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

import (
	crypticnet "cryptic-net"
	"crypto/ed25519"
	"crypto/rand"
	"fmt"
	"io"
	"io/fs"
	"net"
	"time"

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

// TODO this should one day not be hardcoded
var ipCIDRMask = func() net.IPMask {
	_, ipNet, err := net.ParseCIDR("10.10.0.0/16")
	if err != nil {
		panic(err)
	}
	return ipNet.Mask
}()

// HostCert contains the certificate and private key files which will need to
// be present on a particular host. Each file is PEM encoded.
type HostCert struct {
	CACert   []byte
	HostKey  []byte
	HostCert []byte
}

// CACert contains the certificate and private files which can be used to create
// HostCerts. Each file is PEM encoded.
type CACert struct {
	CACert []byte
	CAKey  []byte
}

// NewHostCert generates a new key/cert for a nebula host using the CA key
// which will be found in the adminFS.
func NewHostCert(
	adminFS fs.FS, host crypticnet.NebulaHost,
) (
	HostCert, error,
) {

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

	caKeyPEM, err := fs.ReadFile(adminFS, "nebula/certs/ca.key")
	if err != nil {
		return HostCert{}, fmt.Errorf("reading ca.key from admin fs: %w", err)
	}

	caKey, _, err := cert.UnmarshalEd25519PrivateKey(caKeyPEM)
	if err != nil {
		return HostCert{}, fmt.Errorf("unmarshaling ca.key: %w", err)
	}

	caCrtPEM, err := fs.ReadFile(adminFS, "nebula/certs/ca.crt")
	if err != nil {
		return HostCert{}, fmt.Errorf("reading ca.crt from admin fs: %w", err)
	}

	caCrt, _, err := cert.UnmarshalNebulaCertificateFromPEM(caCrtPEM)
	if err != nil {
		return HostCert{}, fmt.Errorf("unmarshaling ca.crt: %w", err)
	}

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

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

	ip := net.ParseIP(host.IP)
	if ip == nil {
		return HostCert{}, fmt.Errorf("invalid host ip %q", host.IP)
	}

	ipNet := &net.IPNet{
		IP:   ip,
		Mask: ipCIDRMask,
	}

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

	hostCrt := cert.NebulaCertificate{
		Details: cert.NebulaCertificateDetails{
			Name:      host.Name,
			Ips:       []*net.IPNet{ipNet},
			NotBefore: time.Now(),
			NotAfter:  expireAt,
			PublicKey: hostPub,
			IsCA:      false,
			Issuer:    issuer,
		},
	}

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

	if err := hostCrt.Sign(caKey); err != nil {
		return HostCert{}, fmt.Errorf("signing host cert with ca.key: %w", err)
	}

	hostKeyPEM := cert.MarshalX25519PrivateKey(hostKey)

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

	return HostCert{
		CACert:   caCrtPEM,
		HostKey:  hostKeyPEM,
		HostCert: hostCrtPEM,
	}, nil
}

// NewCACert generates a CACert. The domain should be the network's root domain,
// and is included in the signing certificate's Name field.
func NewCACert(domain string) (CACert, error) {

	pubKey, privKey, err := ed25519.GenerateKey(rand.Reader)
	if err != nil {
		panic(fmt.Errorf("generating ed25519 key: %w", err))
	}

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

	caCrt := cert.NebulaCertificate{
		Details: cert.NebulaCertificateDetails{
			Name:      fmt.Sprintf("%s cryptic-net root cert", domain),
			NotBefore: now,
			NotAfter:  expireAt,
			PublicKey: pubKey,
			IsCA:      true,
		},
	}

	if err := caCrt.Sign(privKey); err != nil {
		return CACert{}, fmt.Errorf("signing caCrt: %w", err)
	}

	caKeyPEM := cert.MarshalEd25519PrivateKey(privKey)

	caCrtPem, err := caCrt.MarshalToPEM()
	if err != nil {
		return CACert{}, fmt.Errorf("marshaling caCrt: %w", err)
	}

	return CACert{
		CACert: caCrtPem,
		CAKey:  caKeyPEM,
	}, nil
}