onasty @ eb4c605

package jwtutil

import (

	"crypto/rand"

	"encoding/hex"

	"errors"

	"time"

	"github.com/golang-jwt/jwt/v5"

)

var (

	ErrUnexpectedSigningMethod = errors.New("unexpected signing method")

	ErrTokenSignatureInvalid   = errors.New("token signature invalid")

	ErrTokenExpired            = errors.New("token expired")

)

type JWTTokenizer interface {

	// AccessToken generates a new access token with the given [Payload].

	AccessToken(pl Payload) (string, error)

	// RefreshToken generates a random string of 64 chars.

	RefreshToken() (string, error)

	// Parse parses the token and returns its [Payload].

	Parse(token string) (Payload, error)

}

// Payload the access token payload

type Payload struct {

	UserID string

}

var _ JWTTokenizer = (*JWTUtil)(nil)

type JWTUtil struct {

	signingKey     string

	accessTokenTTL time.Duration

}

func NewJWTUtil(signingKey string, accessTokenTTL time.Duration) *JWTUtil {

	return &JWTUtil{

		signingKey:     signingKey,

		accessTokenTTL: accessTokenTTL,

	}

}

func (j *JWTUtil) AccessToken(pl Payload) (string, error) {

	tok := jwt.NewWithClaims(jwt.SigningMethodHS256, jwt.RegisteredClaims{

		Subject:   pl.UserID,

		ExpiresAt: jwt.NewNumericDate(time.Now().Add(j.accessTokenTTL)),

	})

	return tok.SignedString([]byte(j.signingKey))

}

func (j *JWTUtil) RefreshToken() (string, error) {

	b := make([]byte, 32)

	if _, err := rand.Read(b); err != nil {

		return "", err

	}

	return hex.EncodeToString(b), nil

}

func (j *JWTUtil) Parse(token string) (Payload, error) {

	var claims jwt.RegisteredClaims

	_, err := jwt.ParseWithClaims(token, &claims, func(t *jwt.Token) (any, error) {

		if _, ok := t.Method.(*jwt.SigningMethodHMAC); !ok {

			return nil, ErrUnexpectedSigningMethod

		}

		return []byte(j.signingKey), nil

	})

	if errors.Is(err, jwt.ErrTokenExpired) {

		return Payload{}, ErrTokenExpired

	}

	if errors.Is(err, jwt.ErrTokenSignatureInvalid) {

		return Payload{}, ErrTokenSignatureInvalid

	}

	return Payload{

		UserID: claims.Subject,

	}, err

}