/*
   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 signerverifier

import (
	"context"
	"crypto"
	"crypto/ecdsa"
	"crypto/elliptic"
	"crypto/rand"
	"crypto/x509"
	"encoding/pem"
	"fmt"
	"io"

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

func LoadKeyPair(priv []byte) (dsse.SignerVerifier, error) {
	privateKey, err := parsePriv(priv)
	if err != nil {
		return nil, err
	}
	return NewECDSASignerVerifier(privateKey)
}

func parsePriv(privkeyBytes []byte) (*ecdsa.PrivateKey, error) {
	p, _ := pem.Decode(privkeyBytes)
	if p == nil {
		return nil, fmt.Errorf("privkey file does not contain any PEM data")
	}
	if p.Type != "EC PRIVATE KEY" {
		return nil, fmt.Errorf("privkey file does not contain a priavte key")
	}
	privKey, err := x509.ParseECPrivateKey(p.Bytes)
	if err != nil {
		return nil, fmt.Errorf("error failed to parse public key: %w", err)
	}

	return privKey, nil
}

func GenKeyPair() (dsse.SignerVerifier, error) {
	signer, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
	if err != nil {
		return nil, err
	}
	return NewECDSASignerVerifier(signer)
}

// ensure it implements crypto.Signer.
var _ crypto.Signer = (*cryptoSignerWrapper)(nil)

type cryptoSignerWrapper struct {
	sv dsse.SignerVerifier
}

// Public implements crypto.Signer.
func (c *cryptoSignerWrapper) Public() crypto.PublicKey {
	return c.sv.Public()
}

// Sign implements crypto.Signer.
func (c *cryptoSignerWrapper) Sign(_ io.Reader, digest []byte, _ crypto.SignerOpts) (signature []byte, err error) {
	return c.sv.Sign(context.Background(), digest)
}

func AsCryptoSigner(signer dsse.SignerVerifier) (crypto.Signer, error) {
	return &cryptoSignerWrapper{sv: signer}, nil
}