/*
Copyright 2014 Google Inc. All rights reserved.

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 util

import (
	"bytes"
	"crypto/rand"
	"crypto/rsa"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/pem"
	"errors"
	"fmt"
	"io/ioutil"
	"math/big"
	"net"
	"os"
	"path/filepath"
	"time"
)

// GenerateSelfSignedCert creates a self-signed certificate and key for the given host.
// Host may be an IP or a DNS name
// The certificate will be created with file mode 0644. The key will be created with file mode 0600.
// If the certificate or key files already exist, they will be overwritten.
// Any parent directories of the certPath or keyPath will be created as needed with file mode 0755.
func GenerateSelfSignedCert(host, certPath, keyPath string) error {
	priv, err := rsa.GenerateKey(rand.Reader, 2048)
	if err != nil {
		return err
	}

	template := x509.Certificate{
		SerialNumber: big.NewInt(1),
		Subject: pkix.Name{
			CommonName: fmt.Sprintf("%s@%d", host, time.Now().Unix()),
		},
		NotBefore: time.Now(),
		NotAfter:  time.Now().Add(time.Hour * 24 * 365),

		KeyUsage:              x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature,
		ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
		BasicConstraintsValid: true,
	}

	if ip := net.ParseIP(host); ip != nil {
		template.IPAddresses = append(template.IPAddresses, ip)
	} else {
		template.DNSNames = append(template.DNSNames, host)
	}

	derBytes, err := x509.CreateCertificate(rand.Reader, &template, &template, &priv.PublicKey, priv)
	if err != nil {
		return err
	}

	// Generate cert
	certBuffer := bytes.Buffer{}
	if err := pem.Encode(&certBuffer, &pem.Block{Type: "CERTIFICATE", Bytes: derBytes}); err != nil {
		return err
	}

	// Generate key
	keyBuffer := bytes.Buffer{}
	if err := pem.Encode(&keyBuffer, &pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(priv)}); err != nil {
		return err
	}

	// Write cert
	if err := os.MkdirAll(filepath.Dir(certPath), os.FileMode(0755)); err != nil {
		return err
	}
	if err := ioutil.WriteFile(certPath, certBuffer.Bytes(), os.FileMode(0644)); err != nil {
		return err
	}

	// Write key
	if err := os.MkdirAll(filepath.Dir(keyPath), os.FileMode(0755)); err != nil {
		return err
	}
	if err := ioutil.WriteFile(keyPath, keyBuffer.Bytes(), os.FileMode(0600)); err != nil {
		return err
	}

	return nil
}

// CertPoolFromFile returns an x509.CertPool containing the certificates in the given PEM-encoded file.
// Returns an error if the file could not be read, a certificate could not be parsed, or if the file does not contain any certificates
func CertPoolFromFile(filename string) (*x509.CertPool, error) {
	certs, err := certificatesFromFile(filename)
	if err != nil {
		return nil, err
	}
	pool := x509.NewCertPool()
	for _, cert := range certs {
		pool.AddCert(cert)
	}
	return pool, nil
}

// certificatesFromFile returns the x509.Certificates contained in the given PEM-encoded file.
// Returns an error if the file could not be read, a certificate could not be parsed, or if the file does not contain any certificates
func certificatesFromFile(file string) ([]*x509.Certificate, error) {
	if len(file) == 0 {
		return nil, errors.New("error reading certificates from an empty filename")
	}
	pemBlock, err := ioutil.ReadFile(file)
	if err != nil {
		return nil, err
	}
	certs, err := certsFromPEM(pemBlock)
	if err != nil {
		return nil, fmt.Errorf("error reading %s: %s", file, err)
	}
	return certs, nil
}

// certsFromPEM returns the x509.Certificates contained in the given PEM-encoded byte array
// Returns an error if a certificate could not be parsed, or if the data does not contain any certificates
func certsFromPEM(pemCerts []byte) ([]*x509.Certificate, error) {
	ok := false
	certs := []*x509.Certificate{}
	for len(pemCerts) > 0 {
		var block *pem.Block
		block, pemCerts = pem.Decode(pemCerts)
		if block == nil {
			break
		}
		// Only use PEM "CERTIFICATE" blocks without extra headers
		if block.Type != "CERTIFICATE" || len(block.Headers) != 0 {
			continue
		}

		cert, err := x509.ParseCertificate(block.Bytes)
		if err != nil {
			return certs, err
		}

		certs = append(certs, cert)
		ok = true
	}

	if !ok {
		return certs, errors.New("could not read any certificates")
	}
	return certs, nil
}
