//
// Copyright 2022 The Sigstore 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 app

import (
	"crypto/x509"
	"fmt"
	"math/big"
	"os"
	"path/filepath"
	"strconv"
	"strings"

	"github.com/digitorus/timestamp"
	"github.com/sigstore/sigstore/pkg/cryptoutils"
	"github.com/sigstore/timestamp-authority/cmd/timestamp-cli/app/format"
	"github.com/sigstore/timestamp-authority/pkg/log"
	"github.com/sigstore/timestamp-authority/pkg/verification"
	"github.com/spf13/cobra"
	"github.com/spf13/viper"
)

type verifyCmdOutput struct {
	TimestampPath   string
	ParsedTimestamp timestamp.Timestamp
}

func (v *verifyCmdOutput) String() string {
	return fmt.Sprintf("Successfully verified timestamp %s", v.TimestampPath)
}

func addVerifyFlags(cmd *cobra.Command) {
	cmd.Flags().Var(NewFlagValue(fileFlag, ""), "artifact", "path to an blob with signed data")
	cmd.MarkFlagRequired("artifact") //nolint:errcheck
	cmd.Flags().Var(NewFlagValue(fileFlag, ""), "timestamp", "path to timestamp response to verify")
	cmd.MarkFlagRequired("timestamp") //nolint:errcheck
	cmd.Flags().Var(NewFlagValue(fileFlag, ""), "certificate-chain", "path to file with PEM-encoded certificate chain. Ordered from intermediate CA certificate that issued the TSA certificate, ending with the root CA certificate.")
	cmd.Flags().String("nonce", "", "optional nonce passed with the request")
	cmd.Flags().Var(NewFlagValue(oidFlag, ""), "oid", "optional TSA policy OID passed with the request")
	cmd.Flags().String("common-name", "", "expected leaf certificate subject common name")
	cmd.Flags().Var(NewFlagValue(fileFlag, ""), "certificate", "path to file with PEM-encoded leaf certificate")
	cmd.Flags().Var(NewFlagValue(fileFlag, ""), "intermediate-certificates", "path to file with PEM-encoded intermediate certificates. Must be called with the root-certificate flag.")
	cmd.Flags().Var(NewFlagValue(fileFlag, ""), "root-certificates", "path to file with a PEM-encoded root certificates. Optionally can be called with the intermediate-certificates flag.")
}

var verifyCmd = &cobra.Command{
	Use:   "verify",
	Short: "Verify timestamp",
	Long:  "Verify the timestamp response using a timestamp certificate chain.",
	PreRunE: func(cmd *cobra.Command, _ []string) error {
		if err := viper.BindPFlags(cmd.Flags()); err != nil {
			log.CliLogger.Fatal("Error initializing cmd line args: ", err)
		}
		return nil
	},
	Run: format.WrapCmd(func(_ []string) (interface{}, error) {
		return runVerify()
	}),
}

func runVerify() (interface{}, error) {
	tsrPath := viper.GetString("timestamp")
	tsrBytes, err := os.ReadFile(filepath.Clean(tsrPath))
	if err != nil {
		return nil, fmt.Errorf("error reading request from file: %w", err)
	}

	artifactPath := viper.GetString("artifact")
	artifact, err := os.Open(filepath.Clean(artifactPath))
	if err != nil {
		return nil, err
	}

	opts, err := newVerifyOpts()
	if err != nil {
		return verifyCmdOutput{TimestampPath: tsrPath}, fmt.Errorf("failed to created VerifyOpts: %w", err)
	}

	ts, err := verification.VerifyTimestampResponse(tsrBytes, artifact, opts)
	if err != nil {
		return verifyCmdOutput{TimestampPath: tsrPath}, fmt.Errorf("failed to verify timestamp: %w", err)
	}

	return &verifyCmdOutput{TimestampPath: tsrPath, ParsedTimestamp: *ts}, nil
}

func newVerifyOpts() (verification.VerifyOpts, error) {
	opts := verification.VerifyOpts{}

	oid, err := getOID()
	if err != nil {
		return verification.VerifyOpts{}, fmt.Errorf("failed to parse value from oid flag: %w", err)
	}
	opts.OID = oid

	certPathFlagVal := viper.GetString("certificate")
	if certPathFlagVal != "" {
		cert, err := parseTSACertificate(certPathFlagVal)
		if err != nil {
			return verification.VerifyOpts{}, fmt.Errorf("failed to parse cert flag value from PEM file: %w", err)
		}
		opts.TSACertificate = cert
	}

	roots, intermediates, err := getRootAndIntermediateCerts()
	if err != nil {
		return verification.VerifyOpts{}, fmt.Errorf("failed to parse root and intermediate certs from certificate-chain flag: %w", err)
	}
	opts.Roots = roots
	opts.Intermediates = intermediates

	nonce, err := getNonce()
	if err != nil {
		return verification.VerifyOpts{}, fmt.Errorf("failed to parse value from nonce flag: %w", err)
	}
	opts.Nonce = nonce

