package transport

import (
	"crypto/rand"
	"crypto/rsa"
	"crypto/tls"
	"crypto/x509"
	"encoding/pem"
	"io/ioutil"
	"math/big"
)

/*
	Example for self-signed certificates by openssl:

	Self CA:
	openssl genrsa -out ca.key 2048
	openssl req -x509 -new -nodes -key ca.key -subj "/CN=example.ca.com" -days 5000 -out ca.crt

	Server:
	openssl genrsa -out server.key 2048
	openssl req -new -key server.key -subj "/CN=example.server.com" -out server.csr
	openssl x509 -req -in server.csr -CA ca.crt -CAkey ca.key -CAcreateserial -out server.crt -days 5000

	Client:
	openssl genrsa -out client.key 2048
	openssl req -new -key client.key -subj "/CN=example.client.com" -out client.csr
	openssl x509 -req -in client.csr -CA ca.crt -CAkey ca.key -CAcreateserial -out client.crt -days 5000

*/

func newCustomTLSKeyPair(certfile, keyfile string) (*tls.Certificate, error) {
	tlsCert, err := tls.LoadX509KeyPair(certfile, keyfile)
	if err != nil {
		return nil, err
	}
	return &tlsCert, nil
}

func newRandomTLSKeyPair() *tls.Certificate {
	key, err := rsa.GenerateKey(rand.Reader, 1024)
	if err != nil {
		panic(err)
	}
	template := x509.Certificate{SerialNumber: big.NewInt(1)}
	certDER, err := x509.CreateCertificate(
		rand.Reader,
		&template,
		&template,
		&key.PublicKey,
		key)
	if err != nil {
		panic(err)
	}
	keyPEM := pem.EncodeToMemory(&pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(key)})
	certPEM := pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: certDER})

	tlsCert, err := tls.X509KeyPair(certPEM, keyPEM)
	if err != nil {
		panic(err)
	}
	return &tlsCert
}

// Only supprt one ca file to add
func newCertPool(caPath string) (*x509.CertPool, error) {
	pool := x509.NewCertPool()

	caCrt, err := ioutil.ReadFile(caPath)
	if err != nil {
		return nil, err
	}

	pool.AppendCertsFromPEM(caCrt)

	return pool, nil
}

func NewServerTLSConfig(certPath, keyPath, caPath string) (*tls.Config, error) {
	var base = &tls.Config{}

	if certPath == "" || keyPath == "" {
		// server will generate tls conf by itself
		cert := newRandomTLSKeyPair()
		base.Certificates = []tls.Certificate{*cert}
	} else {
		cert, err := newCustomTLSKeyPair(certPath, keyPath)
		if err != nil {
			return nil, err
		}

		base.Certificates = []tls.Certificate{*cert}
	}

	if caPath != "" {
		pool, err := newCertPool(caPath)
		if err != nil {
			return nil, err
		}

		base.ClientAuth = tls.RequireAndVerifyClientCert
		base.ClientCAs = pool
	}

	return base, nil
}

func NewClientTLSConfig(certPath, keyPath, caPath, servearName string) (*tls.Config, error) {
	var base = &tls.Config{}

	if certPath == "" || keyPath == "" {
		// client will not generate tls conf by itself
	} else {
		cert, err := newCustomTLSKeyPair(certPath, keyPath)
		if err != nil {
			return nil, err
		}

		base.Certificates = []tls.Certificate{*cert}
	}

	if caPath != "" {
		pool, err := newCertPool(caPath)
		if err != nil {
			return nil, err
		}

		base.RootCAs = pool
		base.ServerName = servearName
		base.InsecureSkipVerify = false
	} else {
		base.InsecureSkipVerify = true
	}

	return base, nil
}