package tlsutil

import (
	"crypto/tls"
	"crypto/x509"
	"encoding/pem"
	"fmt"
	"io/ioutil"
	"net"
	"strings"
	"time"

	"github.com/hashicorp/nomad/nomad/structs/config"
)

// supportedTLSVersions are the current TLS versions that Nomad supports
var supportedTLSVersions = map[string]uint16{
	"tls10": tls.VersionTLS10,
	"tls11": tls.VersionTLS11,
	"tls12": tls.VersionTLS12,
}

// supportedTLSCiphers are the complete list of TLS ciphers supported by Nomad
var supportedTLSCiphers = map[string]uint16{
	"TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305":    tls.TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305,
	"TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305":  tls.TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305,
	"TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256":   tls.TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,
	"TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256": tls.TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,
	"TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384":   tls.TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,
	"TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384": tls.TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,
	"TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256":   tls.TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256,
	"TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA":      tls.TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA,
	"TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256": tls.TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256,
	"TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA":    tls.TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA,
	"TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA":      tls.TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA,
	"TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA":    tls.TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA,
	"TLS_RSA_WITH_AES_128_GCM_SHA256":         tls.TLS_RSA_WITH_AES_128_GCM_SHA256,
	"TLS_RSA_WITH_AES_256_GCM_SHA384":         tls.TLS_RSA_WITH_AES_256_GCM_SHA384,
	"TLS_RSA_WITH_AES_128_CBC_SHA256":         tls.TLS_RSA_WITH_AES_128_CBC_SHA256,
	"TLS_RSA_WITH_AES_128_CBC_SHA":            tls.TLS_RSA_WITH_AES_128_CBC_SHA,
	"TLS_RSA_WITH_AES_256_CBC_SHA":            tls.TLS_RSA_WITH_AES_256_CBC_SHA,
}

// defaultTLSCiphers are the TLS Ciphers that are supported by default
var defaultTLSCiphers = []string{
	"TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384",
	"TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384",
	"TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305",
	"TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305",
	"TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256",
	"TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256",
	"TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384",
	"TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384",
	"TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256",
	"TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256",
}

// RegionSpecificWrapper is used to invoke a static Region and turns a
// RegionWrapper into a Wrapper type.
func RegionSpecificWrapper(region string, tlsWrap RegionWrapper) Wrapper {
	if tlsWrap == nil {
		return nil
	}
	return func(conn net.Conn) (net.Conn, error) {
		return tlsWrap(region, conn)
	}
}

// RegionWrapper is a function that is used to wrap a non-TLS connection and
// returns an appropriate TLS connection or error. This takes a Region as an
// argument.
type RegionWrapper func(region string, conn net.Conn) (net.Conn, error)

// Wrapper wraps a connection and enables TLS on it.
type Wrapper func(conn net.Conn) (net.Conn, error)

// Config used to create tls.Config
type Config struct {
	// VerifyIncoming is used to verify the authenticity of incoming connections.
	// This means that TCP requests are forbidden, only allowing for TLS. TLS connections
	// must match a provided certificate authority. This can be used to force client auth.
	VerifyIncoming bool

	// VerifyOutgoing is used to verify the authenticity of outgoing connections.
	// This means that TLS requests are used, and TCP requests are not made. TLS connections
	// must match a provided certificate authority. This is used to verify authenticity of
	// server nodes.
	VerifyOutgoing bool

	// VerifyServerHostname is used to enable hostname verification of servers. This
	// ensures that the certificate presented is valid for server.<datacenter>.<domain>.
	// This prevents a compromised client from being restarted as a server, and then
	// intercepting request traffic as well as being added as a raft peer. This should be
	// enabled by default with VerifyOutgoing, but for legacy reasons we cannot break
	// existing clients.
	VerifyServerHostname bool

	// CAFile is a path to a certificate authority file. This is used with VerifyIncoming
	// or VerifyOutgoing to verify the TLS connection.
	CAFile string

	// CertFile is used to provide a TLS certificate that is used for serving TLS connections.
	// Must be provided to serve TLS connections.
	CertFile string

	// KeyFile is used to provide a TLS key that is used for serving TLS connections.
	// Must be provided to serve TLS connections.
	KeyFile string

	// KeyLoader dynamically reloads TLS configuration.
	KeyLoader *config.KeyLoader

	// CipherSuites have a default safe configuration, or operators can override
	// these values for acceptable safe alternatives.
	CipherSuites []uint16

	// PreferServerCipherSuites controls whether the server selects the
	// client's most preferred ciphersuite, or the server's most preferred
	// ciphersuite. If true then the server's preference, as expressed in
	// the order of elements in CipherSuites, is used.
	PreferServerCipherSuites bool

