package jwt

import (

	"crypto"

	"crypto/rand"

	"crypto/rsa"

)

// Implements the RSA family of signing methods signing methods

// Expects *rsa.PrivateKey for signing and *rsa.PublicKey for validation

type SigningMethodRSA struct {

	Name string

	Hash crypto.Hash

}

// Specific instances for RS256 and company

var (

	SigningMethodRS256 *SigningMethodRSA

	SigningMethodRS384 *SigningMethodRSA

	SigningMethodRS512 *SigningMethodRSA

)

func init() {

	// RS256

	SigningMethodRS256 = &SigningMethodRSA{"RS256", crypto.SHA256}

	RegisterSigningMethod(SigningMethodRS256.Alg(), func() SigningMethod {

		return SigningMethodRS256

	})

	// RS384

	SigningMethodRS384 = &SigningMethodRSA{"RS384", crypto.SHA384}

	RegisterSigningMethod(SigningMethodRS384.Alg(), func() SigningMethod {

		return SigningMethodRS384

	})

	// RS512

	SigningMethodRS512 = &SigningMethodRSA{"RS512", crypto.SHA512}

	RegisterSigningMethod(SigningMethodRS512.Alg(), func() SigningMethod {

		return SigningMethodRS512

	})

}

func (m *SigningMethodRSA) Alg() string {

	return m.Name

}

// Implements the Verify method from SigningMethod

// For this signing method, must be an *rsa.PublicKey structure.

func (m *SigningMethodRSA) Verify(signingString, signature string, key interface{}) error {

	var err error

	// Decode the signature

	var sig []byte

	if sig, err = DecodeSegment(signature); err != nil {

		return err

	}

	var rsaKey *rsa.PublicKey

	var ok bool

	if rsaKey, ok = key.(*rsa.PublicKey); !ok {

		return ErrInvalidKeyType

	}

	// Create hasher

	if !m.Hash.Available() {

		return ErrHashUnavailable

	}

	hasher := m.Hash.New()

	hasher.Write([]byte(signingString))

	// Verify the signature

	return rsa.VerifyPKCS1v15(rsaKey, m.Hash, hasher.Sum(nil), sig)

}

// Implements the Sign method from SigningMethod

// For this signing method, must be an *rsa.PrivateKey structure.

func (m *SigningMethodRSA) Sign(signingString string, key interface{}) (string, error) {

	var rsaKey *rsa.PrivateKey

	var ok bool

	// Validate type of key

	if rsaKey, ok = key.(*rsa.PrivateKey); !ok {

		return "", ErrInvalidKey

	}

	// Create the hasher

	if !m.Hash.Available() {

		return "", ErrHashUnavailable

	}

	hasher := m.Hash.New()

	hasher.Write([]byte(signingString))

	// Sign the string and return the encoded bytes

	if sigBytes, err := rsa.SignPKCS1v15(rand.Reader, rsaKey, m.Hash, hasher.Sum(nil)); err == nil {

		return EncodeSegment(sigBytes), nil

	} else {

		return "", err

	}

}