ResultReader.php

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<?php
class Dataface_ResultReader implements Iterator {

        private $sql = null;
        
        private $start = null;
        
        private $limit = null;
        
        
        private $bufferSize = 30;
        
        private $buffer = null;
        
        private $bufferStartPos = null;
        
        private $currPos = null;
        
        private $db = null;
        
        private $decorator = null;
        
        public function __construct( $sql, $db,  $bufferSize=30, $decorator = null){
                $this->db = $db;
                $this->start = 0;
                $this->limit = null;
                $this->bufferSize = $bufferSize;
                $this->buffer = null;
                $this->bufferStartPos = null;
                $this->currPos = $this->start;
                $this->sql = $sql;
                $this->decorator = $decorator;
                
                if ( preg_match('/^([\s\S]+)\slimit\s+(\d+)(\s*,\s*(\d+)\s*)?\s*$/i', $this->sql, $matches) ){
                        $this->sql = $matches[1];
                        if ( isset($matches[4]) ){
                                $this->limit = intval($matches[4]);
                                $this->start = intval($matches[2]);
                        } else {
                                $this->start = 0;
                                $this->limit = intval($matches[2]);
                        }
                }
                if ( isset($this->limit) and  $this->limit < $this->bufferSize ) $this->bufferSize = $this->limit;
        }
        
        public function __destruct(){
                $this->buffer = null;
        }
        
        
        public function rewind(){
                $this->currPos = $this->start;
                
                if ( !isset($this->bufferStartPos) ){
                        // The buffer isn't set yet so we are at the beginning
                        return;
                } else if ( $this->bufferStartPos > $this->start ){
                        // The buffer is beyond the first buffer set
                        // so we reset the buffer now
                        $this->buffer = null;
                        $this->bufferStartPos = null;
                } else {
                        // The buffer is not beyond the first set
                        // so the buffer is good.
                }
                
        }
        
        public function getQuery($start, $limit){
                return $this->sql.' limit '.$start.', '.$limit;
        }
        
        private function loadBuffer(){
                if ( $this->currPos >= $this->bufferStartPos + $this->bufferSize ){
                        $this->bufferStartPos += $this->bufferSize;
                } else if ( !isset($this->bufferStartPos) ){
                        $this->bufferStartPos = $this->start;
                } else {
                        return;
                }
                $q = array();
                $q['-skip'] = $this->bufferStartPos;
                $q['-limit'] = $this->bufferSize;
                if ( isset($this->limit ) ){
                        $q['-limit'] = min($this->bufferSize, $this->start+$this->limit-$this->bufferStartPos);
                }
                if ( $q['-limit'] > 0 ){
                        $this->buffer = array();
                        $res = mysql_query($this->getQuery($q['-skip'], $q['-limit']), $this->db);
                        if ( !$res ) throw new Exception(mysql_error($this->db));
                        
                        while ($row = mysql_fetch_object($res) ){
                                if ( isset($this->decorator) and is_callable($this->decorator) ){
                                        $row = call_user_func($this->decorator, $row);
                                }
                                $this->buffer[] = $row;
                        }
                        @mysql_free_result($res);
                } else {
                        $this->buffer = array();
                }
        
        }
        
        public function current(){
                $this->loadBuffer();
                return $this->buffer[$this->currPos-$this->bufferStartPos];
        }
        
        public function key(){
                return $this->currPos;
        }
        
        public function next(){
                ++$this->currPos;
        }
        
        public function valid(){
                $this->loadBuffer();
                return isset($this->buffer[$this->currPos-$this->bufferStartPos]);
        }
}