	// MinVersion contains the minimum SSL/TLS version that is accepted.
	MinVersion uint16
}

func NewTLSConfiguration(newConf *config.TLSConfig, verifyIncoming, verifyOutgoing bool) (*Config, error) {
	ciphers, err := ParseCiphers(newConf)
	if err != nil {
		return nil, err
	}

	minVersion, err := ParseMinVersion(newConf.TLSMinVersion)
	if err != nil {
		return nil, err
	}

	return &Config{
		VerifyIncoming:           verifyIncoming,
		VerifyOutgoing:           verifyOutgoing,
		VerifyServerHostname:     newConf.VerifyServerHostname,
		CAFile:                   newConf.CAFile,
		CertFile:                 newConf.CertFile,
		KeyFile:                  newConf.KeyFile,
		KeyLoader:                newConf.GetKeyLoader(),
		CipherSuites:             ciphers,
		MinVersion:               minVersion,
		PreferServerCipherSuites: newConf.TLSPreferServerCipherSuites,
	}, nil
}

// AppendCA opens and parses the CA file and adds the certificates to
// the provided CertPool.
func (c *Config) AppendCA(pool *x509.CertPool) error {
	if c.CAFile == "" {
		return nil
	}

	// Read the file
	data, err := ioutil.ReadFile(c.CAFile)
	if err != nil {
		return fmt.Errorf("Failed to read CA file: %v", err)
	}

	block, rest := pem.Decode(data)
	if err := validateCertificate(block); err != nil {
		return err
	}

	for len(rest) > 0 {
		block, rest = pem.Decode(rest)
		if err := validateCertificate(block); err != nil {
			return err
		}
	}

	if !pool.AppendCertsFromPEM(data) {
		return fmt.Errorf("Failed to add any CA certificates")
	}

	return nil
}

// validateCertificate checks to ensure a certificate is valid. If it is not,
// return a descriptive error of why the certificate is invalid.
func validateCertificate(block *pem.Block) error {
	if block == nil {
		return fmt.Errorf("Failed to decode CA file from pem format")
	}

	// Parse the certificate to ensure that it is properly formatted
	if _, err := x509.ParseCertificates(block.Bytes); err != nil {
		return fmt.Errorf("Failed to parse CA file: %v", err)
	}

	return nil
}

// LoadKeyPair is used to open and parse a certificate and key file
func (c *Config) LoadKeyPair() (*tls.Certificate, error) {
	if c.CertFile == "" || c.KeyFile == "" {
		return nil, nil
	}

	if c.KeyLoader == nil {
		return nil, fmt.Errorf("No Keyloader object to perform LoadKeyPair")
	}

	cert, err := c.KeyLoader.LoadKeyPair(c.CertFile, c.KeyFile)
	if err != nil {
		return nil, fmt.Errorf("Failed to load cert/key pair: %v", err)
	}
	return cert, err
}

// OutgoingTLSConfig generates a TLS configuration for outgoing
// requests. It will return a nil config if this configuration should
// not use TLS for outgoing connections. Provides a callback to
// fetch certificates, allowing for reloading on the fly.
func (c *Config) OutgoingTLSConfig() (*tls.Config, error) {
	// If VerifyServerHostname is true, that implies VerifyOutgoing
	if c.VerifyServerHostname {
		c.VerifyOutgoing = true
	}
	if !c.VerifyOutgoing {
		return nil, nil
	}
	// Create the tlsConfig
	tlsConfig := &tls.Config{
		RootCAs:                  x509.NewCertPool(),
		InsecureSkipVerify:       true,
		CipherSuites:             c.CipherSuites,
		MinVersion:               c.MinVersion,
		PreferServerCipherSuites: c.PreferServerCipherSuites,
	}
	if c.VerifyServerHostname {
		tlsConfig.InsecureSkipVerify = false
	}

	// Ensure we have a CA if VerifyOutgoing is set
	if c.VerifyOutgoing && c.CAFile == "" {
		return nil, fmt.Errorf("VerifyOutgoing set, and no CA certificate provided!")
	}

	// Parse the CA cert if any
	err := c.AppendCA(tlsConfig.RootCAs)
	if err != nil {
		return nil, err
	}

	cert, err := c.LoadKeyPair()
	if err != nil {
		return nil, err
	} else if cert != nil {
		tlsConfig.GetCertificate = c.KeyLoader.GetOutgoingCertificate
		tlsConfig.GetClientCertificate = c.KeyLoader.GetClientCertificate
	}

	return tlsConfig, nil
}

// OutgoingTLSWrapper returns a a Wrapper based on the OutgoingTLS
// configuration. If hostname verification is on, the wrapper
// will properly generate the dynamic server name for verification.
func (c *Config) OutgoingTLSWrapper() (RegionWrapper, error) {
	// Get the TLS config
	tlsConfig, err := c.OutgoingTLSConfig()
	if err != nil {
		return nil, err
	}

	// Check if TLS is not enabled
	if tlsConfig == nil {
		return nil, nil
	}

	// Generate the wrapper based on hostname verification
	if c.VerifyServerHostname {
		wrapper := func(region string, conn net.Conn) (net.Conn, error) {
			conf := tlsConfig.Clone()
			conf.ServerName = "server." + region + ".nomad"
			return WrapTLSClient(conn, conf)
		}
		return wrapper, nil
	} else {
		wrapper := func(dc string, c net.Conn) (net.Conn, error) {
			return WrapTLSClient(c, tlsConfig)
		}
		return wrapper, nil
	}

