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

import (
	"fmt"
	"net"
	"net/netip"
	"time"

	"github.com/slackhq/nebula/cert"
)

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

// HostPrivateCredentials contains the private key files which will
// need to be present on a particular host.
type HostPrivateCredentials struct {
	EncryptingPrivateKey EncryptingPrivateKey
	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 {
	Cert       Certificate
	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
}

// NewHostCert generates and signs a new host certificate containing the given
// public key.
func NewHostCert(
	caCreds CACredentials,
	hostPub EncryptingPublicKey,
	hostName HostName,
	ip netip.Addr,
) (
	Certificate, error,
) {
	var (
		caCert  = caCreds.Public.Cert
		ipSlice = net.IP(ip.AsSlice())
	)

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

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

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

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

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

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

	return Certificate{hostCert}, 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 HostName, ip netip.Addr,
) (
	pub HostPublicCredentials, priv HostPrivateCredentials, err error,
) {

	var (
		encPrivKey = NewEncryptingPrivateKey()
		encPubKey  = encPrivKey.PublicKey()

		signingPubKey, signingPrivKey = GenerateSigningPair()
	)

	hostCert, err := NewHostCert(caCreds, encPubKey, hostName, ip)
	if err != nil {
		err = fmt.Errorf("creating host certificate: %w", err)
		return
	}

	pub = HostPublicCredentials{
		Cert:       hostCert,
		SigningKey: signingPubKey,
	}

	priv = HostPrivateCredentials{
		EncryptingPrivateKey: encPrivKey,
		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 IPNet) (CACredentials, error) {
	var (
		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{(*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)
	}

	return CACredentials{
		Public: CAPublicCredentials{
			Cert:       Certificate{caCert},
			SigningKey: signingPubKey,
		},
		SigningPrivateKey: signingPrivKey,
	}, nil
}