php script change when submitting a form data - php

Question

I built a script named add_post.php that submit form data in database.
The script is here:
<?php include ("includes/header.php"); ?>
<div class="content" style="text-align: center;">
<header>
<h1 style="color: rgb(245, 106, 106);">ADMIN AREA</h1><br/>
<p>Movie Post Area</p>
</header>
</div>
</section>
<?php
include("includes/startsession.php");
if(isset($_SESSION['username'])){
?>
<Section>
<?php
if(isset($_POST['submit'])){
$name =mysqli_real_escape_string($con, trim($_POST['name']));
$description = mysqli_real_escape_string($con, trim($_POST['description']));
$year = mysqli_real_escape_string($con, trim($_POST['year']));
$popularity = mysqli_real_escape_string($con, trim($_POST['popularity']));
$download_link = mysqli_real_escape_string($con, trim($_POST['download']));
$tags = mysqli_real_escape_string($con, trim($_POST['tags']));
//upload the name to the temporary folder
$images = mysqli_real_escape_string($con, trim($_FILES['image']['name']));
//select the image from the temporary folder
$images_tmp = $_FILES['image']['tmp_name'];
//move the uploaded image to the `images` folder
move_uploaded_file($images_tmp, "../images/$images");
$output_form = false;
if( empty($name) || empty($description) || empty($year) || empty($popularity) || empty($download_link) || empty($tags) || empty($images)){
echo '<h2>Oops! You seem to forget writing something</h2>';
$output_form = true;
}
if( (!empty($name)) && (!empty($description)) && (!empty($year)) && (!empty($popularity)) && (!empty($download_link)) && (!empty($tags)) && (!empty($images))){
$insert = "INSERT INTO movies (name, description, year, image, popularity, download_link, tags)
VALUES ('$name', '$description', '$year', '$images', '$popularity', '$download_link', '$tags') " or die(mysqli_error);
$run = mysqli_query($con, $insert);
echo "<h2>The Movie has been added.<h2>";
echo 'RESET';
}
} else{
$output_form = true;
$name = '';
$description = '';
$year = '';
$popularity = '';
$download_link = '';
$tags = '';
$images = '';
}
?>
<?php if($output_form = true){ ?>
<form enctype="multipart/form-data" method="post" action="<?php echo $_SERVER['PHP_SELF'];?>">
<div class="row uniform">
<div class="6u 12u$(xsmall)" style="float:none">
<label>Movie Name</label>
<input type="text" name="name" value="<?php echo $name; ?>" id="demo-name" value="" placeholder="Enter Movie Name" />
</div>
<br/>
<div class="6u 12u$(xsmall)" style="float:none">
<label>Description</label>
<textarea name="description" id="demo-message" placeholder="Enter Description" rows="6"><?php echo $description; ?></textarea>
</div>
<br/>
<div class="6u 12u$(xsmall)" style="float:none">
<label>Year</label>
<input type="text" name="year" value="<?php echo $year; ?>" id="demo-name" placeholder="Enter Year" />
</div>
<br/>
<div class="6u 12u$(xsmall)" style="float:none">
<label>Image</label>
<input type="file" name="image" value="<?php echo $images; ?>" id="demo-name" class="special" />
</div>
<div class="12u$" style="float:none">
<div class="select-wrapper">
<label>Popularity</label>
<select name="popularity" id="demo-category">
<option <?php if ($popularity == 'Yes'){echo 'selected';} ?> >Yes</option>
<option <?php if ($popularity == 'No'){echo 'selected';} ?> >No</option>
</select>
</div>
</div>
<div class="6u 12u$(xsmall)" style="float:none">
<label>Download Link</label>
<input type="text" name="download" value="<?php echo $download_link; ?>" id="demo-name" value="" placeholder="Enter Download Link" />
</div>
<div class="6u 12u$(xsmall)" style="float:none">
<label>Tags</label>
<input type="text" name="tags" value="<?php echo $tags; ?>" id="demo-name" value="" placeholder="Enter Tags seperated by commas(,)" />
</div>
<!-- Break -->
<div class="12u$" style="float:none">
<ul class="actions">
<li><input type="submit" name="submit" value="ADD MOVIE" class="special" /></li>
</ul>
</div>
</div>
</form>
<?php } ?>
<?php
} else{
header('Location: login.php');
}
?>
when I submit the form the page returns the script of index.php. When i refresh the page then the page shows the content of add_post.php and above all the data content of the form did not add to the database.
I don't know whats causing this problem and how to fix it.