$days = array();
$weekdays = ["Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday"];

array_push($days,["days"=>"Monday","subject"=>["AI"]]);
array_push($days,["days" => "Sunday","subject" => ["OOAD","AI"]]);
array_push($days,["days"=>"Tuesday","subject"=>["OOAD"]]);

$sortedDays = array();


for($i = 0 ; $i <= 6 ; $i++){
    for($j = 0 ; $j < count($days) ; $j++){
        if($days[$j]["days"] == $weekdays[$i]){
        array_push($sortedDays,$days[$j]);
        }
    }
}