/*
Copyright 2022 CAcert Inc.
SPDX-License-Identifier: Apache-2.0

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 config

import (
	"crypto"
	"crypto/elliptic"
	"crypto/x509"
	"crypto/x509/pkix"
	"errors"
	"fmt"
	"io"
	"path"
	"strings"
	"time"

	"gopkg.in/yaml.v3"

	"git.cacert.org/cacert-gosigner/internal/x509/openssl"
	"git.cacert.org/cacert-gosigner/internal/x509/revoking"
	"git.cacert.org/cacert-gosigner/internal/x509/signing"
)

const minRSABits = 2048

type Serial struct {
	Device  string
	Baud    int
	Timeout time.Duration
}

type Settings struct {
	Organization  *pkix.Name
	ValidityYears struct {
		Root, Subordinate int
	}
	URLPatterns struct {
		Ocsp, CRL, Issuer string
	}
	Serial *Serial
}

type SettingsError struct {
	msg string
}

func (se SettingsError) Error() string {
	return fmt.Sprintf("invalid Settings %s", se.msg)
}

func (s *Settings) UnmarshalYAML(n *yaml.Node) error {
	data := struct {
		Organization struct {
			Country       []string `yaml:"country"`
			Organization  []string `yaml:"organization"`
			Locality      []string `yaml:"locality"`
			StreetAddress []string `yaml:"street-address"`
			PostalCode    []string `yaml:"postal-code"`
		} `yaml:"organization"`
		ValidityYears struct {
			Root        int `yaml:"root"`
			Subordinate int `yaml:"subordinate"`
		} `yaml:"validity-years"`
		URLPatterns struct {
			Ocsp   string `yaml:"ocsp"`
			CRL    string `yaml:"crl"`
			Issuer string `yaml:"issuer"`
		} `yaml:"url-patterns"`
		Serial struct {
			Device        string `yaml:"device"`
			Baud          int    `yaml:"baud"`
			TimeoutMillis int    `yaml:"timeout-millis"`
		} `yaml:"serial"`
	}{}

	err := n.Decode(&data)
	if err != nil {
		return fmt.Errorf("could not decode YAML: %w", err)
	}

	if data.Organization.Organization == nil {
		return SettingsError{"you need to specify 'organization'"}
	}

	if data.ValidityYears.Root == 0 || data.ValidityYears.Subordinate == 0 {
		return SettingsError{"you must specify validity years for 'root' and 'subordinate'"}
	}

	if data.ValidityYears.Root < data.ValidityYears.Subordinate {
		return SettingsError{"validity of root CA certificates must be equal or greater than those of" +
			" subordinate CA certificates"}
	}

	if data.URLPatterns.Ocsp == "" {
		return SettingsError{"you must specify an 'ocsp' URL pattern"}
	}

	if strings.Count(data.URLPatterns.Ocsp, "%s") > 1 {
		return SettingsError{"url-pattern 'ocsp' must contain zero or one '%s' placeholder"}
	}

	if data.URLPatterns.CRL == "" {
		return SettingsError{"you must specify an 'crl' URL pattern"}
	}

	if strings.Count(data.URLPatterns.CRL, "%s") != 1 {
		return SettingsError{"url-pattern 'crl' must contain one '%s' placeholder"}
	}

	if data.URLPatterns.Issuer == "" {
		return SettingsError{"you must specify an 'issuer' URL pattern"}
	}

	if strings.Count(data.URLPatterns.Issuer, "%s") != 1 {
		return SettingsError{"url-pattern 'issuer' must contain one '%s' placeholder"}
	}

	if data.Serial.Device == "" {
		return SettingsError{"you must specify a serial 'device'"}
	}

	if data.Serial.Baud == 0 {
		data.Serial.Baud = 115200
	}

	if data.Serial.TimeoutMillis == 0 {
		data.Serial.TimeoutMillis = 5000
	}

	s.Organization = &pkix.Name{}
	s.Organization.Organization = data.Organization.Organization
	s.Organization.Country = data.Organization.Country
	s.Organization.Locality = data.Organization.Locality
	s.Organization.StreetAddress = data.Organization.StreetAddress
	s.Organization.PostalCode = data.Organization.PostalCode

