/*
 * Minio Cloud Storage, (C) 2015, 2016, 2017 Minio, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package cmd

import (
	"bytes"
	"crypto"
	"crypto/ecdsa"
	"crypto/tls"
	"crypto/x509"
	"encoding/pem"
	"io/ioutil"
	"os"
)

// TLSPrivateKeyPassword is the environment variable which contains the password used
// to decrypt the TLS private key. It must be set if the TLS private key is
// password protected.
const TLSPrivateKeyPassword = "MINIO_CERT_PASSWD"

func parsePublicCertFile(certFile string) (x509Certs []*x509.Certificate, err error) {
	// Read certificate file.
	var data []byte
	if data, err = ioutil.ReadFile(certFile); err != nil {
		return nil, err
	}

	// Trimming leading and tailing white spaces.
	data = bytes.TrimSpace(data)

	// Parse all certs in the chain.
	current := data
	for len(current) > 0 {
		var pemBlock *pem.Block
		if pemBlock, current = pem.Decode(current); pemBlock == nil {
			return nil, uiErrSSLUnexpectedData(nil).Msg("Could not read PEM block from file %s", certFile)
		}

		var x509Cert *x509.Certificate
		if x509Cert, err = x509.ParseCertificate(pemBlock.Bytes); err != nil {
			return nil, uiErrSSLUnexpectedData(err)
		}

		x509Certs = append(x509Certs, x509Cert)
	}

	if len(x509Certs) == 0 {
		return nil, uiErrSSLUnexpectedData(nil).Msg("Empty public certificate file %s", certFile)
	}

	return x509Certs, nil
}

func getRootCAs(certsCAsDir string) (*x509.CertPool, error) {
	// Get all CA file names.
	var caFiles []string
	fis, err := readDir(certsCAsDir)
	if err != nil {
		return nil, err
	}
	for _, fi := range fis {
		// Skip all directories.
		if hasSuffix(fi, slashSeparator) {
			continue
		}
		// We are only interested in regular files here.
		caFiles = append(caFiles, pathJoin(certsCAsDir, fi))
	}
	if len(caFiles) == 0 {
		return nil, nil
	}

	rootCAs, err := x509.SystemCertPool()
	if err != nil {
		// In some systems like Windows, system cert pool is not supported.
		// Hence we create a new cert pool.
		rootCAs = x509.NewCertPool()
	}

	// Load custom root CAs for client requests
	for _, caFile := range caFiles {
		caCert, err := ioutil.ReadFile(caFile)
		if err != nil {
			return nil, err
		}

		rootCAs.AppendCertsFromPEM(caCert)
	}

	return rootCAs, nil
}

// load an X509 key pair (private key , certificate) from the provided
// paths. The private key may be encrypted and is decrypted using the
// ENV_VAR: MINIO_CERT_PASSWD.
func loadX509KeyPair(certFile, keyFile string) (tls.Certificate, error) {
	certPEMBlock, err := ioutil.ReadFile(certFile)
	if err != nil {
		return tls.Certificate{}, uiErrSSLUnexpectedError(err)
	}
	keyPEMBlock, err := ioutil.ReadFile(keyFile)
	if err != nil {
		return tls.Certificate{}, uiErrSSLUnexpectedError(err)
	}
	key, rest := pem.Decode(keyPEMBlock)
	if len(rest) > 0 {
		return tls.Certificate{}, uiErrSSLUnexpectedData(nil).Msg("The private key contains additional data")
	}
	if x509.IsEncryptedPEMBlock(key) {
		password, ok := os.LookupEnv(TLSPrivateKeyPassword)
		if !ok {
			return tls.Certificate{}, uiErrSSLNoPassword(nil)
		}
		decryptedKey, decErr := x509.DecryptPEMBlock(key, []byte(password))
		if decErr != nil {
			return tls.Certificate{}, uiErrSSLWrongPassword(decErr)
		}
		keyPEMBlock = pem.EncodeToMemory(&pem.Block{Type: key.Type, Bytes: decryptedKey})
	}
	cert, err := tls.X509KeyPair(certPEMBlock, keyPEMBlock)
	if err != nil {
		return tls.Certificate{}, uiErrSSLUnexpectedData(nil).Msg(err.Error())
	}
	return cert, nil
}

func getSSLConfig() (x509Certs []*x509.Certificate, rootCAs *x509.CertPool, tlsCert *tls.Certificate, secureConn bool, err error) {
	if !(isFile(getPublicCertFile()) && isFile(getPrivateKeyFile())) {
		return nil, nil, nil, false, nil
	}

	if x509Certs, err = parsePublicCertFile(getPublicCertFile()); err != nil {
		return nil, nil, nil, false, err
	}

	var cert tls.Certificate
	if cert, err = loadX509KeyPair(getPublicCertFile(), getPrivateKeyFile()); err != nil {
		return nil, nil, nil, false, err
	}
	// Ensure that the private key is not a P-384 or P-521 EC key.
	// The Go TLS stack does not provide constant-time implementations of P-384 and P-521.
	if priv, ok := cert.PrivateKey.(crypto.Signer); ok {
		if pub, ok := priv.Public().(*ecdsa.PublicKey); ok {
			if name := pub.Params().Name; name == "P-384" || name == "P-521" { // unfortunately there is no cleaner way to check
				return nil, nil, nil, false, uiErrSSLUnexpectedData(nil).Msg("tls: the ECDSA curve '%s' is not supported", name)
			}
		}

	}

	tlsCert = &cert

	if rootCAs, err = getRootCAs(getCADir()); err != nil {
		return nil, nil, nil, false, err
	}

	secureConn = true
	return x509Certs, rootCAs, tlsCert, secureConn, nil
}