// Package quicutil provides convenience functions that generate self-signed
// certificates for QUIC connections that don't require PKI, such as trusted
// connections over a local network, or connections where a different
// verification mechanism is used.
//
// Do not use this for applications where PKI is needed, such as for public
// websites!
package quicutil

import (
	"context"
	"crypto/ed25519"
	"crypto/rand"
	"crypto/tls"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/pem"
	"math/big"
	"net"
	"time"

	"github.com/quic-go/quic-go"
)

// Listen generates a new self-signed certificate and then listens
// for QUIC connections on a given net.PacketConn.
func Listen(conn net.PacketConn, config *quic.Config) (*quic.Listener, error) {
	tlsConf, err := GenerateSelfSignedCert()
	if err != nil {
		return nil, err
	}
	return quic.Listen(conn, tlsConf, config)
}

// ListenAddr generates a new self-signed certificate and then listens
// for QUIC connections on a given address.
func ListenAddr(addr string, config *quic.Config) (*quic.Listener, error) {
	tlsConf, err := GenerateSelfSignedCert()
	if err != nil {
		return nil, err
	}
	return quic.ListenAddr(addr, tlsConf, config)
}

// DialAddr establishes a new insecure QUIC connection to a server using a net.PacketConn.
func Dial(ctx context.Context, conn net.PacketConn, addr net.Addr, config *quic.Config) (quic.Connection, error) {
	return quic.Dial(ctx, conn, addr, &tls.Config{InsecureSkipVerify: true}, config)
}

// DialAddr establishes a new insecure QUIC connection to a server.
func DialAddr(ctx context.Context, addr string, config *quic.Config) (quic.Connection, error) {
	return quic.DialAddr(ctx, addr, &tls.Config{InsecureSkipVerify: true}, config)
}

// GenerateSelfSignedCert generates a new self-signed Ed25519 TLS certificate.
func GenerateSelfSignedCert() (*tls.Config, error) {
	// Generate a new Ed25519 key
	pubkey, privkey, err := ed25519.GenerateKey(rand.Reader)
	if err != nil {
		return nil, err
	}

	// Generate a self-signed certificate template
	certTemplate := x509.Certificate{
		SerialNumber: big.NewInt(1),
		Subject: pkix.Name{
			Organization: []string{"Self-Signed Certificate"},
		},
		NotBefore:             time.Now(),
		NotAfter:              time.Date(9999, time.December, 31, 23, 59, 0, 0, time.UTC), // Valid until 31 December 9999 23:59 UTC
		KeyUsage:              x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature,
		ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
		BasicConstraintsValid: true,
	}

	// Generate the certificate
	certDER, err := x509.CreateCertificate(rand.Reader, &certTemplate, &certTemplate, pubkey, privkey)
	if err != nil {
		return nil, err
	}

	// Convert private key to PKCS #8 form
	keyData, err := x509.MarshalPKCS8PrivateKey(privkey)
	if err != nil {
		return nil, err
	}

	// Create PEM-encoded certificate and private key blocks
	certPEM := pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: certDER})
	keyPEM := pem.EncodeToMemory(&pem.Block{Type: "ED25519 PRIVATE KEY", Bytes: keyData})

	// Create a new TLS certificate and key pair from the PEM-encoded data
	tlsCert, err := tls.X509KeyPair(certPEM, keyPEM)
	if err != nil {
		return nil, err
	}

	// Create and configure a TLS config
	tlsConfig := &tls.Config{
		Certificates: []tls.Certificate{tlsCert},
	}

	return tlsConfig, nil
}