Upload gambar dengan validasi nama

<?php
require_once "core/init.php";

if(!isset($_SESSION['user'])){
	header('location: login.php');
}

require_once "view/header.php";


$error = '';

if(isset($_POST['submit'])){
	$time = time();
	$nama_gambar = $_FILES['gambar']['name'];
	$gambar = $_FILES['gambar']['name'];
	$ukuran = $_FILES['gambar']['size'];
	$error = $_FILES['gambar']['error'];
	$asal  = $_FILES['gambar']['tmp_name'];
	$judul = $_POST['judul'];
	$konten = $_POST['konten'];
	$tag = $_POST['tag'];
	$format = pathinfo($gambar, PATHINFO_EXTENSION);
	$namafile = "images/".$gambar;

	if($error === 0){
		if($ukuran < 500000){
			if($format === "jpg"){
				if(file_exists($namafile)){
					$namafile = str_replace(".jpg","",$namafile);
					$namafile = $namafile . "_" .$time . ".jpg";
					$gambar   = $namafile;
				}
					move_uploaded_file($asal, $namafile);
			}else{
				echo 'harus jpg';
			}
		}else{
			echo 'file besar';
		}
	}else{
		echo 'error';
	}

	if(!empty(trim($judul)) && !empty(trim($konten))){
		if(tambah_data($judul,$namafile, $konten, $tag)){
			header('location: index.php');
		}else{
			$error = 'Ada masalah saat menambah data';
		}
	}else{
		$error = 'Judul dan isi harus di isi';
	}
}

?>

<form action="" method="post" enctype="multipart/form-data">
	<label for="judul">Judul</label><br>
	<input type="text" name="judul" value=""><br><br>

	<input type="file" name="gambar">
	<br><br>
	<label for="konten">isi</label><br>
	<textarea name="konten" rows="8" cols="40"></textarea><br><br>

	<label for="tag">tag</label><br>
	<input type="text" name="tag" value=""><br><br>

	<div id="error"><?=$error ?></div><br>

	<input type="submit" name="submit" value="submit">
</form>

<?php
require_once "view/footer.php";
?>