package aws

import (
	"crypto/x509"
	"encoding/base64"
	"encoding/pem"
	"fmt"
	"math/big"

	"github.com/fatih/structs"
	"github.com/hashicorp/vault/logical"
	"github.com/hashicorp/vault/logical/framework"
)

// dsaSignature represents the contents of the signature of a signed
// content using digital signature algorithm.
type dsaSignature struct {
	R, S *big.Int
}

// As per AWS documentation, this public key is valid for US East (N. Virginia),
// US West (Oregon), US West (N. California), EU (Ireland), EU (Frankfurt),
// Asia Pacific (Tokyo), Asia Pacific (Seoul), Asia Pacific (Singapore),
// Asia Pacific (Sydney), and South America (Sao Paulo).
//
// It's also the same certificate, but for some reason listed separately, for
// GovCloud (US)
const genericAWSPublicCertificate = `-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
`

// pathListCertificates creates a path that enables listing of all
// the AWS public certificates registered with Vault.
func pathListCertificates(b *backend) *framework.Path {
	return &framework.Path{
		Pattern: "config/certificates/?",

		Callbacks: map[logical.Operation]framework.OperationFunc{
			logical.ListOperation: b.pathCertificatesList,
		},

		HelpSynopsis:    pathListCertificatesHelpSyn,
		HelpDescription: pathListCertificatesHelpDesc,
	}
}

func pathConfigCertificate(b *backend) *framework.Path {
	return &framework.Path{
		Pattern: "config/certificate/" + framework.GenericNameRegex("cert_name"),
		Fields: map[string]*framework.FieldSchema{
			"cert_name": &framework.FieldSchema{
				Type:        framework.TypeString,
				Description: "Name of the certificate.",
			},
			"aws_public_cert": &framework.FieldSchema{
				Type:        framework.TypeString,
				Description: "AWS Public cert required to verify PKCS7 signature of the EC2 instance metadata.",
			},
		},

		ExistenceCheck: b.pathConfigCertificateExistenceCheck,

		Callbacks: map[logical.Operation]framework.OperationFunc{
			logical.CreateOperation: b.pathConfigCertificateCreateUpdate,
			logical.UpdateOperation: b.pathConfigCertificateCreateUpdate,
			logical.ReadOperation:   b.pathConfigCertificateRead,
			logical.DeleteOperation: b.pathConfigCertificateDelete,
		},

		HelpSynopsis:    pathConfigCertificateSyn,
		HelpDescription: pathConfigCertificateDesc,
	}
}

// Establishes dichotomy of request operation between CreateOperation and UpdateOperation.
// Returning 'true' forces an UpdateOperation, CreateOperation otherwise.
func (b *backend) pathConfigCertificateExistenceCheck(req *logical.Request, data *framework.FieldData) (bool, error) {
	certName := data.Get("cert_name").(string)
	if certName == "" {
		return false, fmt.Errorf("missing cert_name")
	}
	entry, err := b.awsPublicCertificateEntry(req.Storage, certName)
	if err != nil {
		return false, err
	}
	return entry != nil, nil
}

// pathCertificatesList is used to list all the AWS public certificates registered with Vault.
func (b *backend) pathCertificatesList(
	req *logical.Request, data *framework.FieldData) (*logical.Response, error) {
	b.configMutex.RLock()
	defer b.configMutex.RUnlock()

	certs, err := req.Storage.List("config/certificate/")
	if err != nil {
		return nil, err
	}
	return logical.ListResponse(certs), nil
}

// Decodes the PEM encoded certiticate and parses it into a x509 cert.
func decodePEMAndParseCertificate(certificate string) (*x509.Certificate, error) {
	// Decode the PEM block and error out if a block is not detected in the first attempt.
	decodedPublicCert, rest := pem.Decode([]byte(certificate))
	if len(rest) != 0 {
		return nil, fmt.Errorf("invalid certificate; should be one PEM block only")
	}

	// Check if the certificate can be parsed.
	publicCert, err := x509.ParseCertificate(decodedPublicCert.Bytes)
	if err != nil {
		return nil, err
	}
	if publicCert == nil {
		return nil, fmt.Errorf("invalid certificate; failed to parse certificate")
	}
	return publicCert, nil
}

// awsPublicCertificates returns a slice of all the parsed AWS public
// certificates, that were registered using `config/certificate/<cert_name>` endpoint.
// This method will also append default certificate in the backend, to the slice.
func (b *backend) awsPublicCertificates(s logical.Storage) ([]*x509.Certificate, error) {
	var certs []*x509.Certificate

	// Append the generic certificate provided in the AWS EC2 instance metadata documentation.
	decodedCert, err := decodePEMAndParseCertificate(genericAWSPublicCertificate)
	if err != nil {
		return nil, err
	}
	certs = append(certs, decodedCert)

	// Get the list of all the registered certificates.
	registeredCerts, err := s.List("config/certificate/")
	if err != nil {
		return nil, err
	}

