package auth

import (
	"database/sql"
	"encoding/base64"
	"errors"
	"time"

	"github.com/go-webauthn/webauthn/webauthn"
	"golang.org/x/crypto/bcrypt"
)

var (
	ErrInvalidCredentials = errors.New("invalid username or password")
	ErrUserNotFound       = errors.New("user not found")
	ErrUserExists         = errors.New("username already exists")
)

// User represents an authenticated user
type User struct {
	ID           int64
	Username     string
	PasswordHash string
	CreatedAt    time.Time
}

// Service handles authentication operations
type Service struct {
	db *sql.DB
}

// NewService creates a new auth service
func NewService(db *sql.DB) *Service {
	return &Service{db: db}
}

// Authenticate verifies username and password, returns user ID if valid
func (s *Service) Authenticate(username, password string) (*User, error) {
	user, err := s.GetUserByUsername(username)
	if err != nil {
		if errors.Is(err, ErrUserNotFound) {
			return nil, ErrInvalidCredentials
		}
		return nil, err
	}

	if err := bcrypt.CompareHashAndPassword([]byte(user.PasswordHash), []byte(password)); err != nil {
		return nil, ErrInvalidCredentials
	}

	return user, nil
}

// GetUserByUsername retrieves a user by username
func (s *Service) GetUserByUsername(username string) (*User, error) {
	var user User
	err := s.db.QueryRow(
		`SELECT id, username, password_hash, created_at FROM users WHERE username = ?`,
		username,
	).Scan(&user.ID, &user.Username, &user.PasswordHash, &user.CreatedAt)

	if err == sql.ErrNoRows {
		return nil, ErrUserNotFound
	}
	if err != nil {
		return nil, err
	}

	return &user, nil
}

// GetUserByID retrieves a user by ID
func (s *Service) GetUserByID(id int64) (*User, error) {
	var user User
	err := s.db.QueryRow(
		`SELECT id, username, password_hash, created_at FROM users WHERE id = ?`,
		id,
	).Scan(&user.ID, &user.Username, &user.PasswordHash, &user.CreatedAt)

	if err == sql.ErrNoRows {
		return nil, ErrUserNotFound
	}
	if err != nil {
		return nil, err
	}

	return &user, nil
}

// CreateUser creates a new user with the given username and password
func (s *Service) CreateUser(username, password string) (*User, error) {
	// Check if user exists
	_, err := s.GetUserByUsername(username)
	if err == nil {
		return nil, ErrUserExists
	}
	if !errors.Is(err, ErrUserNotFound) {
		return nil, err
	}

	// Hash password
	hash, err := bcrypt.GenerateFromPassword([]byte(password), bcrypt.DefaultCost)
	if err != nil {
		return nil, err
	}

	// Insert user
	result, err := s.db.Exec(
		`INSERT INTO users (username, password_hash) VALUES (?, ?)`,
		username, string(hash),
	)
	if err != nil {
		return nil, err
	}

	id, err := result.LastInsertId()
	if err != nil {
		return nil, err
	}

	return s.GetUserByID(id)
}

// UserCount returns the number of users in the database
func (s *Service) UserCount() (int, error) {
	var count int
	err := s.db.QueryRow(`SELECT COUNT(*) FROM users`).Scan(&count)
	return count, err
}

// EnsureDefaultUser creates a default admin user if no users exist
func (s *Service) EnsureDefaultUser(username, password string) error {
	count, err := s.UserCount()
	if err != nil {
		return err
	}

	if count == 0 {
		_, err = s.CreateUser(username, password)
		return err
	}

	return nil
}

// WebAuthnUser wraps User to implement the webauthn.User interface
type WebAuthnUser struct {
	*User
	credentials []webauthn.Credential
}

func (u *WebAuthnUser) WebAuthnID() []byte {
	b := make([]byte, 8)
	id := u.ID
	for i := range 8 {
		b[i] = byte(id >> (i * 8))
	}
	return b
}

func (u *WebAuthnUser) WebAuthnName() string        { return u.Username }
func (u *WebAuthnUser) WebAuthnDisplayName() string  { return u.Username }
func (u *WebAuthnUser) WebAuthnCredentials() []webauthn.Credential { return u.credentials }

