//
// Copyright 2021 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 fulcioroots

import (
	"bytes"
	"crypto/x509"
	"fmt"
	"os"
	"sync"

	"github.com/sigstore/cosign/v3/pkg/cosign/env"
	"github.com/sigstore/sigstore/pkg/cryptoutils"
	"github.com/sigstore/sigstore/pkg/fulcioroots"
)

var (
	rootsOnce        sync.Once
	roots            *x509.CertPool
	intermediates    *x509.CertPool
	singletonRootErr error
)

// Get returns the Fulcio root certificate.
//
// If the SIGSTORE_ROOT_FILE environment variable is set, the root config found
// there will be used instead of the normal Fulcio roots.
func Get() (*x509.CertPool, error) {
	rootsOnce.Do(func() {
		roots, intermediates, singletonRootErr = initRoots()
	})
	return roots, singletonRootErr
}

// GetIntermediates returns the Fulcio intermediate certificates.
//
// If the SIGSTORE_ROOT_FILE environment variable is set, the root config found
// there will be used instead of the normal Fulcio intermediates.
func GetIntermediates() (*x509.CertPool, error) {
	rootsOnce.Do(func() {
		roots, intermediates, singletonRootErr = initRoots()
	})
	return intermediates, singletonRootErr
}

// ReInit reinitializes the global roots and intermediates, overriding the sync.Once lock.
// This is only to be used for tests, where the trust root environment variables may change after the roots are initialized in the module.
func ReInit() error {
	roots, intermediates, singletonRootErr = initRoots()
	return singletonRootErr
}

func initRoots() (*x509.CertPool, *x509.CertPool, error) {
	rootPool := x509.NewCertPool()
	// intermediatePool should be nil if no intermediates are found
	var intermediatePool *x509.CertPool

	rootEnv := env.Getenv(env.VariableSigstoreRootFile)
	if rootEnv != "" {
		raw, err := os.ReadFile(rootEnv)
		if err != nil {
			return nil, nil, fmt.Errorf("error reading root PEM file: %w", err)
		}
		certs, err := cryptoutils.UnmarshalCertificatesFromPEM(raw)
		if err != nil {
			return nil, nil, fmt.Errorf("error unmarshalling certificates: %w", err)
		}
		for _, cert := range certs {
			// root certificates are self-signed
			if bytes.Equal(cert.RawSubject, cert.RawIssuer) {
				rootPool.AddCert(cert)
			} else {
				if intermediatePool == nil {
					intermediatePool = x509.NewCertPool()
				}
				intermediatePool.AddCert(cert)
			}
		}
	} else {
		var err error
		rootPool, err = fulcioroots.Get()
		if err != nil {
			return nil, nil, err
		}
		intermediatePool, err = fulcioroots.GetIntermediates()
		if err != nil {
			return nil, nil, err
		}
	}
	return rootPool, intermediatePool, nil
}
