<?php
function format_timestamp(int $timestamp)
{
    $days = (int) floor($timestamp / (60.0 * 60.0 * 24.0));
    $years = (int) floor($days / 365);
    $hours = (int) floor(round($timestamp / (60 * 60)) % 24);
    $minutes = (int) floor(round($timestamp % (60 * 60)) / 60);
    $seconds = (int) floor($timestamp % 60);

    if ($years == 0 && $days == 0 && $hours == 0 && $minutes == 0) {
        return "$seconds second" . ($seconds > 1 ? "s" : "");
    } else if ($years == 0 && $days == 0 && $hours == 0) {
        return "$minutes minute" . ($minutes > 1 ? "s" : "");
    } else if ($years == 0 && $days == 0) {
        return "$hours hour" . ($hours > 1 ? "s" : "");
    } else if ($years == 0) {
        return "$days day" . ($days > 1 ? "s" : "");
    } else {
        return "$years year" . ($years > 1 ? "s" : "");
    }
}