls.X25519MLKEM768,
		`X25519MLKEM768`: tls.X25519MLKEM768,
	}
)

// Certificates defines traefik certificates type
// Certs and Keys could be either a file path, or the file content itself.
type Certificates []Certificate

// GetCertificates retrieves the certificates as slice of tls.Certificate.
func (c Certificates) GetCertificates() []tls.Certificate {
	var certs []tls.Certificate

	for _, certificate := range c {
		cert, err := certificate.GetCertificate()
		if err != nil {
			log.Debug().Err(err).Msg("Error while getting certificate")
			continue
		}

		certs = append(certs, cert)
	}

	return certs
}

// Certificate holds a SSL cert/key pair
// Certs and Key could be either a file path, or the file content itself.
type Certificate struct {
	CertFile types.FileOrContent `json:"certFile,omitempty" toml:"certFile,omitempty" yaml:"certFile,omitempty"`
	KeyFile  types.FileOrContent `json:"keyFile,omitempty" toml:"keyFile,omitempty" yaml:"keyFile,omitempty" loggable:"false"`
}

// GetCertificate returns a tls.Certificate matching the configured CertFile and KeyFile.
func (c *Certificate) GetCertificate() (tls.Certificate, error) {
	certContent, err := c.CertFile.Read()
	if err != nil {
		return tls.Certificate{}, fmt.Errorf("unable to read CertFile: %w", err)
	}

	keyContent, err := c.KeyFile.Read()
	if err != nil {
		return tls.Certificate{}, fmt.Errorf("unable to read KeyFile: %w", err)
	}

	cert, err := tls.X509KeyPair(certContent, keyContent)
	if err != nil {
		return tls.Certificate{}, fmt.Errorf("unable to parse TLS certificate: %w", err)
	}

	return cert, nil
}

// GetCertificateFromBytes returns a tls.Certificate matching the configured CertFile and KeyFile.
// It assumes that the configured CertFile and KeyFile are of byte type.
func (c *Certificate) GetCertificateFromBytes() (tls.Certificate, error) {
	cert, err := tls.X509KeyPair([]byte(c.CertFile), []byte(c.KeyFile))
	if err != nil {
		return tls.Certificate{}, fmt.Errorf("unable to parse TLS certificate: %w", err)
	}

	return cert, nil
}

// GetTruncatedCertificateName truncates the certificate name.
func (c *Certificate) GetTruncatedCertificateName() string {
	certName := c.CertFile.String()

	// Truncate certificate information only if it's a well formed certificate content with more than 50 characters
	if !c.CertFile.IsPath() && strings.HasPrefix(certName, certificateHeader) && len(certName) > len(certificateHeader)+50 {
		certName = strings.TrimPrefix(c.CertFile.String(), certificateHeader)[:50]
	}

	return certName
}

// FileOrContent hold a file path or content.
type FileOrContent string

func (f FileOrContent) String() string {
	return string(f)
}

// IsPath returns true if the FileOrContent is a file path, otherwise returns false.
func (f FileOrContent) IsPath() bool {
	_, err := os.Stat(f.String())
	return err == nil
}

func (f FileOrContent) Read() ([]byte, error) {
	var content []byte
	if f.IsPath() {
		var err error
		content, err = os.ReadFile(f.String())
		if err != nil {
			return nil, err
		}
	} else {
		content = []byte(f)
	}
	return content, nil
}

// VerifyPeerCertificate verifies the chain certificates and their URI.
func VerifyPeerCertificate(uri string, cfg *tls.Config, rawCerts [][]byte) error {
	// TODO: Refactor to avoid useless verifyChain (ex: when insecureskipverify is false)
	cert, err := verifyChain(cfg.RootCAs, rawCerts)
	if err != nil {
		return err
	}

	if len(uri) > 0 {
		return verifyServerCertMatchesURI(uri, cert)
	}

	return nil
}

// verifyServerCertMatchesURI verifies that the given certificate contains the specified URI in its SANs.
func verifyServerCertMatchesURI(uri string, cert *x509.Certificate) error {
	if cert == nil {
		return errors.New("peer certificate mismatch: no peer certificate presented")
	}

	for _, certURI := range cert.URIs {
		if strings.EqualFold(certURI.String(), uri) {
			return nil
		}
	}

	return fmt.Errorf("peer certificate mismatch: no SAN URI in peer certificate matches %s", uri)
}

// verifyChain performs standard TLS verification without enforcing remote hostname matching.
func verifyChain(rootCAs *x509.CertPool, rawCerts [][]byte) (*x509.Certificate, error) {
	// Fetch leaf and intermediates. This is based on code form tls handshake.
	if len(rawCerts) < 1 {
		return nil, errors.New("tls: no certificates from peer")
	}

	certs := make([]*x509.Certificate, len(rawCerts))
	for i, asn1Data := range rawCerts {
		cert, err := x509.ParseCertificate(asn1Data)
		if err != nil {
			return nil, fmt.Errorf("tls: failed to parse certificate from peer: %w", err)
		}

		certs[i] = cert
	}

	opts := x509.VerifyOptions{
		Roots:         rootCAs,
		Intermediates: x509.NewCertPool(),
	}

	// All but the first cert are intermediates
	for _, cert := range certs[1:] {
		opts.Intermediates.AddCert(cert)
	}

	_, err := certs[0].Verify(opts)
	if err != nil {
		return nil, err
	}

	return certs[0], nil
}
