WooCommerce Discount based on Cart Item

We will give a discount on the total order with conditions based on our cart item.

Here is the basic structure of our code

//discount 
add_action('woocommerce_cart_calculate_fees' , 'custom_discount', 10, 1);
function custom_discount( $cart ){

    if ( is_admin() && ! defined( 'DOING_AJAX' ) )
        return;

     // Iterating through each item in cart
	$discount = 0;
	foreach( $cart->get_cart() as $cart_item ){
		// Getting an instance of the product object
		// $product = wc_get_product( $cart_item['product_id'] );
                   // $cat = $product->get_category_ids();
		
		//for item subtotal
$sub_total = $cart_item['line_total'];
		
		if ($sub_total>1000) {
			$discount += -10;
		}
		
		
	}

	## Applied discount (no products on sale) ##
	$cart->add_fee( 'Buffet over $1000 order', $discount);
		
}