package netxlite

import (
	"context"
	"crypto/tls"
	"crypto/x509"
	"errors"
	"fmt"
	"net"
	"time"
)

var (
	tlsVersionString = map[uint16]string{
		tls.VersionTLS10: "TLSv1",
		tls.VersionTLS11: "TLSv1.1",
		tls.VersionTLS12: "TLSv1.2",
		tls.VersionTLS13: "TLSv1.3",
		0:                "", // guarantee correct behaviour
	}

	tlsCipherSuiteString = map[uint16]string{
		tls.TLS_RSA_WITH_RC4_128_SHA:                "TLS_RSA_WITH_RC4_128_SHA",
		tls.TLS_RSA_WITH_3DES_EDE_CBC_SHA:           "TLS_RSA_WITH_3DES_EDE_CBC_SHA",
		tls.TLS_RSA_WITH_AES_128_CBC_SHA:            "TLS_RSA_WITH_AES_128_CBC_SHA",
		tls.TLS_RSA_WITH_AES_256_CBC_SHA:            "TLS_RSA_WITH_AES_256_CBC_SHA",
		tls.TLS_RSA_WITH_AES_128_CBC_SHA256:         "TLS_RSA_WITH_AES_128_CBC_SHA256",
		tls.TLS_RSA_WITH_AES_128_GCM_SHA256:         "TLS_RSA_WITH_AES_128_GCM_SHA256",
		tls.TLS_RSA_WITH_AES_256_GCM_SHA384:         "TLS_RSA_WITH_AES_256_GCM_SHA384",
		tls.TLS_ECDHE_ECDSA_WITH_RC4_128_SHA:        "TLS_ECDHE_ECDSA_WITH_RC4_128_SHA",
		tls.TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA:    "TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA",
		tls.TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA:    "TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA",
		tls.TLS_ECDHE_RSA_WITH_RC4_128_SHA:          "TLS_ECDHE_RSA_WITH_RC4_128_SHA",
		tls.TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA:     "TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA",
		tls.TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA:      "TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA",
		tls.TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA:      "TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA",
		tls.TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256: "TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256",
		tls.TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256:   "TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256",
		tls.TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256:   "TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256",
		tls.TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256: "TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256",
		tls.TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384:   "TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384",
		tls.TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384: "TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384",
		tls.TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305:    "TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305",
		tls.TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305:  "TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305",
		tls.TLS_AES_128_GCM_SHA256:                  "TLS_AES_128_GCM_SHA256",
		tls.TLS_AES_256_GCM_SHA384:                  "TLS_AES_256_GCM_SHA384",
		tls.TLS_CHACHA20_POLY1305_SHA256:            "TLS_CHACHA20_POLY1305_SHA256",
		0:                                           "", // guarantee correct behaviour
	}
)

// TLSVersionString returns a TLS version string.
func TLSVersionString(value uint16) string {
	if str, found := tlsVersionString[value]; found {
		return str
	}
	return fmt.Sprintf("TLS_VERSION_UNKNOWN_%d", value)
}

// TLSCipherSuiteString returns the TLS cipher suite as a string.
func TLSCipherSuiteString(value uint16) string {
	if str, found := tlsCipherSuiteString[value]; found {
		return str
	}
	return fmt.Sprintf("TLS_CIPHER_SUITE_UNKNOWN_%d", value)
}

// NewDefaultCertPool returns a copy of the default x509
// certificate pool that we bundle from Mozilla.
func NewDefaultCertPool() *x509.CertPool {
	pool := x509.NewCertPool()
	// Assumption: AppendCertsFromPEM cannot fail because we
	// run this function already in the generate.go file
	pool.AppendCertsFromPEM([]byte(pemcerts))
	return pool
}

// ErrInvalidTLSVersion indicates that you passed us a string
// that does not represent a valid TLS version.
var ErrInvalidTLSVersion = errors.New("invalid TLS version")

// ConfigureTLSVersion configures the correct TLS version into
// the specified *tls.Config or returns an error.
func ConfigureTLSVersion(config *tls.Config, version string) error {
	switch version {
	case "TLSv1.3":
		config.MinVersion = tls.VersionTLS13
		config.MaxVersion = tls.VersionTLS13
	case "TLSv1.2":
		config.MinVersion = tls.VersionTLS12
		config.MaxVersion = tls.VersionTLS12
	case "TLSv1.1":
		config.MinVersion = tls.VersionTLS11
		config.MaxVersion = tls.VersionTLS11
	case "TLSv1.0", "TLSv1":
		config.MinVersion = tls.VersionTLS10
		config.MaxVersion = tls.VersionTLS10
	case "":
		// nothing
	default:
		return ErrInvalidTLSVersion
	}
	return nil
}

// TLSConn is any tls.Conn-like structure.
type TLSConn interface {
	// net.Conn is the embedded conn.
	net.Conn

	// ConnectionState returns the TLS connection state.
	ConnectionState() tls.ConnectionState

	// Handshake performs the handshake.
	Handshake() error
}

// TLSHandshaker is the generic TLS handshaker.
type TLSHandshaker interface {
	// Handshake creates a new TLS connection from the given connection and
	// the given config. This function DOES NOT take ownership of the connection
	// and it's your responsibility to close it on failure.
	Handshake(ctx context.Context, conn net.Conn, config *tls.Config) (
		net.Conn, tls.ConnectionState, error)
}

