TIME AGO in PHP

<?php

//DATE FORMAT
//echo date("F d Y H:i:s");


// TESTING
function test($ts){

    echo time_passed($ts) . '<br />';
} 


test(time());
test(strtotime("January 30 2017 07:41:08"));
test(time()-(60*17));
test(time()-((60*60*2) + (60*55)));
test(time()-(60*60*3+60));
test(strtotime('-1 day'));
test(strtotime('-13 days'));
test(strtotime('January 30 2017 07:31:08'));
test(strtotime('July 23 2016'));
test(strtotime('November 18 1999'));
test(strtotime('March 1 1937'));

//TESTING- end

//FUNCTION 
function time_passed($timestamp){
    //type cast, current time, difference in timestamps
    $timestamp      = (int) $timestamp;
    $current_time   = time();
    $diff           = $current_time - $timestamp;
   
    //intervals in seconds
    $intervals      = array (
        'year' => 31556926, 'month' => 2629744, 'week' => 604800, 'day' => 86400, 'hour' => 3600, 'minute'=> 60
    );
   
    //now we just find the difference
    if ($diff == 0)
    {
        return 'just now';
    }  

    if ($diff < 60)
    {
        return $diff == 1 ? $diff . ' second ago' : $diff . ' seconds ago';
    }      

    if ($diff >= 60 && $diff < $intervals['hour'])
    {
        $diff = floor($diff/$intervals['minute']);
        return $diff == 1 ? $diff . ' minute ago' : $diff . ' minutes ago';
    }      

    if ($diff >= $intervals['hour'] && $diff < $intervals['day'])
    {
        $diff = floor($diff/$intervals['hour']);
        return $diff == 1 ? $diff . ' hour ago' : $diff . ' hours ago';
    }  

    if ($diff >= $intervals['day'] && $diff < $intervals['week'])
    {
        $diff = floor($diff/$intervals['day']);
        return $diff == 1 ? $diff . ' day ago' : $diff . ' days ago';
    }  

    if ($diff >= $intervals['week'] && $diff < $intervals['month'])
    {
        $diff = floor($diff/$intervals['week']);
        return $diff == 1 ? $diff . ' week ago' : $diff . ' weeks ago';
    }

    if ($diff >= $intervals['month'] && $diff < $intervals['year'])
    {
        $diff = floor($diff/$intervals['month']);
        return $diff == 1 ? $diff . ' month ago' : $diff . ' months ago';
    }  

    if ($diff >= $intervals['year'])
    {
        $diff = floor($diff/$intervals['year']);
        return $diff == 1 ? $diff . ' year ago' : $diff . ' years ago';
    }
}

?>