package database

import (
	"crypto/sha256"
	"database/sql"
	"encoding/hex"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"time"

	_ "modernc.org/sqlite"
)

// UserDB is the global database handle for user data.
var UserDB *sql.DB

// InitUserDB opens (or creates) the user database and initializes the users table.
func InitUserDB(dbPath string) error {
	dir := filepath.Dir(dbPath)
	if dir != "." {
		if err := os.MkdirAll(dir, 0755); err != nil {
			return fmt.Errorf("failed to create database directory: %w", err)
		}
	}

	var err error
	UserDB, err = sql.Open("sqlite", dbPath)
	if err != nil {
		return fmt.Errorf("failed to open user database: %w", err)
	}

	UserDB.SetMaxOpenConns(1) // SQLite serializes writes.
	UserDB.SetMaxIdleConns(1)
	UserDB.SetConnMaxLifetime(5 * time.Minute)

	if err := UserDB.Ping(); err != nil {
		return fmt.Errorf("failed to ping user database: %w", err)
	}

	// Use the rollback journal (DELETE) instead of WAL.
	//
	// WAL memory-maps a -shm index file. modernc.org/sqlite (a C-to-Go
	// transpile) is built without SEH on Windows, so an I/O page fault on that
	// mapping (common when the database lives on an SMB/network share)
	// terminates the process with EXCEPTION_IN_PAGE_ERROR instead of being
	// caught and retried. With SetMaxOpenConns(1) above, WAL provides no
	// concurrency benefit either, so the rollback journal is strictly better.
	if _, err := UserDB.Exec("PRAGMA journal_mode=DELETE"); err != nil {
		return fmt.Errorf("failed to set journal mode: %w", err)
	}

	// Wait up to 5 seconds for a busy database instead of immediately failing with SQLITE_BUSY.
	if _, err := UserDB.Exec("PRAGMA busy_timeout=5000"); err != nil {
		return fmt.Errorf("failed to set busy timeout: %w", err)
	}

	if err := initUserTable(); err != nil {
		return fmt.Errorf("failed to initialize user table: %w", err)
	}

	return nil
}

func initUserTable() error {
	createTableSQL := `
	CREATE TABLE IF NOT EXISTS users (
		id INTEGER PRIMARY KEY AUTOINCREMENT,
		username TEXT NOT NULL UNIQUE,
		password TEXT NOT NULL,
		level TEXT NOT NULL DEFAULT 'admin',
		register_date TEXT NOT NULL
	);`
	_, err := UserDB.Exec(createTableSQL)
	return err
}

// HashPassword returns the SHA-256 hex hash of a password.
func HashPassword(password string) string {
	hash := sha256.Sum256([]byte(password))
	return hex.EncodeToString(hash[:])
}

// ErrUsersExist is returned by RegisterFirstUser when the users table is not
// empty. Registration is only ever allowed for the very first user.
var ErrUsersExist = errors.New("registration rejected: only the first user can be registered via this endpoint")

// RegisterFirstUser atomically creates the first user, but only while the users
// table is empty. The emptiness check and the insert run inside a single
// transaction. Because InitUserDB caps the pool at one connection, a concurrent
// registration blocks at Begin until the in-flight transaction commits, so it
// cannot observe the table as empty between the check and the insert. This
// closes the check-then-insert race two simultaneous first-run registrations
// would otherwise hit.
func RegisterFirstUser(username, password, level string) (int64, error) {
	hashedPassword := HashPassword(password)
	registerDate := time.Now().Format("2006-01-02 15:04:05")

	tx, err := UserDB.Begin()
	if err != nil {
		return 0, fmt.Errorf("failed to begin transaction: %w", err)
	}
	defer tx.Rollback()

	var count int
	if err := tx.QueryRow("SELECT COUNT(*) FROM users").Scan(&count); err != nil {
		return 0, fmt.Errorf("failed to check existing users: %w", err)
	}
	if count > 0 {
		return 0, errors.New("registration closed: users already exist")
	}

	result, err := tx.Exec(
		"INSERT INTO users (username, password, level, register_date) VALUES (?, ?, ?, ?)",
		username, hashedPassword, level, registerDate,
	)
	if err != nil {
		return 0, fmt.Errorf("failed to create user: %w", err)
	}

	if err := tx.Commit(); err != nil {
		return 0, fmt.Errorf("failed to commit user creation: %w", err)
	}
	return result.LastInsertId()
}

// GetUserByUsername retrieves a user by username and validates the password.
func GetUserByUsername(username, password string) (int64, string, string, string, error) {
	hashedPassword := HashPassword(password)

	var id int64
	var dbUsername string
	var level string
	var registerDate string

	err := UserDB.QueryRow(
		"SELECT id, username, level, register_date FROM users WHERE username = ? AND password = ?",
		username, hashedPassword,
	).Scan(&id, &dbUsername, &level, &registerDate)

	if err == sql.ErrNoRows {
		return 0, "", "", "", fmt.Errorf("invalid username or password")
	}
	if err != nil {
		return 0, "", "", "", fmt.Errorf("database error: %w", err)
	}

	return id, dbUsername, level, registerDate, nil
}

// GetUserCount returns the total number of users in the database.
func GetUserCount() (int, error) {
	var count int
	err := UserDB.QueryRow("SELECT COUNT(*) FROM users").Scan(&count)
	return count, err
}

// GetUserByID retrieves a user by their ID.
func GetUserByID(id int64) (string, string, string, error) {
	var username string
	var level string
	var registerDate string

	err := UserDB.QueryRow(
		"SELECT username, level, register_date FROM users WHERE id = ?",
		id,
	).Scan(&username, &level, &registerDate)

	if err == sql.ErrNoRows {
		return "", "", "", fmt.Errorf("user not found")
	}
	if err != nil {
		return "", "", "", fmt.Errorf("database error: %w", err)
	}

	return username, level, registerDate, nil
}

// CloseUserDB closes the user database connection.
func CloseUserDB() {
	if UserDB != nil {
		UserDB.Close()
	}
}