Caching API Wrapper (Twitch.TV API v5 & Helix)

<?php
class TwitchAPI {
    public $url;
    public $cachedir = "/home/user/somedir";
    public $cachetime = 60;
    public $oauth = null;
    private $clientid = "";

    private function getFromTwitch($u,$f) {
        // Last updated 2018-04-13 for v5 Kraken to v"New" Helix transition
        $s = curl_init();
        $headers[] = 'Client-ID: '.$this->clientid;
        if ($this->oauth != null) {
            $headers[] = 'Authorization: OAuth '.$this->oauth;
            // clear after each use
            $this->oauth = null;
        }
        if (preg_match('/\/kraken\//',$u)) {
            $headers[] = 'Accept: application/vnd.twitchtv.v5+json';
        }
        curl_setopt($s,CURLOPT_HTTPHEADER,$headers);
        // clear after each use
        $headers = null;
        curl_setopt($s,CURLOPT_URL,$u);
        curl_setopt($s,CURLOPT_RETURNTRANSFER, 1);
        $data = curl_exec($s);
        curl_close($s);
        $fp = fopen($f,"w");
        fwrite($fp,$data);
        fclose($fp);
        return $data;
    }

    function get($apiurl = "api.twitch.tv",$secure = true) {
        $prefix = "http://";
        if ($secure) { $prefix = "https://"; }
        $inturl = $prefix.$apiurl."/".$this->url;
        $md5 = md5($inturl);
        $cachefile = $this->cachedir."/".$md5;
        if (file_exists($cachefile)) {
            $mtime = filemtime($cachefile);
            $time = time();
            if (($time - $mtime) > $this->cachetime) {
                return $this->getFromTwitch($inturl,$cachefile);
            } else {
                return file_get_contents($cachefile);
            }
        } else {
            return $this->getFromTwitch($inturl,$cachefile);
        }
    }
}