// Copyright 2019 Yunion
//
// 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 certs

import (
	"crypto"
	"crypto/x509"
	"fmt"

	"yunion.io/x/pkg/errors"

	certutil "yunion.io/x/onecloud/pkg/util/tls/cert"
	pkiutil "yunion.io/x/onecloud/pkg/util/tls/pki"
)

type certKeyLocation struct {
	pkiDir     string
	caBaseName string
	baseName   string
	uxName     string
}

// validateSignedCert tries to load a x509 certificate and private key from pkiDir and validates
// that the cert is signed by a given CA
func validateSignedCert(l certKeyLocation) error {
	// Try to load CA
	caCert, err := pkiutil.TryLoadCertFromDisk(l.pkiDir, l.caBaseName)
	if err != nil {
		return errors.Wrapf(err, "failure loading certificate authority for %s", l.uxName)
	}

	return validateSignedCertWithCA(l, caCert)
}

// validateSignedCertWithCA tries to load a certificate and validate it with the given caCert
func validateSignedCertWithCA(l certKeyLocation, caCert *x509.Certificate) error {
	// Try to load key and signed certificate
	signedCert, _, err := pkiutil.TryLoadCertAndKeyFromDisk(l.pkiDir, l.baseName)
	if err != nil {
		return errors.Wrapf(err, "failure loading certificate for %s", l.uxName)
	}

	// Check if the cert is signed by the CA
	if err := signedCert.CheckSignatureFrom(caCert); err != nil {
		return errors.Wrapf(err, "certificate %s is not signed by corresponding CA", l.uxName)
	}
	return nil
}

// validatePrivatePublicKey tries to load a private key from pkiDir
func validatePrivatePublicKey(l certKeyLocation) error {
	// Try to load key
	_, _, err := pkiutil.TryLoadPrivatePublicKeyFromDisk(l.pkiDir, l.baseName)
	if err != nil {
		return errors.Wrapf(err, "failure loading key for %s", l.uxName)
	}
	return nil
}

// writeCertificateAuthorithyFilesIfNotExist write a new certificate Authority to the given path.
// If there already is a certificate file at the given path; tries to load it and check if the values in the
// existing and the expected certificate equals. If they do; will just skip writing the file as it's up-to-date,
// otherwise this function returns an error.
func writeCertificateAuthorithyFilesIfNotExist(pkiDir string, baseName string, caCert *x509.Certificate, caKey crypto.Signer) error {

	// If cert or key exists, we should try to load them
	if pkiutil.CertOrKeyExist(pkiDir, baseName) {

		// Try to load .crt and .key from the PKI directory
		caCert, _, err := pkiutil.TryLoadCertAndKeyFromDisk(pkiDir, baseName)
		if err != nil {
			return errors.Wrapf(err, "failure loading %s certificate", baseName)
		}

		// Check if the existing cert is a CA
		if !caCert.IsCA {
			return errors.Errorf("certificate %s is not a CA", baseName)
		}

		// kubeadm doesn't validate the existing certificate Authority more than this;
		// Basically, if we find a certificate file with the same path; and it is a CA
		// kubeadm thinks those files are equal and doesn't bother writing a new file
		fmt.Printf("[certs] Using the existing %q certificate and key\n", baseName)
	} else {
		// Write .crt and .key files to disk
		fmt.Printf("[certs] Generating %q certificate and key\n", baseName)

		if err := pkiutil.WriteCertAndKey(pkiDir, baseName, caCert, caKey); err != nil {
			return errors.Wrapf(err, "failure while saving %s certificate and key", baseName)
		}
	}
	return nil
}

// writeCertificateFilesIfNotExist write a new certificate to the given path.
// If there already is a certificate file at the given path; kubeadm tries to load it and check if the values in the
// existing and the expected certificate equals. If they do; kubeadm will just skip writing the file as it's up-to-date,
// otherwise this function returns an error.
func writeCertificateFilesIfNotExist(pkiDir string, baseName string, signingCert *x509.Certificate, cert *x509.Certificate, key crypto.Signer, cfg *certutil.Config) error {

	// Checks if the signed certificate exists in the PKI directory
	if pkiutil.CertOrKeyExist(pkiDir, baseName) {
		// Try to load signed certificate .crt and .key from the PKI directory
		signedCert, _, err := pkiutil.TryLoadCertAndKeyFromDisk(pkiDir, baseName)
		if err != nil {
			return errors.Wrapf(err, "failure loading %s certificate", baseName)
		}

		// Check if the existing cert is signed by the given CA
		if err := signedCert.CheckSignatureFrom(signingCert); err != nil {
			return errors.Errorf("certificate %s is not signed by corresponding CA", baseName)
		}

		// Check if the certificate has the correct attributes
		if err := validateCertificateWithConfig(signedCert, baseName, cfg); err != nil {
			return err
		}

		fmt.Printf("[certs] Using the existing %q certificate and key\n", baseName)
	} else {
		// Write .crt and .key files to disk
		fmt.Printf("[certs] Generating %q certificate and key\n", baseName)

		if err := pkiutil.WriteCertAndKey(pkiDir, baseName, cert, key); err != nil {
			return errors.Wrapf(err, "failure while saving %s certificate and key", baseName)
		}
		if pkiutil.HasServerAuth(cert) {
			fmt.Printf("[certs] %s serving cert is signed for DNS names %v and IPs %v\n", baseName, cert.DNSNames, cert.IPAddresses)
		}
	}

	return nil
}

// validateCertificateWithConfig makes sure that a given certificate is valid at
// least for the SANs defined in the configuration.
func validateCertificateWithConfig(cert *x509.Certificate, baseName string, cfg *certutil.Config) error {
	for _, dnsName := range cfg.AltNames.DNSNames {
		if err := cert.VerifyHostname(dnsName); err != nil {
			return errors.Wrapf(err, "certificate %s is invalid", baseName)
		}
	}
	for _, ipAddress := range cfg.AltNames.IPs {
		if err := cert.VerifyHostname(ipAddress.String()); err != nil {
			return errors.Wrapf(err, "certificate %s is invalid", baseName)
		}
	}
	return nil
}