PHP でタイムスタンプを人間が判読できる相対日付と時刻に変換するにはどうすればよいですか?

function time2str($ts)
{
    // Handle non-numeric timestamps
    if (!ctype_digit($ts)) {
        $ts = strtotime($ts);
    }

    $diff = time() - $ts;

    // Handle current time
    if ($diff == 0) {
        return 'now';
    }

    // Handle past timestamps
    if ($diff > 0) {
        $day_diff = floor($diff / 86400);
        if ($day_diff == 0) {
            // Handle minutes and hours ago
            if ($diff < 60) {
                return 'just now';
            } elseif ($diff < 120) {
                return '1 minute ago';
            } elseif ($diff < 3600) {
                return floor($diff / 60) . ' minutes ago';
            } elseif ($diff < 7200) {
                return '1 hour ago';
            } elseif ($diff < 86400) {
                return floor($diff / 3600) . ' hours ago';
            }
        } elseif ($day_diff == 1) {
            return 'Yesterday';
        } elseif ($day_diff < 7) {
            return $day_diff . ' days ago';
        } elseif ($day_diff < 31) {
            return ceil($day_diff / 7) . ' weeks ago';
        } elseif ($day_diff < 60) {
            return 'last month';
        } else {
            return date('F Y', $ts);
        }
    }

    // Handle future timestamps
    else {
        $diff = abs($diff);
        $day_diff = floor($diff / 86400);
        if ($day_diff == 0) {
            // Handle minutes and hours from now
            if ($diff < 120) {
                return 'in a minute';
            } elseif ($diff < 3600) {
                return 'in ' . floor($diff / 60) . ' minutes';
            } elseif ($diff < 7200) {
                return 'in an hour';
            } elseif ($diff < 86400) {
                return 'in ' . floor($diff / 3600) . ' hours';
            }
        } elseif ($day_diff == 1) {
            return 'Tomorrow';
        } elseif ($day_diff < 4) {
            return date('l', $ts);
        } elseif ($day_diff < 7 + (7 - date('w'))) {
            return 'next week';
        } elseif (ceil($day_diff / 7) < 4) {
            return 'in ' . ceil($day_diff / 7) . ' weeks';
        } elseif (date('n', $ts) == date('n') + 1) {
            return 'next month';
        } else {
            return date('F Y', $ts);
        }
    }
}