/*
   Copyright Docker attest authors

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
*/

package tlog

import (
	"context"
	"crypto/rand"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/pem"
	"fmt"
	"math/big"
	"time"

	"github.com/docker/attest/signerverifier"
	"github.com/secure-systems-lab/go-securesystemslib/dsse"
)

const (
	DefaultRekorURL = "https://rekor.sigstore.dev"
)

type TransparencyLog interface {
	UploadEntry(ctx context.Context, subject string, payload, signature []byte, signer dsse.SignerVerifier) (*DockerTLExtension, error)
	VerifyEntry(ctx context.Context, entry *DockerTLExtension, payload, publicKey []byte) (time.Time, error)
}

type Payload struct {
	Algorithm string
	Hash      string
	Signature string
	PublicKey string
}

type DockerTLExtension struct {
	Kind string `json:"kind"`
	Data any    `json:"data"`
}

// CreateX509Cert generates a self-signed x509 cert for TL submission.
func CreateX509Cert(subject string, signer dsse.SignerVerifier) ([]byte, error) {
	// encode ephemeral public key
	ecPub, err := x509.MarshalPKIXPublicKey(signer.Public())
	if err != nil {
		return nil, fmt.Errorf("error marshaling public key: %w", err)
	}

	template := x509.Certificate{
		SerialNumber:            big.NewInt(1),
		Subject:                 pkix.Name{CommonName: subject},
		RawSubjectPublicKeyInfo: ecPub,
		NotBefore:               time.Now(),
		NotAfter:                time.Now().Add(365 * 24 * time.Hour), // valid for 1 year
		KeyUsage:                x509.KeyUsageDigitalSignature,
		ExtKeyUsage:             []x509.ExtKeyUsage{x509.ExtKeyUsageCodeSigning},
		BasicConstraintsValid:   true,
		DNSNames:                []string{subject},
		IsCA:                    false,
	}

	// dsse.SignerVerifier doesn't implement cypto.Signer exactly

	csigner, err := signerverifier.AsCryptoSigner(signer)
	if err != nil {
		return nil, fmt.Errorf("error converting signer to crypto.Signer: %w", err)
	}
	// create a self-signed X.509 certificate
	certDER, err := x509.CreateCertificate(rand.Reader, &template, &template, signer.Public(), csigner)
	if err != nil {
		return nil, fmt.Errorf("error creating X.509 certificate: %w", err)
	}
	certBlock := &pem.Block{Type: "CERTIFICATE", Bytes: certDER}
	return pem.EncodeToMemory(certBlock), nil
}