	s.ValidityYears.Root = data.ValidityYears.Root
	s.ValidityYears.Subordinate = data.ValidityYears.Subordinate

	s.URLPatterns.Ocsp = data.URLPatterns.Ocsp
	s.URLPatterns.CRL = data.URLPatterns.CRL
	s.URLPatterns.Issuer = data.URLPatterns.Issuer

	s.Serial = &Serial{
		Device:  data.Serial.Device,
		Baud:    data.Serial.Baud,
		Timeout: time.Duration(data.Serial.TimeoutMillis) * time.Millisecond,
	}

	return nil
}

type KeyStorage struct {
	Label  string
	Module string
}

func (k *KeyStorage) UnmarshalYAML(n *yaml.Node) error {
	ks := struct {
		TokenType string `yaml:"type"`
		Label     string `yaml:"label"`
		Module    string `yaml:"module"`
	}{}

	err := n.Decode(&ks)
	if err != nil {
		return fmt.Errorf("could not decode YAML: %w", err)
	}

	switch ks.TokenType {
	case "softhsm":
		k.Module = SoftHsmModule
	case "p11module":
		if ks.Module == "" {
			return errors.New("specify a 'module' field when using the 'p11module' type")
		}

		k.Module = ks.Module
	default:
		return fmt.Errorf("unsupported KeyStorage type '%s'", ks.TokenType)
	}

	if ks.Label == "" {
		return errors.New("element 'label' must be specified")
	}

	k.Label = ks.Label

	return nil
}

type CARepository interface {
	revoking.Repository
	signing.Repository
}

type SignerConfig struct {
	global       *Settings                      `yaml:"Settings"`
	caMap        map[string]*CaCertificateEntry `yaml:"CAs"`
	keyStorage   map[string]*KeyStorage         `yaml:"KeyStorage"`
	repositories map[string]CARepository
}

func (c *SignerConfig) GetCADefinition(label string) (*CaCertificateEntry, error) {
	entry, ok := c.caMap[label]
	if !ok {
		return nil, fmt.Errorf("no CA definition found for label %s", label)
	}

	return entry, nil
}

func (c *SignerConfig) CalculateValidity(cert *CaCertificateEntry, relativeTo time.Time) (time.Time, time.Time) {
	var notBefore, notAfter time.Time
	notBefore = relativeTo

	if cert.IsRoot() {
		notAfter = notBefore.AddDate(c.global.ValidityYears.Root, 0, 0)
	} else {
		notAfter = notBefore.AddDate(c.global.ValidityYears.Subordinate, 0, 0)
	}

	return notBefore, notAfter
}

func (c *SignerConfig) CalculateSubject(cert *CaCertificateEntry) pkix.Name {
	subject := pkix.Name{
		Country:       c.global.Organization.Country,
		Organization:  c.global.Organization.Organization,
		Locality:      c.global.Organization.Locality,
		StreetAddress: c.global.Organization.StreetAddress,
		PostalCode:    c.global.Organization.PostalCode,
	}
	subject.CommonName = cert.CommonName

	return subject
}

func (c *SignerConfig) CertificateFileName(label string) string {
	return fmt.Sprintf("%s.crt", label)
}

func (c *SignerConfig) BuildIssuerURL(cert *CaCertificateEntry) string {
	return fmt.Sprintf(c.global.URLPatterns.Issuer, cert.Parent)
}

func (c *SignerConfig) BuildOCSPURL(cert *CaCertificateEntry) string {
	// in case the configuration specifies a placeholder
	if strings.Count(c.global.URLPatterns.Ocsp, "%s") == 1 {
		return fmt.Sprintf(c.global.URLPatterns.Ocsp, cert.Parent)
	}

	return c.global.URLPatterns.Ocsp
}

func (c *SignerConfig) BuildCRLUrl(label string) string {
	return fmt.Sprintf(c.global.URLPatterns.CRL, label)
}

func (c *SignerConfig) GetParentCA(label string) (*CaCertificateEntry, error) {
	entry, ok := c.caMap[label]
	if !ok {
		return nil, fmt.Errorf("no CA definition for %s", label)
	}

	if entry.IsRoot() {
		return nil, fmt.Errorf("CA %s is a root CA and has no parent", label)
	}