}

// Wrap a net.Conn into a client tls connection, performing any
// additional verification as needed.
//
// As of go 1.3, crypto/tls only supports either doing no certificate
// verification, or doing full verification including of the peer's
// DNS name. For consul, we want to validate that the certificate is
// signed by a known CA, but because consul doesn't use DNS names for
// node names, we don't verify the certificate DNS names. Since go 1.3
// no longer supports this mode of operation, we have to do it
// manually.
func WrapTLSClient(conn net.Conn, tlsConfig *tls.Config) (net.Conn, error) {
	var err error
	var tlsConn *tls.Conn

	tlsConn = tls.Client(conn, tlsConfig)

	// If crypto/tls is doing verification, there's no need to do
	// our own.
	if tlsConfig.InsecureSkipVerify == false {
		return tlsConn, nil
	}

	if err = tlsConn.Handshake(); err != nil {
		tlsConn.Close()
		return nil, err
	}

	// The following is lightly-modified from the doFullHandshake
	// method in crypto/tls's handshake_client.go.
	opts := x509.VerifyOptions{
		Roots:         tlsConfig.RootCAs,
		CurrentTime:   time.Now(),
		DNSName:       "",
		Intermediates: x509.NewCertPool(),
	}

	certs := tlsConn.ConnectionState().PeerCertificates
	for i, cert := range certs {
		if i == 0 {
			continue
		}
		opts.Intermediates.AddCert(cert)
	}

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

	return tlsConn, err
}

// IncomingTLSConfig generates a TLS configuration for incoming requests
func (c *Config) IncomingTLSConfig() (*tls.Config, error) {
	// Create the tlsConfig
	tlsConfig := &tls.Config{
		ClientCAs:                x509.NewCertPool(),
		ClientAuth:               tls.NoClientCert,
		CipherSuites:             c.CipherSuites,
		MinVersion:               c.MinVersion,
		PreferServerCipherSuites: c.PreferServerCipherSuites,
	}

	// Parse the CA cert if any
	err := c.AppendCA(tlsConfig.ClientCAs)
	if err != nil {
		return nil, err
	}

	// Add cert/key
	cert, err := c.LoadKeyPair()
	if err != nil {
		return nil, err
	} else if cert != nil {
		tlsConfig.GetCertificate = c.KeyLoader.GetOutgoingCertificate
	}

	// Check if we require verification
	if c.VerifyIncoming {
		tlsConfig.ClientAuth = tls.RequireAndVerifyClientCert
		if c.CAFile == "" {
			return nil, fmt.Errorf("VerifyIncoming set, and no CA certificate provided!")
		}
		if cert == nil {
			return nil, fmt.Errorf("VerifyIncoming set, and no Cert/Key pair provided!")
		}
	}

	return tlsConfig, nil
}

// ParseCiphers parses ciphersuites from the comma-separated string into
// recognized slice
func ParseCiphers(tlsConfig *config.TLSConfig) ([]uint16, error) {
	suites := []uint16{}

	cipherStr := strings.TrimSpace(tlsConfig.TLSCipherSuites)

	var ciphers []string
	if cipherStr == "" {
		ciphers = defaultTLSCiphers

	} else {
		ciphers = strings.Split(tlsConfig.TLSCipherSuites, ",")
	}
	for _, cipher := range ciphers {
		c, ok := supportedTLSCiphers[cipher]
		if !ok {
			return suites, fmt.Errorf("unsupported TLS cipher %q", cipher)
		}
		suites = append(suites, c)
	}

	return suites, nil
}

// ParseMinVersion parses the specified minimum TLS version for the Nomad agent
func ParseMinVersion(version string) (uint16, error) {
	if version == "" {
		return supportedTLSVersions["tls12"], nil
	}

	vers, ok := supportedTLSVersions[version]
	if !ok {
		return 0, fmt.Errorf("unsupported TLS version %q", version)
	}

	return vers, nil
}

// ShouldReloadRPCConnections compares two TLS Configurations and determines
// whether they differ such that RPC connections should be reloaded
func ShouldReloadRPCConnections(old, new *config.TLSConfig) (bool, error) {
	var certificateInfoEqual bool
	var rpcInfoEqual bool

	// If already configured with TLS, compare with the new TLS configuration
	if new != nil {
		var err error
		certificateInfoEqual, err = new.CertificateInfoIsEqual(old)
		if err != nil {
			return false, err
		}
	} else if new == nil && old == nil {
		certificateInfoEqual = true
	}

	if new != nil && old != nil && new.EnableRPC == old.EnableRPC {
		rpcInfoEqual = true
	}

	return (!rpcInfoEqual || !certificateInfoEqual), nil
}