/*
Copyright 2020 The cert-manager 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 pki

import (
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/asn1"
	"errors"
)

// Copied from x509.go
var (
	OIDExtensionKeyUsage         = []int{2, 5, 29, 15}
	OIDExtensionExtendedKeyUsage = []int{2, 5, 29, 37}
)

// RFC 5280, 4.2.1.12  Extended Key Usage
//
// anyExtendedKeyUsage OBJECT IDENTIFIER ::= { id-ce-extKeyUsage 0 }
//
// id-kp OBJECT IDENTIFIER ::= { id-pkix 3 }
//
// id-kp-serverAuth             OBJECT IDENTIFIER ::= { id-kp 1 }
// id-kp-clientAuth             OBJECT IDENTIFIER ::= { id-kp 2 }
// id-kp-codeSigning            OBJECT IDENTIFIER ::= { id-kp 3 }
// id-kp-emailProtection        OBJECT IDENTIFIER ::= { id-kp 4 }
// id-kp-timeStamping           OBJECT IDENTIFIER ::= { id-kp 8 }
// id-kp-OCSPSigning            OBJECT IDENTIFIER ::= { id-kp 9 }
var (
	oidExtKeyUsageAny                            = asn1.ObjectIdentifier{2, 5, 29, 37, 0}
	oidExtKeyUsageServerAuth                     = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 3, 1}
	oidExtKeyUsageClientAuth                     = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 3, 2}
	oidExtKeyUsageCodeSigning                    = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 3, 3}
	oidExtKeyUsageEmailProtection                = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 3, 4}
	oidExtKeyUsageIPSECEndSystem                 = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 3, 5}
	oidExtKeyUsageIPSECTunnel                    = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 3, 6}
	oidExtKeyUsageIPSECUser                      = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 3, 7}
	oidExtKeyUsageTimeStamping                   = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 3, 8}
	oidExtKeyUsageOCSPSigning                    = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 3, 9}
	oidExtKeyUsageMicrosoftServerGatedCrypto     = asn1.ObjectIdentifier{1, 3, 6, 1, 4, 1, 311, 10, 3, 3}
	oidExtKeyUsageNetscapeServerGatedCrypto      = asn1.ObjectIdentifier{2, 16, 840, 1, 113730, 4, 1}
	oidExtKeyUsageMicrosoftCommercialCodeSigning = asn1.ObjectIdentifier{1, 3, 6, 1, 4, 1, 311, 2, 1, 22}
	oidExtKeyUsageMicrosoftKernelCodeSigning     = asn1.ObjectIdentifier{1, 3, 6, 1, 4, 1, 311, 61, 1, 1}
)

// extKeyUsageOIDs contains the mapping between an ExtKeyUsage and its OID.
var extKeyUsageOIDs = []struct {
	extKeyUsage x509.ExtKeyUsage
	oid         asn1.ObjectIdentifier
}{
	{x509.ExtKeyUsageAny, oidExtKeyUsageAny},
	{x509.ExtKeyUsageServerAuth, oidExtKeyUsageServerAuth},
	{x509.ExtKeyUsageClientAuth, oidExtKeyUsageClientAuth},
	{x509.ExtKeyUsageCodeSigning, oidExtKeyUsageCodeSigning},
	{x509.ExtKeyUsageEmailProtection, oidExtKeyUsageEmailProtection},
	{x509.ExtKeyUsageIPSECEndSystem, oidExtKeyUsageIPSECEndSystem},
	{x509.ExtKeyUsageIPSECTunnel, oidExtKeyUsageIPSECTunnel},
	{x509.ExtKeyUsageIPSECUser, oidExtKeyUsageIPSECUser},
	{x509.ExtKeyUsageTimeStamping, oidExtKeyUsageTimeStamping},
	{x509.ExtKeyUsageOCSPSigning, oidExtKeyUsageOCSPSigning},
	{x509.ExtKeyUsageMicrosoftServerGatedCrypto, oidExtKeyUsageMicrosoftServerGatedCrypto},
	{x509.ExtKeyUsageNetscapeServerGatedCrypto, oidExtKeyUsageNetscapeServerGatedCrypto},
	{x509.ExtKeyUsageMicrosoftCommercialCodeSigning, oidExtKeyUsageMicrosoftCommercialCodeSigning},
	{x509.ExtKeyUsageMicrosoftKernelCodeSigning, oidExtKeyUsageMicrosoftKernelCodeSigning},
}

