<?PHP
    class Pager implements Iterator
    {
        // Stuff you set...
        public $page;        // Current page (will be recalculated if outside valid range)
        public $perPage;     // Number of records per page
        public $numRecords;  // Total number of records

        // Stuff we calculate...
        public $numPages;    // Number of pages required to display $numRecords records
        public $firstRecord; // Index of first record on current page
        public $lastRecord;  // Index of last record on current page

        private $records;    // Used when iterating over object

        // Initialize the pager object with your settings and calculate the resultant values
        public function __construct($page, $per_page, $num_records)
        {
            $this->page = $page;
            $this->perPage = $per_page;
            $this->numRecords = $num_records;
            $this->calculate();
        }

        // Do the math.
        // Note: Pager always calculates there to be *at least* 1 page. Even if there are 0 records, we still,
        // by convention, assume it takes 1 page to display those 0 records. While mathematically stupid, it
        // makes sense from a UI perspective.
        public function calculate()
        {
            $this->numPages = ceil($this->numRecords / $this->perPage);
            if($this->numPages == 0) $this->numPages = 1;

            $this->page = intval($this->page);
            if($this->page < 1) $this->page = 1;
            if($this->page > $this->numPages) $this->page = $this->numPages;

            $this->firstRecord = (int) ($this->page - 1) * $this->perPage;
            $this->lastRecord  = (int) $this->firstRecord + $this->perPage - 1;
            if($this->lastRecord >= $this->numRecords) $this->lastRecord = $this->numRecords - 1;

            $this->records = range($this->firstRecord, $this->lastRecord, 1);
        }

        // Will return current page if no previous page exists
        public function prevPage()
        {
            return max(1, $this->page - 1);
        }

        // Will return current page if no next page exists
        public function nextPage()
        {
            return min($this->numPages, $this->page + 1);
        }

        // Is there a valid previous page?
        public function hasPrevPage()
        {
            return $this->page > 1;
        }

        // Is there a valid next page?
        public function hasNextPage()
        {
            return $this->page < $this->numPages;
        }

        public function rewind()
        {
            reset($this->records);
        }

        public function current()
        {
            return current($this->records);
        }

        public function key()
        {
            return key($this->records);
        }

        public function next()
        {
            return next($this->records);
        }

        public function valid()
        {
            return $this->current() !== false;
        }
    }