<?php

require_once __DIR__ . '/db.php';

if (session_status() === PHP_SESSION_NONE) {
    session_set_cookie_params([
        'lifetime' => 0,
        'path' => '/',
        'secure' => !empty($_SERVER['HTTPS']) && $_SERVER['HTTPS'] !== 'off',
        'httponly' => true,
        'samesite' => 'Lax',
    ]);
    session_start();
}

function send_private_no_store_headers(): void
{
    if (headers_sent()) {
        return;
    }

    header('Cache-Control: no-store, no-cache, must-revalidate, max-age=0');
    header('Pragma: no-cache');
    header('Expires: 0');
    header('X-Content-Type-Options: nosniff');
    header('Referrer-Policy: same-origin');
}

function csrf_token(): string
{
    if (empty($_SESSION['csrf_token'])) {
        $_SESSION['csrf_token'] = bin2hex(random_bytes(32));
    }

    return $_SESSION['csrf_token'];
}

function csrf_field(): string
{
    return '<input type="hidden" name="csrf_token" value="' .
        htmlspecialchars(csrf_token(), ENT_QUOTES, 'UTF-8') .
        '">';
}

function verify_csrf_token(?string $token): bool
{
    return is_string($token)
        && isset($_SESSION['csrf_token'])
        && hash_equals($_SESSION['csrf_token'], $token);
}

function require_valid_csrf_for_post(): void
{
    if (($_SERVER['REQUEST_METHOD'] ?? '') !== 'POST') {
        return;
    }

    if (verify_csrf_token($_POST['csrf_token'] ?? null)) {
        return;
    }

    http_response_code(419);
    exit('Invalid CSRF token.');
}

function enable_csrf_form_injection(): void
{
    if (PHP_SAPI === 'cli' || defined('FINANCIAL_CSRF_INJECTION_ENABLED')) {
        return;
    }

    define('FINANCIAL_CSRF_INJECTION_ENABLED', true);

    ob_start(static function (string $buffer): string {
        if (
            stripos($buffer, '<form') === false ||
            !preg_match('/method\s*=\s*["\']?post/i', $buffer)
        ) {
            return $buffer;
        }

        $field = csrf_field();

        return preg_replace_callback(
            '/<form\b([^>]*)>/i',
            static function (array $matches) use ($field): string {
                $tag = $matches[0];

                if (
                    stripos($tag, 'method="post"') === false &&
                    stripos($tag, "method='post'") === false &&
                    !preg_match('/method\s*=\s*post/i', $tag)
                ) {
                    return $tag;
                }

                if (stripos($tag, 'csrf_token') !== false) {
                    return $tag;
                }

                return $tag . $field;
            },
            $buffer
        ) ?? $buffer;
    });
}

function throttle_login_attempts(string $username): void
{
    $key = 'login_attempts_' . hash('sha256', strtolower($username) . '|' . ($_SERVER['REMOTE_ADDR'] ?? ''));
    $now = time();
    $attempt = $_SESSION[$key] ?? ['count' => 0, 'first_at' => $now];

    if (($now - (int)$attempt['first_at']) > 900) {
        $attempt = ['count' => 0, 'first_at' => $now];
    }

    if ((int)$attempt['count'] >= 8) {
        throw new RuntimeException('로그인 시도가 많습니다. 잠시 후 다시 시도하세요.');
    }

    $attempt['count']++;
    $_SESSION[$key] = $attempt;
}

function clear_login_attempts(string $username): void
{
    $key = 'login_attempts_' . hash('sha256', strtolower($username) . '|' . ($_SERVER['REMOTE_ADDR'] ?? ''));
    unset($_SESSION[$key]);
}

function login_user(array $user, bool $remember = false): void
{
    session_regenerate_id(true);

    $_SESSION['user_id'] = (int)$user['id'];
    $_SESSION['username'] = $user['username'];

    if ($remember) {
        $token = bin2hex(random_bytes(32));
        $tokenHash = hash('sha256', $token);
        $expiresAt = date('Y-m-d H:i:s', strtotime('+30 days'));

        $pdo = db();
        $stmt = $pdo->prepare("
            UPDATE users
            SET remember_token = ?, remember_expires_at = ?
            WHERE id = ?
        ");
        $stmt->execute([$tokenHash, $expiresAt, $user['id']]);

        setcookie(
            'remember_token',
            $token,
            [
                'expires' => strtotime('+30 days'),
                'path' => '/',
                'secure' => true,
                'httponly' => true,
                'samesite' => 'Lax',
            ]
        );
    }
}

function logout_user(): void
{
    if (!empty($_SESSION['user_id'])) {
        $pdo = db();
        $stmt = $pdo->prepare("
            UPDATE users
            SET remember_token = NULL, remember_expires_at = NULL
            WHERE id = ?
        ");
        $stmt->execute([$_SESSION['user_id']]);
    }

    setcookie(
        'remember_token',
        '',
        [
            'expires' => time() - 3600,
            'path' => '/',
            'secure' => true,
            'httponly' => true,
            'samesite' => 'Lax',
        ]
    );

    $_SESSION = [];
    if (ini_get('session.use_cookies')) {
        $params = session_get_cookie_params();
        setcookie(session_name(), '', time() - 42000, $params['path'], $params['domain'] ?? '', $params['secure'] ?? false, $params['httponly'] ?? false);
    }
    session_destroy();
}

function try_auto_login(): void
{
    if (!empty($_SESSION['user_id'])) {
        return;
    }

    if (empty($_COOKIE['remember_token'])) {
        return;
    }

    $token = $_COOKIE['remember_token'];
    $tokenHash = hash('sha256', $token);

    $pdo = db();
    $stmt = $pdo->prepare("
        SELECT *
        FROM users
        WHERE remember_token = ?
          AND remember_expires_at IS NOT NULL
          AND remember_expires_at > NOW()
        LIMIT 1
    ");
    $stmt->execute([$tokenHash]);
    $user = $stmt->fetch();

    if (!$user) {
        setcookie(
            'remember_token',
            '',
            [
                'expires' => time() - 3600,
                'path' => '/',
                'secure' => true,
                'httponly' => true,
                'samesite' => 'Lax',
            ]
        );
        return;
    }

    $_SESSION['user_id'] = (int)$user['id'];
    $_SESSION['username'] = $user['username'];

    $newToken = bin2hex(random_bytes(32));
    $newHash = hash('sha256', $newToken);
    $expiresAt = date('Y-m-d H:i:s', strtotime('+30 days'));

    $stmt = $pdo->prepare("
        UPDATE users
        SET remember_token = ?, remember_expires_at = ?
        WHERE id = ?
    ");
    $stmt->execute([$newHash, $expiresAt, $user['id']]);

    setcookie(
        'remember_token',
        $newToken,
        [
            'expires' => strtotime('+30 days'),
            'path' => '/',
            'secure' => true,
            'httponly' => true,
            'samesite' => 'Lax',
        ]
    );
}

function check_auth(): void
{
    try_auto_login();

    if (empty($_SESSION['user_id'])) {
        header('Location: /login.php');
        exit;
    }

    send_private_no_store_headers();
}

function user_id(): int
{
    return (int)($_SESSION['user_id'] ?? 0);
}

send_private_no_store_headers();
require_valid_csrf_for_post();
enable_csrf_form_injection();