/*
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 (
	"crypto/rsa"
	"encoding/asn1"
	"errors"
	"math/big"
)

// pkcs1PrivateKey is a structure which mirrors the PKCS#1 ASN.1 for an RSA private key.
type pkcs1PrivateKey struct {
	Version int
	N       *big.Int
	E       int
	D       *big.Int
	P       *big.Int
	Q       *big.Int
	// We ignore these values, if present, because rsa will calculate them.
	Dp   *big.Int `asn1:"optional"`
	Dq   *big.Int `asn1:"optional"`
	Qinv *big.Int `asn1:"optional"`

	AdditionalPrimes []pkcs1AdditionalRSAPrime `asn1:"optional,omitempty"`
}

type pkcs1AdditionalRSAPrime struct {
	Prime *big.Int

	// We ignore these values because rsa will calculate them.
	Exp   *big.Int
	Coeff *big.Int
}

// ParsePKCS1PrivateKey returns an RSA private key from its ASN.1 PKCS#1 DER encoded form.
func ParsePKCS1PrivateKey(der []byte) (*rsa.PrivateKey, error) {
	var priv pkcs1PrivateKey
	rest, err := asn1.Unmarshal(der, &priv)
	if len(rest) > 0 {
		return nil, asn1.SyntaxError{Msg: "trailing data"}
	}
	if err != nil {
		return nil, err
	}

	if priv.Version > 1 {
		return nil, errors.New("x509: unsupported private key version")
	}

	if priv.N.Sign() <= 0 || priv.D.Sign() <= 0 || priv.P.Sign() <= 0 || priv.Q.Sign() <= 0 {
		return nil, errors.New("x509: private key contains zero or negative value")
	}

	key := new(rsa.PrivateKey)
	key.PublicKey = rsa.PublicKey{
		E: priv.E,
		N: priv.N,
	}

	key.D = priv.D
	key.Primes = make([]*big.Int, 2+len(priv.AdditionalPrimes))
	key.Primes[0] = priv.P
	key.Primes[1] = priv.Q
	for i, a := range priv.AdditionalPrimes {
		if a.Prime.Sign() <= 0 {
			return nil, errors.New("x509: private key contains zero or negative prime")
		}
		key.Primes[i+2] = a.Prime
		// We ignore the other two values because rsa will calculate
		// them as needed.
	}

	err = key.Validate()
	if err != nil {
		return nil, err
	}
	key.Precompute()

	return key, nil
}

// MarshalPKCS1PrivateKey converts a private key to ASN.1 DER encoded form.
func MarshalPKCS1PrivateKey(key *rsa.PrivateKey) []byte {
	key.Precompute()

	version := 0
	if len(key.Primes) > 2 {
		version = 1
	}

	priv := pkcs1PrivateKey{
		Version: version,
		N:       key.N,
		E:       key.PublicKey.E,
		D:       key.D,
		P:       key.Primes[0],
		Q:       key.Primes[1],
		Dp:      key.Precomputed.Dp,
		Dq:      key.Precomputed.Dq,
		Qinv:    key.Precomputed.Qinv,
	}

	priv.AdditionalPrimes = make([]pkcs1AdditionalRSAPrime, len(key.Precomputed.CRTValues))
	for i, values := range key.Precomputed.CRTValues {
		priv.AdditionalPrimes[i].Prime = key.Primes[2+i]
		priv.AdditionalPrimes[i].Exp = values.Exp
		priv.AdditionalPrimes[i].Coeff = values.Coeff
	}

	b, _ := asn1.Marshal(priv)
	return b
}

// rsaPublicKey reflects the ASN.1 structure of a PKCS#1 public key.
type rsaPublicKey struct {
	N *big.Int
	E int
}
