Custom file upload with nonce - Wordpress

custom-file-upload-wordpress.php

<!-- Image preview Script -->
<script>
	jQuery(document).ready(function($){
     function imagePreview(uploader) {
	        if (uploader.files && uploader.files[0]) {
	            $("#display-upload-image").attr("src", window.URL.createObjectURL(uploader.files[0]));
	        }
	    }
		$("#sample_image").change(function() {
	        imagePreview(this);
	    });
	});
</script>
<?php $get_image = get_option('sample_image') ? : ''; ?>
<form id="ct-theme-settings-form" method="POST" enctype="multipart/form-data">
  <?php wp_nonce_field( 'save_upload_form_sample', 'save_upload_form_sample_fields' ); ?>
  <?php if (wp_attachment_is('image',$get_image)) : ?>
    <img id="display-upload-image" src="<?php echo wp_get_attachment_url( $get_image ); ?>" width="100" height="100" style="object-fit: contain; display: block; margin-bottom: 10px;">
  <?php endif; ?>
  <input style="width: 25em;" name="sample_image" type="file" id="sample_image" value="">
  <input type="submit" id="submit" value="Save">
</form>

<?php
function upload_image_session() {
	if( isset( $_POST['save_upload_form_sample_fields'] ) && wp_verify_nonce( $_POST['save_upload_form_sample_fields'], 'save_upload_form_sample' )) {
		//$_POST['ct-save-settings-error'] = false;
		if( isset( $_FILES["sample_image"] ) && !empty( $_FILES["sample_image"] && !empty( $_FILES["sample_image"]["tmp_name"] ) ) ) {
			$upload_logo = wp_upload_bits( $_FILES["sample_image"]["name"], null, file_get_contents( $_FILES["sample_image"]["tmp_name"] ) );
			if ( !$upload_logo['error'] ) {
		        $filename = $upload_logo['file'];
		        $wp_filetype = wp_check_filetype($filename, null);
		        $attachment = array(
		          'post_mime_type' => $wp_filetype['type'],
		          'post_title' => sanitize_file_name($filename),
		          'post_content' => '',
		          'post_status' => 'inherit'
		        );
		        $attachment_id = wp_insert_attachment($attachment, $filename);
		       // $attachment_data = wp_generate_attachment_metadata( $attachment_id, $filename );
		        //$logo_url = wp_get_attachment_url( $attachment_id );
		        update_option( 'sample_image', $attachment_id );
		    }
		}
		update_option( 'ct_theme_settings', $_POST);
	}
}
add_action( 'init', 'upload_image_session');