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
}