/*
Copyright 2020 Clastix Labs.

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 cert

import (
	"bytes"
	"crypto/rand"
	"crypto/rsa"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/pem"
	"math/big"
	"time"
)

type CA interface {
	GenerateCertificate(opts CertificateOptions) (certificatePem *bytes.Buffer, certificateKey *bytes.Buffer, err error)
	CACertificatePem() (b *bytes.Buffer, err error)
	CAPrivateKeyPem() (b *bytes.Buffer, err error)
	ExpiresIn(now time.Time) (time.Duration, error)
	ValidateCert(certificate *x509.Certificate) error
}

type CapsuleCA struct {
	certificate *x509.Certificate
	key         *rsa.PrivateKey
}

func (c CapsuleCA) ValidateCert(certificate *x509.Certificate) (err error) {
	pool := x509.NewCertPool()
	pool.AddCert(c.certificate)

	_, err = certificate.Verify(x509.VerifyOptions{
		Roots:       pool,
		CurrentTime: time.Time{},
	})
	return
}

func (c CapsuleCA) isAlreadyValid(now time.Time) bool {
	return now.After(c.certificate.NotBefore)
}

func (c CapsuleCA) isExpired(now time.Time) bool {
	return now.Before(c.certificate.NotAfter)
}

func (c CapsuleCA) ExpiresIn(now time.Time) (time.Duration, error) {
	if !c.isExpired(now) {
		return time.Nanosecond, CaExpiredError{}
	}
	if !c.isAlreadyValid(now) {
		return time.Nanosecond, CaNotYetValidError{}
	}
	return time.Duration(c.certificate.NotAfter.Unix()-now.Unix()) * time.Second, nil
}

func (c CapsuleCA) CACertificatePem() (b *bytes.Buffer, err error) {
	var crtBytes []byte
	crtBytes, err = x509.CreateCertificate(rand.Reader, c.certificate, c.certificate, &c.key.PublicKey, c.key)
	if err != nil {
		return
	}
	b = new(bytes.Buffer)
	err = pem.Encode(b, &pem.Block{
		Type:  "CERTIFICATE",
		Bytes: crtBytes,
	})
	return b, err
}

func (c CapsuleCA) CAPrivateKeyPem() (b *bytes.Buffer, err error) {
	b = new(bytes.Buffer)
	return b, pem.Encode(b, &pem.Block{
		Type:  "RSA PRIVATE KEY",
		Bytes: x509.MarshalPKCS1PrivateKey(c.key),
	})
}

func GenerateCertificateAuthority() (s *CapsuleCA, err error) {
	s = &CapsuleCA{
		certificate: &x509.Certificate{
			SerialNumber: big.NewInt(2019),
			Subject: pkix.Name{
				Organization:  []string{"Clastix"},
				Country:       []string{"UK"},
				Province:      []string{""},
				Locality:      []string{"London"},
				StreetAddress: []string{"27, Old Gloucester Street"},
				PostalCode:    []string{"WC1N 3AX"},
			},
			NotBefore:             time.Now(),
			NotAfter:              time.Now().AddDate(10, 0, 0),
			IsCA:                  true,
			ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageClientAuth, x509.ExtKeyUsageServerAuth},
			KeyUsage:              x509.KeyUsageDigitalSignature | x509.KeyUsageCertSign,
			BasicConstraintsValid: true,
		},
	}

	s.key, err = rsa.GenerateKey(rand.Reader, 4096)
	if err != nil {
		return nil, err
	}

	return
}

func NewCertificateAuthorityFromBytes(certBytes, keyBytes []byte) (s *CapsuleCA, err error) {
	var b *pem.Block

	b, _ = pem.Decode(certBytes)
	var cert *x509.Certificate
	if cert, err = x509.ParseCertificate(b.Bytes); err != nil {
		return
	}

	b, _ = pem.Decode(keyBytes)
	var key *rsa.PrivateKey
	if key, err = x509.ParsePKCS1PrivateKey(b.Bytes); err != nil {
		return
	}

	s = &CapsuleCA{
		certificate: cert,
		key:         key,
	}

	return
}

func (c *CapsuleCA) GenerateCertificate(opts CertificateOptions) (certificatePem *bytes.Buffer, certificateKey *bytes.Buffer, err error) {
	var certPrivKey *rsa.PrivateKey
	certPrivKey, err = rsa.GenerateKey(rand.Reader, 4096)
	if err != nil {
		return nil, nil, err
	}

	cert := &x509.Certificate{
		SerialNumber: big.NewInt(1658),
		Subject: pkix.Name{
			Organization:  []string{"Clastix"},
			Country:       []string{"UK"},
			Province:      []string{""},
			Locality:      []string{"London"},
			StreetAddress: []string{"27, Old Gloucester Street"},
			PostalCode:    []string{"WC1N 3AX"},
		},
		DNSNames:     opts.DNSNames(),
		NotBefore:    time.Now().AddDate(0, 0, -1),
		NotAfter:     opts.ExpirationDate(),
		SubjectKeyId: []byte{1, 2, 3, 4, 6},
		ExtKeyUsage:  []x509.ExtKeyUsage{x509.ExtKeyUsageClientAuth, x509.ExtKeyUsageServerAuth},
		KeyUsage:     x509.KeyUsageDigitalSignature,
	}

	var certBytes []byte
	certBytes, err = x509.CreateCertificate(rand.Reader, cert, c.certificate, &certPrivKey.PublicKey, c.key)
	if err != nil {
		return nil, nil, err
	}

	certificatePem = new(bytes.Buffer)
	err = pem.Encode(certificatePem, &pem.Block{
		Type:  "CERTIFICATE",
		Bytes: certBytes,
	})
	if err != nil {
		return
	}

	certificateKey = new(bytes.Buffer)
	err = pem.Encode(certificateKey, &pem.Block{
		Type:  "RSA PRIVATE KEY",
		Bytes: x509.MarshalPKCS1PrivateKey(certPrivKey),
	})
	if err != nil {
		return
	}

	return
}