	if entry.Parent == "" {
		return nil, fmt.Errorf("parent for %s is empty", label)
	}

	parent, ok := c.caMap[entry.Parent]
	if !ok {
		return nil, fmt.Errorf("parent %s for %s not found in signer config", entry.Parent, label)
	}

	return parent, nil
}

// RootCAs returns the labels of all configured root CAs
func (c *SignerConfig) RootCAs() []string {
	roots := make([]string, 0)

	for label, entry := range c.caMap {
		if entry.IsRoot() {
			roots = append(roots, label)
		}
	}

	return roots
}

// SubordinateCAs returns the labels of all configured subordinate CAs
func (c *SignerConfig) SubordinateCAs() []string {
	subordinates := make([]string, 0)

	for label, entry := range c.caMap {
		if !entry.IsRoot() {
			subordinates = append(subordinates, label)
		}
	}

	return subordinates
}

func (c *SignerConfig) GetKeyStorage(label string) (*KeyStorage, error) {
	keyStorage, ok := c.keyStorage[label]

	if !ok {
		return nil, fmt.Errorf("could not find storage definition with label %s", label)
	}

	return keyStorage, nil
}

func (c *SignerConfig) GetSerial() *Serial {
	return c.global.Serial
}

func (c *SignerConfig) Repository(name string) (CARepository, error) {
	var (
		repo CARepository
		ok   bool
		err  error
	)

	repo, ok = c.repositories[name]
	if !ok {
		repo, err = openssl.NewFileRepository(path.Join("repos", name))
		if err != nil {
			return nil, fmt.Errorf("could not create repository for %s: %w", name, err)
		}

		c.repositories[name] = repo
	}

	return repo, nil
}

// LoadConfiguration reads YAML configuration from the given reader as a SignerConfig structure
func LoadConfiguration(r io.Reader) (*SignerConfig, error) {
	config := struct {
		Global     *Settings                      `yaml:"Settings"`
		CAs        map[string]*CaCertificateEntry `yaml:"CAs"`
		KeyStorage map[string]*KeyStorage         `yaml:"KeyStorage"`
	}{}

	decoder := yaml.NewDecoder(r)
	err := decoder.Decode(&config)

	if err != nil {
		return nil, fmt.Errorf("could not parse YAML configuration: %w", err)
	}

	if config.Global == nil {
		return nil, errors.New("configuration entry 'Settings' is missing or empty")
	}

	if config.CAs == nil {
		return nil, errors.New("configuration entry 'CAs' is missing or empty")
	}

	if config.KeyStorage == nil {
		return nil, errors.New("configuration entry 'KeyStorage' is missing or empty")
	}

	return &SignerConfig{
		global:       config.Global,
		caMap:        config.CAs,
		keyStorage:   config.KeyStorage,
		repositories: make(map[string]CARepository),
	}, nil
}

type PrivateKeyInfo struct {
	Algorithm             x509.PublicKeyAlgorithm
	EccCurve              elliptic.Curve
	RSABits               int
	CRLSignatureAlgorithm x509.SignatureAlgorithm
}

func (p *PrivateKeyInfo) UnmarshalYAML(value *yaml.Node) error {
	internalStructure := struct {
		Algorithm             string `yaml:"algorithm"`
		EccCurve              string `yaml:"ecc-curve,omitempty"`
		RSABits               *int   `yaml:"rsa-bits,omitempty"`
		CRLSignatureAlgorithm string `yaml:"crl-signature-algorithm,omitempty"`
	}{}

	err := value.Decode(&internalStructure)
	if err != nil {
		return fmt.Errorf("could not unmarshal private key info: %w", err)
	}

	switch internalStructure.Algorithm {
	case "RSA":
		p.Algorithm = x509.RSA

		if internalStructure.RSABits == nil {
			return errors.New("element 'rsa-bits' with RSA key length required for algorithm RSA")
		}

		p.RSABits = *internalStructure.RSABits

		if p.RSABits < minRSABits {
			return fmt.Errorf("RSA keys must have a length of at least %d bits", minRSABits)
		}

		p.CRLSignatureAlgorithm = determineRSASignatureAlgorithm(internalStructure.CRLSignatureAlgorithm)
	case "EC":
		p.Algorithm = x509.ECDSA