// OIDFromExtKeyUsage returns the ASN1 Identifier for a x509.ExtKeyUsage
func OIDFromExtKeyUsage(eku x509.ExtKeyUsage) (oid asn1.ObjectIdentifier, ok bool) {
	for _, pair := range extKeyUsageOIDs {
		if eku == pair.extKeyUsage {
			return pair.oid, true
		}
	}
	return
}

func ExtKeyUsageFromOID(oid asn1.ObjectIdentifier) (eku x509.ExtKeyUsage, ok bool) {
	for _, pair := range extKeyUsageOIDs {
		if oid.Equal(pair.oid) {
			return pair.extKeyUsage, true
		}
	}
	return
}

// asn1BitLength returns the bit-length of bitString by considering the
// most-significant bit in a byte to be the "first" bit. This convention
// matches ASN.1, but differs from almost everything else.
func asn1BitLength(bitString []byte) int {
	bitLen := len(bitString) * 8

	for i := range bitString {
		b := bitString[len(bitString)-i-1]

		for bit := uint(0); bit < 8; bit++ {
			if (b>>bit)&1 == 1 {
				return bitLen
			}
			bitLen--
		}
	}

	return 0
}

// Copied from x509.go
func reverseBitsInAByte(in byte) byte {
	b1 := in>>4 | in<<4
	b2 := b1>>2&0x33 | b1<<2&0xcc
	b3 := b2>>1&0x55 | b2<<1&0xaa
	return b3
}

// Adapted from x509.go
func MarshalKeyUsage(usage x509.KeyUsage) (pkix.Extension, error) {
	ext := pkix.Extension{Id: OIDExtensionKeyUsage, Critical: true}

	var a [2]byte
	a[0] = reverseBitsInAByte(byte(usage))
	a[1] = reverseBitsInAByte(byte(usage >> 8))

	l := 1
	if a[1] != 0 {
		l = 2
	}

	bitString := a[:l]
	var err error
	ext.Value, err = asn1.Marshal(asn1.BitString{Bytes: bitString, BitLength: asn1BitLength(bitString)})
	return ext, err
}

func UnmarshalKeyUsage(value []byte) (usage x509.KeyUsage, err error) {
	var asn1bits asn1.BitString
	var rest []byte

	if rest, err = asn1.Unmarshal(value, &asn1bits); err != nil {
		return usage, err
	} else if len(rest) != 0 {
		return usage, errors.New("x509: trailing data after X.509 KeyUsage")
	}

	var usageInt int
	for i := 0; i < 9; i++ {
		if asn1bits.At(i) != 0 {
			usageInt |= 1 << uint(i)
		}
	}

	return x509.KeyUsage(usageInt), nil
}

// Adapted from x509.go
func MarshalExtKeyUsage(extUsages []x509.ExtKeyUsage, unknownUsages []asn1.ObjectIdentifier) (pkix.Extension, error) {
	ext := pkix.Extension{Id: OIDExtensionExtendedKeyUsage}

	oids := make([]asn1.ObjectIdentifier, len(extUsages)+len(unknownUsages))
	for i, u := range extUsages {
		if oid, ok := OIDFromExtKeyUsage(u); ok {
			oids[i] = oid
		} else {
			return ext, errors.New("x509: unknown extended key usage")
		}
	}

	copy(oids[len(extUsages):], unknownUsages)

	var err error
	ext.Value, err = asn1.Marshal(oids)
	return ext, err
}

func UnmarshalExtKeyUsage(value []byte) (extUsages []x509.ExtKeyUsage, unknownUsages []asn1.ObjectIdentifier, err error) {
	var asn1ExtendedUsages []asn1.ObjectIdentifier
	var rest []byte

	if rest, err = asn1.Unmarshal(value, &asn1ExtendedUsages); err != nil {
		return extUsages, unknownUsages, err
	} else if len(rest) != 0 {
		return extUsages, unknownUsages, errors.New("x509: trailing data after X.509 ExtendedKeyUsage")
	}

	for _, asnExtUsage := range asn1ExtendedUsages {
		if eku, ok := ExtKeyUsageFromOID(asnExtUsage); ok {
			extUsages = append(extUsages, eku)
		} else {
			unknownUsages = append(unknownUsages, asnExtUsage)
		}
	}

	return extUsages, unknownUsages, nil
}
