package security

import (
	"errors"
	"time"

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

const TokenAudience = "KRA"

var (
	ErrEmptySigningKey       = errors.New("empty JWT signing key")
	ErrInvalidClaims         = errors.New("invalid token claims")
	ErrTokenExpired          = errors.New("token expired")
	ErrTokenMalformed        = errors.New("token malformed")
	ErrTokenSignatureInvalid = errors.New("token signature invalid")
	ErrTokenNotValidYet      = errors.New("token not valid yet")
	ErrTokenInvalid          = errors.New("token invalid")
)

type Claims struct {
	UUID            string
	ID              uint
	Username        string
	NickName        string
	AuthorityID     uint `json:"AuthorityId"`
	BufferTime      int64
	UserType        string
	MustChangePwd   bool  `json:"mustChangePwd"`
	PasswordVersion int64 `json:"passwordVersion,omitempty"`
	jwt.RegisteredClaims
}

func Generate(secret, issuer string, expires, buffer time.Duration, userID, authorityID uint, uuid, username, nickname string, mustChange bool, passwordVersion int64) (string, *Claims, error) {
	if err := validateSigningOptions(secret, expires, buffer); err != nil {
		return "", nil, err
	}
	now := time.Now()
	claims := &Claims{UUID: uuid, ID: userID, Username: username, NickName: nickname, AuthorityID: authorityID, BufferTime: int64(buffer / time.Second), UserType: "admin", MustChangePwd: mustChange, PasswordVersion: passwordVersion, RegisteredClaims: jwt.RegisteredClaims{Audience: jwt.ClaimStrings{TokenAudience}, Issuer: issuer, IssuedAt: jwt.NewNumericDate(now), NotBefore: jwt.NewNumericDate(now.Add(-time.Second)), ExpiresAt: jwt.NewNumericDate(now.Add(expires))}}
	token, err := Sign(secret, claims)
	return token, claims, err
}

func Sign(secret string, claims *Claims) (string, error) {
	if secret == "" {
		return "", ErrEmptySigningKey
	}
	if claims == nil {
		return "", ErrInvalidClaims
	}
	return jwt.NewWithClaims(jwt.SigningMethodHS256, claims).SignedString([]byte(secret))
}

func Parse(tokenString, secret string) (*Claims, error) {
	return parse(tokenString, secret, "")
}

// ParseWithIssuer validates a KRA admin token and its configured issuer.
func ParseWithIssuer(tokenString, secret, issuer string) (*Claims, error) {
	return parse(tokenString, secret, issuer)
}

func parse(tokenString, secret, issuer string) (*Claims, error) {
	if secret == "" {
		return nil, ErrEmptySigningKey
	}
	options := []jwt.ParserOption{
		jwt.WithValidMethods([]string{jwt.SigningMethodHS256.Alg()}),
		jwt.WithAudience(TokenAudience),
		jwt.WithExpirationRequired(),
		jwt.WithNotBeforeRequired(),
		jwt.WithLeeway(time.Second),
	}
	if issuer != "" {
		options = append(options, jwt.WithIssuer(issuer))
	}
	token, err := jwt.ParseWithClaims(tokenString, &Claims{}, func(token *jwt.Token) (any, error) {
		if token.Method != jwt.SigningMethodHS256 {
			return nil, errors.New("unexpected signing method")
		}
		return []byte(secret), nil
	}, options...)
	if err != nil {
		switch {
		case errors.Is(err, jwt.ErrTokenExpired):
			return nil, ErrTokenExpired
		case errors.Is(err, jwt.ErrTokenMalformed):
			return nil, ErrTokenMalformed
		case errors.Is(err, jwt.ErrTokenSignatureInvalid):
			return nil, ErrTokenSignatureInvalid
		case errors.Is(err, jwt.ErrTokenNotValidYet):
			return nil, ErrTokenNotValidYet
		default:
			return nil, ErrTokenInvalid
		}
	}
	if !token.Valid {
		return nil, ErrTokenInvalid
	}
	claims, ok := token.Claims.(*Claims)
	if !ok {
		return nil, ErrInvalidClaims
	}
	return claims, nil
}

func validateSigningOptions(secret string, expires, buffer time.Duration) error {
	if secret == "" {
		return ErrEmptySigningKey
	}
	if expires <= 0 {
		return errors.New("JWT expiration must be positive")
	}
	if buffer < 0 {
		return errors.New("JWT buffer must not be negative")
	}
	return nil
}