		if internalStructure.EccCurve == "" {
			return errors.New("element 'ecc-curve' required for algorithm EC")
		}

		p.EccCurve, err = nameToCurve(internalStructure.EccCurve)
		if err != nil {
			return err
		}

		p.CRLSignatureAlgorithm = determineECDSASignatureAlgorithm(internalStructure.CRLSignatureAlgorithm)
	case "":
		return errors.New("element 'algorithm' must be specified as 'EC' or 'RSA'")
	default:
		return fmt.Errorf(
			"unsupported key algorithm %s, use either 'EC' or 'RSA'",
			internalStructure.Algorithm,
		)
	}

	return nil
}

func determineRSASignatureAlgorithm(algorithm string) x509.SignatureAlgorithm {
	switch strings.ToLower(algorithm) {
	case "sha1withrsa", "sha1":
		return x509.SHA1WithRSA
	case "sha384withrsa", "sha384":
		return x509.SHA384WithRSA
	case "sha512withrsa", "sha512":
		return x509.SHA512WithRSA
	default:
		return x509.SHA256WithRSA
	}
}

func determineECDSASignatureAlgorithm(algorithm string) x509.SignatureAlgorithm {
	switch strings.ToLower(algorithm) {
	case "sha1withecdsa", "sha1":
		return x509.ECDSAWithSHA1
	case "sha384withecdsa", "sha384":
		return x509.ECDSAWithSHA384
	case "sha512withecdsa", "sha512":
		return x509.ECDSAWithSHA512
	default:
		return x509.ECDSAWithSHA256
	}
}

func (p *PrivateKeyInfo) MarshalYAML() (interface{}, error) {
	internalStructure := struct {
		Algorithm string `yaml:"algorithm"`
		EccCurve  string `yaml:"ecc-curve,omitempty"`
		RSABits   *int   `yaml:"rsa-bits,omitempty"`
	}{}

	switch p.Algorithm {
	case x509.RSA:
		internalStructure.Algorithm = "RSA"
		internalStructure.RSABits = &p.RSABits
	case x509.ECDSA:
		internalStructure.Algorithm = "EC"

		curveName, err := curveToName(p.EccCurve)
		if err != nil {
			return nil, err
		}

		internalStructure.EccCurve = curveName
	}

	return internalStructure, nil
}

func curveToName(curve elliptic.Curve) (string, error) {
	switch curve {
	case elliptic.P224():
		return "P-224", nil
	case elliptic.P256():
		return "P-256", nil
	case elliptic.P384():
		return "P-384", nil
	case elliptic.P521():
		return "P-521", nil
	default:
		return "", fmt.Errorf("unsupported EC curve %s", curve)
	}
}

// nameToCurve maps a curve name to an elliptic curve
func nameToCurve(name string) (elliptic.Curve, error) {
	switch name {
	case "P-224", "secp224r1":
		return elliptic.P224(), nil
	case "P-256", "secp256r1":
		return elliptic.P256(), nil
	case "P-384", "secp384r1":
		return elliptic.P384(), nil
	case "P-521", "secp521r1":
		return elliptic.P521(), nil
	default:
		return nil, fmt.Errorf("unsupported EC curve %s", name)
	}
}

var validProfileUsages = map[string]signing.ProfileUsage{
	"ocsp": signing.UsageOCSP,

	"client":        signing.UsageClient,
	"code":          signing.UsageCode,
	"person":        signing.UsagePerson,
	"server":        signing.UsageServer,
	"server_client": signing.UsageServerClient,

	"org_client":        signing.UsageOrgClient,
	"org_code":          signing.UsageOrgCode,
	"org_email":         signing.UsageOrgEmail,
	"org_person":        signing.UsageOrgPerson,
	"org_server":        signing.UsageOrgServer,
	"org_server_client": signing.UsageOrgServerClient,
}

func ParseUsage(u string) (signing.ProfileUsage, error) {
	usage, ok := validProfileUsages[u]
	if !ok {
		return signing.UsageInvalid, fmt.Errorf("unsupported profile usage: %s", u)
	}

	return usage, nil
}

type Profile struct {
	Name   string
	UseFor signing.ProfileUsage
	Years  int
	Months int
	Days   int
}

