/*
 * Copyright 2018 Intel Corporation, 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 auth

import (
	"bytes"
	"crypto"
	"crypto/tls"
	"crypto/x509"
	"encoding/base64"
	"encoding/pem"
	"golang.org/x/crypto/openpgp"
	"golang.org/x/crypto/openpgp/packet"
	"io/ioutil"

	smsconfig "sms/config"
	smslogger "sms/log"
)

// GetTLSConfig initializes a tlsConfig using the CA's certificate
// This config is then used to enable the server for mutual TLS
func GetTLSConfig(caCertFile string, certFile string, keyFile string) (*tls.Config, error) {

	// Initialize tlsConfig once
	caCert, err := ioutil.ReadFile(caCertFile)

	if smslogger.CheckError(err, "Read CA Cert file") != nil {
		return nil, err
	}

	caCertPool := x509.NewCertPool()
	caCertPool.AppendCertsFromPEM(caCert)

	tlsConfig := &tls.Config{
		// Change to RequireAndVerify once we have mandatory certs
		ClientAuth: tls.VerifyClientCertIfGiven,
		ClientCAs:  caCertPool,
		MinVersion: tls.VersionTLS12,
	}

	certPEMBlk, err := readPEMBlock(certFile)
	if smslogger.CheckError(err, "Read Cert File") != nil {
		return nil, err
	}

	keyPEMBlk, err := readPEMBlock(keyFile)
	if smslogger.CheckError(err, "Read Key File") != nil {
		return nil, err
	}

	tlsConfig.Certificates = make([]tls.Certificate, 1)
	tlsConfig.Certificates[0], err = tls.X509KeyPair(certPEMBlk, keyPEMBlk)
	if smslogger.CheckError(err, "Load x509 cert and key") != nil {
		return nil, err
	}

	tlsConfig.BuildNameToCertificate()
	return tlsConfig, nil
}

func readPEMBlock(filename string) ([]byte, error) {

	pemData, err := ioutil.ReadFile(filename)

	if smslogger.CheckError(err, "Read PEM File") != nil {
		return nil, err
	}

	pemBlock, rest := pem.Decode(pemData)
	if len(rest) > 0 {
		smslogger.WriteWarn("Pemfile has extra data")
	}

	if x509.IsEncryptedPEMBlock(pemBlock) {
		pByte, err := base64.StdEncoding.DecodeString(smsconfig.SMSConfig.Password)
		if smslogger.CheckError(err, "Decode PEM Password") != nil {
			return nil, err
		}

		pemData, err = x509.DecryptPEMBlock(pemBlock, pByte)
		if smslogger.CheckError(err, "Decrypt PEM Data") != nil {
			return nil, err
		}
		var newPEMBlock pem.Block
		newPEMBlock.Type = pemBlock.Type
		newPEMBlock.Bytes = pemData
		// Converting back to PEM from DER data you get from
		// DecryptPEMBlock
		pemData = pem.EncodeToMemory(&newPEMBlock)
	}

	return pemData, nil
}

// GeneratePGPKeyPair produces a PGP key pair and returns
// two things:
// A base64 encoded form of the public part of the entity
// A base64 encoded form of the private key
func GeneratePGPKeyPair() (string, string, error) {

	var entity *openpgp.Entity
	config := &packet.Config{
		DefaultHash: crypto.SHA256,
	}

	entity, err := openpgp.NewEntity("aaf.sms.init", "PGP Key for unsealing", "", config)
	if smslogger.CheckError(err, "Create Entity") != nil {
		return "", "", err
	}

	// Sign the identity in the entity
	for _, id := range entity.Identities {
		err = id.SelfSignature.SignUserId(id.UserId.Id, entity.PrimaryKey, entity.PrivateKey, nil)
		if smslogger.CheckError(err, "Sign Entity") != nil {
			return "", "", err
		}
	}

	// Sign the subkey in the entity
	for _, subkey := range entity.Subkeys {
		err := subkey.Sig.SignKey(subkey.PublicKey, entity.PrivateKey, nil)
		if smslogger.CheckError(err, "Sign Subkey") != nil {
			return "", "", err
		}
	}

	buffer := new(bytes.Buffer)
	entity.Serialize(buffer)
	pbkey := base64.StdEncoding.EncodeToString(buffer.Bytes())

	buffer.Reset()
	entity.SerializePrivate(buffer, nil)
	prkey := base64.StdEncoding.EncodeToString(buffer.Bytes())

	return pbkey, prkey, nil
}

// EncryptPGPString takes data and a public key and encrypts using that
// public key
func EncryptPGPString(data string, pbKey string) (string, error) {

	pbKeyBytes, err := base64.StdEncoding.DecodeString(pbKey)
	if smslogger.CheckError(err, "Decoding Base64 Public Key") != nil {
		return "", err
	}

	dataBytes := []byte(data)

	pbEntity, err := openpgp.ReadEntity(packet.NewReader(bytes.NewBuffer(pbKeyBytes)))
	if smslogger.CheckError(err, "Reading entity from PGP key") != nil {
		return "", err
	}

	// encrypt string
	buf := new(bytes.Buffer)
	out, err := openpgp.Encrypt(buf, []*openpgp.Entity{pbEntity}, nil, nil, nil)
	if smslogger.CheckError(err, "Creating Encryption Pipe") != nil {
		return "", err
	}

	_, err = out.Write(dataBytes)
	if smslogger.CheckError(err, "Writing to Encryption Pipe") != nil {
		return "", err
	}

	err = out.Close()
	if smslogger.CheckError(err, "Closing Encryption Pipe") != nil {
		return "", err
	}

	crp := base64.StdEncoding.EncodeToString(buf.Bytes())
	return crp, nil
}

// DecryptPGPString decrypts a PGP encoded input string and returns
// a base64 representation of the decoded string
func DecryptPGPString(data string, prKey string) (string, error) {

	// Convert private key to bytes from base64
	prKeyBytes, err := base64.StdEncoding.DecodeString(prKey)
	if smslogger.CheckError(err, "Decoding Base64 Private Key") != nil {
		return "", err
	}

	dataBytes, err := base64.StdEncoding.DecodeString(data)
	if smslogger.CheckError(err, "Decoding base64 data") != nil {
		return "", err
	}

	prEntity, err := openpgp.ReadEntity(packet.NewReader(bytes.NewBuffer(prKeyBytes)))
	if smslogger.CheckError(err, "Read Entity") != nil {
		return "", err
	}

	prEntityList := &openpgp.EntityList{prEntity}
	message, err := openpgp.ReadMessage(bytes.NewBuffer(dataBytes), prEntityList, nil, nil)
	if smslogger.CheckError(err, "Decrypting Message") != nil {
		return "", err
	}

	var retBuf bytes.Buffer
	retBuf.ReadFrom(message.UnverifiedBody)

	return retBuf.String(), nil
}

// ReadFromFile reads a file and loads the PGP key into
// a string
func ReadFromFile(fileName string) (string, error) {

	data, err := ioutil.ReadFile(fileName)
	if smslogger.CheckError(err, "Read from file") != nil {
		return "", err
	}
	return string(data), nil
}

// WriteToFile writes a PGP key into a file.
// It will truncate the file if it exists
func WriteToFile(data string, fileName string) error {

	err := ioutil.WriteFile(fileName, []byte(data), 0600)
	if smslogger.CheckError(err, "Write to file") != nil {
		return err
	}
	return nil
}