/**
     * Writes directives to WP .htaccess / nginx.conf
     * returns true if modifications has been made
     */
    private function rules_core_add($config, $exs)
    {
        $path = Util_Rule::get_pgcache_rules_core_path();
        if ($path === false) {
            return;
        }
        $original_data = @file_get_contents($path);
        if ($original_data === false) {
            $original_data = '';
        }
        $data = $original_data;
        if ($has_wpsc = Util_Rule::has_rules($data, W3TC_MARKER_BEGIN_PGCACHE_WPSC, W3TC_MARKER_END_PGCACHE_WPSC)) {
            $data = Util_Rule::erase_rules($data, W3TC_MARKER_BEGIN_PGCACHE_WPSC, W3TC_MARKER_END_PGCACHE_WPSC);
        }
        $rules = $this->rules_core_generate($config);
        $rules_missing = strstr(Util_Rule::clean_rules($data), Util_Rule::clean_rules($rules)) === false;
        if (!$has_wpsc && !$rules_missing) {
            return;
        }
        // modification of file not required
        $replace_start = strpos($data, W3TC_MARKER_BEGIN_PGCACHE_CORE);
        $replace_end = strpos($data, W3TC_MARKER_END_PGCACHE_CORE);
        if ($replace_start !== false && $replace_end !== false && $replace_start < $replace_end) {
            $replace_length = $replace_end - $replace_start + strlen(W3TC_MARKER_END_PGCACHE_CORE) + 1;
        } else {
            $replace_start = false;
            $replace_length = 0;
            $search = array(W3TC_MARKER_BEGIN_BROWSERCACHE_NO404WP => 0, W3TC_MARKER_BEGIN_WORDPRESS => 0, W3TC_MARKER_END_MINIFY_CORE => strlen(W3TC_MARKER_END_MINIFY_CORE) + 1, W3TC_MARKER_END_BROWSERCACHE_CACHE => strlen(W3TC_MARKER_END_BROWSERCACHE_CACHE) + 1, W3TC_MARKER_END_PGCACHE_CACHE => strlen(W3TC_MARKER_END_PGCACHE_CACHE) + 1, W3TC_MARKER_END_MINIFY_CACHE => strlen(W3TC_MARKER_END_MINIFY_CACHE) + 1);
            foreach ($search as $string => $length) {
                $replace_start = strpos($data, $string);
                if ($replace_start !== false) {
                    $replace_start += $length;
                    break;
                }
            }
        }
        if ($replace_start !== false) {
            $data = Util_Rule::trim_rules(substr_replace($data, $rules, $replace_start, $replace_length));
        } else {
            $data = Util_Rule::trim_rules($data . $rules);
        }
        try {
            Util_WpFile::write_to_file($path, $data);
        } catch (Util_WpFile_FilesystemOperationException $ex) {
            if ($has_wpsc) {
                $exs->push(new Util_WpFile_FilesystemModifyException($ex->getMessage(), $ex->credentials_form(), sprintf(__('Edit file <strong>%s</strong> and remove all lines between and including
								<strong>%s</strong> and <strong>%s</strong> markers.', 'w3-total-cache'), $path, W3TC_MARKER_BEGIN_PGCACHE_WPSC, W3TC_MARKER_END_PGCACHE_WPSC), $path));
            }
            if ($rules_missing) {
                if (strpos($data, W3TC_MARKER_BEGIN_PGCACHE_CORE) !== false) {
                    $exs->push(new Util_WpFile_FilesystemModifyException($ex->getMessage(), $ex->credentials_form(), sprintf(__('Edit file <strong>%s</strong> and replace all lines between and including
									<strong>%s</strong> and <strong>%s</strong> markers with:', 'w3-total-cache'), $path, W3TC_MARKER_BEGIN_PGCACHE_CORE, W3TC_MARKER_END_PGCACHE_CORE), $path, $rules));
                } else {
                    $exs->push(new Util_WpFile_FilesystemModifyException($ex->getMessage(), $ex->credentials_form(), sprintf(__('Edit file <strong>%s</strong> and add the following rules above the WordPress
									directives:'), $path), $path, $rules));
                }
            }
            return;
        }
        Util_Rule::after_rules_modified();
    }