	// Iterate through each certificate, parse and append it to a slice.
	for _, cert := range registeredCerts {
		certEntry, err := b.awsPublicCertificateEntry(s, cert)
		if err != nil {
			return nil, err
		}
		if certEntry == nil {
			return nil, fmt.Errorf("certificate storage has a nil entry under the name:%s\n", cert)
		}
		decodedCert, err := decodePEMAndParseCertificate(certEntry.AWSPublicCert)
		if err != nil {
			return nil, err
		}
		certs = append(certs, decodedCert)
	}

	return certs, nil
}

// awsPublicCertificate is used to get the configured AWS Public Key that is used
// to verify the PKCS#7 signature of the instance identity document.
func (b *backend) awsPublicCertificateEntry(s logical.Storage, certName string) (*awsPublicCert, error) {
	b.configMutex.RLock()
	defer b.configMutex.RUnlock()

	entry, err := s.Get("config/certificate/" + certName)
	if err != nil {
		return nil, err
	}
	if entry == nil {
		return nil, nil
	}

	var result awsPublicCert
	if err := entry.DecodeJSON(&result); err != nil {
		return nil, err
	}
	return &result, nil
}

// pathConfigCertificateDelete is used to delete the previously configured AWS Public Key
// that is used to verify the PKCS#7 signature of the instance identity document.
func (b *backend) pathConfigCertificateDelete(req *logical.Request, data *framework.FieldData) (*logical.Response, error) {
	b.configMutex.Lock()
	defer b.configMutex.Unlock()

	certName := data.Get("cert_name").(string)
	if certName == "" {
		return logical.ErrorResponse("missing cert_name"), nil
	}

	return nil, req.Storage.Delete("config/certificate/" + certName)
}

// pathConfigCertificateRead is used to view the configured AWS Public Key that is
// used to verify the PKCS#7 signature of the instance identity document.
func (b *backend) pathConfigCertificateRead(
	req *logical.Request, data *framework.FieldData) (*logical.Response, error) {
	certName := data.Get("cert_name").(string)
	if certName == "" {
		return logical.ErrorResponse("missing cert_name"), nil
	}

	certificateEntry, err := b.awsPublicCertificateEntry(req.Storage, certName)
	if err != nil {
		return nil, err
	}
	if certificateEntry == nil {
		return nil, nil
	}

	return &logical.Response{
		Data: structs.New(certificateEntry).Map(),
	}, nil
}

// pathConfigCertificateCreateUpdate is used to register an AWS Public Key that is
// used to verify the PKCS#7 signature of the instance identity document.
func (b *backend) pathConfigCertificateCreateUpdate(
	req *logical.Request, data *framework.FieldData) (*logical.Response, error) {
	certName := data.Get("cert_name").(string)
	if certName == "" {
		return logical.ErrorResponse("missing cert_name"), nil
	}

	// Check if there is already a certificate entry registered.
	certEntry, err := b.awsPublicCertificateEntry(req.Storage, certName)
	if err != nil {
		return nil, err
	}
	if certEntry == nil {
		certEntry = &awsPublicCert{}
	}

	// Check if the value is provided by the client.
	certStrData, ok := data.GetOk("aws_public_cert")
	if ok {
		if certBytes, err := base64.StdEncoding.DecodeString(certStrData.(string)); err == nil {
			certEntry.AWSPublicCert = string(certBytes)
		} else {
			certEntry.AWSPublicCert = certStrData.(string)
		}
	} else {
		// aws_public_cert should be supplied for both create and update operations.
		// If it is not provided, throw an error.
		return logical.ErrorResponse("missing aws_public_cert"), nil
	}

	// If explicitly set to empty string, error out.
	if certEntry.AWSPublicCert == "" {
		return logical.ErrorResponse("invalid aws_public_cert"), nil
	}

	// Verify the certificate by decoding it and parsing it.
	publicCert, err := decodePEMAndParseCertificate(certEntry.AWSPublicCert)
	if err != nil {
		return nil, err
	}
	if publicCert == nil {
		return logical.ErrorResponse("invalid certificate; failed to decode and parse certificate"), nil
	}

	b.configMutex.Lock()
	defer b.configMutex.Unlock()
	// If none of the checks fail, save the provided certificate.
	entry, err := logical.StorageEntryJSON("config/certificate/"+certName, certEntry)
	if err != nil {
		return nil, err
	}

	if err := req.Storage.Put(entry); err != nil {
		return nil, err
	}

	return nil, nil
}

// Struct awsPublicCert holds the AWS Public Key that is used to verify the PKCS#7 signature
// of the instnace identity document.
type awsPublicCert struct {
	AWSPublicCert string `json:"aws_public_cert" structs:"aws_public_cert" mapstructure:"aws_public_cert"`
}

const pathConfigCertificateSyn = `
Configure the AWS Public Key that is used to verify the PKCS#7 signature of the identidy document.
`

const pathConfigCertificateDesc = `
AWS Public Key which is used to verify the PKCS#7 signature of the identity document,
varies by region. The public key can be found in AWS EC2 instance metadata documentation.
The default key that is used to verify the signature is the one that is applicable for
following regions: US East (N. Virginia), US West (Oregon), US West (N. California),
EU (Ireland), EU (Frankfurt), Asia Pacific (Tokyo), Asia Pacific (Seoul), Asia Pacific (Singapore),
Asia Pacific (Sydney), and South America (Sao Paulo).

If the instances belongs to region other than the above, the public key for the corresponding
regions should be registered using this endpoint. PKCS#7 is verified using a collection
of certificates containing the default certificate and all the registered certificates
added using this endpoint.
`
const pathListCertificatesHelpSyn = `
Lists all the AWS public certificates that are registered with Vault.
`
const pathListCertificatesHelpDesc = `
Certificates will be listed by their respective names that were used during registration.
`