	commonNameFlagVal := viper.GetString("common-name")
	opts.CommonName = commonNameFlagVal

	return opts, nil
}

func getNonce() (*big.Int, error) {
	nonceFlagVal := viper.GetString("nonce")
	if nonceFlagVal == "" {
		return nil, nil
	}

	nonce := new(big.Int)
	nonce, ok := nonce.SetString(nonceFlagVal, 10)
	if !ok {
		return nil, fmt.Errorf("failed to convert string to big.Int")
	}
	return nonce, nil
}

func getRootAndIntermediateCerts() ([]*x509.Certificate, []*x509.Certificate, error) {
	certChainPEM := viper.GetString("certificate-chain")
	rootPEM := viper.GetString("root-certificates")
	intermediatePEM := viper.GetString("intermediate-certificates")

	// the verify flag must be called with either one of the two flag combinations:
	// 1. Called with the --root-certificates flag and optionally the --intermediate-certificates flag
	// 2. Called with only the --certificate-chain flag

	// this early exit if statement is only entered if neither of those combinations is valid
	if !((rootPEM != "" && certChainPEM == "") || (intermediatePEM == "" && rootPEM == "" && certChainPEM != "")) {
		return nil, nil, fmt.Errorf("the verify command must be called with either only the --certificate-chain flag or with the --root-certificates and --intermediate-certificates flags")
	}

	// return root and intermediate certificates when they've been passed
	// together with the certificate-chain flag
	if certChainPEM != "" {
		pemBytes, err := os.ReadFile(filepath.Clean(certChainPEM))
		if err != nil {
			return nil, nil, fmt.Errorf("error reading request from file: %w", err)
		}

		certs, err := cryptoutils.UnmarshalCertificatesFromPEM(pemBytes)
		if err != nil {
			return nil, nil, fmt.Errorf("failed to parse intermediate and root certs from PEM file: %w", err)
		}

		if len(certs) == 0 {
			return nil, nil, fmt.Errorf("expected at least one certificate to represent the root")
		}

		// intermediate certs are above the root certificate in the PEM file
		intermediateCerts := certs[0 : len(certs)-1]
		// the root certificate is last in the PEM file
		rootCerts := []*x509.Certificate{certs[len(certs)-1]}

		return rootCerts, intermediateCerts, nil
	}

	// return root and intermediate certificates when they've been passed
	// separately with the root-certificate and intermediate-certificates flags
	rootPEMBytes, err := os.ReadFile(filepath.Clean(rootPEM))
	if err != nil {
		return nil, nil, fmt.Errorf("error reading request from file: %w", err)
	}

	rootCerts, err := cryptoutils.UnmarshalCertificatesFromPEM(rootPEMBytes)
	if err != nil {
		return nil, nil, fmt.Errorf("failed to parse intermediate and root certs from PEM file: %w", err)
	}

	if len(rootCerts) == 0 {
		return nil, nil, fmt.Errorf("expected at least one certificate to represent the root")
	}

	if intermediatePEM == "" {
		return rootCerts, []*x509.Certificate{}, nil
	}

	// parse intermediate certificates
	intermediatePEMBytes, err := os.ReadFile(filepath.Clean(intermediatePEM))
	if err != nil {
		return nil, nil, fmt.Errorf("error reading request from file: %w", err)
	}

	intermediateCerts, err := cryptoutils.UnmarshalCertificatesFromPEM(intermediatePEMBytes)
	if err != nil {
		return nil, nil, fmt.Errorf("failed to parse intermediate and root certs from PEM file: %w", err)
	}

	if len(intermediateCerts) == 0 {
		return nil, nil, fmt.Errorf("expected at least one intermediate certificate")
	}

	return rootCerts, intermediateCerts, nil
}

func getOID() ([]int, error) {
	oidFlagVal := viper.GetString("oid")
	if oidFlagVal == "" {
		return nil, nil
	}

	oidStrSlice := strings.Split(oidFlagVal, ".")
	oid := make([]int, len(oidStrSlice))
	for i, el := range oidStrSlice {
		intVar, err := strconv.Atoi(el)
		if err != nil {
			return nil, err
		}
		oid[i] = intVar
	}

	return oid, nil
}

func parseTSACertificate(certPath string) (*x509.Certificate, error) {
	pemBytes, err := os.ReadFile(filepath.Clean(certPath))
	if err != nil {
		return nil, fmt.Errorf("error reading TSA's certificate file: %w", err)
	}

	certs, err := cryptoutils.UnmarshalCertificatesFromPEM(pemBytes)
	if err != nil {
		return nil, fmt.Errorf("failed to parse TSA certificate during verification: %w", err)
	}
	if len(certs) != 1 {
		return nil, fmt.Errorf("expected one certificate, received %d instead", len(certs))
	}

	return certs[0], nil
}

func init() {
	initializePFlagMap()
	addVerifyFlags(verifyCmd)
	rootCmd.AddCommand(verifyCmd)
}