package core

import (
	"encoding/json"
	"errors"
	"time"

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

type JWT struct {
	signingKey      []byte
	lifetimeMinutes int
}
type JWTOptions struct {
	SigningKey      string
	LifetimeMinutes int
}

var j *JWT

func newJWT(opts JWTOptions) *JWT {
	j = &JWT{
		signingKey:      []byte(opts.SigningKey),
		lifetimeMinutes: opts.LifetimeMinutes,
	}
	return j
}
func resolveJWT() *JWT {
	return j
}

// LifetimeMinutes returns the configured token lifetime in minutes.
func (j *JWT) LifetimeMinutes() int {
	return j.lifetimeMinutes
}

type claims struct {
	J []byte
	jwt.RegisteredClaims
}

func (j *JWT) GenerateToken(payload map[string]interface{}) (string, error) {
	expiresAt := time.Now().Add(time.Duration(j.lifetimeMinutes) * time.Minute)
	claims, err := mapClaims(payload, expiresAt)
	if err != nil {
		return "", err
	}
	t := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
	token, err := t.SignedString(j.signingKey)
	if err != nil {
		return "", err
	}
	return token, nil
}

// DecodeTokenIgnoreExpiry decodes a token's payload without validating its expiration.
// It is used to inspect tokens that may already be expired (e.g. sliding session renewal),
// while still verifying the signature and the token structure.
func (j *JWT) DecodeTokenIgnoreExpiry(token string) (payload map[string]interface{}, err error) {
	t, err := jwt.ParseWithClaims(token, &claims{}, func(token *jwt.Token) (interface{}, error) {
		return j.signingKey, nil
	}, jwt.WithoutClaimsValidation())
	if err != nil {
		return nil, err
	}
	c, ok := t.Claims.(*claims)
	if !ok {
		return nil, errors.New("error decoding token")
	}
	err = json.Unmarshal(c.J, &payload)
	if err != nil {
		return nil, err
	}
	return payload, nil
}

// ExpiresAtIgnoreExpiry returns the expiration time carried by the token, without
// validating it. It verifies the signature and returns the token's "exp" claim.
func (j *JWT) ExpiresAtIgnoreExpiry(token string) (time.Time, error) {
	t, err := jwt.ParseWithClaims(token, &claims{}, func(token *jwt.Token) (interface{}, error) {
		return j.signingKey, nil
	}, jwt.WithoutClaimsValidation())
	if err != nil {
		return time.Time{}, err
	}
	c, ok := t.Claims.(*claims)
	if !ok {
		return time.Time{}, errors.New("error decoding token")
	}
	if c.ExpiresAt == nil {
		return time.Time{}, errors.New("token has no expiration")
	}
	return time.Unix(c.ExpiresAt.Unix(), 0), nil
}

func (j *JWT) DecodeToken(token string) (payload map[string]interface{}, err error) {
	t, err := jwt.ParseWithClaims(token, &claims{}, func(token *jwt.Token) (interface{}, error) {
		return j.signingKey, nil
	})
	if err != nil {
		return nil, err
	}
	c, ok := t.Claims.(*claims)
	if !ok {
		return nil, errors.New("error decoding token")
	}
	expiresAt := time.Unix(c.ExpiresAt.Unix(), 0)
	et := time.Now().Compare(expiresAt)
	if et != -1 {
		return nil, errors.New("token has expired")
	}
	err = json.Unmarshal(c.J, &payload)
	if err != nil {
		return nil, err
	}
	return payload, nil
}

func (j *JWT) HasExpired(token string) (bool, error) {
	_, err := jwt.ParseWithClaims(token, &claims{}, func(token *jwt.Token) (interface{}, error) {
		return j.signingKey, nil
	})
	if err != nil {
		if errors.Is(err, jwt.ErrTokenExpired) {
			return true, nil
		}
		return true, err
	}
	return false, nil
}

func mapClaims(data map[string]interface{}, expiresAt time.Time) (jwt.Claims, error) {
	j, err := json.Marshal(data)
	if err != nil {
		return claims{}, err
	}
	r := claims{
		j,
		jwt.RegisteredClaims{
			ExpiresAt: jwt.NewNumericDate(expiresAt),
		},
	}
	return r, nil
}