/**
 * Format a timestamp to display its age (5 days ago, in 3 days, etc.).
 *
 * @param   int     $timestamp
 * @param   int     $now
 * @return  string
 */
function timetostr($timestamp, $now = null) {
    $age = ($now ?: time()) - $timestamp;
    $future = ($age < 0);
    $age = abs($age);

    $age = (int)($age / 60);        // minutes ago
    if ($age == 0) return $future ?"momentarily" :"just now";

    $scales = [
        ["minute","minutes", 60],
        ["hour","hours", 24],
        ["day","days", 7],
        ["week","weeks", 4.348214286],     // average with leap year every 4 years
        ["month","months", 12],
        ["year","years", 10],
        ["decade","decades", 10],
        ["century","centuries", 1000],
        ["millenium","millenia", PHP_INT_MAX]
    ];

    foreach ($scales as list($singular, $plural, $factor)) {
        if ($age == 0)
            return $future
                ?"in less than 1 $singular"
                :"less than 1 $singular ago";
        if ($age == 1)
            return $future
                ?"in 1 $singular"
                :"1 $singular ago";
        if ($age < $factor)
            return $future
                ?"in $age $plural"
                :"$age $plural ago";
        $age = (int)($age / $factor);
    }
}