Stack Exchange Answers Atom Feed

stackexchangeatom.php

<?php

function oops ($message = '')
{
    http_response_code(400);
    die($message);
}

function get_json ($url)
{
    $json = json_decode(gzdecode(file_get_contents($url)), true);
    if (isset($json['backoff']))
        oops('Backoff!');
    return $json['items'];
}

function format_date ($date)
{
    return gmdate('Y-m-d\TH:i:s\Z', $date);
}

$site = $_GET['site'];
if (preg_match('#^[a-z\.]+$#', $site) == 0)
    oops('Wrong site!');

$mode = $_GET['mode'];
if ($mode != 'answers')
    oops('Wrong mode!');

header('Content-type: text/html; charset=utf-8');

$seinfo = get_json("https://api.stackexchange.com/2.2/info?site={$site}&filter=!7nFLaVmuZ..LGXU.WToUuFgUGa0j9Phai8")[0]['site'];
$seanswers = get_json("https://api.stackexchange.com/2.2/answers?order=desc&sort=creation&site={$site}&filter=!*c8AgooR)8mGi4bMMz*-hGVrFJcmOwIQNoF5e");

$feed = new SimpleXMLElement('<?xml version="1.0" encoding="utf-8"?><feed xmlns="http://www.w3.org/2005/Atom"/>');
$feed->addChild('title', $seinfo['name'] . ' Answers');
$feed->addChild('subtitle', 'For ' . $seinfo['audience']);
$feed->addChild('icon', $seinfo['icon_url']);
$feed->addChild('logo', $seinfo['logo_url']);
$feed->addChild('id', $seinfo['site_url'] . '/feeds');
$feed->addChild('updated', format_date($seanswers[0]['creation_date']));
$link = $feed->addChild('link');
$link->addAttribute('href', $seinfo['site_url']);
$author = $feed->addChild('author');
$author->addChild('name', $seinfo['name'] . ' Atom');

foreach ($seanswers as $seanswer) {
    $entry = $feed->addChild('entry');
    $entry->addChild('title', $seanswer['title']);
    $link = $entry->addChild('link');
    $link->addAttribute('href', $seanswer['link']);
    $entry->addChild('id', $seanswer['link']);
    $entry->addChild('updated', format_date($seanswer['creation_date']));
    $content = $entry->addChild('content', $seanswer['body']);
    $content->addAttribute('type', 'html');
    $author = $entry->addChild('author');
    $author->addChild('name', $seanswer['owner']['display_name']);
    $author->addChild('uri', $seanswer['owner']['link']);
}

header('Content-type: application/atom+xml');
echo($feed->asXML());