// NewTLSHandshakerStdlib creates a new TLS handshaker using the
// go standard library to create TLS connections.
func NewTLSHandshakerStdlib(logger Logger) TLSHandshaker {
	return &tlsHandshakerLogger{
		TLSHandshaker: &tlsHandshakerConfigurable{},
		Logger:        logger,
	}
}

// tlsHandshakerConfigurable is a configurable TLS handshaker that
// uses by default the standard library's TLS implementation.
type tlsHandshakerConfigurable struct {
	// NewConn is the OPTIONAL factory for creating a new connection. If
	// this factory is not set, we'll use the stdlib.
	NewConn func(conn net.Conn, config *tls.Config) TLSConn

	// Timeout is the OPTIONAL timeout imposed on the TLS handshake. If zero
	// or negative, we will use default timeout of 10 seconds.
	Timeout time.Duration
}

var _ TLSHandshaker = &tlsHandshakerConfigurable{}

// defaultCertPool is the cert pool we use by default. We store this
// value into a private variable to enable for unit testing.
var defaultCertPool = NewDefaultCertPool()

// Handshake implements Handshaker.Handshake. This function will
// configure the code to use the built-in Mozilla CA if the config
// field contains a nil RootCAs field.
//
// Bug
//
// Until Go 1.17 is released, this function will not honour
// the context. We'll however always enforce an overall timeout.
func (h *tlsHandshakerConfigurable) Handshake(
	ctx context.Context, conn net.Conn, config *tls.Config,
) (net.Conn, tls.ConnectionState, error) {
	timeout := h.Timeout
	if timeout <= 0 {
		timeout = 10 * time.Second
	}
	defer conn.SetDeadline(time.Time{})
	conn.SetDeadline(time.Now().Add(timeout))
	if config.RootCAs == nil {
		config = config.Clone()
		config.RootCAs = defaultCertPool
	}
	tlsconn := h.newConn(conn, config)
	if err := tlsconn.Handshake(); err != nil {
		return nil, tls.ConnectionState{}, err
	}
	return tlsconn, tlsconn.ConnectionState(), nil
}

// newConn creates a new TLSConn.
func (h *tlsHandshakerConfigurable) newConn(conn net.Conn, config *tls.Config) TLSConn {
	if h.NewConn != nil {
		return h.NewConn(conn, config)
	}
	return tls.Client(conn, config)
}

// defaultTLSHandshaker is the default TLS handshaker.
var defaultTLSHandshaker = &tlsHandshakerConfigurable{}

// tlsHandshakerLogger is a TLSHandshaker with logging.
type tlsHandshakerLogger struct {
	// TLSHandshaker is the underlying handshaker.
	TLSHandshaker TLSHandshaker

	// Logger is the underlying logger.
	Logger Logger
}

var _ TLSHandshaker = &tlsHandshakerLogger{}

// Handshake implements Handshaker.Handshake
func (h *tlsHandshakerLogger) Handshake(
	ctx context.Context, conn net.Conn, config *tls.Config,
) (net.Conn, tls.ConnectionState, error) {
	h.Logger.Debugf(
		"tls {sni=%s next=%+v}...", config.ServerName, config.NextProtos)
	start := time.Now()
	tlsconn, state, err := h.TLSHandshaker.Handshake(ctx, conn, config)
	elapsed := time.Since(start)
	if err != nil {
		h.Logger.Debugf(
			"tls {sni=%s next=%+v}... %s in %s", config.ServerName,
			config.NextProtos, err, elapsed)
		return nil, tls.ConnectionState{}, err
	}
	h.Logger.Debugf(
		"tls {sni=%s next=%+v}... ok in %s {next=%s cipher=%s v=%s}",
		config.ServerName, config.NextProtos, elapsed, state.NegotiatedProtocol,
		TLSCipherSuiteString(state.CipherSuite),
		TLSVersionString(state.Version))
	return tlsconn, state, nil
}

// TLSDialer is the TLS dialer
type TLSDialer struct {
	// Config is the OPTIONAL tls config.
	Config *tls.Config

	// Dialer is the MANDATORY dialer.
	Dialer Dialer

	// TLSHandshaker is the MANDATORY TLS handshaker.
	TLSHandshaker TLSHandshaker
}

// DialTLSContext dials a TLS connection.
func (d *TLSDialer) DialTLSContext(ctx context.Context, network, address string) (net.Conn, error) {
	host, port, err := net.SplitHostPort(address)
	if err != nil {
		return nil, err
	}
	conn, err := d.Dialer.DialContext(ctx, network, address)
	if err != nil {
		return nil, err
	}
	config := d.config(host, port)
	tlsconn, _, err := d.TLSHandshaker.Handshake(ctx, conn, config)
	if err != nil {
		conn.Close()
		return nil, err
	}
	return tlsconn, nil
}

// config creates a new config. If d.Config is nil, then we start
// from an empty config. Otherwise, we clone d.Config.
//
// We set the ServerName field if not already set.
//
// We set the ALPN if the port is 443 or 853, if not already set.
func (d *TLSDialer) config(host, port string) *tls.Config {
	config := d.Config
	if config == nil {
		config = &tls.Config{}
	}
	config = config.Clone() // operate on a clone
	if config.ServerName == "" {
		config.ServerName = host
	}
	if len(config.NextProtos) <= 0 {
		switch port {
		case "443":
			config.NextProtos = []string{"h2", "http/1.1"}
		case "853":
			config.NextProtos = []string{"dot"}
		}
	}
	return config
}