package jwt

import (
	"bytes"
	"crypto"
	"crypto/hmac"
	"errors"
)

type SigningMethodHMAC struct {
	Name string
	Hash crypto.Hash
}

var (
	SigningMethodHS256 *SigningMethodHMAC
	SigningMethodHS384 *SigningMethodHMAC
	SigningMethodHS512 *SigningMethodHMAC
)

func init() {
	// HS256
	SigningMethodHS256 = &SigningMethodHMAC{"HS256", crypto.SHA256}
	RegisterSigningMethod(SigningMethodHS256.Alg(), func() SigningMethod {
		return SigningMethodHS256
	})

	// HS384
	SigningMethodHS384 = &SigningMethodHMAC{"HS384", crypto.SHA384}
	RegisterSigningMethod(SigningMethodHS384.Alg(), func() SigningMethod {
		return SigningMethodHS384
	})

	// HS512
	SigningMethodHS512 = &SigningMethodHMAC{"HS512", crypto.SHA512}
	RegisterSigningMethod(SigningMethodHS512.Alg(), func() SigningMethod {
		return SigningMethodHS512
	})
}

func (m *SigningMethodHMAC) Alg() string {
	return m.Name
}

func (m *SigningMethodHMAC) Verify(signingString, signature string, key []byte) error {
	// Key
	var sig []byte
	var err error
	if sig, err = DecodeSegment(signature); err == nil {
		hasher := hmac.New(m.Hash.New, key)
		hasher.Write([]byte(signingString))

		if !bytes.Equal(sig, hasher.Sum(nil)) {
			err = errors.New("Signature is invalid")
		}
	}
	return err
}

func (m *SigningMethodHMAC) Sign(signingString string, key []byte) (string, error) {
	hasher := hmac.New(m.Hash.New, key)
	hasher.Write([]byte(signingString))

	return EncodeSegment(hasher.Sum(nil)), nil
}