package db

import (
	"crypto/rand"
	"crypto/subtle"
	"encoding/base64"
	"errors"
	"fmt"
	"strings"
	"time"

	"github.com/google/uuid"
	"golang.org/x/crypto/argon2"
	"gorm.io/gorm"
)

type User struct {
	ID        uint   `gorm:"primaryKey"`
	User      string `gorm:"uniqueIndex"`
	Password  string
	Admin     bool
	CreatedAt time.Time
	UpdatedAt time.Time
	DeletedAt gorm.DeletedAt
}

func NewUser(db *gorm.DB, username string, password string, admin bool) error {
	// Generate a new UUID for the user
	id, err := uuid.NewRandom()
	if err != nil {
		return err
	}

	// Hash the password using argon2id
	hashedPassword, err := HashPassword(password)
	if err != nil {
		return err
	}

	// Create a new user record
	user := &User{
		ID:       uint(id.ID()),
		User:     username,
		Password: hashedPassword,
		Admin:    admin,
	}
	return db.Create(user).Error
}

func Authenticate(db *gorm.DB, username string, password string) (*User, error) {
	// Get the user record by username
	var user User
	if err := db.Where("user = ?", username).First(&user).Error; err != nil {
		return nil, errors.New("user not found")
	}

	// Compare the hashed password with the provided password
	valid, err := comparePassword(user.Password, password)
	if err != nil {
		return nil, err
	}
	if !valid {
		return nil, errors.New("invalid password")
	}

	return &user, nil
}

const (
	pwdSaltSize = 16
	pwdHashSize = 32
	pwdParams   = "m=65536,t=2,p=1"
	pwdAlgo     = "argon2id"
)

func HashPassword(password string) (string, error) {
	// Generate a salt for the password hash
	salt := make([]byte, pwdSaltSize)
	if _, err := rand.Read(salt); err != nil {
		return "", err
	}

	// Hash the password using argon2id
	hash := argon2.IDKey([]byte(password), salt, 2, 64*1024, 1, pwdHashSize)

	// Encode the salt and hash as a string in PHC format
	encodedSalt := base64.RawStdEncoding.EncodeToString(salt)
	encodedHash := base64.RawStdEncoding.EncodeToString(hash)
	return fmt.Sprintf("$%s$%s$%s$%s", pwdAlgo, pwdParams, encodedSalt, encodedHash), nil
}

var errInvalidDBPasswordFormat = errors.New("invalid password format in db")
func comparePassword(hashedPassword string, password string) (bool, error) {
	// Extract the salt and hash from the hashed password string
	fields := strings.Split(hashedPassword, "$")
	if len(fields) != 5 || fields[1] != pwdAlgo || fields[2] != pwdParams {
		return false, errInvalidDBPasswordFormat
	}
	encodedSalt, encodedHash := fields[3], fields[4]

	// Decode the salt and hash from base64
	salt, err := base64.RawStdEncoding.DecodeString(encodedSalt)
	if err != nil {
		return false, err
	}
	hash, err := base64.RawStdEncoding.DecodeString(encodedHash)
	if err != nil {
		return false, err
	}

	// Hash the password using the extracted salt and parameters
	computedHash := argon2.IDKey([]byte(password), salt, 2, 64*1024, 1, pwdHashSize)

	// Compare the computed hash with the stored hash
	return subtle.ConstantTimeCompare(hash, computedHash) == 1, nil
}

// DeleteUser deletes a user with the specified username from the database.
func DeleteUser(db *gorm.DB, username string) error {
	// Find the user by username
	var user User
	if err := db.Where("user = ?", username).First(&user).Error; err != nil {
		return err
	}

	// Delete the user
	if err := db.Delete(&user).Error; err != nil {
		return err
	}

	return nil
}

func ChangeUser(db *gorm.DB, username string, updatedUser *User) error {
	// Retrieve the existing user
	var existingUser User
	if err := db.Where("user = ?", username).First(&existingUser).Error; err != nil {
		return err
	}

	// Update the user fields
	existingUser.User = updatedUser.User
	existingUser.Password = updatedUser.Password
	existingUser.Admin = updatedUser.Admin

	// Save the updated user to the database
	if err := db.Save(&existingUser).Error; err != nil {
		return err
	}

	return nil
}

func CreateAdminUser(db *gorm.DB, adminUsername string) error {
	// Check if the admin user already exists
	var admins []User
	if err := db.Unscoped().Limit(1).Where("user = ?", adminUsername).Find(&admins).Error; err != nil {
		return err
	}
	if len(admins) > 0 {
		// already exists
		return nil
	}

	// Generate a random 24-char password
	passwordBytes := make([]byte, 24)
	if _, err := rand.Read(passwordBytes); err != nil {
		return err
	}
	password := base64.URLEncoding.EncodeToString(passwordBytes)

	// Create the admin user
	if err := NewUser(db, adminUsername, password, true); err != nil {
		return err
	}

	// Print out the generated password
	fmt.Printf("Generated password for admin user %s: %s\n", adminUsername, password)

	return nil
}