package server

import (
	"bytes"
	"crypto/rand"
	"crypto/rsa"
	"crypto/sha1"
	"crypto/sha256"
	"crypto/tls"
	"fmt"

	"github.com/juju/errors"
	. "github.com/siddontang/go-mysql/mysql"
)

func (c *Conn) handleAuthSwitchResponse() error {
	authData, err := c.readAuthSwitchRequestResponse()
	if err != nil {
		return err
	}

	switch c.authPluginName {
	case AUTH_NATIVE_PASSWORD:
		if err := c.acquirePassword(); err != nil {
			return err
		}
		if !bytes.Equal(CalcPassword(c.salt, []byte(c.password)), authData) {
			return ErrAccessDenied
		}
		return nil

	case AUTH_CACHING_SHA2_PASSWORD:
		if !c.cachingSha2FullAuth {
			// Switched auth method but no MoreData packet send yet
			if err := c.compareCacheSha2PasswordAuthData(authData); err != nil {
				return err
			} else {
				if c.cachingSha2FullAuth {
					return c.handleAuthSwitchResponse()
				}
				return nil
			}
		}
		// AuthMoreData packet already sent, do full auth
		if err := c.handleCachingSha2PasswordFullAuth(authData); err != nil {
			return err
		}
		c.writeCachingSha2Cache()
		return nil

	case AUTH_SHA256_PASSWORD:
		cont, err := c.handlePublicKeyRetrieval(authData)
		if err != nil {
			return err
		}
		if !cont {
			return nil
		}
		if err := c.acquirePassword(); err != nil {
			return err
		}
		return c.compareSha256PasswordAuthData(authData, c.password)

	default:
		return errors.Errorf("unknown authentication plugin name '%s'", c.authPluginName)
	}
}

func (c *Conn) handleCachingSha2PasswordFullAuth(authData []byte) error {
	if err := c.acquirePassword(); err != nil {
		return err
	}
	if tlsConn, ok := c.Conn.Conn.(*tls.Conn); ok {
		if !tlsConn.ConnectionState().HandshakeComplete {
			return errors.New("incomplete TSL handshake")
		}
		// connection is SSL/TLS, client should send plain password
		// deal with the trailing \NUL added for plain text password received
		if l := len(authData); l != 0 && authData[l-1] == 0x00 {
			authData = authData[:l-1]
		}
		if bytes.Equal(authData, []byte(c.password)) {
			return nil
		}
		return ErrAccessDenied
	} else {
		// client either request for the public key or send the encrypted password
		if len(authData) == 1 && authData[0] == 0x02 {
			// send the public key
			if err := c.writeAuthMoreDataPubkey(); err != nil {
				return err
			}
			// read the encrypted password
			var err error
			if authData, err = c.readAuthSwitchRequestResponse(); err != nil {
				return err
			}
		}
		// the encrypted password
		// decrypt
		dbytes, err := rsa.DecryptOAEP(sha1.New(), rand.Reader, (c.serverConf.tlsConfig.Certificates[0].PrivateKey).(*rsa.PrivateKey), authData, nil)
		if err != nil {
			return err
		}
		plain := make([]byte, len(c.password)+1)
		copy(plain, c.password)
		for i := range plain {
			j := i % len(c.salt)
			plain[i] ^= c.salt[j]
		}
		if bytes.Equal(plain, dbytes) {
			return nil
		}
		return ErrAccessDenied
	}
}

func (c *Conn) writeCachingSha2Cache() {
	// write cache
	if c.password == "" {
		return
	}
	// SHA256(PASSWORD)
	crypt := sha256.New()
	crypt.Write([]byte(c.password))
	m1 := crypt.Sum(nil)
	// SHA256(SHA256(PASSWORD))
	crypt.Reset()
	crypt.Write(m1)
	m2 := crypt.Sum(nil)
	// caching_sha2_password will maintain an in-memory hash of `user`@`host` => SHA256(SHA256(PASSWORD))
	c.serverConf.cacheShaPassword.Store(fmt.Sprintf("%s@%s", c.user, c.Conn.LocalAddr()), m2)
}