//
// Copyright (c) SAS Institute Inc.
//
// 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 appmanifest

import (
	"crypto"
	"crypto/x509"
	"encoding/base64"
	"errors"
	"fmt"

	"github.com/beevik/etree"
	"github.com/sassoftware/relic/lib/pkcs7"
	"github.com/sassoftware/relic/lib/pkcs9"
	"github.com/sassoftware/relic/lib/x509tools"
	"github.com/sassoftware/relic/lib/xmldsig"
	"github.com/sassoftware/relic/signers/sigerrors"
)

type ManifestSignature struct {
	Signature       *pkcs9.TimestampedSignature
	Hash            crypto.Hash
	AssemblyName    string
	AssemblyVersion string
	PublicKeyToken  string
}

// Extract and verify signature on an application manifest. Does not verify X509 chains.
func Verify(manifest []byte) (*ManifestSignature, error) {
	doc := etree.NewDocument()
	if err := doc.ReadFromString(string(manifest)); err != nil {
		return nil, err
	}
	root := doc.Root()
	primary, err := xmldsig.Verify(root, "Signature", nil)
	if err != nil {
		if _, ok := err.(sigerrors.NotSignedError); ok {
			return nil, err
		}
		return nil, fmt.Errorf("invalid primary signature: %w", err)
	}
	license := root.FindElement("Signature/KeyInfo/msrel:RelData/r:license")
	if license == nil {
		return nil, sigerrors.NotSignedError{Type: "application manifest"}
	}
	secondary, err := xmldsig.Verify(license, "issuer/Signature", nil)
	if err != nil {
		if _, ok := err.(sigerrors.NotSignedError); ok {
			return nil, err
		}
		return nil, fmt.Errorf("invalid authenticode signature: %w", err)
	}
	if !x509tools.SameKey(primary.PublicKey, secondary.PublicKey) {
		return nil, errors.New("signatures were made with different keys")
	}
	asi := root.SelectElement("assemblyIdentity")
	if asi == nil {
		return nil, errors.New("missing assemblyIdentity")
	}
	token, err := PublicKeyToken(primary.PublicKey)
	if err != nil {
		return nil, err
	}
	if token2 := asi.SelectAttrValue("publicKeyToken", ""); token2 != token {
		return nil, fmt.Errorf("publicKeyToken mismatch: expected %s, got %s", token, token2)
	}
	sig := pkcs7.Signature{Intermediates: secondary.Certificates, Certificate: secondary.Leaf()}
	if sig.Certificate == nil {
		return nil, errors.New("leaf x509 certificate not found")
	}
	ts := &pkcs9.TimestampedSignature{Signature: sig}
	if tse := license.FindElement("r:issuer/Signature/Object/as:Timestamp"); tse != nil {
		blob, err := base64.StdEncoding.DecodeString(tse.Text())
		if err != nil {
			return nil, fmt.Errorf("invalid timestamp: %w", err)
		}
		timestamp, err := pkcs7.Unmarshal(blob)
		if err != nil {
			return nil, fmt.Errorf("invalid timestamp: %w", err)
		}

		cs, err := VerifyTimestamp(timestamp, secondary.EncryptedDigest, secondary.Certificates)
		if err != nil {
			return nil, fmt.Errorf("invalid timestamp: %w", err)
		}
		ts.CounterSignature = cs
	}
	return &ManifestSignature{
		Signature:       ts,
		AssemblyName:    asi.SelectAttrValue("name", ""),
		AssemblyVersion: asi.SelectAttrValue("version", ""),
		Hash:            primary.Hash,
		PublicKeyToken:  token,
	}, nil
}

func VerifyTimestamp(timestamp *pkcs7.ContentInfoSignedData, encryptedDigest []byte, extraCerts []*x509.Certificate) (*pkcs9.CounterSignature, error) {
	var cs *pkcs9.CounterSignature
	var err error

	if timestamp.Content.ContentInfo.ContentType.Equal(pkcs9.OidTSTInfo) {
		// pkcs9 timestamp
		cs, err = pkcs9.Verify(timestamp, encryptedDigest, extraCerts)
	} else {
		// legacy timestamp
		cs, err = pkcs9.VerifyMicrosoftToken(timestamp, encryptedDigest)
	}

	return cs, err
}
