// Copyright 2014 ISRG.  All rights reserved
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.

package core

import (
	"crypto"
	"crypto/ecdsa"
	"crypto/rand"
	"crypto/rsa"
	"crypto/sha1"
	"crypto/sha256"
	"crypto/sha512"
	"crypto/x509"
	"encoding/asn1"
	"encoding/base64"
	"encoding/json"
	"errors"
	blog "github.com/letsencrypt/boulder/log"
	"hash"
	"io"
	"math/big"
	"net/url"
	"strings"
)

// Errors

type NotSupportedError string
type MalformedRequestError string
type UnauthorizedError string
type NotFoundError string
type SyntaxError string
type SignatureValidationError string
type CertificateIssuanceError string

func (e NotSupportedError) Error() string        { return string(e) }
func (e MalformedRequestError) Error() string    { return string(e) }
func (e UnauthorizedError) Error() string        { return string(e) }
func (e NotFoundError) Error() string            { return string(e) }
func (e SyntaxError) Error() string              { return string(e) }
func (e SignatureValidationError) Error() string { return string(e) }
func (e CertificateIssuanceError) Error() string { return string(e) }

// Base64 functions

func pad(x string) string {
	switch len(x) % 4 {
	case 2:
		return x + "=="
	case 3:
		return x + "="
	}
	return x
}

func unpad(x string) string {
	return strings.Replace(x, "=", "", -1)
}

func B64enc(x []byte) string {
	return unpad(base64.URLEncoding.EncodeToString(x))
}

func B64dec(x string) ([]byte, error) {
	return base64.URLEncoding.DecodeString(pad(x))
}

// Random stuff

// RandomString returns a randomly generated string of the requested length.
func RandomString(byteLength int) string {
	b := make([]byte, byteLength)
	_, err := io.ReadFull(rand.Reader, b)
	if err != nil {
		ohdear := "RandomString entropy failure? " + err.Error()
		logger := blog.GetAuditLogger()
		logger.EmergencyExit(ohdear)
	}
	return B64enc(b)
}

func NewToken() string {
	return RandomString(32)
}

// Fingerprints

func Fingerprint256(data []byte) string {
	d := sha256.New()
	_, _ = d.Write(data) // Never returns an error
	return B64enc(d.Sum(nil))
}

// URLs that automatically marshal/unmarshal to JSON strings
type AcmeURL url.URL

func (u AcmeURL) String() string {
	url := url.URL(u)
	return url.String()
}

func (u AcmeURL) PathSegments() (segments []string) {
	segments = strings.Split(u.Path, "/")
	if len(segments) > 0 && len(segments[0]) == 0 {
		segments = segments[1:]
	}
	return
}

func (u AcmeURL) MarshalJSON() ([]byte, error) {
	uu := url.URL(u)
	return json.Marshal(uu.String())
}

func (u *AcmeURL) UnmarshalJSON(data []byte) error {
	var str string
	if err := json.Unmarshal(data, &str); err != nil {
		return err
	}

	uu, err := url.Parse(str)
	*u = AcmeURL(*uu)
	return err
}

// The missing CertificateRequest.Verify() method
func VerifyCSR(csr *x509.CertificateRequest) error {
	// Compute the hash of the TBSCertificateRequest
	var hashID crypto.Hash
	var hash hash.Hash
	switch csr.SignatureAlgorithm {
	case x509.SHA1WithRSA:
		fallthrough
	case x509.ECDSAWithSHA1:
		hashID = crypto.SHA1
		hash = sha1.New()
	case x509.SHA256WithRSA:
		fallthrough
	case x509.ECDSAWithSHA256:
		hashID = crypto.SHA256
		hash = sha256.New()
	case x509.SHA384WithRSA:
		fallthrough
	case x509.ECDSAWithSHA384:
		hashID = crypto.SHA384
		hash = sha512.New384()
	case x509.SHA512WithRSA:
		fallthrough
	case x509.ECDSAWithSHA512:
		hashID = crypto.SHA512
		hash = sha512.New()
	default:
		return errors.New("Unsupported CSR signing algorithm")
	}
	_, _ = hash.Write(csr.RawTBSCertificateRequest) // Never returns an error
	inputHash := hash.Sum(nil)

	// Verify the signature using the public key in the CSR
	switch csr.SignatureAlgorithm {
	case x509.SHA1WithRSA:
		fallthrough
	case x509.SHA256WithRSA:
		fallthrough
	case x509.SHA384WithRSA:
		fallthrough
	case x509.SHA512WithRSA:
		rsaKey := csr.PublicKey.(*rsa.PublicKey)
		return rsa.VerifyPKCS1v15(rsaKey, hashID, inputHash, csr.Signature)
	case x509.ECDSAWithSHA1:
		fallthrough
	case x509.ECDSAWithSHA256:
		fallthrough
	case x509.ECDSAWithSHA384:
		fallthrough
	case x509.ECDSAWithSHA512:
		ecKey := csr.PublicKey.(*ecdsa.PublicKey)

		var sig struct{ R, S *big.Int }
		_, err := asn1.Unmarshal(csr.Signature, &sig)
		if err != nil {
			return err
		}

		if ecdsa.Verify(ecKey, inputHash, sig.R, sig.S) {
			return nil
		} else {
			return errors.New("Invalid ECDSA signature on CSR")
		}
	}

	return errors.New("Unsupported CSR signing algorithm")
}