package libp2pquic

import (
	"crypto/ecdsa"
	"crypto/elliptic"
	"crypto/rand"
	"crypto/tls"
	"crypto/x509"
	"errors"
	"math/big"
	"time"

	"github.com/gogo/protobuf/proto"
	ic "github.com/libp2p/go-libp2p-crypto"
	pb "github.com/libp2p/go-libp2p-crypto/pb"
)

// mint certificate selection is broken.
const hostname = "quic.ipfs"

func generateConfig(privKey ic.PrivKey) (*tls.Config, error) {
	key, hostCert, err := keyToCertificate(privKey)
	if err != nil {
		return nil, err
	}
	// The ephemeral key used just for a couple of connections (or a limited time).
	ephemeralKey, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
	if err != nil {
		return nil, err
	}
	// Sign the ephemeral key using the host key.
	// This is the only time that the host's private key of the peer is needed.
	// Note that this step could be done asynchronously, such that a running node doesn't need access its private key at all.
	certTemplate := &x509.Certificate{
		DNSNames:     []string{hostname},
		SerialNumber: big.NewInt(1),
		NotBefore:    time.Now().Add(-24 * time.Hour),
		NotAfter:     time.Now().Add(30 * 24 * time.Hour),
	}
	certDER, err := x509.CreateCertificate(rand.Reader, certTemplate, hostCert, ephemeralKey.Public(), key)
	if err != nil {
		return nil, err
	}
	cert, err := x509.ParseCertificate(certDER)
	if err != nil {
		return nil, err
	}
	return &tls.Config{
		ServerName:         hostname,
		InsecureSkipVerify: true, // This is not insecure here. We will verify the cert chain ourselves.
		ClientAuth:         tls.RequireAnyClientCert,
		Certificates: []tls.Certificate{{
			Certificate: [][]byte{cert.Raw, hostCert.Raw},
			PrivateKey:  ephemeralKey,
		}},
	}, nil
}

func getRemotePubKey(chain []*x509.Certificate) (ic.PubKey, error) {
	if len(chain) == 0 || len(chain) > 4 {
		return nil, errors.New("expected between 1 and 4 certificates in the chain")
	}
	rootCert := chain[len(chain)-1]
	roots := x509.NewCertPool()
	roots.AddCert(rootCert) // the last certificate is the root CA cert
	var intermediates *x509.CertPool
	if len(chain) > 2 {
		intermediates = x509.NewCertPool()
		for i := 1; i < len(chain)-1; i++ {
			intermediates.AddCert(chain[i])
		}
	}
	verifyOpts := x509.VerifyOptions{
		Roots:         roots,
		Intermediates: intermediates,
	}
	if _, err := chain[0].Verify(x509.VerifyOptions{Roots: roots}); err != nil {
		return nil, err
	}
	remotePubKey, err := x509.MarshalPKIXPublicKey(rootCert.PublicKey)
	if err != nil {
		return nil, err
	}
	return ic.UnmarshalRsaPublicKey(remotePubKey)
}

func keyToCertificate(sk ic.PrivKey) (interface{}, *x509.Certificate, error) {
	sn, err := rand.Int(rand.Reader, big.NewInt(1<<62))
	if err != nil {
		return nil, nil, err
	}
	tmpl := &x509.Certificate{
		SerialNumber: sn,
		NotBefore:    time.Now().Add(-24 * time.Hour),
		NotAfter:     time.Now().Add(30 * 24 * time.Hour),
		IsCA:         true,
		BasicConstraintsValid: true,
	}

	var publicKey, privateKey interface{}
	keyBytes, err := sk.Bytes()
	if err != nil {
		return nil, nil, err
	}
	pbmes := new(pb.PrivateKey)
	if err := proto.Unmarshal(keyBytes, pbmes); err != nil {
		return nil, nil, err
	}
	switch pbmes.GetType() {
	case pb.KeyType_RSA:
		k, err := x509.ParsePKCS1PrivateKey(pbmes.GetData())
		if err != nil {
			return nil, nil, err
		}
		publicKey = &k.PublicKey
		privateKey = k
	// TODO: add support for ECDSA
	default:
		return nil, nil, errors.New("unsupported key type for TLS")
	}
	certDER, err := x509.CreateCertificate(rand.Reader, tmpl, tmpl, publicKey, privateKey)
	if err != nil {
		return nil, nil, err
	}
	cert, err := x509.ParseCertificate(certDER)
	if err != nil {
		return nil, nil, err
	}
	return privateKey, cert, nil
}