รบกวนช่วยอธิบายโค๊ดหน้า function ให้หน่อยค่ะ พอดีไม่เข้าใจโค๊ดค่ะ

<?php
	class MyClass{
		public function selQuery($sqlTxt){
			if(preg_match('/SELECT/', strtoupper($sqlTxt))){
				$result = mysql_query($sqlTxt);
				$num = mysql_num_rows($result);
				if($num > 0){
					$arrRec = array();
					while($rs = mysql_fetch_assoc($result)){
						array_push($arrRec,$rs);
					}
					return $arrRec;
				}else{
					echo null;
				}
			}else{
				echo null;
			}
		}

		public function query($sql){
			if(@mysql_query($sql))
				return true;
			else
				return false;
		}
		
		public function chkUniqData($tablename,$field,$data){
			$result = mysql_query("Select $field From $tablename Where $field = '$data'");
			$num = mysql_num_rows($result);
			if($num >= 1)
				return false;
			else
				return true;
		}

		public function random_id($len){
			srand((double)microtime()*10000000);
			$chars = "0123456789";
			$ret_str = "";
			$count = 0;
			$chars2 = "";
			while($count<strlen($chars)){
				for($i=0;$i<$len;$i++){
					$chars2 .= $chars[$count];
				}
				$count++;
			}
			$num = strlen($chars2);
			for($i = 0; $i < $len; $i++)
				{
					$ret_str.= $chars2[rand()%$num];
					$ret_str.=""; 
				}
			return $ret_str; 
		}

		public function getDateFormat($timestamp, $type = "d"){
			$d = date("d", $timestamp);
			$m = date("m", $timestamp);
			$y = date("Y", $timestamp)+543;
			$h = date("H", $timestamp);
			$i = date("i", $timestamp);
			$s = date("s", $timestamp);
			$thai_m = array("มกราคม","กุมภาพันธ์","มีนาคม","เมษายน","พฤษภาคม","มิถุนายน","กรกฏาคม","สิงหาคม",
				"กันยายน","ตุลาคม","พฤศจิกายน","ธันวาคม");
			if($type == "d"){
				return $d." ".$thai_m[$m-1]." ".$y;
			}else if($type == "dt"){
				return $d." ".$thai_m[$m-1]." ".$y.", เวลา ".$h.":".$i."น.";
			}
		}

		public function uploadPhoto($arrFile,$name,$dirnm,$limit=0,$option='w'){
			$array_last=explode(".", $arrFile['name']);
			$c=count($array_last)-1;
			$filename=strtolower($array_last[$c]);
			$photo_name = $name.'.'.$filename;
			$chk=false;
			$arrAuthorList=array('jpg','jpeg','gif','png');
			foreach($arrAuthorList as $key){
				if($key==$filename){
					$chk=true;
					break;
				}
			}
			if($chk){
				copy($arrFile['tmp_name'], $dirnm.$photo_name);
				$images = $dirnm.$photo_name;
				$img_size=GetimageSize($images);
				if($option=='w' AND $limit>0){
					if($img_size[0]>$limit){
						$img_width=$limit;
						$img_height=round($img_width*$img_size[1]/$img_size[0]);
					}else{
						$img_width=$img_size[0];
						$img_height=$img_size[1];
					}
				}else if($option=='h' AND $limit>0){
					if($img_size[1]>$limit){
						$img_height=$limit;
						$img_width=round($img_height*$img_size[0]/$img_size[1]);
					}else{
						$img_width=$img_size[0];
						$img_height=$img_size[1];
					}
				}else{
					$img_width=$img_size[0];
					$img_height=$img_size[1];
				}

				if($filename=="jpg" or $filename=="jpeg"){
					$newImg=ImageCreateFromJPEG($images);
					$newX=ImagesX($newImg);
					$newY=ImagesY($newImg);
					$images_fin=ImageCreateTrueColor($img_width, $img_height);
					ImageCopyResampled($images_fin, $newImg, 0, 0, 0, 0, $img_width+1, $img_height+1, $newX, $newY); 
					ImageJPEG($images_fin, $dirnm.$photo_name);
				}else if($filename=="gif"){
					$newImg=ImageCreateFromGIF($images);
					$newX=ImagesX($newImg);
					$newY=ImagesY($newImg);
					$images_fin=ImageCreateTrueColor($img_width, $img_height);
					ImageCopyResampled($images_fin, $newImg, 0, 0, 0, 0, $img_width+1, $img_height+1, $newX, $newY); 
					ImageGIF($images_fin, $dirnm.$photo_name);
				}else if($filename=="png"){
					$newImg=ImageCreateFromPNG($images);
					$newX=ImagesX($newImg);
					$newY=ImagesY($newImg);
					$images_fin=ImageCreateTrueColor($img_width, $img_height);
					ImageCopyResampled($images_fin, $newImg, 0, 0, 0, 0, $img_width+1, $img_height+1, $newX, $newY); 
					ImagePNG($images_fin, $dirnm.$photo_name);
				}

				ImageDestroy($newImg);
				ImageDestroy($images_fin);

				unlink($arrFile['tmp_name']);
				return $photo_name;
			}else{
				return null;
			}
		}

		public function randomNum($num){
			srand((double)microtime()*10000000);
			$n = rand()%$num;
			return $n;
		}

		public function randNonUniqe($num){
			srand((double)microtime()*10000000);
			$a = array();
			while (count($a) < $num) {
			  $n = rand()%$num;
			  if (!in_array($n, $a)) array_push($a,$n);
			}
			return $a;
		}

		public function getItemsFromCart($cart){
			if (isset($cart)) { 
				$items = explode(',',$cart); //ใช้คอมม่าเป็นตัวแยกข้อมูล
				$contents = array(); 
				foreach ($items as $item) {    
					$contents[$item] = (isset($contents[$item])) ? $contents[$item] + 1 : 1;   //นำค่าที่ได้มาเก็บในaray
				}
				return $contents;
			}else{
				return "";
			}
		}
	}
?>