<?php
// Admin authentication: sessions, login throttling and CSRF protection.

if (basename($_SERVER['SCRIPT_FILENAME'] ?? '') === basename(__FILE__)) {
    http_response_code(403);
    exit;
}

require_once __DIR__ . '/db.php';

// Log out after this long without activity
const ADMIN_IDLE_TIMEOUT = 4 * 60 * 60;
// Failed logins allowed from one IP address within the lockout window
const LOGIN_MAX_FAILURES = 5;
const LOGIN_LOCKOUT_MINUTES = 15;

function startAdminSession(): void {
    if (session_status() === PHP_SESSION_ACTIVE) return;

    $https = !empty($_SERVER['HTTPS']) && $_SERVER['HTTPS'] !== 'off';
    session_name('rfe_admin');
    session_set_cookie_params([
        'lifetime' => 0,
        // Only sent to the admin pages, not the rest of the site or other apps on the domain
        'path'     => rtrim(dirname($_SERVER['SCRIPT_NAME']), '/') . '/',
        'secure'   => $https,
        'httponly' => true,
        'samesite' => 'Strict',
    ]);
    ini_set('session.use_strict_mode', '1');
    session_start();

    // Admin pages should never be cached, framed or indexed
    header('Cache-Control: no-store');
    header('X-Frame-Options: DENY');
    header('X-Robots-Tag: noindex, nofollow');

    if (isset($_SESSION['admin_id'], $_SESSION['last_activity']) && time() - $_SESSION['last_activity'] > ADMIN_IDLE_TIMEOUT) {
        logoutAdmin();
        session_start();
    }
    $_SESSION['last_activity'] = time();
}

function currentAdmin(): ?array {
    startAdminSession();
    if (!isset($_SESSION['admin_id'])) return null;

    $stmt = getDB()->prepare('SELECT id, username FROM admins WHERE id = ?');
    $stmt->execute([$_SESSION['admin_id']]);
    return $stmt->fetch() ?: null;
}

// Call at the top of every admin page; sends anyone not logged in to the login page
function requireAdmin(): array {
    $admin = currentAdmin();
    if ($admin === null) {
        header('Location: login.php');
        exit;
    }
    return $admin;
}

function loginLockedOut(PDO $db, string $ip): bool {
    $stmt = $db->prepare(
        'SELECT COUNT(*) FROM login_attempts
         WHERE ip_address = ? AND attempted_at > NOW() - INTERVAL ' . LOGIN_LOCKOUT_MINUTES . ' MINUTE'
    );
    $stmt->execute([$ip]);
    return $stmt->fetchColumn() >= LOGIN_MAX_FAILURES;
}

// Returns null on success, or an error message to show on the login form
function attemptLogin(string $username, string $password): ?string {
    startAdminSession();
    $db = getDB();
    $ip = $_SERVER['REMOTE_ADDR'] ?? '';

    $db->exec('DELETE FROM login_attempts WHERE attempted_at < NOW() - INTERVAL 1 DAY');
    if (loginLockedOut($db, $ip)) {
        return 'Too many failed logins. Please wait ' . LOGIN_LOCKOUT_MINUTES . ' minutes and try again.';
    }

    $stmt = $db->prepare('SELECT id, password_hash FROM admins WHERE username = ?');
    $stmt->execute([$username]);
    $admin = $stmt->fetch();

    // Verify against a dummy hash for unknown usernames so response time doesn't reveal which usernames exist
    $hash = $admin['password_hash'] ?? '$2y$10$lH52eP6Hg.ZFcO9AwUw/lOzZ9REOgwKxOJrLCqF9eKJGV0a4OiYNG';
    if (!password_verify($password, $hash) || !$admin) {
        $db->prepare('INSERT INTO login_attempts (ip_address) VALUES (?)')->execute([$ip]);
        return 'Incorrect username or password.';
    }

    if (password_needs_rehash($admin['password_hash'], PASSWORD_DEFAULT)) {
        $db->prepare('UPDATE admins SET password_hash = ? WHERE id = ?')
           ->execute([password_hash($password, PASSWORD_DEFAULT), $admin['id']]);
    }
    $db->prepare('UPDATE admins SET last_login_at = NOW() WHERE id = ?')->execute([$admin['id']]);
    $db->prepare('DELETE FROM login_attempts WHERE ip_address = ?')->execute([$ip]);

    // New session ID on login to prevent session fixation
    session_regenerate_id(true);
    $_SESSION = ['admin_id' => (int)$admin['id'], 'last_activity' => time()];
    return null;
}

function logoutAdmin(): void {
    $_SESSION = [];
    $params = session_get_cookie_params();
    setcookie(session_name(), '', [
        'expires'  => time() - 3600,
        'path'     => $params['path'],
        'secure'   => $params['secure'],
        'httponly' => true,
        'samesite' => 'Strict',
    ]);
    session_destroy();
}

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

function csrfField(): string {
    return '<input type="hidden" name="csrf_token" value="' . csrfToken() . '">';
}

// Call at the start of handling any POST; stops the request if the token is missing or wrong
function verifyCsrf(): void {
    startAdminSession();
    $token = $_POST['csrf_token'] ?? '';
    if (!is_string($token) || empty($_SESSION['csrf_token']) || !hash_equals($_SESSION['csrf_token'], $token)) {
        http_response_code(400);
        exit('Your session has expired. Please go back, reload the page and try again.');
    }
}