package handlers

import (
	"bytes"
	"crypto/sha256"
	"crypto/x509"
	"encoding/pem"
	"errors"
	"fmt"
	"io/ioutil"
	"os"
	"os/exec"
	"time"

	log "github.com/sirupsen/logrus"
)

type SigningRequestRegistry struct {
	caCertificates []*x509.Certificate
	caChainMap     map[string][]string
	requests       map[string]chan *responseData
}

func NewSigningRequestRegistry(caCertificates []*x509.Certificate) *SigningRequestRegistry {
	return &SigningRequestRegistry{
		caCertificates: caCertificates,
		caChainMap:     make(map[string][]string),
		requests:       make(map[string]chan *responseData),
	}
}

type SigningRequestAttributes struct {
	CommonName   string
	CSRBytes     []byte
	RequestToken string
}

func (registry *SigningRequestRegistry) AddSigningRequest(request *requestData) (string, error) {
	requestToken, csrBytes, err := validateCsr(request.Csr)
	if err != nil {
		return "", err
	}
	requestAttributes := &SigningRequestAttributes{
		CommonName:   request.CommonName,
		CSRBytes:     csrBytes,
		RequestToken: requestToken,
	}
	go func() {
		responseChannel := make(chan *responseData, 1)
		registry.requests[requestToken] = responseChannel
		registry.signCertificate(responseChannel, requestAttributes)
	}()
	return requestToken, nil
}

func validateCsr(csr string) (string, []byte, error) {
	csrBlock, _ := pem.Decode([]byte(csr))
	if csrBlock == nil {
		return "", nil, errors.New("request data did not contain valid PEM data")
	}
	if csrBlock.Type != "CERTIFICATE REQUEST" {
		return "", nil, fmt.Errorf("request is not valid, type in PEM data is %s", csrBlock.Type)
	}
	var err error
	var csrContent *x509.CertificateRequest
	csrContent, err = x509.ParseCertificateRequest(csrBlock.Bytes)
	if err != nil {
		return "", nil, err
	}
	if err = csrContent.CheckSignature(); err != nil {
		log.Errorf("invalid CSR signature %v", err)
		return "", nil, err
	}

	// generate request token as defined in CAB Baseline Requirements 1.7.3 Request Token definition
	requestToken := fmt.Sprintf(
		"%s%x", time.Now().UTC().Format("200601021504"), sha256.Sum256(csrContent.Raw),
	)
	log.Debugf("generated request token %s", requestToken)
	return requestToken, csrContent.Raw, nil
}

func (registry *SigningRequestRegistry) signCertificate(channel chan *responseData, request *SigningRequestAttributes) {
	responseData, err := registry.sign(request)
	if err != nil {
		log.Error(err)
		close(channel)
		return
	}
	channel <- responseData
}

func (registry *SigningRequestRegistry) sign(request *SigningRequestAttributes) (*responseData, error) {
	log.Infof("handling signing request %s", request.RequestToken)
	subjectDN := fmt.Sprintf("/CN=%s", request.CommonName)

	var err error
	var csrFile *os.File
	if csrFile, err = ioutil.TempFile("", "*.csr.pem"); err != nil {
		log.Errorf("could not open temporary file: %s", err)
		return nil, err
	}
	if err = pem.Encode(csrFile, &pem.Block{
		Type:  "CERTIFICATE REQUEST",
		Bytes: request.CSRBytes,
	}); err != nil {
		log.Errorf("could not write CSR to file: %s", err)
		return nil, err
	}
	if err = csrFile.Close(); err != nil {
		log.Errorf("could not close CSR file: %s", err)
		return nil, err
	}
	defer func(file *os.File) {
		err = os.Remove(file.Name())
		if err != nil {
			log.Errorf("could not remove temporary file: %s", err)
		}
	}(csrFile)

	// simulate a delay during certificate creation
	time.Sleep(5 * time.Second)

	opensslCommand := exec.Command(
		"openssl", "ca", "-config", "ca.cnf", "-name", "email_ca",
		"-policy", "policy_match", "-extensions", "email_ext",
		"-batch", "-subj", subjectDN, "-utf8", "-rand_serial", "-in", csrFile.Name())
	var out, cmdErr bytes.Buffer
	opensslCommand.Stdout = &out
	opensslCommand.Stderr = &cmdErr
	err = opensslCommand.Run()
	if err != nil {
		log.Error(err)
		log.Error(cmdErr.String())
		return nil, err
	}

	var block *pem.Block
	if block, _ = pem.Decode(out.Bytes()); block == nil {
		err = fmt.Errorf("could not decode pem")
		return nil, err
	}
	var certificate *x509.Certificate
	if certificate, err = x509.ParseCertificate(block.Bytes); err != nil {
		return nil, err
	}

	var caChain []string
	if caChain, err = registry.getCAChain(certificate); err != nil {
		return nil, err
	}

	response := &responseData{
		Certificate: string(pem.EncodeToMemory(&pem.Block{
			Type:  "CERTIFICATE",
			Bytes: certificate.Raw,
		})),
		CAChain: caChain,
	}
	return response, nil
}

func (registry *SigningRequestRegistry) GetResponseChannel(requestUuid string) (chan *responseData, error) {
	if responseChannel, exists := registry.requests[requestUuid]; exists {
		delete(registry.requests, requestUuid)
		return responseChannel, nil
	} else {
		return nil, errors.New("no request found")
	}
}

func (registry *SigningRequestRegistry) getCAChain(certificate *x509.Certificate) ([]string, error) {
	issuerString := string(certificate.RawIssuer)

	if value, exists := registry.caChainMap[issuerString]; exists {
		return value, nil
	}

	result := make([]string, 0)

	appendCert := func(cert *x509.Certificate) {
		result = append(
			result,
			string(pem.EncodeToMemory(&pem.Block{Bytes: cert.Raw, Type: "CERTIFICATE"})))
		log.Debugf("added %s to cachain", result[len(result)-1])
	}

	var previous *x509.Certificate
	var count = 0
	for {
		if len(registry.caCertificates) == 0 {
			return nil, errors.New("no CA certificates loaded")
		}
		if count > len(registry.caCertificates) {
			return nil, errors.New("could not construct certificate chain")
		}
		for _, caCert := range registry.caCertificates {
			if previous == nil {
				if bytes.Equal(caCert.RawSubject, certificate.RawIssuer) {
					previous = caCert
					appendCert(caCert)
				}
			} else if bytes.Equal(previous.RawSubject, previous.RawIssuer) {
				registry.caChainMap[issuerString] = result
				return result, nil
			} else if bytes.Equal(caCert.RawSubject, previous.RawIssuer) {
				previous = caCert
				appendCert(caCert)
			} else {
				log.Debugf("skipped certificate %s", caCert.Subject)
			}
		}
		count++
	}
}