// SaveWebAuthnCredential stores a new WebAuthn credential for a user
func (s *Service) SaveWebAuthnCredential(userID int64, cred *webauthn.Credential, name string) error {
	credID := base64.RawURLEncoding.EncodeToString(cred.ID)
	_, err := s.db.Exec(
		`INSERT INTO webauthn_credentials (id, user_id, public_key, attestation_type, aaguid, sign_count, name)
		 VALUES (?, ?, ?, ?, ?, ?, ?)`,
		credID, userID, cred.PublicKey, cred.AttestationType, cred.Authenticator.AAGUID, cred.Authenticator.SignCount, name,
	)
	return err
}

// GetWebAuthnCredentials returns all WebAuthn credentials for a user
func (s *Service) GetWebAuthnCredentials(userID int64) ([]webauthn.Credential, error) {
	rows, err := s.db.Query(
		`SELECT id, public_key, attestation_type, aaguid, sign_count FROM webauthn_credentials WHERE user_id = ?`,
		userID,
	)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var creds []webauthn.Credential
	for rows.Next() {
		var (
			credIDStr       string
			publicKey       []byte
			attestationType string
			aaguid          []byte
			signCount       uint32
		)
		if err := rows.Scan(&credIDStr, &publicKey, &attestationType, &aaguid, &signCount); err != nil {
			return nil, err
		}
		credID, err := base64.RawURLEncoding.DecodeString(credIDStr)
		if err != nil {
			return nil, err
		}
		creds = append(creds, webauthn.Credential{
			ID:              credID,
			PublicKey:       publicKey,
			AttestationType: attestationType,
			Authenticator: webauthn.Authenticator{
				AAGUID:    aaguid,
				SignCount: signCount,
			},
		})
	}
	return creds, rows.Err()
}

// WebAuthnCredentialInfo holds display info for a stored passkey
type WebAuthnCredentialInfo struct {
	ID        string
	Name      string
	CreatedAt time.Time
}

// GetWebAuthnCredentialInfos returns display info for a user's passkeys
func (s *Service) GetWebAuthnCredentialInfos(userID int64) ([]WebAuthnCredentialInfo, error) {
	rows, err := s.db.Query(
		`SELECT id, name, created_at FROM webauthn_credentials WHERE user_id = ? ORDER BY created_at DESC`,
		userID,
	)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var infos []WebAuthnCredentialInfo
	for rows.Next() {
		var info WebAuthnCredentialInfo
		if err := rows.Scan(&info.ID, &info.Name, &info.CreatedAt); err != nil {
			return nil, err
		}
		infos = append(infos, info)
	}
	return infos, rows.Err()
}

// DeleteWebAuthnCredential removes a WebAuthn credential by its ID
func (s *Service) DeleteWebAuthnCredential(credID string) error {
	result, err := s.db.Exec(`DELETE FROM webauthn_credentials WHERE id = ?`, credID)
	if err != nil {
		return err
	}
	n, _ := result.RowsAffected()
	if n == 0 {
		return errors.New("credential not found")
	}
	return nil
}

// UpdateWebAuthnCredentialSignCount updates the sign count after a successful assertion
func (s *Service) UpdateWebAuthnCredentialSignCount(credID string, signCount uint32) error {
	_, err := s.db.Exec(`UPDATE webauthn_credentials SET sign_count = ? WHERE id = ?`, signCount, credID)
	return err
}

// GetUserWithCredentials returns a WebAuthnUser with loaded credentials
func (s *Service) GetUserWithCredentials(userID int64) (*WebAuthnUser, error) {
	user, err := s.GetUserByID(userID)
	if err != nil {
		return nil, err
	}
	creds, err := s.GetWebAuthnCredentials(userID)
	if err != nil {
		return nil, err
	}
	return &WebAuthnUser{User: user, credentials: creds}, nil
}

// FindUserByCredentialID finds the user who owns a given credential ID (for discoverable login)
func (s *Service) FindUserByCredentialID(credID []byte) (*WebAuthnUser, error) {
	credIDStr := base64.RawURLEncoding.EncodeToString(credID)
	var userID int64
	err := s.db.QueryRow(`SELECT user_id FROM webauthn_credentials WHERE id = ?`, credIDStr).Scan(&userID)
	if err == sql.ErrNoRows {
		return nil, ErrUserNotFound
	}
	if err != nil {
		return nil, err
	}
	return s.GetUserWithCredentials(userID)
}