// Package nebula contains helper functions and types which are useful for
// setting up nebula configs, processes, and deployments.
package nebula

import (
	"crypto/rand"
	"fmt"
	"io"
	"net"
	"time"

	"github.com/slackhq/nebula/cert"
	"golang.org/x/crypto/curve25519"
)

// HostPublicCredentials contains certificate and signing public keys which are
// able to be broadcast publicly.
type HostPublicCredentials struct {
	CertPEM    string
	SigningKey SigningPublicKey
}

// HostPrivateCredentials contains the private key files which will
// need to be present on a particular host.
type HostPrivateCredentials struct {
	PrivateKeyPEM     string
	SigningPrivateKey SigningPrivateKey
}

// CAPublicCredentials contains certificate and signing public keys which are
// able to be broadcast publicly. The signing public key is the same one which
// is embedded into the certificate.
type CAPublicCredentials struct {
	CertPEM    string
	SigningKey SigningPublicKey
}

// CACredentials contains the certificate and private files which can be used to
// create and validate HostCredentials. Each file is PEM encoded.
type CACredentials struct {
	Public            CAPublicCredentials
	SigningPrivateKey SigningPrivateKey
}

// NewHostCertPEM generates and signs a new host certificate containing the
// given public key.
func NewHostCertPEM(
	caCreds CACredentials, hostPubPEM string, hostName string, ip net.IP,
) (
	string, error,
) {
	hostPub, _, err := cert.UnmarshalX25519PublicKey([]byte(hostPubPEM))
	if err != nil {
		return "", fmt.Errorf("unmarshaling public key PEM: %w", err)
	}

	caCert, _, err := cert.UnmarshalNebulaCertificateFromPEM([]byte(caCreds.Public.CertPEM))
	if err != nil {
		return "", fmt.Errorf("unmarshaling ca.crt: %w", err)
	}

	issuer, err := caCert.Sha256Sum()
	if err != nil {
		return "", fmt.Errorf("getting ca.crt issuer: %w", err)
	}

	expireAt := caCert.Details.NotAfter.Add(-1 * time.Second)

	subnet := caCert.Details.Subnets[0]
	if !subnet.Contains(ip) {
		return "", fmt.Errorf("invalid ip %q, not contained by network subnet %q", ip, subnet)
	}

	hostCert := cert.NebulaCertificate{
		Details: cert.NebulaCertificateDetails{
			Name: hostName,
			Ips: []*net.IPNet{{
				IP:   ip,
				Mask: subnet.Mask,
			}},
			NotBefore: time.Now(),
			NotAfter:  expireAt,
			PublicKey: hostPub,
			IsCA:      false,
			Issuer:    issuer,
		},
	}

	if err := hostCert.CheckRootConstrains(caCert); err != nil {
		return "", fmt.Errorf("validating certificate constraints: %w", err)
	}

	if err := signCert(&hostCert, caCreds.SigningPrivateKey); err != nil {
		return "", fmt.Errorf("signing host cert with ca.key: %w", err)
	}

	hostCertPEM, err := hostCert.MarshalToPEM()
	if err != nil {
		return "", fmt.Errorf("marshalling host.crt: %w", err)
	}

	return string(hostCertPEM), nil
}

// NewHostCredentials generates a new key/cert for a nebula host using the CA
// key which will be found in the adminFS.
func NewHostCredentials(
	caCreds CACredentials, hostName string, ip net.IP,
) (
	pub HostPublicCredentials, priv HostPrivateCredentials, err error,
) {

	// The logic here is largely based on
	// https://github.com/slackhq/nebula/blob/v1.4.0/cmd/nebula-cert/sign.go

	var hostPub, hostKey []byte
	{
		var pubkey, privkey [32]byte
		if _, err = io.ReadFull(rand.Reader, privkey[:]); err != nil {
			err = fmt.Errorf("reading random bytes to form private key: %w", err)
			return
		}
		curve25519.ScalarBaseMult(&pubkey, &privkey)
		hostPub, hostKey = pubkey[:], privkey[:]
	}

	signingPubKey, signingPrivKey := GenerateSigningPair()

	hostPubPEM := cert.MarshalX25519PublicKey(hostPub)
	hostKeyPEM := cert.MarshalX25519PrivateKey(hostKey)

	hostCertPEM, err := NewHostCertPEM(caCreds, string(hostPubPEM), hostName, ip)
	if err != nil {
		err = fmt.Errorf("creating host certificate: %w", err)
		return
	}

	pub = HostPublicCredentials{
		CertPEM:    hostCertPEM,
		SigningKey: signingPubKey,
	}

	priv = HostPrivateCredentials{
		PrivateKeyPEM:     string(hostKeyPEM),
		SigningPrivateKey: signingPrivKey,
	}

	return
}

// NewCACredentials generates a CACredentials. The domain should be the network's root domain,
// and is included in the signing certificate's Name field.
func NewCACredentials(domain string, subnet *net.IPNet) (CACredentials, error) {

	// The logic here is largely based on
	// https://github.com/slackhq/nebula/blob/v1.4.0/cmd/nebula-cert/ca.go

	signingPubKey, signingPrivKey := GenerateSigningPair()

	now := time.Now()
	expireAt := now.Add(2 * 365 * 24 * time.Hour)

	caCert := cert.NebulaCertificate{
		Details: cert.NebulaCertificateDetails{
			Name:      fmt.Sprintf("%s isle root cert", domain),
			Subnets:   []*net.IPNet{subnet},
			NotBefore: now,
			NotAfter:  expireAt,
			PublicKey: signingPubKey,
			IsCA:      true,
		},
	}

	if err := signCert(&caCert, signingPrivKey); err != nil {
		return CACredentials{}, fmt.Errorf("signing caCert: %w", err)
	}

	certPEM, err := caCert.MarshalToPEM()
	if err != nil {
		return CACredentials{}, fmt.Errorf("marshaling caCert: %w", err)
	}

	return CACredentials{
		Public: CAPublicCredentials{
			CertPEM:    string(certPEM),
			SigningKey: signingPubKey,
		},
		SigningPrivateKey: signingPrivKey,
	}, nil
}

// IPFromHostCertPEM is a convenience function for parsing the IP of a host out
// of its nebula cert.
func IPFromHostCertPEM(hostCertPEM string) (net.IP, error) {

	hostCert, _, err := cert.UnmarshalNebulaCertificateFromPEM([]byte(hostCertPEM))
	if err != nil {
		return nil, fmt.Errorf("unmarshaling host certificate as PEM: %w", err)
	}

	ips := hostCert.Details.Ips
	if len(ips) == 0 {
		return nil, fmt.Errorf("malformed nebula host cert: no IPs")
	}

	return ips[0].IP, nil
}