File upload, uploads only file name

I am working on a simple front end image upload in WordPress. With this piece of code I can upload to the wordpress media section but I only upload the name and url of the file then, no image.

Does anyone know what I need to do to upload the image also?

My form:

<form id="dash_action" method="post" enctype="multipart/form-data">

   <input type="file" name="file" /> 

   <input name="submit" type="submit" class="button" value="<?php _e( 'Save settings' ); ?>" />

</form><!--End dash_action-->

My PHP form handling:

if( isset( $_POST['submit'] ) ) {

    $filename = $_FILES['file']['name'];
    $wp_filetype = wp_check_filetype( basename($filename), null );
    $wp_upload_dir = wp_upload_dir();
    $attachment = array(
        'guid' => $wp_upload_dir['subdir'] . "https://wordpress.stackexchange.com/" . basename( $filename ), 
        'post_mime_type' => $wp_filetype['type'],
        'post_title' => preg_replace( '/\.[^.]+$/', '', basename( $filename ) ),
        'post_content' => '',
        'post_status' => 'inherit'
    );
    $attach_id = wp_insert_attachment( $attachment, $filename, 37 );
    require_once( ABSPATH . 'wp-admin/includes/image.php' );
    $attach_data = wp_generate_attachment_metadata( $attach_id, $filename );
    wp_update_attachment_metadata( $attach_id, $attach_data );  

}

The WordPress codex states that “The file MUST be on the uploads directory”. I’ve added a line to move the uploaded file into the uploads directory and changed the guid path.

if( isset( $_POST['submit'] ) ) {

    $filename = $_FILES['file']['name'];
    $wp_filetype = wp_check_filetype( basename($filename), null );
    $wp_upload_dir = wp_upload_dir();

    // Move the uploaded file into the WordPress uploads directory
    move_uploaded_file( $_FILES['file']['tmp_name'], $wp_upload_dir['path']  . "https://wordpress.stackexchange.com/" . $filename );

    $attachment = array(
        'guid' => $wp_upload_dir['url'] . "https://wordpress.stackexchange.com/" . basename( $filename ), 
        'post_mime_type' => $wp_filetype['type'],
        'post_title' => preg_replace( '/\.[^.]+$/', '', basename( $filename ) ),
        'post_content' => '',
        'post_status' => 'inherit'
    );

    $filename = $wp_upload_dir['path']  . "https://wordpress.stackexchange.com/" . $filename;

    $attach_id = wp_insert_attachment( $attachment, $filename, 37 );
    require_once( ABSPATH . 'wp-admin/includes/image.php' );
    $attach_data = wp_generate_attachment_metadata( $attach_id, $filename );
    wp_update_attachment_metadata( $attach_id, $attach_data );  

}