/*
Copyright 2014 The Kubernetes Authors.

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 crypto

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

// FoundCertOrKey returns true if the certificate or key files already exists,
// otherwise returns false.
func FoundCertOrKey(certPath, keyPath string) bool {
	if canReadFile(certPath) || canReadFile(keyPath) {
		return true
	}

	return false
}

// If the file represented by path exists and
// readable, returns true otherwise returns false.
func canReadFile(path string) bool {
	f, err := os.Open(path)
	if err != nil {
		return false
	}

	defer f.Close()

	return true
}

// GenerateSelfSignedCert creates a self-signed certificate and key for the given host.
// Host may be an IP or a DNS name
// You may also specify additional subject alt names (either ip or dns names) for the certificate
// 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, alternateIPs []net.IP, alternateDNS []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 | x509.KeyUsageCertSign,
		ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
		BasicConstraintsValid: true,
		IsCA: true,
	}

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

	template.IPAddresses = append(template.IPAddresses, alternateIPs...)
	template.DNSNames = append(template.DNSNames, alternateDNS...)

	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 := WriteCertToPath(certPath, certBuffer.Bytes()); err != nil {
		return err
	}

	// Write key
	if err := WriteKeyToPath(keyPath, keyBuffer.Bytes()); err != nil {
		return err
	}

	return nil
}

// WriteCertToPath writes the pem-encoded certificate data to certPath.
// The certificate file will be created with file mode 0644.
// If the certificate file already exists, it will be overwritten.
// The parent directory of the certPath will be created as needed with file mode 0755.
func WriteCertToPath(certPath string, data []byte) error {
	if err := os.MkdirAll(filepath.Dir(certPath), os.FileMode(0755)); err != nil {
		return err
	}
	if err := ioutil.WriteFile(certPath, data, os.FileMode(0644)); err != nil {
		return err
	}
	return nil
}

// WriteKeyToPath writes the pem-encoded key data to keyPath.
// The key file will be created with file mode 0600.
// If the key file already exists, it will be overwritten.
// The parent directory of the keyPath will be created as needed with file mode 0755.
func WriteKeyToPath(keyPath string, data []byte) error {
	if err := os.MkdirAll(filepath.Dir(keyPath), os.FileMode(0755)); err != nil {
		return err
	}
	if err := ioutil.WriteFile(keyPath, data, 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
}