type CaCertificateEntry struct {
	KeyInfo     *PrivateKeyInfo
	CommonName  string
	MaxPathLen  int // maximum path length should be 0 for CAs that issue end entity certificates
	ExtKeyUsage []x509.ExtKeyUsage
	Certificate *x509.Certificate
	KeyPair     crypto.Signer
	Parent      string
	Storage     string
	Profiles    []Profile
}

func (c *CaCertificateEntry) UnmarshalYAML(value *yaml.Node) error {
	var m struct {
		KeyInfo    *PrivateKeyInfo `yaml:"key-info"`
		CommonName string          `yaml:"common-name"`
		// maximum path length should be 0 for CAs that issue end entity certificates
		MaxPathLen  int      `yaml:"max-path-len,omitempty"`
		ExtKeyUsage []string `yaml:"ext-key-usages,omitempty"`
		Parent      string   `yaml:"parent"`
		Storage     string   `yaml:"storage"`
		Profiles    []struct {
			Name     string `yaml:"name"`
			UseFor   string `yaml:"use-for"`
			Validity struct {
				Years  int `yaml:"years"`
				Months int `yaml:"months"`
				Days   int `yaml:"days"`
			} `yaml:"validity"`
		} `yaml:"profiles"`
	}

	err := value.Decode(&m)
	if err != nil {
		return fmt.Errorf("could not unmarshal CA certificate entry: %w", err)
	}

	if m.KeyInfo == nil {
		return errors.New("element 'key-info' must be set")
	}

	c.KeyInfo = m.KeyInfo

	if m.CommonName == "" {
		return errors.New("element 'common-name' must be set")
	}

	c.CommonName = m.CommonName
	c.MaxPathLen = m.MaxPathLen

	if m.Parent == "" && m.ExtKeyUsage != nil {
		return errors.New("a root CA must not specify 'ext-key-usages'")
	}

	c.Parent = m.Parent

	if m.ExtKeyUsage != nil {
		c.ExtKeyUsage, err = mapExtKeyUsageNames(m.ExtKeyUsage)
		if err != nil {
			return err
		}
	}

	if m.Storage != "" {
		c.Storage = m.Storage
	} else {
		c.Storage = "default"
	}

	if m.Profiles != nil {
		c.Profiles = make([]Profile, len(m.Profiles))

		for i, prof := range m.Profiles {
			usage, err := ParseUsage(prof.UseFor)
			if err != nil {
				return fmt.Errorf("config error: %w", err)
			}

			if prof.Validity.Years <= 0 && prof.Validity.Months <= 0 && prof.Validity.Days <= 0 {
				prof.Validity.Years, prof.Validity.Months, prof.Validity.Days = defaultValidity(usage)
			}

			c.Profiles[i] = Profile{
				Name:   prof.Name,
				UseFor: usage,
				Years:  prof.Validity.Years,
				Months: prof.Validity.Months,
				Days:   prof.Validity.Days,
			}
		}
	}

	return nil
}

func defaultValidity(useFor signing.ProfileUsage) (years int, months int, days int) {
	switch useFor {
	case signing.UsagePerson, signing.UsageOrgPerson, signing.UsageOrgEmail:
		return 2, 0, 0
	default:
		return 1, 0, 0
	}
}

func (c *CaCertificateEntry) IsRoot() bool {
	return c.Parent == ""
}

func mapExtKeyUsageNames(usages []string) ([]x509.ExtKeyUsage, error) {
	extKeyUsages := make([]x509.ExtKeyUsage, len(usages))

	for idx, usage := range usages {
		switch usage {
		case "client":
			extKeyUsages[idx] = x509.ExtKeyUsageClientAuth
		case "code":
			extKeyUsages[idx] = x509.ExtKeyUsageCodeSigning
		case "email":
			extKeyUsages[idx] = x509.ExtKeyUsageEmailProtection
		case "server":
			extKeyUsages[idx] = x509.ExtKeyUsageServerAuth
		case "ocsp":
			extKeyUsages[idx] = x509.ExtKeyUsageOCSPSigning
		default:
			return nil, fmt.Errorf("unsupported extended key usage %s", usage)
		}
	}

	return extKeyUsages, nil
}