Service.php

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<?php
namespace Elgg\Ajax;

use Elgg\Amd\Config;
use Elgg\Http\Input;
use Elgg\PluginHooksService;
use Elgg\Services\AjaxResponse;
use Elgg\SystemMessagesService;
use RuntimeException;
use Symfony\Component\HttpFoundation\JsonResponse;

class Service {

    private $hooks;

    private $msgs;

    private $input;

    private $amd_config;

    private $response_sent = false;

    public function __construct(PluginHooksService $hooks, SystemMessagesService $msgs, Input $input, Config $amdConfig) {
        $this->hooks = $hooks;
        $this->msgs = $msgs;
        $this->input = $input;
        $this->amd_config = $amdConfig;

        if ($this->input->get('elgg_fetch_messages', true)) {
            $message_filter = [$this, 'appendMessages'];
            $this->hooks->registerHandler(AjaxResponse::RESPONSE_HOOK, 'all', $message_filter, 999);
        }

        if ($this->input->get('elgg_fetch_deps', true)) {
            $deps_filter = [$this, 'appendDeps'];
            $this->hooks->registerHandler(AjaxResponse::RESPONSE_HOOK, 'all', $deps_filter, 999);
        }
    }

    public function isAjax2Request() {
        $version = _elgg_services()->request->headers->get('X-Elgg-Ajax-API');
        return ($version === '2');
    }

    public function isReady() {
        return !$this->response_sent && $this->isAjax2Request();
    }

    public function decodeJson($string) {
        if (!is_string($string)) {
            return $string;
        }
        $object = json_decode($string);
        return ($object === null) ? $string : $object;
    }

    public function respondFromOutput($output, $hook_type = '', $try_decode = true) {
        if ($try_decode) {
            $output = $this->decodeJson($output);
        }

        $api_response = new Response();
        $api_response->setData((object)[
            'value' => $output,
        ]);
        $api_response = $this->filterApiResponse($api_response, $hook_type);
        $response = $this->buildHttpResponse($api_response);

        $this->response_sent = true;
        $response->send();
    }

    public function respondFromApiResponse(AjaxResponse $api_response, $hook_type = '') {
        $api_response = $this->filterApiResponse($api_response, $hook_type);
        $response = $this->buildHttpResponse($api_response);

        $this->response_sent = true;
        $response->send();
    }

    public function respondWithError($msg, $status = 400) {
        $response = new JsonResponse(['error' => $msg], $status);

        $this->response_sent = true;
        $response->send();
    }

    private function filterApiResponse(AjaxResponse $api_response, $hook_type = '') {
        $api_response->setTtl($this->input->get('elgg_response_ttl', 0, false));

        if ($hook_type) {
            $hook = AjaxResponse::RESPONSE_HOOK;
            $api_response = $this->hooks->trigger($hook, $hook_type, null, $api_response);
            if (!$api_response instanceof AjaxResponse) {
                throw new RuntimeException("The value returned by hook [$hook, $hook_type] was not an ApiResponse");
            }
        }

        return $api_response;
    }

    private function buildHttpResponse(AjaxResponse $api_response, $allow_removing_headers = true) {
        if ($api_response->isCancelled()) {
            return new JsonResponse(['error' => "The response was cancelled"], 400);
        }

        $response = new JsonResponse($api_response->getData());

        $ttl = $api_response->getTtl();
        if ($ttl > 0) {
            // Required to remove headers set by PHP session
            if ($allow_removing_headers) {
                header_remove('Expires');
                header_remove('Pragma');
                header_remove('Cache-Control');
            }

            // JsonRequest sets a default Cache-Control header we don't want
            $response->headers->remove('Cache-Control');

            $response->setClientTtl($ttl);

            // if we don't set Expires, Apache will add a far-off max-age and Expires for us.
            $response->headers->set('Expires', gmdate('D, d M Y H:i:s \G\M\T', time() + $ttl));
        }

        return $response;
    }

    public function appendMessages($hook, $type, AjaxResponse $response, $params) {
        $response->getData()->_elgg_msgs = (object)$this->msgs->dumpRegister();
        return $response;
    }

    public function appendDeps($hook, $type, AjaxResponse $response, $params) {
        $response->getData()->_elgg_deps = (array) $this->amd_config->getDependencies();
        return $response;
    }

}