/**
 * Clamp a number $x between $min and $max
 * 
 * @param int $x
 * @param int $min
 * @param int $max
 * @return int
 */
function clamp ($x, $min, $max) {
    return $x < $min ? $min : ($x > $max ? $max : $x);
}

/**
 * Create a limited sequence
 * 
 * @param int $center
 * @param int $limit
 * @param int $min
 * @param int $max
 * @return int
 */
function limited_range ($center, $limit, $min, $max) {
    $range = array();
    $half  = (int)($limit / 2);
    
    $start = $center - $half;
    $end   = $center + $half;
    
    for ($i = $start; $i < $end; $i ++) {
        $i >= $min && $i <= $max and $range[] = $i;
    }
    
    !in_array($min, $range) and array_unshift($range, $min);
    !in_array($max, $range) and array_push($range, $max);
    
    return $range;
}

/**
 * Generates pagination array
 * 
 * @param int $total - Total of rows/items
 * @param int $ipp   - Items Per Page
 * @param int $page  - Page
 * @return array
 */
function pagination_generate ($total, $ipp, $page) {
    $offset = $total > $ipp ? ($page - 1) * $ipp : 0;
    
    $pages = ceil($total / $ipp);
    $page  = clamp($page, 1, $pages);
    
    $pagination = $pages > 1 ? limited_range($page, clamp($pages, 1, 9), 1, $pages) : array();
    
    $limit = (int)($ipp - ($offset % $ipp));
    
    return compact('limit', 'offset', 'pages', 'page', 'pagination');
}

/**
 * Generates pagination array
 * 
 * @param int $total - Total of rows/items
 * @param int $ipp   - Items Per Page
 * @param int $page  - Page
 * @return array
 */
function pagination_generate ($total, $ipp, $page) {
	$result = [];
	$offset = 0;
	$pages = ceil($total / $ipp);
	$pagination = [];
	
	if ($page >= $pages) {
		$page = $pages;
	}
	
	if ($total > $ipp) {
		$offset = ($page - 1) * $ipp;
	}
	
	if ($pages > 1) {
		for ($i = 0, $c = ($pages > 9) ? 9 : $pages; $i < $c; $i++) {
			if ($pages <= $c) {
				$pagination[] = $i + 1;
			}
			else {
				if ($i === 0) {
					$pagination[$i] = 1;
				}
				else if ($i === $c - 1) {
					$pagination[$i] = $pages;
				}
				else {
					$cell = $page - ceil(($c - 1) / 2) + $i;
					
					if ($cell > $pages - 1 || $cell < 2) {
						continue;
					}
					
					$pagination[] = $cell;
				}
			}
		}
	}
	
	$result['limit']  = (int)($ipp - ($offset % $ipp));
	$result['offset'] = (int)$offset;
	$result['pages']  = (int)$pages;
	$result['page']   = (int)$page;
	$result['pagination'] = $pagination;
	
	return $result;
}

// Создать пагинацию для 20 страниц
// Пагинация на 10-ой странице
$pagination = pagination_generate(100, 5, 10);

foreach ($pagination['pagination'] as $page)  {
    echo "<a href=\"/blogs/tech/page/$page\">$page</a> \n";
}