/*
   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/rand"
	"fmt"

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

type ecdsaVerifier struct {
	publicKey *ecdsa.PublicKey
	keyID     string
}

// ensure ECDSAVerifier implements dsse.Verifier.
var _ dsse.Verifier = (*ecdsaVerifier)(nil)

func NewECDSAVerifier(publicKey crypto.PublicKey) (dsse.Verifier, error) {
	ecdsaPublicKey, ok := (publicKey).(*ecdsa.PublicKey)
	if !ok {
		return nil, fmt.Errorf("public key is not an ECDSA public key")
	}
	return &ecdsaVerifier{
		publicKey: ecdsaPublicKey,
	}, nil
}

func (v *ecdsaVerifier) Verify(_ context.Context, data, signature []byte) error {
	// verify payload ecdsa signature
	ok := ecdsa.VerifyASN1(v.publicKey, util.SHA256(data), signature)
	if !ok {
		return fmt.Errorf("payload signature is not valid")
	}

	return nil
}

func (v *ecdsaVerifier) Public() crypto.PublicKey {
	return v.publicKey
}

func (v *ecdsaVerifier) KeyID() (string, error) {
	if v.keyID != "" {
		return v.keyID, nil
	}
	keyID, err := KeyID(v.publicKey)
	if err != nil {
		return "", fmt.Errorf("failed to get key ID: %w", err)
	}
	v.keyID = keyID
	return v.keyID, nil
}

// must implement dsse.SignerVerifier interface.
var _ dsse.SignerVerifier = (*ecdsa256SignerVerifier)(nil)

type ecdsa256SignerVerifier struct {
	signer crypto.Signer
	dsse.Verifier
}

func NewECDSASignerVerifier(signer crypto.Signer) (dsse.SignerVerifier, error) {
	verifier, err := NewECDSAVerifier(signer.Public())
	if err != nil {
		return nil, fmt.Errorf("failed to create verifier: %w", err)
	}
	sv := &ecdsa256SignerVerifier{
		signer:   signer,
		Verifier: verifier,
	}
	return sv, nil
}

func (s *ecdsa256SignerVerifier) Sign(_ context.Context, data []byte) ([]byte, error) {
	return s.signer.Sign(rand.Reader, data, crypto.SHA256)
}