package auth

import (
	"crypto/rand"
	"encoding/hex"
	"errors"
	"time"

	"github.com/golang-jwt/jwt/v5"
	"golang.org/x/crypto/bcrypt"

	"github.com/llamalink/llamalink/internal/db"
)

var (
	ErrInvalidAdminCredentials = errors.New("invalid username or password")
	ErrAdminNotFound         = errors.New("admin user not found")
	ErrAdminInactive         = errors.New("admin user is inactive")
)

type AdminClaims struct {
	Username string `json:"username"`
	jwt.RegisteredClaims
}

type AdminJWTService struct {
	secret []byte
	ttl    time.Duration
}

func NewAdminJWTService(secret []byte, ttlSeconds int) *AdminJWTService {
	return &AdminJWTService{
		secret: secret,
		ttl:    time.Duration(ttlSeconds) * time.Second,
	}
}

func (s *AdminJWTService) IssueToken(user *db.AdminUser) (string, time.Time, error) {
	expiresAt := time.Now().Add(s.ttl)
	claims := &AdminClaims{
		Username: user.Username,
		RegisteredClaims: jwt.RegisteredClaims{
			Subject:   user.ID.String(),
			ExpiresAt: jwt.NewNumericDate(expiresAt),
			IssuedAt:  jwt.NewNumericDate(time.Now()),
		},
	}
	token := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
	tokenStr, err := token.SignedString(s.secret)
	return tokenStr, expiresAt, err
}

func (s *AdminJWTService) VerifyToken(tokenStr string) (*AdminClaims, error) {
	token, err := jwt.ParseWithClaims(tokenStr, &AdminClaims{}, func(token *jwt.Token) (interface{}, error) {
		if _, ok := token.Method.(*jwt.SigningMethodHMAC); !ok {
			return nil, errors.New("unexpected signing method")
		}
		return s.secret, nil
	})
	if err != nil {
		return nil, err
	}
	claims, ok := token.Claims.(*AdminClaims)
	if !ok || !token.Valid {
		return nil, errors.New("invalid token")
	}
	return claims, nil
}

func ValidateAdminPassword(user *db.AdminUser, password string) error {
	if !user.IsActive {
		return ErrAdminInactive
	}
	if err := bcrypt.CompareHashAndPassword([]byte(user.PasswordHash), []byte(password)); err != nil {
		return ErrInvalidAdminCredentials
	}
	return nil
}

func GenerateSecureToken(length int) (string, error) {
	bytes := make([]byte, length)
	if _, err := rand.Read(bytes); err != nil {
		return "", err
	}
	return hex.EncodeToString(bytes), nil
}