/*
Copyright Suzhou Tongji Fintech Research Institute 2017 All Rights Reserved.
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 sm2

import (
	"encoding/pem"
	"errors"
	"io/ioutil"
	"os"
	"runtime"
	"sync"
)

// Possible certificate files; stop after finding one.
var certFiles = []string{
	"/etc/ssl/certs/ca-certificates.crt",                // Debian/Ubuntu/Gentoo etc.
	"/etc/pki/tls/certs/ca-bundle.crt",                  // Fedora/RHEL 6
	"/etc/ssl/ca-bundle.pem",                            // OpenSUSE
	"/etc/pki/tls/cacert.pem",                           // OpenELEC
	"/etc/pki/ca-trust/extracted/pem/tls-ca-bundle.pem", // CentOS/RHEL 7
}

// CertPool is a set of certificates.
type CertPool struct {
	bySubjectKeyId map[string][]int
	byName         map[string][]int
	certs          []*Certificate
}

// NewCertPool returns a new, empty CertPool.
func NewCertPool() *CertPool {
	return &CertPool{
		bySubjectKeyId: make(map[string][]int),
		byName:         make(map[string][]int),
	}
}

// Possible directories with certificate files; stop after successfully
// reading at least one file from a directory.
var certDirectories = []string{
	"/etc/ssl/certs",               // SLES10/SLES11, https://golang.org/issue/12139
	"/system/etc/security/cacerts", // Android
}

var (
	once           sync.Once
	systemRoots    *CertPool
	systemRootsErr error
)

func systemRootsPool() *CertPool {
	once.Do(initSystemRoots)
	return systemRoots
}

func initSystemRoots() {
	systemRoots, systemRootsErr = loadSystemRoots()
}

func (c *Certificate) systemVerify(opts *VerifyOptions) (chains [][]*Certificate, err error) {
	return nil, nil
}

func loadSystemRoots() (*CertPool, error) {
	roots := NewCertPool()
	var firstErr error
	for _, file := range certFiles {
		data, err := ioutil.ReadFile(file)
		if err == nil {
			roots.AppendCertsFromPEM(data)
			return roots, nil
		}
		if firstErr == nil && !os.IsNotExist(err) {
			firstErr = err
		}
	}

	for _, directory := range certDirectories {
		fis, err := ioutil.ReadDir(directory)
		if err != nil {
			if firstErr == nil && !os.IsNotExist(err) {
				firstErr = err
			}
			continue
		}
		rootsAdded := false
		for _, fi := range fis {
			data, err := ioutil.ReadFile(directory + "/" + fi.Name())
			if err == nil && roots.AppendCertsFromPEM(data) {
				rootsAdded = true
			}
		}
		if rootsAdded {
			return roots, nil
		}
	}

	return nil, firstErr
}

// SystemCertPool returns a copy of the system cert pool.
//
// Any mutations to the returned pool are not written to disk and do
// not affect any other pool.
func SystemCertPool() (*CertPool, error) {
	if runtime.GOOS == "windows" {
		// Issue 16736, 18609:
		return nil, errors.New("crypto/x509: system root pool is not available on Windows")
	}

	return loadSystemRoots()
}

// findVerifiedParents attempts to find certificates in s which have signed the
// given certificate. If any candidates were rejected then errCert will be set
// to one of them, arbitrarily, and err will contain the reason that it was
// rejected.
func (s *CertPool) findVerifiedParents(cert *Certificate) (parents []int, errCert *Certificate, err error) {
	if s == nil {
		return
	}
	var candidates []int

	if len(cert.AuthorityKeyId) > 0 {
		candidates = s.bySubjectKeyId[string(cert.AuthorityKeyId)]
	}
	if len(candidates) == 0 {
		candidates = s.byName[string(cert.RawIssuer)]
	}

	for _, c := range candidates {
		if err = cert.CheckSignatureFrom(s.certs[c]); err == nil {
			parents = append(parents, c)
		} else {
			errCert = s.certs[c]
		}
	}

	return
}

func (s *CertPool) contains(cert *Certificate) bool {
	if s == nil {
		return false
	}

	candidates := s.byName[string(cert.RawSubject)]
	for _, c := range candidates {
		if s.certs[c].Equal(cert) {
			return true
		}
	}

	return false
}

// AddCert adds a certificate to a pool.
func (s *CertPool) AddCert(cert *Certificate) {
	if cert == nil {
		panic("adding nil Certificate to CertPool")
	}

	// Check that the certificate isn't being added twice.
	if s.contains(cert) {
		return
	}

	n := len(s.certs)
	s.certs = append(s.certs, cert)

	if len(cert.SubjectKeyId) > 0 {
		keyId := string(cert.SubjectKeyId)
		s.bySubjectKeyId[keyId] = append(s.bySubjectKeyId[keyId], n)
	}
	name := string(cert.RawSubject)
	s.byName[name] = append(s.byName[name], n)
}

// AppendCertsFromPEM attempts to parse a series of PEM encoded certificates.
// It appends any certificates found to s and reports whether any certificates
// were successfully parsed.
//
// On many Linux systems, /etc/ssl/cert.pem will contain the system wide set
// of root CAs in a format suitable for this function.
func (s *CertPool) AppendCertsFromPEM(pemCerts []byte) (ok bool) {
	for len(pemCerts) > 0 {
		var block *pem.Block
		block, pemCerts = pem.Decode(pemCerts)
		if block == nil {
			break
		}
		if block.Type != "CERTIFICATE" || len(block.Headers) != 0 {
			continue
		}

		cert, err := ParseCertificate(block.Bytes)
		if err != nil {
			continue
		}

		s.AddCert(cert)
		ok = true
	}

	return
}

// Subjects returns a list of the DER-encoded subjects of
// all of the certificates in the pool.
func (s *CertPool) Subjects() [][]byte {
	res := make([][]byte, len(s.certs))
	for i, c := range s.certs {
		res[i] = c.RawSubject
	}
	return res
}