Alert When wp-config.php, .htaccess or Root Files Change

$wpide_root_snapshot = function () {
    $root  = ABSPATH;
    $files = array();

    foreach ( (array) glob( $root . '{*.php,.htaccess,.user.ini,php.ini}', GLOB_BRACE ) as $path ) {
        if ( is_file( $path ) ) {
            $files[ basename( $path ) ] = md5_file( $path );
        }
    }

    $config = dirname( ABSPATH ) . '/wp-config.php';
    if ( ! isset( $files['wp-config.php'] ) && is_file( $config ) ) {
        $files['../wp-config.php'] = md5_file( $config );
    }

    return $files;
};

add_action( 'init', function () {
    if ( ! wp_next_scheduled( 'wpide_root_files_check' ) ) {
        wp_schedule_event( time() + HOUR_IN_SECONDS, 'daily', 'wpide_root_files_check' );
    }
} );

add_action( 'wpide_root_files_check', function () use ( $wpide_root_snapshot ) {
    $now = $wpide_root_snapshot();
    $old = get_option( 'wpide_root_files' );
    update_option( 'wpide_root_files', $now, false );

    if ( ! is_array( $old ) ) {
        return;
    }

    $lines = array();
    foreach ( array_diff_key( $now, $old ) as $file => $hash ) {
        $lines[] = 'New file: ' . $file;
    }
    foreach ( array_diff_key( $old, $now ) as $file => $hash ) {
        $lines[] = 'Removed: ' . $file;
    }
    foreach ( array_intersect_key( $now, $old ) as $file => $hash ) {
        if ( $old[ $file ] !== $hash ) {
            $lines[] = 'Changed: ' . $file;
        }
    }

    if ( $lines ) {
        wp_mail( get_option( 'admin_email' ), sprintf( '[%s] Files in the site root changed', wp_specialchars_decode( get_bloginfo( 'name' ), ENT_QUOTES ) ), implode( "\n", $lines ) . "\n\nCore updates change some of these files; if you did not update WordPress or edit them, check them now." );
    }
} );